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Extension > Yard and Garden News > July 2010

Saturday, July 31, 2010

Contents: August 1, 2010

In this issue of the Yard and Garden News:

Imidacloprid, Found in Most Homeowner Insecticides, is Translocated to Nectar and Pollen and Kills Good Bugs

Dr. Vera Krischik, Department of Entomology, University of Minnesota

Native plants used in restoration for wildlife and food plants from apples to zucchini require pollinators. Bees and other beneficial insects offer valuable ecosystem services in both natural and managed agriculture ecosystems, so it is essential to protect them. Pollinators and beneficial insects are experiencing serious decline due to insecticide use, lack of nutritionally rich native plants for pollen and nectar, and lack of habitat. Continued loss of pollinators will have an impact on the natural resources and the economy. This issue has been addressed by the Xerces Society, National Research Council Report, the Congressional Research Report, testimony by the National Academy of Sciences to the US Congress, and the media in newspapers and television programs.

Systemic neonicotinyl insecticides used on landscape plants and crops are considered as a major factor in pollinator decline. After the 1998 ban in France of the systemic seed treatment Gaucho (active ingredient, imidacloprid), French researchers found that imidacloprid is translocated from coated seeds at planting thru the growing plant to nectar and pollen in flowers. In May 2008 a large number of bees died in Germany and the government banned the use of 5 neonicotinyl insecticides, including imidacloprid and clothianidin. A similar event was document in April 2010 by bee researchers at Purdue University. However, in the US use of these 5 neonicotinyl insecticides is very common in greenhouse, landscape, and crops. Almost all of the seed and furrow insecticide applications to corn, canola, soybean, and potato use neonicotinyl insecticides. Native plants grown in greenhouses and transplanted outside may contain high levels of imidacloprid which may kill pollinators.

Research in Vera Krischik's lab in the Department of Entomology at the University of Minnesota demonstrated that nectar and pollen from greenhouse plants treated with soil applications of imidacloprid contained significantly higher amounts of imidacloprid and its metabolites, than from a Gaucho-seed treatment. The label of Gaucho states that 0.375 mg AI for corn and 0.11 mg AI of for canola of imidacloprid should be applied. The greenhouse rate used on perennial landscape plants states that 300 mg AI/ 3gallon pot with 1 plant can be used. This is an 800 times higher rate for corn and 2700 times higher rate for canola. Consequently, greenhouse and urban landscapes use higher concentrations of imidacloprid, which are often reapplied and used at peak flowering, which results in higher concentration being translocated directly to flowers. Consequently, these levels have great potential to alter behavior or kill pollinators and beneficial insects more than the seed treatment Gaucho where most of the research has been done.

Our research on greenhouse rates of imidacloprid showed that the amount of imidacloprid found in nectar of 2 flowering plants was 20 ppb to 41 ppb from a single soil application compared to 1.9 ppb imidacloprid in sunflower nectar and 0.6 to 0.8 ppb in canola nectar from a seed treatment. For buckwheat and milkweed landscape plants, a label rate of soil applied imidacloprid (Marathon 1%G) was translocated to buckwheat nectar at 16 ppb (Krischik et al. 2007) and milkweed at 41 ppb/flower (Krischik et al. 2010). These concentration of caused high mortality of beneficial insects, such as lady beetles, lacewings, and a small parasitic wasp (Smith and Krischik 1990, Rogers et al. 2007, Krischik et al. 2007, Krischik et. al 2010).

There are multiple ways that plants in urban landscapes can contain imidacloprid -contaminated nectar, since it is commonly applied in the landscape for many pests (Krischik and Davidson 2004) and many greenhouse plants are treated with prior to sale and transplanting. Imidacloprid may persist in nectar for a long time, since soil applications were effective against foliar pests for 1 to 2 years in containers (Szczepaniec and Raupp 2007, Gupta and Krischik 2007, Tenczar and Krischik 2007) and landscape trees (Cowles et al. 2006, Frank et al. 2007, Tenczar and Krischik, 2007). Injections of concentrated volumes of imidacloprid (Imicide, Pointer) applied to trees trunks and roots were effective for 12 months for ash (McCullough et al. 2003) and linden (Johnson and Williamson 2007). A soil application of imidacloprid to Eucalyptus tree resulted in 500 ppb in nectar and pollen, which will kill any insect feeding on nectar and pollen. Tree injections of imidacloprid at flowering are cause for concern, since linden flowers are a good source of nectar and pollen for bees, butterflies, and other beneficial insects.

Practice IPM and only use insecticides if you actually witness an insect and associated problem. Think kindly and widely of the need to conserve pollinators and beneficial insects. Apple, cranberries, blueberries, almond, citrus and 45% of our food plants need pollinators.

Rose Classes and their Performance in Minnesota: Part 2

Kathy Zuzek, UMN Extension Educator

Old Garden Roses

The earliest rose classes fall within a group of roses called the Old Garden Roses. These are the classes that were in existence before 1867 when the first Hybrid Tea was developed. The earliest classes in chronological order are the Gallicas, Damasks, Albas, Centifolias, and Mosses. These five classes were all in existence before 1800 and share some common traits. With few exceptions, they bloom only in spring on previous year's canes. In contrast to the Hybrid Teas, these roses are valued for their mature flowers rather than their buds. Buds are often round or globular and open to produce blooms that are cupped, domed, or are shallow saucers. Oftentimes small inner petals are enclosed within larger outer petals; sometimes petals are produced in a quartered arrangement. Colors among these 5 classes are restricted to pink, white, mauve, maroon, or purple.

Gallicas are the oldest class of Old Garden Roses and are known for their beautiful fragrance and blooms of rich colors like deep pink, violet, mauve, purple, or crimson. You can also find varieties with striped or mottled petals (Photo 1, below). Leaves are typically dark green, stiff, and a bit rugose or wrinkled. Plant habit is compact and upright and many Gallicas will sucker (Photo 2, below). At the Minnesota Landscape Arboretum (MLA), Gallica canes typically suffer some winter injury. They commonly die back to the snowline. If snow cover is absent, they often die back to the ground. When dieback to the ground occurs in Gallica cultivars or any other cultivar that blooms on previous years' wood, flowering does not occur the following spring bloom. 'Alika' is a very hardy Gallica and rarely suffers from winter injury at the MLA. Many Gallicas at the MLA show high levels of blackspot tolerance.

The first Damask rose was probably a hybrid created in nature from a Gallica rose and Rosa phoenicea, a species rose with small white flowers. Damask blooms are usually a clear pink or white and are known for their strong fragrance. Typical leaves are gray-green, downy on the underside, and composed of long leaflets. Damasks produce long arching canes but at the MLA, some winter injury is common among Damask cultivars so plant height is often reduced. Most cultivars have slight levels of blackspot infections. 'Cesonie' is a very black spot-tolerant Damask cultivar (Photos 3&4, below).

Albas were created when a natural hybrid occurred between a Damask rose and Rosa canina, a European rose species often called the dog rose. Alba flowers are usually white, ivory, or light pink and leaves are gray-green or blue-green. Albas are typically taller and hardier than Gallicas, Damasks, Centifolias, and Mosses but some winter injury to canes still occurs at the MLA. 'Alba semi-plena' (Photos 5&6, below) has historically shown the best combination of winter hardiness and blackspot tolerance among Albas at the MLA.

Centifolias were developed by the Dutch in the 1600s from R. canina, R. gallica, R. moschata, and R. phoenicea. Flower buds are globular and open to display pink or white, fragrant, cupped blooms (Photos 7, below). Flowers have a high number of tightly packed petals that envelop each other like leaves of a cabbage, hence the common name "cabbage rose". Leaves are smoother and less wrinkled than Gallica foliage. Cabbage roses are taller like the Albas and the Damasks and their plant habit is often described as floppy or lanky (Photo 8, below). At the MLA, some winter injury is common can reduce plant height the following summer. Blackspot infections are more severe on Centifolias than on the Albas, Damasks, and Gallicas.

In the late 1600's a spontaneous mutation occurred on a Centifolia roses that resulted in the development of balsamic-scented glandular growths that look like moss on the stems and flowers of the rose. These mutated plants or sports were called the Moss Roses. The development of new moss rose varieties was a fad in the last half of the 19th century and cultivars were developed that ranged from small to large in plant habit with white, pink, and maroon blooms that had either soft or hard, prickly moss covering stems, flowers and occasionally leaves. Winter injury on Moss Roses is common at the MLA. 'Henri Martin' is a particularly black spot-tolerant cultivar (Photo 9, below).

In the late 1700's R. chinensis, the China rose, and R. odorata, the tea rose, arrived in Europe from Asia. China roses have an open and airy plant habit, sparse foliage, and blooms that are shapeless compared to the Old Garden Roses. The tea rose is very similar to the China rose except that it is less hardy, has larger blooms that open from tall elegant buds, and flower scent is similar to fresh tea leaves. What excited gardeners and breeders was the ability of both the China rose and the tea rose to bloom repeatedly through the growing season. Soon repeat-flowering plants were created by combining the Gallicas, Damasks, Centifolias, and Mosses with the China rose and the Tea rose and four new rose classes developed. Portlands and Bourbons are both descended from the Damask and China roses. Portland Roses are known for their short stems and compact plant habit, dense foliage, and attractive purple, pink, or white flower forms. Bourbons are known for fragrant, rich-colored, many-petalled blooms that are produced on tall arching canes. In warmer climates bourbons are used as climbers and pillar roses. Hybrid Perpetuals resulted from crosses among many rose classes when rose exhibitions became popular. In this class, plants were selected for lovely flower buds and flowers. Plant habit was of little concern. As a result, hybrid perpetual plants are often described as clumsy and too large. Tea Roses, known for their tall, elegant buds, were created when R. odorata was crossed with the Bourbon roses and another rose class called the Noisettes. All four of these classes are more suited to growth in warmer climates and are not adequately hardy for Zone 4 winters.

Modern Roses

When Tea Roses were hybridized with the Hybrid Perpetuals, the Hybrid Tea class was created and the era of modern roses was started. Hybrid Teas with their tall elegant buds and beautiful flower form (Photos 10, below) dominated the rose world as a garden plant in the last half of the 20th century. They are not hardy in Minnesota and are typically very susceptible to blackspot.

The first Polyantha Rose was probably the result of an accidental cross of a China Rose and R. multiflora. Polyanthas are a class of small-statured roses who inherited their large clusters of small one-inch flowers and superior hardiness from their R. multiflora ancestor. 'The Fairy' (Photo 11, below) and its darker pink sport 'Lovely Fairy', are reliably crown-hardy and very black spot-tolerant in the southern half of Minnesota and bloom freely all through the growing season. The Northern Accent Roses 'Ole', 'Sven', and 'Lena' are crown-hardy with rapid spring regrowth in Zones 3&4, have high blackspot-tolerance, and flower throughout the growing season.

When Polyantha Roses were combined with Hybrid Teas, Floribunda Roses were created. Floribundas produce blooms in clusters like their Polyantha parent but also have the more elegant bud and flower form and the decreased cold hardiness of their Hybrid Tea ancestors. Floribundas are typically not hardy in Minnesota. Two cultivars that are Zone 4-hardy and black spot-tolerant are 'Nearly Wild' and 'Chuckles' (Photo 12, below). Both show high levels of blackspot tolerance.

Hybrid Rugosa cultivars are descended from R. rugosa with its rugose or wrinkled foliage and large colorful round hips. There are two types of Hybrid Rugosa cultivars. The first are plants that are 100% rugosa and typically show no winter injury, little blackspot incidence, produce mauve, white, or pink blooms through the growing season (Photo 13, below), and produce a beautiful crop of large round colorful hips in fall (Photo 14, below). These plants thrive even in the coldest parts of Minnesota as long as 1) soil pH is neutral or slightly acidic and 2) rose stem borer and mossy rose galls are removed and destroyed promptly. Examples in this group include 'Blanc Double de Coubert', 'David Thompson', 'Frau Dagmar Hartopp', and 'Jen's Munk'. The second group of Hybrid Rugosas have one R. rugosa parent , but the 2nd parent is a non-rugosa rose such as a Shrub Rose, a Hybrid Tea, a Floribunda, or a Miniature Rose. This group usually has less rugose foliage, few or no hips, more susceptibility to blackspot, a wider variety of flower color, and a dramatic loss of cane hardiness that prevents them from being grown in Zone 3 and oftentimes Zone 4.

Shrub Roses are a "catch all" category for roses with diverse genetic backgrounds that don't fit anywhere else. Common traits among this group include a "shrubby" plant habit compared to cultivars in other modern rose classes, increased winter hardiness, and improved disease resistance. Some are repeat-blooming. Others bloom only in spring. Minnesota gardeners can enjoy the shrub roses that resulted from Canadian breeding efforts in the 20th century and resulted in older cultivars like 'Therese Bugnet' or 'Lillian Gibson' and newer cultivars in the Explorer (Photo 15, below) and Parkland/Morden Series. Gardeners in the southern half of Minnesota can also take advantage of some of the repeat-blooming cultivars developed by Dr. Buck at Iowa State University during the last half of the 20th century such as 'Applejack', 'Country Dancer', 'Folksinger', 'Prairie Flower', 'Prairie Harvest', and 'Prairie Princess'. Newer Zone 4 additions to the shrub group that rebloom and show high blackspot tolerance include 'Candy Oh! Vivid Red', 'Carefree Delight', 'Carefree Spirit', 'Golden Eye', 'Pink Gnome', 'Polar Joy', and 'Snowdrift.'









Home Lawn and Landscape Turfgrass Fertilizer Recommendations Being Revised to be More Environmentally Sensitive

Bob Mugaas, UMN Extension Educator; Dr. Brian Horgan, Associate Professor and Extension Turfgrass Specialist; and Dr. Carl Rosen, Professor and Extension Soil Scientist.

Bob Mugaas
New research results from the University of Minnesota and the University of Wisconsin-Madison necessitate updating our current lawn/turfgrass fertilizer recommendations. For the past 20 to 30 years, one of the more important fertilizer application times was considered to be the end of October and into early November in the Twin Cities and southern Minnesota. Indeed, lawns respond positively with good green color and active growth significantly earlier the following spring when given about 1# of N per 1000 square feet late in the previous growing season. This application came to be known as a late fall or more accurately a late season fertilization. In most years, this typically coincided with about the last mowing of year and with hoses put away or irrigation systems winterized for the year.

Even though this research was conducted on creeping bentgrass these findings demonstrate that nitrogen uptake late in the season is significantly less than when applied around Labor Day to the middle of September. So, what happens (or potentially can happen) to the remaining nitrogen not used or taken up by the grass plants? Other recent research on Kentucky bluegrass at Michigan State University points to increased leaching of N fertilizers when plants are not actively growing which is often the case with the late season fertilization. Nitrogen can also be converted to a gaseous form and lost back to the atmosphere. In some situations it can even be lost through runoff, particularly when soils are frozen. Some may also be taken up by other landscape plants that happen to share the same rootzone as the turfgrass (e.g., trees and shrubs).

Bob Mugaas
So, back to our original question, "If only a small portion of available N is utilized by the grass plant, what happens to the rest of it?" A more complete answer to that question rests with additional research which is ongoing. Nonetheless, available and unused nitrogen can pose additional environmental risks as noted above and be uneconomical for the user. After all, no one wants to be spending money on fertilizer and the labor to apply it if only a small fraction of that material is being utilized by the grass plant with the rest potentially being wasted.

It should be noted that results from the University of Minnesota soil testing lab may indicate significantly less nitrogen be applied on an annual basis depending on information provided about the care and use of the turfgrass area tested as well as the level of soil organic matter present. Leaving clippings on the lawn typically results in about one application of a complete fertilizer (i.e., a fertilizer containing nitrogen, phosphorus and potassium) annually back to the lawn. Hence, when clippings are returned, the amount of nitrogen needed is also reduced. The four options below assume clippings are returned to the lawn.

Bob Mugaas
Likewise, areas with soil test levels of organic matter above 3.1% will also indicate a reduced need for nitrogen. As soil organic matter continues to breakdown over time, there is some nitrogen released back to the soil that in turn becomes available for the grass plants to use. The soil testing lab considers that when suggesting annual amounts of nitrogen to apply.

Based on this current research, the following revised lawn/turfgrass fertilizer programs are suggested. These are applicable to lawns and other turfgrass areas predominantly composed of Kentucky bluegrass with varying amounts of fine fescue and perennial ryegrass. Whenever possible be sure to take a soil test to determine how much fertilizer is needed. It should be noted that ongoing analysis and interpretation of these and other research results may further refine suggested turfgrass fertilizer programs. Hence, it is important to check back periodically on the U of MN Extension website for the latest in lawn fertilizer recommendations.

Irrigated average quality lawns/turfgrass - full sun conditions; soil organic matter >3.1%; clippings not removed
2# N annually

Application timing:

  • Labor Day: 1.0# N per 1000 ft2, (50% slow release N)

  • At first mowing in spring: 0.5# N per 1000 ft2, (20 - 25 % slow release)

  • Memorial Day: 0.5# N per 1000 ft2, (50% slow release)

Irrigated average quality lawns/turfgrass - full sun conditions; soil organic matter <3 data-blogger-escaped-.1="" data-blogger-escaped-br="" data-blogger-escaped-clippings="" data-blogger-escaped-not="" data-blogger-escaped-removed="">
2.5# N annually

Application timing:

  • Labor Day: 1.0# N per 1000 ft2, (50% slow release N)

  • At first mowing in spring: 0.5# N per 1000 ft2, (50% slow release N)

  • Memorial Day: 0.5# N per 1000 ft2, (50% slow release N)

  • First week of August: 0.5# N per 1000 ft2, (50% slow release N)

Non-irrigated, average quality lawns/turfgrass - full sun to lightly shaded conditions; soil organic matter <3 data-blogger-escaped-.1="" data-blogger-escaped-clippings="" data-blogger-escaped-em="" data-blogger-escaped-not="" data-blogger-escaped-removed="">

1.5# N annually

Application timing:

  • Labor Day: 1.0# N per 1000 ft2, (50% slow release N)

  • Memorial Day: 0.5# N per 1000 ft2, (50% slow release N)
On occasion, an additional application of N to enhance growth and color may be needed:
Apply at the rate of 0.5# N per 1000 ft2, (50% slow release N; often this will be in late June to early July especially if weather conditions prior to that period have produced abundant and frequent rainfall.)

Non-irrigated, average quality lawns/turfgrass - full sun to lightly shaded conditions; soil organic matter >3.1%; clippings not removed
1# N annually

Application timing:

  • Labor Day: 1.0# N per 1000 ft2, (50% slow release N)
On occasion, an additional application of N to enhance growth and color may be needed:
Apply at the rate of 0.5# N per 1000 ft2, (50% slow release N; often this will be in late May to early July especially if weather conditions prior to that period have produced abundant and frequent rainfall.)

Canna Yellow Streak Virus

Michelle Grabowski, UMN Extension Educator

Leaf streaking due to CaYSV
M. Grabowski, UMN Extension
Cannas are popular tropical plants that can be easily grown in Minnesota if rhizomes are brought indoors and protected from frost each year. In addition to a variety of flower colors, cannas also differ in leaf color. Leaves that are green to greenish blue, reddish purple, bronze, or variegated with white to yellow stripes can all be found in different varieties of canna. It is important to know what color leaves a particular variety should have however, because a very common virus can cause leaf streaking that many gardeners mistake for variegation.

Canna Yellow Streak Virus (CaYSV) causes yellow to brown streaks along leaf veins of infected plants. Severely infected plants may have poor growth and reduced or no flowers.

Although many viruses are transmitted from plant to plant by an insect vector, there is no known vector for CaYSV other than humans. Cannas are propagated by splitting the rhizome of one plant, and growing the pieces into many new plants. If the original plant is infected with the CaYSV, all new plants arising from that plant will also carry the virus. Once infected with CaYSV, a canna is infected for life. The only effective control is to throw out infect rhizomes and start over with healthy virus free plant material.

Field Ants in Home Lawns

Jeffrey Hahn, Asst. UMN Extension Entomologist

Some people are finding field ants nesting in their lawns. Field ants are about 1/4 inch long and black (some species are red and black). Their nests are slightly raised and mound-like and can cover a fairly large area in the ground, up to two feet in diameter. It is not uncommon for people to confuse field ants with carpenter ants. Although these two ants are somewhat similar in size and color, carpenter ants do not nest in the soil. The prefer to nest in cavities in rotting wood or in voids found in buildings. Field ants are most active during the day while carpenter ants are most active at dusk, dawn, and during the night. Because of the mounds created by field ants, some people assume these ants are fire ants. Fire ants are about 1/8th inch long or a little larger. They only occur in the southeastern area of the U.S.; the closest fire ants to Minnesota are in southern Tennessee. Minnesota winters are too cold for fire ants to survive.

Thumbnail image for fieldantnest.jpg
Field ant nest
Unlike cornfield ants which are found in bare or thinning areas of lawns, field ant nests are found in healthy, vigorously growing turf. Despite the appearance of the excavated soil on top of the grass, field ant nests typically do not cause any lasting damage to the grass (just rake the soil periodically to prevent it from mounding up). Field ant activity may also make the turf look like it is being undermined from all of the tunneling but this is not likely - a very large nest would need to be present to cause that kind of damage. However, these nests can cause problems when mowing. The blades can become dulled when they strike the mound. Field ants can also be an issue because they can bite, especially when their nest is disturbed.

It may not always be necessary to treat field ants in your lawn. If the nest is not intrusive in its appearance or cause problems in the maintenance or enjoyment of your grass, then just ignore it. If the nest is troublesome, then your best bet is treat it with a granular insecticide labeled for ants found in turf (follow all label direction carefully). Some people want to try a non-chemical method and will pour hot water on the nest to kill it. However, this is not effective; at best you might get the ants to move to another area of the lawn. Others will try much more dangerous tactics like trying to burn and destroy the nest with gasoline or lighter fluid. Not only does this not destroy the nest but you risk causing injury to yourself and damage to your property in the process.

Garden Calendar: August 1, 2010

Warm wet weather is favoring the growth of many fungal and bacterial leaf spot diseases in the flower garden. To identify which disease or pest problem you are seeing, visit 'What's wrong with my plant?'

For more information about managing leaf spot diseases, read 'Seeing Spots'in the June 1, 2009 Yard and Garden News.

Yard and Garden News Editor: Karl Foord
Technical Editor: Bridget Barton

Friday, July 16, 2010

Contents: July 16, 2010

In this issue of the Yard and Garden News:


Jeffrey Hahn, UMN Extension Entomologist

B Postels2.jpg
Typical springtail
Brenda Postels
The rainy weather that much of Minnesota has experienced this year has lead to increased numbers of springtails in and around homes and other buildings. Springtails are very small, between 1/16th - 1/8th inch long. They are usually slender, elongate insects (there is a group of springtails that is round and stout) with moderate length antennae. Most springtails are dark-colored, brown, grey or black although some species are also white, and some are even iridescent and brightly colored

Springtails are wingless and do not fly but they can jump. Unlike grasshoppers, crickets, and other insects that use large back legs for jumping, a springtail uses a forked appendage called a furcula (located underneath the abdomen) to propel itself. When not in use, a furcula is tucked up under the body, set like a mouse trap. When it is released, it extends down rapidly sending the springtail forward. A springtail can jump many times its body length.

Despite their small size, springtails can occur in tremendously large numbers and are one of the most abundant insects. One source estimates you would find millions of springtails in one hectare (about 2.5 acres) of land. They are associated with damp conditions and are found in soil, leaf litter, lichen, under bark, decaying plant matter, and other areas of high moisture. They feed on fungi, pollen, algae, or decaying organic matter.

They are occur indoors for several reasons. They can be found in the soil of overwatered houseplants and sometimes adjacent areas. They also occur in damp areas with high moisture, e.g. around plumbing leaks and damp basements. They can also move in large numbers indoors from the outside when moist conditions exit around the home. Springtails can vary in abundance indoors from just a handful to very large numbers. Fortunately, however many you find, they are harmless to people and property and are just nuisances.
Typical springtail
Jeff Hahn

If you are finding just a small number of springtails occasionally, just ignore them or physically remove them by hand or with vacuum. However, if you are seeing persistent number of springtails they are associated with a moisture problem. The best management is to dry out these areas with a fan or dehumidifier as springtails do not tolerate dry conditions. Also make any structural changes to correct the moisture problem.

If springtails are migrating in from the outside, check around the house for moisture problems. This could include rainspouts that do not carry the water far enough away from the foundation, landscapes that slope towards buildings, or excessive irrigation. It could even be a moisture problem with the roof. Correcting existing moisture conditions will help decrease springtails. As we receive less rainfall, the number of springtails will also naturally lessen.

Although it may be tempting to spray a springtail problem with an insecticide, the products available are not very effective against them. Moisture control is the most effective strategy.

Leaf Spots are Sprouting in the Vegetable Garden

Michelle Grabowski, UMN Extension Educator

Bact brown spot .jpg
Bacterial brown spot on beans
M. Grabowski, UMN Extension
This summer early warm weather and frequent rain alternating with sunny days have created conditions allowing vegetable gardens to flourish. Many gardeners are amazed at the size of their tomato and corn plants. Recently, however, gardeners have been noticing yellowing and spotting of their prized plants, especially on the lower leaves. This discoloration is caused by several different fungal and bacterial leaf spot pathogens. Unfortunately warm wet weather also favors growth of these pathogens.

Leaf spot fungi and bacteria come into the garden on infected seed or transplants or are blown in on the wind. Many of these pathogens can survive from one season to the next on infected plant debris. Splashing rain carries fungal spores and bacteria from the soil and plant debris onto this year's leaves. Moisture in the plant canopy then allows these pathogens to start new infections. Established leaf spots create a whole new generation of bacteria and fungal spores, starting the cycle all over again.

Luckily several basic cultural control practices can help to keep leaf spot pathogens in check.

  1. Reduce moisture on leaves and fruit by watering the base of the plant with drip irrigation, a soaker hose, or simply by directly the hose at the soil and not the leaves.
  2. Stake plants like tomatoes, runner beans, and cucumbers.
  3. Mulch the soil with straw, wood chips or a plastic mulch to prevent the pathogen from being splashed up onto the lower leaves.
  4. Inspect plants regularly. If a few leaf spots show up, pinch off the infected leaves and remove them from the garden. Never remove more than a third of the plants foliage!
  5. At the end of the growing season, remove infected plants or till under the plant debris to speed up breakdown of infected plant parts.
  6. Rotate crops. Wait 3-4 years to plant the same plant in the same location. It is best to rotate between plant families. Follow tomatoes with broccoli, corn or beans since they are not closely related. Peppers and eggplant should not follow tomatoes since they share many of the same diseases.

The leaf spot diseases below have been recently found in Minnesota.

peppery spot 5.jpg
Peppery spot on turnip
M. Grabowski, UMN
Peppery Leaf Spot - Seen here on turnip leaves, this bacterial leaf spot disease is caused by Pseudomonas syringae pv. maculicola. This disease can occur on turnip, cauliflower, broccoli, and Brussels sprouts. The peppery leaf spot bacteria enter the field on infected seed and then return each year by surviving on plant debris. Bacteria spread from plant to plant by splashing water, on tools, gardener's hands and insects. The outer older leaves are typically infected first. Pinch off severely infected leaves and remove them from the garden. Do not plant any of the susceptible brassicas in the same location for three years.

Alternaria .jpg
Gray spot on Chinese cabbage
M. Grabowski, UMN Extension
Black Spot and Gray Spot - These two fungal diseases of brassicas are caused by Alternaria brassicae and Alternaria brassicicola. Disease can occur on cabbage, cauliflower, Chinese cabbage, broccoli, Brussels sprouts, kohlrabi, kale, turnip, and rutabaga. Leaf spots start out as small dark pinpoint spots, but quickly grow into a large gray to brown circle. Dark rings within the spot make them look like a target. Leaf tissue around the spots turns yellow, and dark brown spots may be seen on the heads of cauliflower and broccoli.

The black spot and gray spot fungi can be blown into the garden on wind or brought in on infected seed. The disease thrives when high humidity occurs. To reduce problems with these fungal leaf spot diseases, remove diseased leaves from the garden and till in infected plants at the end of the season. Be sure to remove weeds from the brassica family because they can harbor these fungi even when vegetable plants are not around.

Early Blight - This common fungal disease of tomatoes is caused by Alternaria solani. The fungus can also infect potatoes and occasionally eggplant and peppers, but the most severe damage in gardens often occurs on the tomato plants. Fruit, stems and leaves can all be infected by the early blight fungus. Infection on all three plant parts results in large brown spots, with concentric dark rings, that look like a bulls eye.

early blight leaf.jpg
Early blight on tomato
M. Grabowski, UMN Extension
Like many leaf spot fungi, the early blight fungus survives in plant debris in the soil from year to year and is splashed on to leaves and fruit by rain or irrigation. It thrives in moist conditions. Reducing moisture around plants through staking, spacing for good air movement, pinching off lower leaves, pruning to one or a few stems, and mulching the soil can all help reduce disease problems. Often cultural controls reduce the disease enough to produce a good crop of tomatoes even though a few leaf spots can still be found on the plant.

Septoria ls2.jpg
Septoria leaf spot on lettuce
M. Grabowski, UMN Extension
Bacterial Brown Spot - This bacterial disease of beans is caused by Pseudomonas syringae pv syringae and can affect both the leaves and pods of the bean plant. Leaves have round brown papery spots. Leaf spots occasionally fall out, resulting in a shot hole appearance of the leaves. Infected bean pods also have brown spots and may be bent or twisted around the infected area. To reduce problems with bacterial spots on beans, space plants to allow good air movement between plants. Stake runner beans. Avoid working in plants when leaves are wet. Instead, wait until a cool dry day to pinch off infected leaves and pods. Remove this diseased material from the garden.

Septoria Leaf Spot - This fungal leaf spot disease of lettuce is caused by Septoria lactucae. Spores from this fungus often come into the garden on seed, but can also survive in plant residue and on some weeds. Gardeners that have problems with Septoria leaf spot of lettuce might consider looking for lettuce seed that is produced in a desert area, like the south western states, as these seeds are less likely to be contaminated by this moisture loving fungus. When growing successive crops of lettuce, be sure to seed the next crop in a location away from any currently diseased plants. Do not plant lettuce in the same area of the garden for one year to allow infected plant debris to break down.

Rose Classes and Their Performance in Minnesota: Part 1

Kathy Zuzek, UMN Extension Educator

The number of rose cultivars in the world defies logic. If you open a copy of Modern Roses 12, the most recent edition of the American Rose Society's rose cultivar list, you will find thousands of rose cultivars or varieties listed along with each rose's class, year of release, the breeder who developed the cultivar, parentage, and descriptions of each cultivar's floral and foliage traits, plant habit and thorns.

Flower of R. acicularis, one of Minnesota's native roses
Kathy Zuzek
Before cultivar selection and development, there were only the species or "wild" roses. There are 120 or more rose species in the world and they are found in the temperate and sub-tropical regions of the Northern Hemisphere: the Middle East, Oriental Asia, Europe, and America. The oldest species have single flowers with only 5 or occasionally 4 petals and bloom only once each year in spring. As mutations occurred in some rose species over the course of time, stamens or the pollen producing part of the plant were replaced by more petals. This gave rise to newer species with semi-double or double flowers that have more than 5 petals. Eventually mutations also arose that led to repeat-flowering rose species that bloom throughout the growing season.

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R. acicularis
David Zlesak
There are 18-20 roses native to the United States. Four of these (R. acicularis, R. arkansana, R. blanda, and R. woodsii) are native to Minnesota. All 4 of these species are single-flowered, pink, and bloom in spring (Photos 1 & 2).

Given the thousands of rose cultivars in the world, you might think that many of the rose species were used in developing all of these cultivars. With few exceptions, only 8 species are ancestors to our rose cultivars and all 8 are from Asia.

As rose cultivars are developed, they are placed into classes. There are 36 classes of roses. Classes that Minnesota gardeners might be familiar with are the Hybrid Teas, the Shrub Roses, or the Hybrid Rugosas. Every rose cultivar is placed in a class with other roses who share common ancestors and/or similar floral, foliage, or plant habit traits.

Which classes and which cultivars can be grown in Minnesota? That depends on a gardener's taste in rose appearance, the choice of how much time he or she wants to devote to maintaining their roses to insure good performance and long term survivability, and a willingness or reluctance to spray pesticides. Some of the biggest factors that impact these decisions are choosing between repeat-blooming and spring-blooming cultivars, cold hardiness and pest tolerance of individual rose cultivars, and the pH of your soil.

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Spring flower display of 'Prairie Wren', a spring-blooming shrub rose
Kathy Zuzek
Most gardeners today are looking for repeat-blooming roses. These are the roses that bloom repeatedly throughout the growing season. There is nothing wrong with this except that it does eliminate the potential for enjoying some of our hardiest and largest cultivars that can produce hundreds of blooms during their one season of bloom to provide a spectacular spring display (Photo 3). Entire classes of roses that bloom only in spring can be eliminated from your list if you want a repeat-flowering rose.

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Green canes below the snowline are alive
 while canes above the snowline are brown and dead
Kathy Zuzek
Gardeners in Minnesota also need to consider cold hardiness. Our hardiest roses that show no cane injury after a Zones 3 (northern Minnesota) or Zone 4 (southern Minnesota) winter where minimum temperatures fall to somewhere between -20 degrees and -40 degrees F belong to only a few classes of roses. Some of these hardy cultivars are repeat bloomers and some are not. Other "hardy" repeat-blooming cultivars within those same few classes will have part of their canes killed by winter injury each year after a typical Minnesota Zone 3 or 4 winter. Oftentimes these cultivars have canes alive in the lower portions of the plants that were protected by snow cover while cane portions above the snowline are winter-killed (Photo 4).

What is important in Minnesota is a plant's ability to re-grow vigorously during the following growing season after experiencing some winter injury. Because repeat-blooming roses produce flowers on the current year's wood, a repeat-blooming plant that grows vigorously in spring and summer after some winter injury can perform beautifully in spite of our harsh winters. There are also entire classes of roses that are not hardy in Minnesota. Unless a gardener is 1) willing to consider a rose as an annual plant or 2) tip and bury roses or provide some other measure of winter protection, these roses should not be grown in Minnesota.
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Blackspot on a rose leaflet
Dave Hansen

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Swellings on a rugosa cane indicate
where rose borer larvae have girdled the rose cane
Dave Hansen
Roses are hosts to many pests. The pests that most impact rose survival in Minnesota are blackspot, the rose stem borer and a wasp that causes mossy rose gall.

Blackspot is a fungus that results in defoliation of rose plants across all classes (Photo 5). Roses without leaves cannot photosynthesize to produce and store the energy reserves that a plant lives on. Many roses that defoliate from blackspot in early or mid-summer also try to produce a new second set of leaves in late summer. This depletes the energy resources of the plant even more. Plants that are susceptible to blackspot are severely weakened by repeated rounds of defoliation and have little ability to survive our harsh winters. Plant size and vigor is diminished with each year of blackspot incidence until finally the rose is too weak to survive over winter. Along with blackspot's impact on winter survivability, few gardeners are willing to tolerate a defoliated rose in their garden. This leaves two options: planting black spot-tolerant roses or repeated fungicidal sprays during the growing season. Some classes of roses have a higher percentage of black spot-tolerant cultivars than other classes.

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Mossy rose gall on a rugosa rose
Dave Hansen.
The rose stem borer (Agrilus aurichalceus) (Photo 6) and the cynipid gall wasp (Diplolepis spinosa) that causes mossy rose gall (Photo 7) can be bothersome pests on cultivars within the Hybrid Rugosa class, especially when rugosas are mass planted. Both pests girdle a cane, resulting in cane mortality from the swelling or gall to the tip of the cane. Large infestations of these pests that are allowed to re-infest year after year can eventually cause so much stress to rugosa roses that they die.

Roses prefer a soil pH of 6.0 to 7.0. As pH increases above these levels, iron chlorosis becomes a problem and can lead to plant stress, low vigor or mortality. Cultivars within the Hybrid Rugosa class are particularly susceptible to iron chlorosis on high pH soils (Photo 8).
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Iron chlorosis on a rugosa rose growing in a high pH soil
David Zlesak

Coming August 1 in Rose Classes and their Performance in Minnesota: Part 2: Descriptions of some common rose classes planted in Minnesota gardens and a look at some attractive, low maintenance cultivars within classes.

Tasty Tomatoes in Containers

Karl Foord, UMN Extension Educator

There is little doubt that one of the best taste treats in a Minnesota Summer is a vine ripe tomato. In this case I am referring to a vine that you grew and a tomato that you picked when you decided it was ripe. In addition the distance it had to travel to your kitchen is measured in feet not thousands of miles. As an aside where did tomatoes come from in the first place?


Photo 1: Tumbler. Karl Foord.

Tomatoes were first domesticated by early Indian civilizations of Mexico. Cultivars were taken to Europe in the mid 1500's and then back to North America by colonists in the early 1700's. Tomatoes were slow to catch on because of their similarity to the poisonous belladonna of the nightshade family. The appeal for tomatoes took hold in the middle of the 19th century. In 1863 there were 23 known cultivars whereas in 1883 there were several hundred cultivars. Presently there are around 7,500 cultivars with a great variety of fruit sizes shapes and colors. Tomatoes also demonstrate different plant types commonly classified as determinate or indeterminate. Determinate, or bush, types bear a full crop all at once and top off at a specific height. Note the mass of flowers positioned above the foliage in the variety 'Tumbler'. Indeterminate varieties develop into vines that never top off and continue producing until killed by frost. Note the smaller inflorescence of flowers located nestled within the vine in the variety 4th of July. kf2.jpg

Photo 2: Fourth of July.Karl Foord.


Photo 3: Tumbler flowers. Karl Foord.

One goal would be to have tomatoes for as long a period during the summer as possible, and one strategy to achieve this is based on variety selection. Many but not all of the early maturing tomato varieties are determinate; however an early maturing determinate tomato is a good way to start the season. An early maturing indeterminate variety will keep fruit coming connecting early and later maturing determinates as well as the late season indeterminates.

There are advantages and disadvantages to growing tomatoes in containers. The advantages may include avoidance of; damage by critters, problems associated with soil born diseases, and most leaf diseases because the leaf surfaces dry quickly when containers can be placed in an airy location such as an elevated deck. The ambiance created by container tomatoes on a deck or patio is very appealing.


Photo 4: Container varieties. Karl Foord.

The disadvantage of containers is water related. Because determinant and indeterminate varieties develop into different size plants they have different combined leaf surface areas and thus different water needs especially at maturity. The indeterminate vines can get big and require a lot of water. If they are grown in small pots that dry quickly the plant will experience problems associated with constant water stress, one of which is blossom end rot. One way to avoid this is to select a pot size related to the tomato cultivar's growth type. In this way one can avoid the water stress problem by having a large enough pot that will hold enough water permitting the plant to be watered only once a day.

A demonstration of variety type matched to pot size is on display at the Minnesota Landscape Arboretum as part of the Powerhouse Plants exhibit.

This demonstration shows 5 different cultivars of various growth types and maturity dates in several different pot sizes (Table 1 and photo of varieties).

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Table 1.

Thursday, July 15, 2010

Garden Calendar: July 16, 2010

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Photo 1: Apple Maggot Traps Karl Foord.

Apple maggot flies are out there! See what I caught in my traps. Note the small plastic bag containing a pheromone to attract the flies.

Correction from July 1 edition of Y&G News. Past editor and Rose expert David Zlesak noted an error in last editions rose pictures. The Frau D.H. rose that is labeled at the Arboretum in the main garden is incorrect. There was one there, but a sucker from a neighboring rose snuck in and people pruned the true Frau out accidentally. See attached picture for correct flower.

Time to renovate strawberries!

We are still in the picking season for summer raspberries.

Wondering what those spots are on your rose? Black spot is common this time of year but so are several other leaf spot diseases. Check out "What's Wrong with my Plant?"

7 29 2009 Frau Dagmar Hartopp IMG_3672 (51).jpg
Photo 2: Frau Dagmar Karl Foord.

Yard and Garden News Editor: Karl Foord
Technical Editor: Bridget Barton

Thursday, July 1, 2010

The Japanese Beetles Are Coming

Jeffrey Hahn, UMN Extension Entomologist
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Japanese beetle
Jeff Hahn
Actually they are already here as their presence was reported on June 21 (in the Twin Cities area). Japanese beetles are typically first active in the Twin Cities the first week of July but the early spring allowed them to emerge sooner than normal. These beetles are broadly oval and about 3/8th inch long with a bright emerald green head and prothorax (the area directly behind the head) and shiny bronze colored wing covers. An important distinguishing feature are the five small white tufts of hair along each side of the abdomen and two larger white tufts on the tip of the abdomen.

Skeletonizing feeding on grape leaf
Jeff Hahn
Japanese beetle adults feed on over 300 different plants, commonly eating the foliage of rose, grape, linden, birch, crab apple, cherry, birch, Norway maple, mountain ash, and willow. They skeletonize the foliage, eating the leaf tissue between the veins. They particularly like to feed on plants in sunny areas and typically will start eating leaves at the top of plants and work their way down. The adults also commonly eat flower blossoms, like rose. Japanese beetle grubs are also pests feeding on the roots of turf grass.

Don't be tempted to use pheromone traps to control the Japanese beetles in your yard and garden. Although they can capture what appears to be an impressive amount of beetles, research has proven that these traps attract more Japanese beetles into the area than they actually capture. You are likely to see more Japanese beetles on your plants as a result. Pheromone traps are a useful monitoring tool to determine if Japanese beetles are in the area but they are not meant to control them.

Japanese beetle damage on rose
Jeff Hahn
If you are only seeing a small or moderate number of Japanese beetles, just handpick them. Pick them off or knock them into a pail of soapy water. This is more effectively done in the evening as Japanese beetles are active feeders during the night but anytime you can do it will help. Remember to check your plants regularly as Japanese beetles are active through September (even into October if we are enjoying a mild fall).
If you are interested in using a low impact insecticide, try a product containing neem. This insecticide deters Japanese beetle from feeding but it's much less effective on large numbers of Japanese beetles. Spinosad, usually effective against other foliage feeding insects, does not have much effect against Japanese beetles. There are a variety of residual garden insecticides that you can spray on the leaves of plants, including carbaryl and pyrethroids such as bifenthrin, cyfluthrin, lambda-cyhalothrin, or permethrin. Repeat applications may be necessary, especially if large numbers are present.

There are a couple of systemic insecticides available to home gardeners, imidacloprid and Safari (dinotefuran). If you are treating trees and shrubs, there will be some lag time (days or weeks) while the product moves up the plant. However, these insecticides are generally long lasting and should only require one treatment during the summer. There has been concern recently about imidacloprid adversely affecting pollinating bees so it would be best to avoid treating plants that are attractive to bees.

Some people want to manage adult Japanese beetles by treating their lawn for Japanese beetle grubs. This would work if the Japanese beetles in your yard and garden only came from your property. However, Japanese beetles are quite mobile, and there will still be a lot of them that will come from outside your yard to find your garden. Only treat your lawn if you are finding damage due to Japanese grubs but don't rely on treating your grass to reduce Japanese beetle adults.

The Top 14 Best Roses for Minnesota

Karl Foord and Kathy Zuzek, UMN Extension Educators

I photographed the rose collection at the Arboretum last week and tried to make sense of the many rose classifications and the varieties within each classification. Twenty three classes are evaluated in the publication Roses for the North(1). The British Association of Rose Breeders (BARB) has identified 30 rose classes, and the American Rose Society has identified 56. Regardless of which system you choose, the situation is complicated. Being faced with this situation, I consulted our rose expert Kathy Zuzek, who is the lead author of the Roses for the North publication. We decided to address the issue with two articles. The first would suggest the best rose cultivars for Minnesota based on Kathy's twenty plus years of experience. The second would be an historical article describing why there are so many categories, what each looks like, and how that category performs in Minnesota. The second article will appear in the July 15 edition of the Yard & Garden News.

The choice of best rose cultivars for Minnesota is based on three criteria, cold hardiness, tolerance to black spot disease, and repeat blooming. Simply put, the rose has to tolerate Minnesota winters through a minimum of cane die back and good regrowth vigor in the spring. The plant must tolerate black spot and not defoliate in July from pressure due to this fungal disease. The plant should produce a good flower show throughout the season.

Fourteen varieties met the criteria mentioned above. Twelve of the varieties are pictured below; varieties Cuthbert Grant and Topaz Jewel were selected but are not pictured below. Consult Roses of the North for more complete descriptions of the selected varieties.








Photo credits: Karl Foord

1. K. Zuzek, M. Richards, S. McNamara, and H. Pellett. Roses for the North - Performance of Shrub and Old Garden Roses at the Minnesota Landscape Arboretum. Minnesota Agricultural Experiment Station University of Minnesota, Minnesota Report 237-1995. 1995.

What's Happening in the Orchard?

Bacterial Blight Blacken Lilac Shoots

Michelle Grabowski, UMN Extension Educator

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Photo 1: Bacterial leaf spot of lilac Photo by M.Grabowski UMN Extension.
Recent wet weather has favored the growth of a bacterial pathogen of lilac called, Pseudomonas syringae pv. syringae. This bacterial pathogen can infect shoots, young twigs, leaves and occasionally flowers. Dark brown to black spots can be seen on infected leaves. The spots are often surrounded by a pale yellow halo. With age, the center of the leaf spot often falls out, resulting in a shot hole appearance to the leaves. Often several spots grow together into large irregular black blotches on the leaves. Even more dramatic is infection of shoots and young stems. Sunken black lesions can be seen on green stems. If the infection encircles the stem, all of the leaves beyond the infection, turn black and wither. This often results in 6-8 inches of blackened withered leaves.

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Photo 2: Bacterial shoot blight of lilac Photo by M.Grabowski UMN Extension.

Although most gardeners are willing to tolerate a few small leaf spots, many blackened withered shoots inspire gardeners to look for solutions. Sanitation is the first step in clearing up this bacterial disease. Choose a cool dry day and prune out infected shoots. Be sure to closely examine the branch before making a cut. Often oblong sunken black lesions can be seen on the stem just below the severely infected shoot. It is important to make the cut low enough on the branch to remove these infections as well. Severely infected leaves can be pinched off if desired but remember to never remove more than 1/3 of a plants leaves. Sterilize pruners between cuts and when the job is done with a 10% bleach solution, Listerine or Lysol. Bacteria are sticky and can be transferred to healthy plants on pruners used to clean up an infection unless the tools are properly cleaned.

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Photo 3: Stem lesion on lilac Photo by M.Grabowski UMN Extension.
Bacterial pathogens thrive in moist conditions. The next step in reducing damage from bacterial blight of lilac is to reduce moisture in the plant canopy. Reposition nearby lawn sprinklers or irrigation systems so that water does not spray onto the lilac leaves. If the plant is dense, prune out several branches to allow better air movement through the bush. This will help the leaves dry quickly after rain and dew. If the bush is crowded by nearby plants, remove weeds and relocate overgrown perennials or other plants to improve air circulation around the lilac.

Often these two simple steps combined with warm dry summer weather, reduce bacterial blight of lilac to the point where only a few small leaf spots remain.

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