Saturday, May 31, 2014
A new form of an old disease has been identified in Minnesota. The fungal pathogen Phomopsis sp. has long been known to cause shoot blight on spruce trees in nurseries and tree farms. The same pathogen has now been found causing cankers, needle loss, branch death and in severe cases tree death of mature spruce trees in the landscape. This disease has been named Phomopsis spruce decline. The first case of Phomopsis spruce decline in Minnesota was identified by the University of Minnesota Plant Diagnostic Clinic this spring (May 2014).
In nurseries and on tree farms, Phomopsis shoot blight causes young needles and shoots to turn brown and curl downward. In some cases dark resinous cankers formed on young stems but damage does not commonly extend beyond that years new growth. Although this disease causes damage in nurseries and on tree farms, it has not been a common problem in landscape trees.
In recent years, Dr. Fulbright of Michigan State University has been researching decline of mature spruce trees in landscapes and on tree farms. Declining trees had discolored needles that would fall off prematurely. The buds at the tip of the branch would remain alive for awhile but eventually the branch would die. These symptoms would often progress from the bottom of the tree up into the canopy. In severe cases the tree died.
Dr. Fulbright's research led to the discovery of a new type of disease caused by an old pathogen. When bark was peeled off branches of declining spruce trees dark brown staining of the wood could be seen. These infections, called cankers, were caused by Phomopsis sp. the same fungal pathogen capable of causing shoot blight in nursery spruce trees. Since then Dr. Fulbright's research group have found Phomopsis infections associated with decline of mature spruce trees in landscapes all throughout Michigan's lower peninsula.
Many questions remain to be answered about Phomopsis spruce decline. It is unknown how or why this pathogen began infecting mature landscape trees. It is known that in nurseries the disease is significantly more severe on stressed trees. It is therefore possible that stress from environmental conditions, other pests or pathogens or other factors have played a role in the development of Phomopsis spruce decline. Several other fungal pathogens infect spruce trees in both Michigan and Minnesota. These pathogens cause needle discoloration and drop, as well as branch cankers. How all of these known pathogens interact with Phomopsis sp. is unclear. At this time there are no management recommendations for trees suffering from Phomopsis spruce decline.
While research on the biology and management of this disease continues, gardeners should do their best to reduce stress on spruce trees as well as all landscape trees. Water trees during times of drought. Mulch the area around the tree with 2-4 inches of wood chips or other organic mulch. Protect trees from damage from weed whips, lawn mowers and other equipment.
For diagnosis of spruce diseases, contact the UMN Plant Diagnostic Clinic at firstname.lastname@example.org or 612-625-1275.
Friday, May 30, 2014
Flea beetles are very small, 1/16th - 1/8th inch long. They are usually dark colored although some can have red or yellow on them. An easy way to identify flea beetles is that they can jump. Flea beetles attack a variety of vegetables, including beans, broccoli, cabbage, potatoes, squash, and radish. Flea beetles chew shallow pits and small holes into leaves. This feeding can be particularly damaging to seedlings and cole crops. Go here for more information on flea beetles, including management.
Colorado potato beetles, including management.
four-lined plant bugs.
Do you have a pine, especially a mugo, Austrian, jack, or red pine, in your yard? Now is a good time to check it for European pine sawfly activity. These insects are caterpillar-like with black heads and gray green bodies and dark green stripes (when they are young the dark green stripes may not be visible). While they are relatively small now, they eventually will grow to be about one inch in length.
Your first clue that European pine sawflies are present could also be finding defoliation on branches. As feeding becomes more severe, it is usually easier to find the damage before seeing the insects. European pine sawflies feed from about mid-May through June on last year's needles. Fortunately, large trees are typically not injured, although it is possible for small trees or shrubs to be severely defoliated. There is only one generation per year.
Photo 2: European pine sawfly defoliation. Note the missing needles and how some needles have turned brown and curled.
Most contact, residual insecticides will work against sawflies. Because sawflies feed in groups, it is possible to spot treat infestations instead of treating entire trees. Examples of effective insecticides include permethrin, bifenthrin, and other pyrethroids, malathion, and carbaryl. Neonicotinoids, such as imidacloprid and acetamiprid, can also effectively manage sawflies. Apply imidacloprid and acetamiprid as sprays directly to the pine (Read the label directions of the specific product you intend to apply to ensure that it is used correctly).
These insecticides are hazardous to bees so don't apply them to flowering plants. Treat plants in late evening to minimize exposure to bees.
Tuesday, May 27, 2014
HORT 1003 Horticulture for the Home Garden, Spring 2014
Kiwi is a tasty treat that is typically thought of as a tropical or warm climate fruit. However, Minnesota gardeners can get in on the action as well. The practice of growing kiwi in Minnesota has been around since University of Minnesota's Professor Samuel Green began growing cold-hardy varieties in 1892.
According to Drs. James Luby and Emily Hoover from the University of Minnesota's Department of Horticultural Science, kiwifruit in Minnesota needs to be one of the following species: Actindia kolomikta 'Arctic Beauty', A. arguta 'Bower Berry', or A. polygama 'Silver Vine' (2). These cold hardy kiwifruits don't look like the fruits you typically pick up at the grocery store. They are hairless, skinless and generally have a much higher sugar content. These fruits are also usually about the size of a grape. A. kolomikta can be grown successfully in most areas of Minnesota because it can survive in USDA Hardiness Zone 3, while A. arguta and A. polygama, both are most successful in the central and southern part of the state, USDA Plant Hardiness Zone 4 (2).
Starting your kiwifruit
Kiwi vines can be found at many retail nurseries during the growing season, according to Luby and Hoover. To produce fruit, one male plant is needed for every six female plants. The female plants produce the berries while the male plants are the source of pollen. To differentiate the plant sexes look for at the structure of the plant and the size. The female blossoms have a center pistil to receive the pollen and are usually twice as large, according to an article by horticulturist Victoria Lee Blackstone (1). The male plant will also typically have much larger flowers than the female. Depending on your location, some varietals will be more successful than others (see chart). A. kolomikta is the top performer throughout Minnesota because of its hardiness. This is also a variety that will taste fairly similar to commercially available kiwi (2).
According to Luby and Hoover, there are multiple components to consider when starting your own kiwifruit vines. The ground must be fairly sloped and shaded from the afternoon sun. This will help keep the fruit in a moist, cool soil that is preferred by the vines. To help retain moisture, the soil can be covered with wood chips, leaves, or pine needles. This can also help control weeds, retain a consistent temperature and promote healthy roots. Although the soil needs to retain moisture, it is also important to choose a site that is well-drained and porosity (2).
The soil should have a pH of neutral to slightly acidic, around 5.5-7.5 (2). U of M Soil Test Lab Kiwifruit will also benefit from a fertilizer containing nitrogen and the chloride form of potassium. The recommended analysis of fertilizer for kiwifruit is 33-0-0, or 33% nitrogen, 0 % available phosphate and 0% soluble potash. This fertilizer should be applied from spring until early July.
Kiwi vines require support. They grow upward in a counter-clockwise direction, so using a pole or trellis will help direct the growth (4). Fencing will also help the vines grow in the proper direction and provide support.
Protecting kiwifruit during Minnesota winters is important. The onset of winter comes with two major issues for these vines: animals and weather protection. In Minnesota, cottontail rabbits can cause extensive damage to plants when they are looking for food in early winter. Fencing your vines will help prevent hungry rabbits from damaging your plants (2). Rabbits and Trees and Shrubs
Proper shading of the plants is important because of all the direct sunlight and the sun reflected off of the snow. Slipping a burlap sack or spiral wrap over the trunks will help protect your vines from sunscald (4).
(1) Blackstone, V.() Differences Between Male & Female Kiwi Vines. SF Gate. http://homeguides.sfgate.com/differences-between-male-female-kiwi-vines-45054.html
(2) Luby, J., & Emily, H. (2010, September 10). Plant and Site Selection. Commercial Fruit Production in Minnesota. Retrieved May 4, 2014, from http://fruit.cfans.umn.edu/kiwifruit/selection/
(3) Kiwifruit Berries. (n.d.). Commercial Fruit Production in Minnesota. Retrieved May 4, 2014, from http://fruit.cfans.umn.edu/kiwifruit/selection/
(4) McKenzie, J., & Emily, H. (2007). Hardy Kiwifruit in Minnesota Gardens. Commercial Fruit Production in Minnesota. Retrieved May 4, 2014, from http://fruit.cfans.umn.edu/?s=kiwi
(5) Trunk Wraps. (n.d.). Commercial Fruit Production in Minnesota. Retrieved May 4, 2014, from http://fruit.cfans.umn.edu/kiwifruit/irrigation_fert_harvest/
Friday, May 23, 2014
New research about bees and pesticides from Harvard University was recently published by Lu et al. in the Bulletin of Insectology. This research examined honey bee colonies that were fed high fructose corn syrup (HFCS) contaminated with two common neonicotinoids (imidacloprid or clothianidin) during late summer and then observed in the following spring. Both the control colonies and the insecticide exposed colonies did well going into fall. While both sets of colonies then declined, the control colony numbers rebounded while the insecticide exposed colonies suffered large losses. The authors' conclusions are that insecticides are the leading explanation for colony collapse disorder (CCD).
While this seems like compelling information on the surface, there are a number of concerns and flaws about this research that should cause readers to examine it very cautiously. The biggest concern for many is the concentration of insecticides which was fed to bees at a rate of 135.8 parts per billion (ppb), in a volume of 1.9 liters of sucrose water per colony per week, for 13 consecutive weeks. This is considered an extremely high concentration and does not represent a realistic rate of pesticide exposure to bees.
Photo 1: There are many factors implicated in the decline of bee health.
The validity of his 2012 study is further held in question by the assumption that significant levels of residues are present in HFCS as a result of neonicotinoid seed treatment of corn, an assumption that was not tested. Eventually Dr. Lu et al. did look at this issue and in a 2013 published paper that found no neonicotinoid residues in any of the tested samples of HFCS and a maximum of 2.2 ppb of imidacloprid present in pollen. This would seem to contradict the premise used in pursuing any of this research.
Other red flags that have been raised include concern for the small sample size which did not allow for sufficient replication and does not allow for such broad conclusions that considers all geographic regions; the failure to fully explain the actual cause for the loss of one of the control colonies; and failing to thoroughly evaluate other commonly accepted stresses in CCD.
It is widely accepted that there are a variety of factors that influence bee health including parasites, diseases, loss of habitat (lack of flowers=poor nutrition), decreased genetic diversity, stresses due to beekeeper and grower practices, in hive pesticides, as well environmental pesticides. More research is needed to better determine which of these factors poses the most important threats to bee health.
Wednesday, May 21, 2014
M. Grabowski, UMN Extension Educator
This time of year, several species of fungi from the genera Gymnosporangium are producing bright orange gelatinous spore producing structures on the branches of Junipers. The brilliant orange color of these fungi gives them their common name: Rust. Cedar apple rust is perhaps the most well known of the Gymnosporangium rust fungi, but here in Minnesota four different species can be found infecting junipers. Hawthorn rust, quince rust and juniper broom rust all produce similar gelatinous bright orange spore producing structures on junipers. Although these fungi can be startling to see, they rarely cause significant damage to the junipers. Spores produced in these orange gelatinous structures will not reinfect the juniper. Instead spores are carried by wind and rain to infect nearby trees and shrubs in the Rosaceae family. Each of the four Gymnosporangium rust fungi infect different members of the Rosaceae family including crabapple, serviceberry, and hawthorn. To learn more read Cedar Apple Rust and other Gymnosporangium Rusts by UMN Extension.
Unlike honey bees and bumble bees which are social insects, andrenid bees are solitary with just one bee living in an individual burrow. However, they are also gregarious meaning that many nests can live close together. Andrenid bees like to nest in dry, sunny sites that contain sparse vegetation. People can become concerned when they see dozens of bees flying around a small area. Fortunately, these bees are very docile and nonaggressive and stings are very rare. People who are allergic to honey bee stings are not necessarily allergic to andrenid bees.
Tolerate andrenid bees as much as possible. They are valuable pollinators and all reasonable efforts should be made to preserve them. Because they like dry sites, you may be able to discourage them by keeping an area well-watered. Gardeners may also be able to work around them by working outside during the evening when these bees are less active. Remember, that these bees are active for only about a month and then go away on their own.
Thursday, May 15, 2014
Pests & Diseases
Be on the Watch for Ticks!
Pictorial Ode to the Dandelion - with Special Recognition of our Pollinators
Tough Native Perennials for Wet Sites
Your Vegetable Garden
Pollination in the Vegetable Garden - Cucurbits
As I have become more aware of pollinators, I have come to accept and perhaps even embrace the "noble" dandelion. Dandelions are an important source of pollen and nectar for bees early in the season when little else is flowering.
Given the problems facing our honey bees and native bees, it might be worth reconsidering dandelions and what they contribute to pollinator health. So with my new attitude I took camera in hand and ventured into the dandelion patch (Photo 1).
Consider how artistic is the dandelion flower when viewed close-up (Photo 2). The flowers each have split lobed stigmas that curl back and sometimes twist into shapes similar to the letter F shape holes cut into violins (Photo 3). Consider also the beautiful orange color of the dandelion pollen as attached to the corbicula or pollen basket of the honey bees (Photo 4).
The dandelion also provides nectar and pollen for our native bees: Mining Bees (Andrena spp.) (Photo 5), Plasterer Bees (Colletes spp.) (Photo 6), and Small Carpenter Bees (Ceratina spp.) (Photo 7). If you use your lawn for recreation and need a dense turf as a playing surface, you may want to control dandelions. However if this is not the way you use your turf, please consider letting some of the dandelions provide forage for our pollinators. In this way you can be a part of the solution to the ills facing our pollinators.
Exhibit 2: Cucumber flowers
Exhibit 4: Male squash bees in squash flower
Cucurbit flowers are short lived flowers that open a few hours after sunrise and are often closed by midday or early afternoon. Both male pollen viability and female stigmatic receptivity are at their highest when the flower opens and for the next few hours. Both pollen viability and stigmatic receptivity decrease significantly as the day progresses. It is important for the female flower to be pollinated as early in the day as possible.
In cucurbits there is one key concept: The quality of the fruit is a function of the number of seeds in the fruit. The number of seeds produced is a function of the number of viable pollen grains deposited on the stigma. The number of pollen grains deposited is a function of the number of visits by pollinators as well as by the type of bee visiting the flower. Expressed as an equation:
Because both male and female sexual parts are not in the same flower, pollen must be transferred from the male flower to the female flower. The pollen is too large and sticky to be transferred by wind and thus requires insect transfer. Bumble bees tend to deposit more pollen per visit than squash bees and squash bees tend to deposit more pollen per visit than honey bees.
To produce quality fruit watermelon need on the average 1,000 grains of pollen deposited, whereas pumpkin, cucumber and cantaloupe need between 300 and 400.
These flowers need to be visited multiple times (@ 10 - 12) by pollinators to achieve satisfactory pollen transfer and seed set.
Like the solanaceous crops in the previous article, these plants prefer higher temperatures and are sensitive to frost. Daytime temperatures in the high 70s or low 80s degrees and nighttime temperatures close to 65 degrees are optimum for seed set and growth. Poor fruit set or misshapen fruit can sometimes be the result of poor weather which has limited pollinator activity leading to poor pollination and insufficient seed set.
Another very interesting thing about squash flowers is that there is a bee that has evolved as a pollinator specific to squash flowers. Surprisingly enough this bee has been named a Squash Bee (Peponapis pruinosa). Another fun thing is that the male squash bees will often spend the night and parts of the day in the protected space created by the squash flower petals (Exhibits 3 & 4). So if you choose to grow squash you get the potential added treat of watching these very interesting bees.
In addition squash bees are solitary ground nesting bees who will often dig their ground nests in the garden near the squash plants. If you find holes in your garden that are a half inch in diameter, it could be the entrance to the squash bees nest. The linked article in the above paragraph has a picture of the entrance to a squash bee nest. If you encounter such a nest in your garden, one option would be to avoid tilling around this nest and encourage next year's squash bees. If you continue to plant squash every year you could end up with permanent residents.
Monday, May 12, 2014
Jeffrey Hahn, Extension Entomologist
Jeffrey Hahn, University of Minnesota
Photo 1: Adult female blacklegged tick. This tick is a potential vector of Lyme disease.
As the amount of time we spend outside increases, be aware that ticks are also active now. There are two common species of ticks in Minnesota, the blacklegged tick (also known as deer tick) and the American dog tick (also called wood tick). While the American dog tick is mostly a nuisance, the blacklegged tick can potentially vector diseases to people, especially Lyme disease.
Take precautions when outdoors, especially in areas where ticks are known to occur. Use repellents, especially DEET to protect against ticks. Also check yourself over carefully after being outdoors for any ticks that may have found you. Remember that a tick has to be biting to be able to transmit a disease; if it is unattached it cannot vector a disease
Jeffrey Hahn, University of Minnesota
Photo 2: Adult female American dog tick. This tick is not an important vector of disease, it is primarily a nuisance
If any ticks are found, it is important that they are correctly identified because blacklegged ticks are important disease vectors while American dog ticks are not. Color and size are not always dependable when identifying ticks and it may be necessary to have specimens identified by an expert.
Friday, May 2, 2014
Ostrich fern (Matteuccia struthiopteris) is a tough native fern (photo 1). Some people may think the ostrich fern is too tough, with its rhizomes and substantial root system. I love the soft feathery fronds and the fact that it will tolerate standing water and survive droughts. In the driest years, the plants are shorter, the rhizomes do not spread, and the plants die back prematurely. In wet years, it begins very aggressively and grows into the adjacent lawn. I transplant it to other shady locations where I want it to grow. The fertile fronds are stiff, much shorter and still standing in the spring when I break them off and push them into the ground as a standing border for the sedge planting that is up the hill under the box elder. This acts as a border signaling my husband where to mow the lawn and not the sedges.
Canada anemone (Anemone canadensis) is another tough native that easily can be too aggressive due to creeping rhizomes. However, the tough conditions of this site keep it in bounds. It is a sea of 1-2 foot tall white flowers in the spring. The foliage is often confused with wild geraniums, but the single white flowers have a cluster of yellow stamens, typical of the buttercup family, and lack the beak-like style of geraniums. Canada anemone foliage makes a thick ground cover that competes well with other weeds, even buckthorn seedlings!
Gooseneck loosestrife (Lysimachia clethroides) is a 2-3 foot tall perennial native to China (photo 2). I am adding it anyway because it has lived in this tough situation as few other plants would. It also has aggressive rhizomes. In dry years the plants are short and do not spread at all, while In wet years it is tall and robust. I step on it to keep it in bounds as I go to the compost pile, or edge it with the lawn mower. The gooseneck flowers are fun to look at and a delight in floral arrangements. It is one plant that blooms regardless of weather conditions.
Other plants (grasses are my favorites!) that I could add in this site are:
Wood oats or Northern sea oats (Chasmanthium latifolium) (photo 3) are native to south central U.S. and marginally hardy in zone 4. This grass self-seeds and although one plant may die, another will likely come up on its own. This is a bunch grass, with no rhizomes. It has the best flowers for dried arrangements and will last for years if picked early before the seeds are fully developed. The pendulous flowers are flat and beautiful in the fall when they turn bronze and yellow. This grass is native in wooded areas along river banks and it prefers wet sites where it can grow to 4 feet. In drier sites it may only be 2 feet tall. A newer form 'River Mist' is yellow and white striped, much shorter e.g. 18 inches, and has only lived as an annual for me.
Prairie cordgrass or slough grass (Spartina pectinata) is a larger, 4-6 foot tall, long-leaved grass for wet sites that will tolerate standing water and lakeshores. Native to prairies and often found in roadside ditches, slough grass has creeping rhizomes ideal for binding lakeshores. This grass is large and coarse, good for larger sites. In areas containing only cattails or reed canarygrass, prairie cordgrass can be added to increase diversity. An ornamental form of prairie cordgrass ('Aureomarginata') has yellow stripes on the foliage and creeping rhizomes. Prairie cordgrass prefers full sun conditions, but can grow in light shade.
Native switchgrass (Panicum virgatum) is in almost every roadside ditch across Minnesota. Many ornamental forms are available; we are trialing 17 of these at the Minnesota Landscape Arboretum Grass Collection (Photo 4). Plan to come in September and pick your favorite. The 2014 Perennial Plant of the Year ('Northwind') was selected by the Perennial Plant Association for its 5 foot tall, stiff upright form and olive green foliage. 'Shenandoah' (4' tall) and 'Ruby Ribbons' (2' tall) both have red foliage and flowers. "Cheyenne Sky' is purple and red and grows to 4 feet tall. Most switchgrass plants will tolerate wet soils quite well. They are taller in wet sites and shorter under dry conditions. Switchgrass is a bunch grass and does not have creeping rhizomes, however, it can self-seed readily. Switchgrass prefers full sun conditions and will only tolerate very light shade.
Thursday, May 1, 2014
Pests & Diseases
Ignore Ash Flower Galls
Pagoda Dogwood Branches Infected with Golden Canker are Unlikely to Leaf Out
Black Leg of Geranium
Wasp Queens Active Now
The Smart Garden: Landscape Design Basics Workshop
Extension on WCCO Radio: Smart Gardens Saturdays 8:00 a.m. to 9:00 a.m.
Your Vegetable Garden
Pollination in the Vegetable Garden - Tomatoes
Tomatoes are heat loving plants that require a long frost-free season and full sun. The flowers have optimal temperature ranges and are sensitive to extremes. The flowers will abort and drop from the plant when extremes are experienced. In early spring when night temperatures drop below 55 degrees F, the blossoms can drop. In summer when daytime temperatures exceed 90 degrees F or when nighttime temperatures remain above 75 degrees F, the flowers can abort. In addition drought stress can also cause flower abortion.
The Tomato Flower
The tomato flower is hermaphroditic containing both male and female organs (Figure 1). The flower is self-fertile but not self-pollinating. The tomato anthers fuse to form a tube that surrounds the style. Pollen is released from pores located on the inside of the tube as shown in Figure 2. The flower requires vibration to shake the pollen grains from the anther pores to the stigmatic surface.
Sufficient pollen movement to achieve maximum fruit set is usually achieved when plants are grown outside and subject to vibration by wind. One reason this works is because the stigma is receptive for a relatively long period of time e.g. from 1-2 days before anther dehiscence to 4-8 days after dehiscence.
Plants grown in glasshouses do not receive enough vibration and are usually pollinated by purchased bumble bees. Bumble bees effect "buzz" pollination by vibrating their flight muscles without moving their wings (Photo 1). This serves to shake the pollen from the anthers where it falls on the stigmatic surface and the body of the bee.
Honeybees will not visit tomato flowers because the flowers have no nectaries and the structure of the flower makes access to pollen difficult.
Find ways to protect your tomato plants from low temperatures in early spring with either water jackets of various types, or row covers to hold ground heat around the plant.