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Friday, September 30, 2011

The Appeal of Integrated Pest Management (IPM)

Karl Foord, UMN Extension Educator

Green lacewing larvae searching for prey on a yarrow flower.

The goal of IPM is to prevent unacceptable levels of pest damage through the use of pest biology and environmental information. It seeks a solution that poses the least possible risk to people and the environment.

The great appeal of IPM is the understanding of the biological systems at play in the garden and the degree one needs to understand them in order to effectively use IPM strategies. This requires a certain knowledge and skill set. One needs to be able to identify the key insect and disease pests and the types of damage they inflict. One needs to understand the biology of these key pests and how climate influences their behavior. It is also important to understand the natural balances that exist in your garden ecology and to be able to identify beneficial organisms that are a part of that balance. The last item is to understand the use of various chemicals and their effects both direct and indirect. This is understandably quite a challenge. Among the many appealing aspects of gardening, one of them must be its challenges.

Most organisms living in your garden are benign in terms of our perspective of fruit or vegetable production. A few are labeled pests because they conflict with our goals, and a few are labeled beneficials because they tend to attack the pest organisms or because they aid in pollination and assure fruit set. Beneficial fungi and bacteria help plants absorb nutrients from the soil in the same way certain strains of E. coli help in the digestion of our food. However, consider the dilemma of labeling a yellow jacket that preys on caterpillars in the summer and feeds on ripe fruit in the fall.

IPM strategy begins with avoidance of the pest problem itself through use of pest-resistant varieties and cultural systems. For example, most fungi require leaf surfaces to be wet for a certain amount of time at a certain temperature for their spores to germinate. Cultural systems that reduce the opportunity for fungal populations to get established include: 1) proper selection of planting site, and 2) planting systems to reduce the time that leaf surfaces remain wet. Most fungal spores are omnipresent waiting for the right climatic conditions to grow, and by eliminating those microclimate conditions in our gardens we are using IPM strategies.

Some situations cannot be avoided by cultural systems and require monitoring of the plants by scouting for the presence of insects and disease. IPM recognizes that the garden exists within an ecosystem and as such there is a dynamic flux between predator and prey insect species, as well as a flux of fungal and bacterial presence based on temperature and moisture conditions.

Lady beetle larvae attacking a winged aphid on cotoneaster leaf.

The elimination of all insects through the use of a broad spectrum insecticide provides the opportunity for the fast reproducing prey species to bounce back and become an even bigger problem, or requires implementation of a time based spray schedule. The IPM strategy is to monitor insect levels and tolerate the presence of pest species as long as it remains below a threshold level. In commercial systems this threshold level is an economic level based on the cost of control materials and their application. For the home gardener this is probably not an economic number but rather an acceptable control point based on the expectations of harvest quality and quantity.

An insect example

Tarnished Plant Bug (Lygus lineolaris) is an insect whose nymph stage feeding can cause significant damage to strawberry fruit creating misshaped "button berry" fruit. In a commercial setting the nymphs would be sampled by walking through a field at 5% bloom and tapping blossom clusters against a white pan looking for the small green nymphs moving across the pan. If 25% of the 20 or more blooms tested have nymphs, the commercial action threshold has been reached and the grower should take action. This sampling would be conducted every few days to keep a close view of the pest situation.

For the home grower depending on the size of your planting, a pan of soapy water could be used instead of a white pan and all blossoms could be tapped with bugs falling into water and drowning. This would certainly reduce the population of tarnished plant bug and might reduce it below your threshold level. Also the plants could be examined for predators of the tarnished plant bug such as other true bugs "damsel bugs" or nabids (Family Nabidae), and big-eyed bugs (Geocorids), ladybird beetles, spiders, and parasitic wasps. Seethe following URL with descriptions of beneficial insects3:
This would be an example of physical removal of the pest as opposed to chemical.

A Disease Example

The use of a fungicide is based on weather conditions and the fungus in question. Leather Rot (Phytophthora cactorum) is a fruit disease of strawberries that is best managed by judicious use of straw mulch. "Straw mulch can reduce fruit diseases better than fungicides."1 Both Gray Mold (Botrytis cinerea) and Anthracnose (Colletotrichum spp.) overwinter on strawberry leaf litter and spores are transferred to flowers by splashing dispersal in heavy rains. If the temperatures are optimal the spores will germinate. Gray mold is a problem when plants are flowering whereas Anthracnose is a problem when the plants are fruiting. The IPM approach to these diseases involves use of straw mulch to reduce splash effects, removal of leaf litter as a source of disease material mostly in the renovation process2, and use of fungicides if weather conditions are optimal for fungal development.

The more you look into IPM, the more the world seems to expand.

Integrated Pest Management Manual for Minnesota Strawberry Fields Minnesota, Department of Agriculture, September, 2007.
Strawberries for the Home Garden

Field Guide for Identification of Pest Insects, Diseases, and Beneficial Organisms in Minnesota Strawberry Fields.

Further references

Managing Pests in Landscapes and Homes - A Homeowner's Guide to IPM in Minnesota

Fruit Flies

Jeffrey Hahn, Asst. Extension Entomologist

Jeff Hahn

Photo 1: Fruit fly

Fruit flies are particularly common in homes during fall. These flies, Drosophila spp., are about 1/8th inch long with a tannish body, and a dark-colored abdomen. An easy way to identify fruit flies is by their bright red eyes. However, their eyes do appear darker after they are dead and may not be as distinctive. Be careful, not every small-sized fly you encounter is automatically a fruit fly. Moth flies, phorid flies (also called humpbacked flies), and fungus gnats can also be common in homes. It is important to know which fly you are seeing because control will vary depending on which fly is present. If you have any doubts as to which fly is in your home, have an expert identify it for you.

Fruit flies can potentially be carried into homes in fruits and vegetables or they could fly in from the outside. Once in homes, they are attracted to fermenting and souring smells, e.g. around garbage containers and produce that is starting to become overripe. Fruit flies lay their eggs in a wide variety of sites as long as they are moist, contains fermenting organic matter, and are in reasonably undisturbed places.

You can help prevent fruit flies by eating fruits and vegetables while they are fresh or keep them refrigerated; do not allow produce to sit out and become overripe. Also, keep the inside of garbage containers clean from food residues. Rinse bottles and cans that you recycle and remove recyclables on a regular basis. Don't forget to periodically clean recycling containers to prevent a build-up of food residue. Remove garbage in tied plastic bags on a regular basis.

If you find you have a persistent problem with fruit flies, the most effective, permanent control is sanitation, i.e. eliminate their food source. Fruit flies are commonly found infesting overripe fruits and vegetables like bananas, tomatoes, potatoes, and onions. Also look for them around soft drink, wine, and beer bottles and cans that are being saved for recycling as well as in the recycling container itself. Another common site is trash containers especially when they are lined with plastic bags (look between the liner and the container). Remember that the source of the infestation may not be where the adult flies are found.

Fruit flies, however, will take advantage of a wide variety of different food sources and there are also plenty of unusual sites where you may discover fruit flies. You may need to be a detective and be imaginative to determine where they are coming from. In one case, fruit flies were infesting a tea maker after tea was brewed but was not cleaned out before it was put away. In another instance, they were found in rotting osage oranges (non-edible fruit that are purported to repel insects, spiders, and rodents) that were left out and forgotten. Remember that fruit flies are found in moist, undisturbed places where fermenting organic material is found.

Some people are tempted to spray fruit flies with an insecticide. While that will kill the flies you see, it is not a long term solution and more will return. Just spraying adults doesn't have any impact on the source of the infestation and the larvae that are developing. As long as a food source still exists, adults will continue to be present.

Fruit fly traps (either store bought or homemade) generally do not eliminate fruit flies. While you may capture some individuals, like spraying, it is difficult to catch them fast enough to actually eliminate them. However, you could use traps to help narrow down where infestations are located. By placing traps in every room, the trap with the most fruit flies usually indicates approximately where the problem can be found.

Clean up Fall Leaves and Clean Up Leaf Spot Diseases

Michelle Grabowski, UMN Extension Educator

M.Grabowski, UMN Extension

Photo 1: Fallen Leaves Infected with Apple Scab

As the weather turns cold, disease management in the yard and garden shifts from thinking about protecting plants this year to working to reduce disease problems next year. Many leaf spot diseases of shade trees overwinter in the fallen leaves below the tree. Apple scab on crab apple and tar spot on maple are two examples. When warm wet spring weather returns, these leaf spotting fungi become active again and produce spores that are then blown or splashed onto new emerging leaves. This starts the disease cycle all over again.

Gardeners can help reduce the amount of leaf spot fungi surviving from one season to the next by raking up and removing leaves from underneath trees that experienced a leaf spot problem this year. Leaves should be properly disposed of in a backyard compost or at a municipal or commercial compost facility. The compost needs to heat up in order to kill the leaf spotting fungi.

Removing leaves will reduce the amount of fungi available to start disease next year. Unfortunately it is not a guarantee that leaf spots will be eliminated. Fungal spores can blow in from neighboring trees and some fungi can infect small twigs in the canopy in addition to leaves. Reducing the amount of fungi directly below the tree can slow the disease down, reduce the number of leaf spots, and possibly even eliminate the problem.

Pruning Trees to Avoid "Disasters"

Karl Foord, UMN Extension Educator

USDA Forest Service
Figure 1: Crown thinning

Karl Foord, UMN Extension Educator
USDA Forest Service
Figure 2: Crown raising

Tree planted in 1997.


I have Autumn Blaze maple trees that produce great fall color and grow very quickly. In the tree trade they are known as "disasters" because they produce a very dense canopy that is subject to limb breakage in ice storms and uprooting in high winds. To avoid my trees becoming disasters I have pruned them to the point where I was pretty high up in the tree and getting in precarious positions. It was time to get an arborist. I took pictures of the trees before pruning and after pruning to see the difference and then looked on line for verification.

The arborist pursued two strategies, crown thinning (Figure 1) and crown raising (Figure 2) both taken from the USDA Forest Service publication, "How to Prune Trees".
The before and after pictures show that some lower limbs were removed and how the center of the tree was opened up, reducing wind resistance and the number of limbs available for ice accumulation.
The trees in the picture were planted in 2000. I have another set of Autumn Blaze maples planting in 1997. What is the value of the trees? If they are damaged in a storm, how much time has been lost? I would rather hedge my bets and see that they are properly pruned. The last photo shows one of the trees planted in 1997.

Calendar: October 1

Julie Weisenhorn

Acer saccharum (Sugar Maple)

Leave a couple inches of stem attached when you pick pumpkins. Since they have almost no frost tolerance, they must be harvested or protected if frost is forecast. Pumpkins ripen best on the vine, but may turn orange in storage if not completely ripe when picked. Wipe them clean with a damp, slightly soapy cloth, then put them in a warm sunny spot for a week or two to cure them. Store in a cool dark place.

Continue to mow the lawn as needed, and rake fallen leaves so grass doesn't mat down and encourage snow mold development. Or, if the leaves aren't too deep, run a power mower over them several times. This chips them into little pieces that filter harmlessly through the grass into the soil, recycling a small amount of nutrients as they break down. Otherwise, use the leaves to protect bulbs and flowering perennials, or compost them.

As the gardening season winds down, so does the Yard and Garden News. Beginning this month, we will go back to a once-monthly publication schedule until April. See you November 1!

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

Thursday, September 15, 2011

Contents: September 15, 2011

In this issue of the Yard and Garden News...

Fall Webworm
The "Cursed" Thistle - Canada thistle Cirsium arvense (L.) Scop
Preserving the Harvest: Growing Everlastings in your Cutting Garden
Swarming Ants During Late Summer
Black Leaves on Black Eyed Susan
What is the Implication of the Freeze Warning on Apple Crops?
Calendar: September 15, 2011

Fall Webworm

Jeffrey Hahn, Asst. Extension Entomologist

Jeff Hahn

Photo 1: Fall webworm feeding on black walnut

Fall webworm, Hyphantria cunea, is a web building moth that is common from mid to late summer.  It is yellowish or greenish with long, fine white hairs with two rows of black spots down its back, growing to about one inch long when fully grown.  However, an easier way to identify fall webworm is from the silken webbing that covers the ends of branches where the caterpillars feed in nonsocial groups.  These caterpillars feed on the leaves of over 100 different species of deciduous trees and shrubs, including black walnut, birch, ash, crab apple, elm, and maple.  

Fortunately, fall webworm normally has little impact on the health of large, vigorously growing, well-established trees (it is possible that small trees or shrubs can be completely defoliated in one season and could be injured).  Fall webworms are usually no worse than an eyesore because of the webs they construct, making management unnecessary.  This is especially during late summer as this feeding has little impact on plant health.  There are also natural enemies that help keep fall webworms in check and prevent serious outbreaks.  

If you want to try to improve the tree's appearance, you can try to pull the webbing and caterpillars off the branches (assuming you can reach them).  Although it may be difficult to remove the entire web, you may be able to damage it enough to eliminate the fall webworms.  You can prune out branches containing webs as along as removal is not excessive or the tree or shrub is left unsightly. Do not attempt to burn webs; this is more harmful to the tree than any control that is achieved.

If there are circumstances where it is necessary to treat fall webworms, they are vulnerable to insecticides if they are applied soon after the caterpillars start to construct their webs.  There are a variety of residual products that can be effective, including permethrin and bifenthrin.  If you wish to use a low impact product, try Bacillus thuringiensis, a bacterial insecticide.  It is specific to butterfly and moth caterpillars and has no impact on other insects as well as people and animals.  Once webs are larger, direct sprays do not penetrate through the webbing very well.  Another option is to use the dinotefuran, a type of systemic insecticide.  Another, systemic insecticide,  imidacloprid, however, is not very effective against caterpillars. 

Wednesday, September 14, 2011

The "Cursed" Thistle - Canada thistle Cirsium arvense (L.) Scop.

Karl Foord, UMN Extension Educator

Photo 1: Canada thistle rosette in lawn.

Whenever I weed my gardens I always manage to find a number of Canada thistle plants, Cirsium arvense (L.) Scop. These are not the rosette seedlings that I see in my lawn which are fairly easily dealt with (photo 1). These are aerial shoots coming from established roots (photo 2). A mixed planting garden bed presents its own set of problems in dealing with this weed. Why is Canada thistle so persistent?

Missouri State University

Photo 2: Canada thistle underground root structure and aerial shoots.

Canada thistle is persistent for three reasons. Seed production, deep roots giving rise to stems, and root pieces that can regenerate plants.

Seed production per plant averages 1,500 seeds per plant but vigorous plants have been known to produce more than 5,000 seeds with viabilities greater than 20 years. So it will take persistence to reduce the seed load in the soil. Lesson 1: never let thistle go to seed. This will not remedy seeds coming in from an adjoining property, and seeds are reported to be able to travel a half mile in the wind.

Purdue University

Photo 3: Two years underground growth of Canada thistle from original one foot of root.

Canada thistle can reliably regenerate from half-inch long cut root pieces. Lesson 2: attempts to dig out the plant or chopping it up will likely not be successful and may only serve to propagate it.

Canada thistle is a perennial with a complex system of deep-seated roots that spread horizontally and give rise to aerial shoots (photo 2). The seedlings grow slowly at first producing a fibrous taproot which thickens and develops lateral roots in 7-9 weeks. Aerial shoots usually develop from buds on the branches of the horizontal system. The root system goes deep (6 - 10 ft.) and wide (> 10 ft. per year) with some 60% of roots existing at depths greater than 2 ft (photos 3 and 4).

Purdue University.

Photo 4: Extensive underground root systems of Canada thistle.

To eliminate Canada thistle one needs to prevent regrowth from the potentially extensive underground root system. The non-chemical approach involves strategies that persist until the starch reserves in the roots are exhausted. The chemical approach involves application of herbicides at the correct dosage avoiding damage to nearby plants.

Simply removing the aerial shoots can eventually exhaust the root reserves. One study showed that mowing the plants would eliminate the top growth similar to pulling the aerial shoots, but will not deplete the starch reserves unless it is repeated at 7-28 day intervals for up to 4 years. It is more likely that the thistle would win given this strategy.

If the plant can be isolated, it can be smothered with an impenetrable barrier like plastic or a landscape weed cloth. This would require clearing out the bed and dedicated time to starving the root system. The key problem here is isolating a plant with a creeping underground root system that could send up shoots in adjoining areas which would replenish the root system.

Photo 5: Canada thistle in sedum bed. A situation where a bedding plant could be isolated from spray on a Canada thistle.

If the chemical route is chosen, a non-selective herbicide like glyphosate (Roundup®), which has little or no soil residual, would be the chemical of choice. In some situations sensitive plants can be separated from the thistle and protected from spray with a physical barrier like plastic (photo 5). The plastic may be removed as soon as the spray dries.

Photo 6: Canada thistle in cotoneaster bed.

In other cases protecting sensitive plants is not possible such as a thistle nestled in a cotoneaster bed (photo 6). In this case one can apply material with a paint brush or spot spray taking care not to get spray material on the sensitive plant, and if you do wash it off immediately.

The goal is to kill the root system by getting as much chemical throughout the plant as possible. Use the lower of label recommendations as higher rates will kill the leaves and not get to the roots making the treatment ineffective. Make sure that the plants are not drought-stressed and that there is plenty of moisture. If the plants are stressed the chemical will not be effectively translocated throughout the root system. Be sure to read and follow all label directions carefully. It is highly likely that multiple applications may be needed to eradicate this weed.

Given the look of the below ground root systems it looks like the most we can hope for with Canada thistle is not elimination but rather a certain level of control.

"Canada Thistle." Midwest Weeds, Missouri State.

"Control Practices for Canada Thistle."
Purdue University, Department of Botany and Plant Pathology.

Preserving the Harvest: Growing Everlastings in your Cutting Garden

Robin Trott, UMN Extension Educator, Douglas County

Robin Trott

Helichrysum (strawflower).

My house has been full of beautiful floral arrangements all summer, and the fall arrangements are outstanding, however, we will soon enter the cold months, and I can't envision a house without the color from my garden. To avoid this, I have made sure to include some everlasting plants in my cutting garden: Limonium sinuata (Statice), Helichrysum (Strawflower), Gomphrena, Achillea (Yarrow), Celosia (Cockscomb), and ornamental Grasses are all good candidates for air-drying. Once dried, I use these everlastings in bouquets, sachets, wreaths and holiday crafts.

Robin Trott

Echinacea (purple coneflower).

Harvest your everlastings when the flowers are not fully open and in good condition. Don't wait too long, because flowers too far along will not dry satisfactorily. Select flowers or seed pods that are as close to perfect looking as possible because flaws, such as insect damage, become more obvious once they are dried. Pick your flowers in the late afternoon, after the heat of the day has passed and before the evening dew has set in. Using a sharp, clean tool, cut flowers close to the base of the plant (to keep stems as long as possible) and remove foliage from the stem to preserve the best color and shape. Group stems together in small bunches so the flower heads do not touch, secure with a rubber band or string and hang upside down in a warm, dry, dark area. Your garage, attic, spare room, garden shed or even a closet will do. With good air circulation, flowers take 1 to 3 weeks to dry completely. Store dried flowers in an airtight container until ready to use. Dried plant material can be stored in cardboard boxes; however, plants are better protected from insects and rodents if they are stored in airtight containers.

Robin Trott
Celosia spicata.

If you have never tried to dry your flowers, and are not sure what to include in your cutting garden, try some of these flowers and seed heads that lend themselves to air drying:

Achillea Spp. (Yarrow) - perennial
Asclepias (Butterfly Weed) - perennial, primarily for seed pods
Astilbe - perennial
Artemisia annua (Sweet Annie) - self seeding annual
Calendula (Pot Marigold) - annual
Celosia - annual
Centaurea cyanus (Bachelor's Buttons) - annual
Echinacea (Purple Cone Flower) - perennial primarily for cones
Eryngium (Sea Holly) - perennial
Helichrysum (Straw Flower) - annual
Hydrangea- woody perennial
Gaillardia (Blanket Flower) - annual
Echinops (Globe Thistle) - perennial
Gomphrena- annual
Physalis alkekengi (Chinese lantern)
Grains (Oats, Wheat, Millet)
Ornamental Grasses
Gypsophila (baby's breath) - perennial
Limonium (statice) - annual
Lunaria annua (Money Plant, Honesty) - annual
Nigella damascena (Love in a mist) - annual, primarily for seed pods
Rudbeckia (Black Eyed Susan) - perennial, primarily for cones
Solidago (Goldenrod) - perennial

Good luck with all your everlasting adventures!

Swarming Ants During Late Summer

Jeffrey Hahn, Asst. Extension Entomologist

Jeff Hahn

Photo 1: Field ant swarmers

There have been numerous sightings of winged ants during August and September throughout Minnesota. These winged ants are reproductives, i.e. new females (soon to be queens) and males. The fly out of their nests at the same time, usually in large numbers for the purpose of mating. After mating, the queens fly off in search of favorable sites to build their own nests and the males die shortly afterwards.

Although nearly all ants swarm, different species do so at different times of the year. Right now cornfield ants and field ants are the primary swarmers that are active. Both of these ants nest in the soil in exposed sites and can be commonly found in lawns and other turf areas. Cornfield ant queens are about 1/4 inch long while field ants are a little larger.

Because of their size, field ants are sometimes mistaken for carpenter ants. However, carpenter ants do not nest in the soil and swarm just during spring. These swarms sometimes are mistaken for termites. However, termite swarms are rare in Minnesota and when they do fly, they occur in the spring. They are also have four wings of equal length which are much longer than their bodies.

Despite the impressive numbers that nests can generate, these swarming ants are harmless. They presence is also temporary, usually lasting just a few days. No control is necessary.

Black Leaves on Black Eyed Susan

Michelle Grabowksi, UMN Extension Educator

J. Beckerman

Photo 1: Septoria Leaf Spot on Rudbeckia

This time of year the beautiful display of yellow flowers put on by Black Eyed Susan plants (Rudbeckia sp.) is often ruined by the plant's leaves turning partly or completely black. The leaf discoloration is caused by the fungal pathogen Septoria rudbeckiae. This pathogen causes dark brown to black leaf spots much earlier in the season. The disease often begins on the lower leaves of the plant and may go unnoticed. As the season progresses, so does the disease.

By September, plants may not have a single green leaf remaining. Septoria rudbeckiae will survive in plant debris, so it is best to remove infected stems and leaves at the end of the season. These should be discarded in a backyard compost that gets hot or at a municipal composting site. Next year, thin plants and remove volunteer seedlings to provide good air movement around plants. Water with drip irrigation or early in the day so leaves dry quickly in the sun. Look for leaf spots early in the season and pinch off infected leaves. Never remove more than 1/3rd of a plants foliage. For more information read Diseases of Rudbeckia.

Q&A: What is the Implication of the Freeze Warning on Apple Crops?

Julie Weisenhorn

Emily Hoover, professor and department head, UMN Department of Horticultural Science

Question: What is the implication of the freeze warning on the apple crop?

Answer: It depends on how cold it gets. The temperature within an orchard is not consistent. The "rule of thumb" is about 10% of the fruit on the tree will freeze if the temperature drops to 28 degrees Fahrenheit and remains so a few hours. Ninety percent of the apples will freeze if the temperature drops to 25 degrees Fahrenheit and remains so for a few hours.

However, the level of sugar in an apple also changes the severity of the event. The higher the amount of sugar, the lower the temperature has to be before freezing will occur because sugar lowers the freezing point of a solution. (Think Chemistry 101). Note that if the fruit freezes on the tree, but is not touched until it thaws, the fruit is fine to harvest.

Emily Hoover is a professor and department head in the UMN Department of Horticultural Science. Her research focuses on apple rootstocks.

Original source: "Over the Backyard Fence," blog of Master Gardener state program director, Julie Weisenhorn.

Calendar: September 15, 2011

Bridget Barton

Three-Mile Drive at the Minnesota Landscape Arboretum, October 2010.

According to the Minneapolis Star Tribune, the Minnesota DNR is predicting the best fall color in ten years, thanks to abundant rain during the growing season, as well as a hot, humid summer. The DNR fall color reports are now available, to help find the most vibrant color in the state. The University of Minnesota Climatology Working Group, a division of the DNR, has more interesting information about the cause of the spectacular color show we enjoy each fall.

The Minnesota Landscape Arboretum and the Minnesota Grape Growers Association are teaming up for the upcoming collaborative, 4X4 Culinary Series at the Arboretum. For the series, U of M Enologist Katie Cook will lead participants through four food and wine pairings over a series of four dinners prepared by leading Twin Cities chefs. Participants can sign up for any or all of the dinners to experience a full array of local wines and meals this fall and winter. More information can be found on the MN Landscape Arboretum website; Kare 11 also did a feature highlighting the series and local wines.

Order spring flowering bulbs to plant later this month or next. Water them thoroughly after planting. Unless there's ample rainfall, continue watering every couple weeks so they develop good roots before winter. Mulch them once the soil freezes. The longer you wait to plant your bulbs, the less likely they'll come through winter successfully. Tulips are more forgiving than other bulbs, but it's still best not to plant them too late.

Can't get enough University of Minnesota Extension News? Follow UMNExt on Twitter!

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

Thursday, September 1, 2011

Emerald Ash Borer Found in Two New Sites

Jeffrey Hahn, Asst. Extension Entomologist

Jeff Hahn

Photo 1: EAB on purple trap

Emerald ash borer (EAB) has been confirmed in two new locations by the Minnesota Dept. of Agriculture (MDA) on Friday August 26. One find was detected in the city of La Crescent in Houston county while the second was found in the Great River Bluffs State Park in Winona county, just eight miles apart. This is the first time EAB has been found in Winona county. Both discoveries were made when an EAB adult was found on sticky purple panel traps that were deployed by the MDA. No infested trees have been found to date, although surveys in those areas are ongoing.

For more information see the MDA news release

Late Breaking News:  On Wednesday August 31, MDA reported that EAB was found on another purple trap about 7 miles northwest of the positive trap location at Great River Bluffs State Park and about 7 miles east of Winona. 

September Ushers in Prime Time for Home Lawn Care Activities

Bob Mugaas, UMN Extension Educator

Bob Mugaas

Late summer lawn and landscape.

The arrival of the Minnesota State Fair and its wrap-up on Labor Day weekend, mark the beginning of one of the best times of the year for initiating and renewing home lawn care activities. When it comes to repairing and rejuvenating your lawn after it has endured the stresses of another summer, avoid the temptation to also be winding down your lawn care efforts once Labor Day has passed. The main reason is that our grass plants are entering a very active period of growth triggered by a shortening of the days, cooler temperatures and usually a return to more frequent rainfall. Following are a number of brief lawn care tips that can help restore any lawn's health and vigor.

1. The middle of August through the middle of September is one of the best times of the year for lawn renovation and reseeding. Practices such as dethatching and aerifying are all best done at this time of year. Again, the primary reason for this is related to the grass plant's active period of growth and recovery during early to mid fall.

2. In addition, our soils are nice and warm from the summer heat. Warmer soil temperatures and ample moisture make this one of the best times of year to be doing some (re)seeding. Grass seed germinates and establishes more quickly increasing the chances of good winter survival. Also, because we have passed the time for many of our annual weed seeds to germinate and grow, there will be virtually no competition from annual weeds such as crabgrass, yellow foxtail, lambsquarters or common ragweed.

3. Putting down some nitrogen(N) fertilizer at the rate of one pound of N per 1000 square feet from late August through about the middle of September will be beneficial. This is the time of year when our grass plants readily absorb the nitrogen applied and use it to support various plant processes during the active fall growth period.

Bob Mugaas

Late summer early fall provides good control of common dandelion.

4. By later in the month, we are getting to the time of year when we can be most effective with herbicides at controlling those perennial broadleaf weedy plants such as dandelions, white clover, creeping Charlie and broadleaf plantain. Like our grass plants, these weedy plants are also actively growing and will actively take up and transport the weed killer throughout the plant giving better control. For example, dandelions are best treated from about mid-September to early October in the Twin Cities area. Plants will be killed this fall but the real difference will be observed next spring when there are few to no dandelions in what may have been a previously heavily infested area. However, this is not the time of year to be putting a preemergence crabgrass killer down hoping to have success next spring. Preemergence crabgrass killers are much more effective when used and applied properly in the spring.

5. One of the most common questions this time of year is, "How long into the fall should I continue to water my lawn?" The easiest answer is to continue watering so long as the plant continues to need water. In other words, if we have extended dry periods in the fall, grass plants will still need water to support active growth at this time of year. Remember that just because temperatures are cooler and days are getting shorter, soils will still dry out during extended periods of no rainfall or supplemental irrigation. It is desirable to gradually lengthen the time interval between watering to allow the soil to slightly dry before adding some water. This will help prepare the grass plants to better survive harsh winter conditions.

Likewise, these same conditions can make it easier to overwater and keep the plants too wet. Overly wet soils are very stressful for grass plants and can significantly increase certain diseases and just generally weaken the plant. As a gauge for your own lawn, check the soil moisture level periodically. If it feels damp to maybe just slightly dry and not wet and sticky that's probably about right for soil moisture during the late summer fall period.

6. At least during the month of September, mowing should continue on a regular basis maintaining a lawn height of about 2.5 to 3.0 inches. Heights can be gradually reduced back to about 2.0 to 2.5 inches by the time we get into late October. Remember that right now and for the next several weeks grass plants can take advantage of higher heights of cut by producing more food via photosynthesis due to more leaf tissue present. That also translates into very active root growth such that roots will extend deeper into the soil and in general develop a more robust root system. Both conditions aid in the uptake of water and nutrients from the soil thereby contributing to a healthier plant.

For many people, September marks the beginning of many family things like vacations ending, children going back to school, volunteer activities resuming and the like. With as busy as things can get in our family lives, try to remember this is also a time of new beginnings and renewal for our grass plants and lawns. Providing some additional nitrogen nutrition, watering during dry periods, mowing regularly and doing some reseeding to those injured and damaged areas of the lawn are all perfect activities for this time of year. In addition, restoring and maintaining a healthy lawn in the fall significantly contributes to better winter survival and a healthier lawn next spring.

For more information on any of the above topics see the lawn section on the University of Minnesota's website under Garden. You can also find lots of information about Minnesota home lawn care on the Sustainable Urban Landscape Information Series website. Got an unfamiliar weed in your lawn? Check out our on-line weed identification guide at "Is this Plant a Weed?" from the Garden link mentioned above. You can also find out how to control many of the common lawn weeds on that site as well.

Giant Swallowtails

Jeffrey Hahn, Asst. Extension Entomologist

Wendy Pritchard

Photo 1: It's a treat to see a giant swallowtail

There have been several reports of people seeing giant swallowtails, Papilio cresphontes, in the Twin Cities areas recently (they undoubtedly have been seen in other areas of Minnesota as well). This is noteworthy as these spectacular butterflies are not native to Minnesota but can occasionally be found during the summer as migrants from the south.

You can recognize a giant swallowtail because of its size, its wingspan ranges from 4" - 5 ½", and its black wings with yellow spots; the yellow spots on the forewings form an 'x'. Don't confuse it with a black swallowtail which also has black wings but is smaller, its wingspan is as large as 3 ½" and the yellow spots on its forewings are parallel and do not cross. Giant swallowtails can not reproduce in Minnesota as they need citrus trees and related plants for food for the larvae.
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