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Extension > Yard and Garden News > Archives > October 2011 Archives

October 2011 Archives

Contents: October 1, 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: http://www.mda.state.mn.us/plants/pestmanagement/ipm/strawberry-guide.aspx
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.

References:
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

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.

USDA Forest Service

Figure 2: Crown raising

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".

Before

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.

After

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.

Tree 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

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