Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
10/2/00
Contacts:
Paula Flynn, Extension Plant Pathology, (515) 294-0581,
pflynn@iastate.edu
Elaine Edwards, Extension Communication Systems, (515)
294-5168, eedwards@iastate.edu
Yard and Garden Column for the Week Beginning Oct. 6
Chores to Combat Disease
By Paula Flynn
Extension Plant Pathologist
Iowa State University Extension
It's easy to lose some of the gardening excitement and motivation at the end of the outdoor growing season. Although not much fun, clean-up chores are important. Getting rid of the problem plant material from this year is a good start to a better-looking landscape next year.
You can thank the resistant survival structures of disease-causing organisms for this extra work. These survival structures even have tough-sounding names, like cleistothecia (pronounced kly-sto-thee-see-a) and sclerotia (scler-o-sha). Many plant pathogens are protected from adverse weather conditions thanks to these suits of armor. Tucked in plant tissue, they are ready to do damage in the spring.
What does clean-up mean? It refers to pulling, digging, pruning, raking, bagging and maybe burning. Tools needed for the job include tough gardening gloves, pruners, a rake and a tiller.
What should you target? A good starting point is the fungi that found your perennials. Some fungi cause spots on leaves. Diseased leaves often turn yellow or brown and drop from the plant or they may wither on the stems. Peony leaf blotch is a common and easily recognized leaf disease. The large purplish leaf spots can be spotted from a distance. Another fungus infects iris leaves, causing small oval-shaped lesions.
What should you do when you spot problems? In the case of perennials such as peony and iris, cut the stems or leaves at the soil line and remove. Annual plants like tomatoes, zinnia, and sunflowers can be pulled up by the roots. Rake and collect any plant debris left behind. This includes tasks like untangling tomato leaves and stems from the stakes or cages.
Leaf spot diseases also may occur on trees, shrubs, fruits and vegetables. It's difficult to make it through a season without at least some blight on the lower leaves of tomatoes. In years with wet spring weather, shade trees often lose leaves to leaf spot diseases such as anthracnose. Even though much of the state was dry for periods this season, fungi still found a way to sneak in some action.
Crowded plantings often are more troubled with leaf spot diseases because poor air circulation favors fungal infections. Divide and replant overgrown plants when appropriate. Timing of watering also can affect leaf spot diseases. It's best to water early in the day so leaves can dry before night.
Stem and root rots caused by fungi also can be a problem in the yard and garden. When a plant has an unhealthy root system, it usually shows up as wilting, stunting or yellowing of leaves. Infected roots tend to show a brown color with the outer portion of the roots rotting off. If garden plants are found to have a rotted root system or stems, remove the diseased plants along with some of the soil adjacent to the roots. This is important because the root- and stem-rotting fungi can infect a number of different perennial species.
When pruning diseased portions of plants, especially on trees and shrubs, remember to make the cut in the healthy tissue below the obvious unhealthy area. This is to make sure all of the diseased tissue has been removed. It's easiest to prune after the leaves have fallen so the problem areas are more visible.
What should you do with the pile of sick plant parts? If allowed, burning is a good way to dispose of the debris, or burying the plant debris is another option. Along those lines, tilling the garden can help speed up the breakdown of small plant parts left behind.
Is it OK to compost the diseased plant material? Probably not. Most of us do not have a true compost pile, one that heats up to temperatures high enough to kill disease-causing organisms. If burning, burying or true composting are not possible, the best option might be to bag the material and send it off to the dump.
If you prefer to avoid end of the season tasks as much as possible, try growing some of the available disease resistant plants to your plan for next year. For instance, select beebalm varieties resistant to powdery mildew. Select crabapples resistant to the scab fungus that causes early loss of leaves. Check descriptions in garden catalogs or in the garden center for more information on resistance.
ml: isugarden
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