The Homeowners Column

The Homeowners Column

Wet Then Dry Brings Diseases

Photo of Sandra Mason

Sandra Mason
Extension Educator, Horticulture
slmason@illinois.edu

Each season brings new thrills and chills in plant land. Nancy Pataky, director of the University of Illinois Plant Clinic, gave a run down on this year's prevalent diseases in a July edition of U of I Extension Home, Yard and Garden Pest Newsletter.

Here are some frequently seen diseases at the U of I Plant Clinic this summer. It coincides with much that we are seeing at University of Illinois Extension - Champaign County office.

We have seen many cases of fungal root rots on herbaceous plants. The earlier wet weather and now drought stress has favored the development of fungal diseases in roots and crowns of many annual and perennial plants. They cause root loss, which the plants may be able to withstand until hot dry conditions. Plants may wilt during the hottest part of the day and then recover at night. In more severe cases plants may show wilting, then dieback of stems.

At the Plant Clinic two fungal wilt diseases, Dutch elm disease and oak wilt, have been confirmed in a few cases. We have not seen too many cases of sudden death of pine due to pine wilt but expect that soon.

The early season fungal leaf diseases were abundant this year because of the cool, wet spring. This includes anthracnose of many plants, including ash, oak, sycamore and maple. New leaves look better, without infection, but old leaves remain tattered for the season. These should be raked and removed when possible.
Other fungal diseases have been easy to find including cedar-quince rust on hawthorn, Sphaeropsis blight of pines, black spot of rose, Cytospora of spruce, and slime molds in general.

The bacterial disease fire blight has been very common on crabapple, apple, pear, and a few other plants in the Rose family. The tip of the branch bending over like a shepherd's hook characterizes this disease. The leaves appear dark brown or black and remain on the branch as though they were burnt. This damage followed by heat and drought may contribute to the decline of many woody plants. Removing the infected branches during dry weather will help to control this disease. Be sure to sterilize pruners with alcohol or bleach between each cut well below the diseased area.

River birch leaves started yellowing particularly early this year and may be stressing these plants enough to cause branch dieback. River birches prefer an acidic soil otherwise a lack of iron will cause the chlorosis or yellowing.

One of the best management techniques to help plants recover from disease is watering during drought periods.

Sources of answers to your gardening questions include:

The Plant Doctor is in. Stop by the Idea Garden on south Lincoln in Urbana on Sundays 1-3 to ask the Master Gardeners your gardening questions.

The 2002 University of Illinois Turfgrass and Landscape Field Day is scheduled for Thursday, August 1, 202, starting at 8:30 am at the Landscape Horticulture Research Center and the Hartley Selections Garden, both on South Lincoln Avenue in Urbana. This annual event is planned to provide current information and education to professional turfgrass, nursery, landscape, and garden center personnel, as well as Master Gardeners and home horticulturists. Specialists will be on hand to answer your plant questions. $25 Advance registration before July 24 includes lunch. For registration information, phone Carol Preston, (217) 333-7738.

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