Answers to your rain questions

Published 1:08 am Sunday, July 22, 2007

For so long I have been advising people how to handle drought situations and how to properly water during dry times, this has obviously changed significantly. Now we are receiving calls about how to deal with excessive rainfall in areas. There are many diseases and problems cause by excessive rainfall in many plant species.

Q. Will all this rain affect my tomatoes?

Whenever we receive steady rainfall over an extended period of time conditions become favorable for the development of a physiological disease referred to as water wilt. Water wilt is common in tomatoes but may also affect peppers, beans and other garden plants.

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The first sign of water wilt is a slight wilting of foliage in the top of plants following several inches of rainfall within a short period. The wilt continues, and the entire plant may collapse within six to 12 hours. Plants growing in well-drained soils generally recover within a day; however, tomatoes planted in heavy, poorly drained soils may not be so fortunate. As a result of poor drainage, roots may be exposed to waterlogged soil conditions for several days, and this often leads to death of tomatoes or other affected garden plants. Under soggy soil conditions, roots use up available supplies of gaseous soil oxygen, which is replaced by toxic levels of carbon dioxide. Roots can’t survive without oxygen, and extended periods without this essential element lead to plant death.

Gardeners shouldn’t count on plant survival, since in most cases root systems have been damaged beyond recovery and plant replacement is often necessary. Water wilt is a good reason to think about making raised-row gardening part of your vegetable production program.

Q. How are the recent rains affecting my trees?

The answer is quite simple; we were in desperate need of rain for vegetable gardens, flowerbeds, trees and all landscape in the yard. Water is always a positive thing when in moderation, however recent excessive rainfall does have negative effects. If roots are exposed to standing water for extended periods, roots often die from “anoxia,” a term which means oxygen starvation. Damage occurs to trees and shrubs in obviously wet areas in the home landscape. Since damaged plants lack the ability to pick up water because of damaged root systems, one of the first symptoms of damage from soggy soils is wilting. Affected trees and shrubs may also show symptoms of nitrogen deficiency (leaf yellowing). After the soil drains, plants with severely damaged roots may subsequently suffer drought stress and eventually die. For many of these plants, the only functioning roots are near the soil surface, and when extended hot and dry weather follows a wet period, surface roots quickly dry out. Plants exposed to prior flooding become more susceptible to Phytophthora root rot or collar rot. Prolonged exposure to wet conditions promotes susceptibility to this disease.

Unfortunately when dealing with trees, not much can be done to improve surface drainage that will allow soggy soils to aerate faster. However, don’t stress about older mature trees, most full grown, well established trees and shrubs should be cope well even after the worst rains. Some trees to watch for are the American beech, crabapple, flowering dogwood, hawthorn, Southern magnolia, pecan, peach and redbud as these are susceptible to problems with excessive rainfall.

David Carter is director of the Adams County Extension Service. He can be reached at