Extension Educator, Horticulture
I anticipate particularly lively conversation during my next pedicure. Can people develop webbed feet? I've sloshed around in my garden so much lately I'm a good candidate to test the hypothesis.
We can buy taller boots, but plants are not so fortunate. Nancy Pataky, director of the U of I Plant Clinic reported in the U of I Extension Home, Yard and Garden Pest Newsletter excessively wet soils can lead to rotted roots and crowns of garden plants.
Generally root rots are caused by soil-inhabiting fungi that could have arrived on plants or soil brought into the garden. Or the fungus may have been there all along but remained inactive or at low populations as long as plants were vigorously growing. Once stress hits due to drought or (more commonly this year) flooding, some roots die and the fungi invades.
Root rots can develop in new transplants as well as mature plants. First plant symptoms of root or crown rots are smaller leaves than normal, slow growth, or rapid wilt on a warm day even with adequate water. The lack of healthy roots hinders the plant from taking up enough water, especially during hot weather so the plants wilt. Plants may appear to recover as weather cools.
Leaves may turn yellow then brown and drop prematurely, usually starting with the older leaves and moving up the plant. Sometimes one stem in the cluster will suddenly wilt, turn brown and easily break off at ground level. Severity of the rot depends on the disease causing fungus, the susceptibility of the host plant, and the soil and moisture conditions.
If a root rot is suspected, Pataky recommends carefully digging the plant and placing the roots in a bucket of water to gently dislodge the soil. Do not wash vigorously all of the rotted tissue will be washed off, often leaving a white root interior that appears healthy. Examine the roots for indications of rotting.
A healthy plant has numerous white fibrous roots. Roots of a diseased plant show various degrees of mushiness and usually are some shade of brown or black, both externally and internally. Healthy roots feel firm. If the roots seem healthy, you could replant the plant perhaps in a drier, more suitable spot.
UI Plant Clinic http://plantclinic.cropsci.illinois.edu/ can help to determine fungus involved, but observing symptoms can also help. Pataky states the major root-rot fungi in Illinois landscapes are Rhizoctonia and Fusarium which appear as a dry rot often with a reddish pink cast; in comparison Pythium and Phytophthora cause a mushy, brown-to-black rot of roots.
Pataky recommends preventing rots from becoming a problem by using sound horticultural practices. This includes use of healthy transplants, proper site preparation to provide good water drainage away from roots, use of balanced fertilizer, and rotation in the garden plantings for 2 or 3 years with unrelated plants to help prevent the buildup of pathogens. Remove infected plants quickly and remove plant residue at the end of the season. Once a pathogen is identified, try to find and use resistant varieties when available. Remember to check the soil for moisture before assuming a wilting plant needs more water.
Even if all of the above practices are followed, rot may still occur especially if we see continued rain. Fungicides are available to control the major groups of fungi. However, fungicides protect plant stems and roots not yet affected. They do not "cure" infected plants. Fungicides may be helpful when a root rot is discovered in a flowerbed and the goal is to preserve remaining healthy plants. Be sure to read and follow all label directions on fungicides. Also be sure the plant and fungus in question is listed on the label.