Extension Educator, Horticulture
I thought for sure in July that I would be writing a story on 10 ways to keep your plants alive during a drought. I knew I would be consoling others and myself on how the death of that drought stricken plant is just an opportunity to plant a new one. Instead our office is getting calls about plant problems related more to excessively wet conditions. I'm not complaining. I'll take this kind of drought any day.
As Nancy Pataky, director of the U of I Plant Clinic reports in the U of I Extension Home, Yard and Garden Pest Newsletter excessively wet soils have led to many cases of rotted roots and crowns on annual and perennial flowers. It may seem surprising, but more problems are being seen with established plants rather than newly planted transplants. Roots of established plants were initially injured by drought.
The first indication of root rots or crown rots is the plants may be stunted, growing slowly, or may wilt easily on a warm day. Sometimes the plants seem to recover as the weather cools. Wilting is not always an indication of a lack of water. The lack of healthy roots hinders the plant from taking up enough water, especially during hot weather. The 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. Pataky states the 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 removing the plant from the ground carefully, placing it in a bucket of water to gently dislodge the soil. Then examine the roots for indications of rotting. If roots are washed too vigorously, all of the rotted tissue will be washed off, often leaving a white root interior that appears healthy, but is actually much thinner than healthy white roots.
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.
Pataky states the major root-rot fungi in Illinois landscapes are Rhizoctonia and Fusarium which appear as a dry rot of roots often with a reddish pink cast and Pythium and Phytophthora which cause a soft, brown-to-black rot of roots. The Plant Clinic can help to determine which fungus, but symptoms can also help suggest the fungus involved.
Pataky recommends preventing rots from becoming a problem in our gardens 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 two or three years with unrelated plants to help prevent the buildup of pathogens in one area. It is also important to remove crop residue at the end of the season to help reduce pathogen survival. 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. Fungicides are available to control the major groups of fungi. However, fungicides protect plant stems and roots not yet affected, but 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 are listed on the label.