The main symptoms of these three diseases are wilting, stunting and death of plants. Close examination of such plants will nearly always allow you to determine if it is a wilt, a root rot or a crown rot. These diseases are usually soil-borne (the causal organism is already present in the soil when the host is planted) as opposed to most other diseases (except nematode diseases), which are usually spread through the air. Some of these diseases may be controlled through the use of soil fungicides and/or soil fumigants, but most are controlled with resistant varieties and cultural practices. Good controls are not available for many of these diseases.
Most diseases that are called wilts are caused by fungi--Fusarium and Verticillium--and a bacterium, Erwinia. Each parasite causes wilts on a wide range of crop plants. When a stem of a plant with one of the fungus wilt diseases is cut lengthwise, a light to dark brown streaking can often be seen in the stem. It is often difficult to determine which of these wilt diseases a plant may have. Plants with Fusarium or Verticillium wilt are usually slower growing than healthy plants and may show stunting effects before wilting occurs. The lower leaves usually turn yellow and wilt first, then yellowing and wilting slowly progress up the plant. Several days to a few weeks may elapse between first evidence of wilting and death of the plant.
Fusarium wilt is a disease of tobacco and several vegetables. Verticillium attacks several vegetables. Erwinia causes a bacterial wilt and blight of corn and curcurbit bacterial wilt.
This includes those diseases in which the causal organism attacks the plant at/or near the soil line. Crown rots are called various names such as collar rot, stem blight, stalk rot and southern blight. Affected plants are generally, at first, unthrifty with leaves smaller and lighter green than normal. Leaves usually turn yellow and, in advanced stages of disease, wilt and die. The crown or base of the stem will be water-soaked, discolored or decayed. With some diseases, this area may dry rot and become shredded. A moldy growth and various colored fungus fruiting bodies often form in this diseased area. Most crops are affected by one or more of this type of disease.
Above-ground symptoms of these diseases are variable. Some plants may show wilt type symptoms and die rapidly; others may become yellow, stunted, slow growing and may not die for some time after the first symptoms are seen. Roots are reduced in size and will be light brown to black in color, with both taproots and feeder roots decayed. Most plants are susceptible to root rots.