Symptoms
The most common symptom is a slight stunting and yellowing of the plants that is not always obvious. Heavily infected plants or plants under additional stress are severely stunted and display symptoms of potassium deficiency that are similar to those caused by other root pathogens. Below-ground symptoms are not obvious, but they include a reduced root system and necrotic lesions on the roots. Small clumps of dirt that cling to egg masses on the roots may be visible with magnification. These clumps are smaller and less obvious than the galls formed on root-knot nematode-infected plants.
Yield losses are determined by the population level of the nematode in the soil and the presence of other stresses. Yield losses in moderately infested fields range from 10% to 25%. In fields under drought stress, yields may exceed 50%. Because of the relatively uniform distribution of reniform nematodes in a field, yield losses are difficult to detect during the growing season.
Causal Agent and Disease Development
The reniform nematode (Rotylenchulus reniformis) is so-called because the adult female is kidney or “reniform” shaped. The reniform nematode is not restricted to sandy soils, and distribution in a field of is more uniform than distribution of the root-knot nematode. Seedlings are infected at any stage of growth. Symptoms are usually not visible until mid to late seas[Image: Picture of root galls due to reniform nematode]on during flower initiation and boll set. Soil sampling is the best way to determine if reniform nematodes are present.
Control
Management of the reniform nematode is accomplished by crop rotation with non-host plants or applying nematicides. Peanuts, corn and sorghum are not hosts for the reniform nematode and make excellent rotation crops. Tobacco, soybeans, rice and most legume winter cover crops, such as clover and vetch, are susceptible to the reniform nematode. Fallowing is not effective because of the large number of weeds that are hosts.
Nematicides are effective at reducing early season infection. The effectiveness of nematicides depends on the population density in the soil. Non-fumigant nematicides, Temik and Nemacur, are applied at planting in the furrow or may be side-dressed. Telone II, an effective fumigant nematicide, is applied 10-14 days preplant. These materials provide a zone of protection around the developing roots of plants the first four to six weeks after planting and permit the establishment of a healthy root system. There is no resistance to the reniform nematode in commercial cotton cultivars.