Crop-threatening levels of root-knot nematodes (RKN) are present in some cotton fields in southeast Missouri. The symptoms of RKN injury will initially be visible 6-8 weeks after cotton emergence and may include yellow-green leaf color, stunt, and these plants may wilt more quickly than healthy plants during a hot afternoon. Plants injured by these nematodes will have swollen areas, galls, visible on infected roots dug from the ground 6-8 weeks after emergence or soon after harvest. Farmers and/or consultants should be cautious about diagnosing the cause of yellow-green leaf color and stunt of midseason cotton because other factors such as low soil pH and drought may cause this, but only RKN causes galls on roots.
There are no reliable methods to test soil in fields for the presence of root-knot nematodes during the winter. These nematodes are dormant in eggs during this time and will not begin to hatch until the soil warms up in late May. Current tests for these nematodes can’t detect eggs in the soil but rely on detecting the newly hatched worms. So soil can be tested for them from early June through October. We learned from experiments in southeast Missouri that the best method for detecting the location of yield-robbing RKN in fields is to examine cotton roots for RKN galls soon after harvest. This method was more reliable, more rapid, and less expensive than analysis of soil samples for root-knot nematodes.
Cotton farmers can take action to protect their crop against these nematodes during 2010, but their options are limited. There are no cotton varieties highly resistant to RKN although some varieties are more tolerant than others. Growers should consider using a nematicide such as Telone prior to planting, Temik at planting, or a seed treatment such as Avicta or Aeris. The crop may be sprayed with Vydate a few weeks after emergence for nematode suppression, but a nematicide such as Temik should have been applied at planting. There are advantages and disadvantages to the use of each of these products.
Following these suggested procedures will give cotton farmers a better chance of producing higher yields and greater profits in 2010. For more information contact Allen Wrather at the University of Missouri Delta Center (Phone: 573-379-5431, E-mail: wratherj@ missouri.edu) or check the Delta Center Web Page (aes.missouri.edu/delta).
REVISED: February 29, 2012