As in 1995, a year of high rainfall amounts and cooler temperatures in April and May, we are again seeing damage caused by the needle nematode. Threshold numbers per 100 cc of soil for degrees of severity are 15, causing a moderate level of damage; 625, a severe level; and above 25, a very severe level of damage. Soil samples received at the University of Illinois Plant Clinic in May of this year from Mason County have ranged from 11 to a high of 124 per 100 cc of soil. A private lab reported a soil sample received from Iroquois County contained 200 needle nematodes per 100 cc of soil. All of these samples came from fields with sandy soil and with a history of continuous corn. An article entitled "It's Time to Scout for Needle Nematode Damage" and published in the Bulletin (no. 9, May 21, 1999) proved to be timely. Additional samples are being received by the Plant Clinic, and assays are under way and should be completed shortly.|
There is little that can be done this growing season in fields already planted to corn. However, damage by nematodes is greater on plants that are under stress from other factors, so the damage can be reduced, in part, by providing plants with optimum growing conditions, including adequate moisture, nutrients, and soil aeration at all times. Controlling other diseases and insects also reduces plant stress. Future rotations should avoid continuous corn, either dent corn, sweet corn, or popcorn. The host range appears to be restricted to the grass family. Therefore, rotating out of corn to soybean or other dicotyledonous crops offers the best approach for controlling the nematode. Because most grassy weeds are host to the needle nematode, it is necessary to control them when the nonhost crop is used in the rotation.
For detailed information on scouting techniques and how to collect a soil sample, please refer to the article in the Bulletin (issue no. 9, May 21, 1999).
For more information on collecting soil samples, refer to Report on Plant Diseases No. 1100, "Collecting and Shipping Soil Samples for Nematode Analysis" (available on the Web at http://www.ag.uiuc.edu/~vista/abstracts/a1100.HTML). Another publication that gives detailed information on corn nematodes is Report on Plant Diseases No. 1106, "The Ectoparasitic Nematodes of Illinois." Both of these publications are available from the Department of Crop Sciences, N-533 Turner Hall, 1102 South Goodwin Ave., Urbana, IL 61801. The cost is $1.00 per copy.--Dale I. Edwards