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Ag pest survey completedBy D. Bruce Bosley CSU Extension Agent, cropping systems Colorado This past summer Ned Tisserat, Colorado State's Extension Wheat Disease conducted a Cooperative Agriculture Pest Survey for nematodes in wheat. This was the first such comprehensive survey done for nematodes in Colorado's wheat fields. Bruce Bosley and Assefa Gebre-Amalek, Regional Extension Pest management specialist, helped in locating fields and overseeing the sampling. We collected more than 500 samples from wheat fields in counties located, for the most part, north of I-70. The main objective of the survey was to look for exotic root knot nematodes and the cereal cyst nematode. The cereal cyst nematode has been found on malting barley fields in the San Luis Valley but has not been previously reported in Eastern Colorado. Nematodes are roundworms that occur worldwide in nearly all environments. Many nematode genera are beneficial to agriculture because they contribute to degradation of crop residue and are important members in the food chain. However, about 15 percent of the species are parasitic to plants and cause crop losses valued at $8 billion annually in the United States and $78 billion worldwide. Most plant-parasite nematodes are tiny (less than 1 mm or 0.04 inch long) and live in soil. Symptoms of nematode damage on crops include stunting and/or yellowing of foliage and stunting, swelling, and/or browning of roots. Unfortunately, it is often difficult to determine that these symptoms are caused by nematodes because high pH, fertility deficiencies, excesses and deficiencies in soil water and other soil conditions frequently cause identical symptoms. Nematode damage can only be confirmed through analysis of soil and root samples. Fortunately the survey did not find any root knot or cereal cyst nematodes. However, it did find relatively high populations of stunt and lesion nematodes. According to Tim Todd, Kansas State's nematologist, the populations found in many fields could lower yields by as much as 3 percent. Ned Tisserat says "this is actually quite high and rivals or exceeds average yield reductions caused by wheat streak mosaic and the rust diseases. Unfortunately, we don't have an economically feasible means of controlling these nematodes at this time. Nevertheless, this is something to keep in mind. Growers in continuous wheat may want to get their fields tested. Also remember that these nematodes will affect corn, so any kind of rotation with that host is not a good idea." Ned plans to continue the nematode survey this year south of I-70. He suspects that stunt and lesion nematode populations may even be higher in this region. Please contact me, Bruce Bosley, about this or other cropping systems or natural resources topics at 970-522-3200, extension 285 in Sterling or 970-542-3540 in Fort Morgan. 1/28/08 Date: 1/23/08
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