Nematodes have been called the “hidden enemy” of soybean because these soilborne, microscopic root pathogens can go unnoticed in a field until yield losses become severe. The number of soybean fields showing visible damage due to nematodes has increased dramatically during the last few years statewide, and most of the time the root-knot nematode is the culprit. There are several likely causes for the increased visibility of nematode issues in general, and root-knot in particular in soybeans.
Widespread changes in cropping systems, including growing soybean in fields that were historically in cotton monoculture and wide adoption of soybean – corn cropping systems may be contributors. To complicate matters, there are very few early-maturing (MG IV – early V) cultivars that are adapted to Arkansas with effective resistance, and the increased incidence of herbicide-resistant weeds as unwelcome residents may provide additional survival and reproduction opportunities for nematodes, particularly root-knot.
Figure 1. Nematode damage in soybean
To help us get a handle on the extent of the nematode issue in the state, the Arkansas Soybean Promotion Board, in partnership with the Arkansas Nematode Diagnostic Laboratory, will be offering a “no cost” opportunity for county agents, consultants, industry representatives, and growers to survey their soybean fields this fall for nematodes.
Beginning immediately, the Arkansas Nematode Diagnostic Laboratory will be accepting soil samples for nematode assay from fields that are currently in soybean, fields that will be in soybean next year, and fields in longer-term cropping systems that included soybean within the last 2-3 years. Under this educational program, our normal cost-recovery fees for nematode assay will be waived thanks to funding assistance from the Soybean Promotion Board.
Early fall is a good time to sample fields for nematode assay. Nematode damage is more visible now than at any other time in the season (Figure 1), and although root-knot isn’t the only nematode of concern for soybean growers, if it is present it can be easily diagnosed this time of year due to the root galling that occurs (Figure 2). Remember, however, that some apparently healthy fields may have nematodes that are not yet causing damage to the crop at a visible level, so keep this in mind when choosing fields to sample.
Figure 2. Root-knot nematode galling on soybean roots
Why not take advantage of your check-off dollars at work and find out if nematodes are a problem (or a potential future problem) on your or your client’s farm? For details about this survey, to participate in this free assay program, or for information on proper sampling and handling of samples, contact your local county agent, the Arkansas Nematode Diagnostic Laboratory at: (870) 777-9702, extension 128; choward@uaex.edu, or call Terry Kirkpatrick at (903) 276-4484.
