Response of soybean cyst nematodes to herbicide application on soybeans

The effect of herbicide applications to V3 soybeans on the reproduction of race 3 soybean cyst nematode (SCN) was measured. The hatching response of SCN eggs to soybean root exudates collected after postemergence herbicide application, the viability of SCN eggs formed on treated plants and the levels of glyceollin in roots of treated soybeans were also measured. Soybeans were treated postemergence with 1X and 2X rates of herbicides plus a recommended adjuvant and/or the adjuvants alone. None of the treatments tested were found to stimulate SCN reproduction. Acifluorfen, bentazon, lactofen, crop oil concentrate (COC) and nonionic surfactant (NIS) treatments reduced soil populations of SCN by 50 to 60% at four and eight weeks after application when compared with the untreated control. Fluazifop-P, sethoxydim, and imazethapyr treatments had no effect on SCN reproduction. Adjuvant treatments were as effective as acifluorfen, bentazon, and lactofen treatments in reducing SCN reproduction. However, no additive effect for adjuvant-herbicide combinations was observed nor did herbicide rate affect SCN reproduction. Treatments reduced SCN reproduction only when applied to soybean plants and exhibited no effect when applied to the soil. All root exudate solutions (RES) increased SCN hatching more than deionized water, but less than ZnSO4 solutions. However, no statistical differences due to herbicide treatment were observed. Filter sterilization of RES increased SCN hatching when compared with the use of non-sterile exudates. Acifluorfen, bentazon and lactofen treatments negatively affected the hatching potential of SCN eggs from adult females that developed on treated plants. Acifluorfen, bentazon, COC and NIS treatments also increased glyceollin levels in soybean roots four days after application. Glyceollin has been shown to accumulate in some soybean roots following infestation with SCN and has been implicated in SCN resistance. Therefore, these herbicide treatments may have indirectly induced a level of SCN resistance in a susceptible soybean, thus lowering SCN reproduction. The use of some postemergence herbicides may be expanded to include SCN management