Influence of Two Herbicides on Soybean Cyst Nematode (Heterodera glycines) Reproduction on Henbit (Lamium amplexicaule) Roots

Soybean cyst nematode (SCN) is the most yield-limiting pathogen of soybean in the United States. Henbit is a prevalent winter annual weed species in no-till fields and is reported to be an alternative host of SCN. A greenhouse study was conducted to evaluate how the development of SCN on henbit roots was affected by herbicide mode of action and time of herbicide application. Henbit plants were grown in watertight pots placed in a water bath bench that kept soil temperature constant (27 ± 1 C) during the study. Ten d after transplanting, pots were inoculated with approximately 1,000 SCN eggs. At 7, 14, or 21 d after inoculation (DAI), henbit plants were sprayed with recommended dose of either glyphosate (870 g ae ha⁻¹) or 2,4-D (1,070 g ae ha⁻¹). The experiment was arranged in a randomized complete block design with five replications per treatment, and two experimental runs separated in time. At 28 DAI, the total number of SCN cysts and eggs, and plant shoot and root dry weight per pot were determined. Henbit root and shoot biomass increased as the time of herbicide application was delayed. Glyphosate reduced root biomass more than 2,4-D, but no differences in shoot biomass were detected. The number of SCN cysts per henbit plant and eggs per cyst increased as the herbicide application was delayed from 7 to 21 DAI. Glyphosate reduced the number of cysts found on henbit roots more than 2,4-D, especially at earlier application times. On plants treated with glyphosate, SCN-females produced only half the number of eggs of SCN-females on henbit plants treated with 2,4-D, regardless of time of application. These results indicate that early control of henbit plants, especially with glyphosate, can reduce SCN reproduction potential in SCN infested fields.Nomenclature: Glyphosate; 2,4-D; henbit, Lamium amplexicaule L. LAMAM; soybean, Glycine max (L.) Merr. ‘ASGROW 3005′; soybean cyst nematode, Heterodera glycines Ichinohe.