Evaluation of Herbicide and Cropping Methods on Emerged Weeds and Buried Weed Seeds

Abstract

Three agricultural fields in Frederick County, Maryland were studied over a two year period during the 1980-1981 growing seasons. The effects of herbicide applications and cropping methods on emerged weed cover and on the number and viability of weed seeds in the plow layer were studied. Soil core samples and weed surveys were taken each year in September to record weed populations. Weed seeds were separated from the soil samples by density flotation, counted, identified to species, and placed in petri dishes within a germinator. The soil was placed in pots in a greenhouse to induce germination, and the number and species of weeds that germinated were recorded. There was no difference in the number of weed seeds found in the soil samples of the three sites. Untreated fields had significantly higher weed coverage than treated fields. In the untreated field more perennial weeds emerged in 1980, but in 1981 more annual weeds emerged in the untreated field than in treated fields. The untreated field had more small seeded plants than the treated fields for both years. However, the untreated field had fewer small seeds in the soil than the treated field in 1980. The data indicate that herbicide applications were effective only in controlling weed coverage. The seed bank remained the same regardless of cultivation methods, cropping scheme, or herbicide applications. The implication is that dormant weed seeds remain a latent problem in agricultural soils.