Weed growth and corn yield as affected by weed species and weed emergence time relative to corn emergence

The development of computerized weed management decision support systems, and the increased reliance on foliar-applied herbicides for weed management, requires a greater understanding of the interactions between weeds and corn to ensure the accuracy of weed management recommendations. A field study was conducted from 2001 to 2003 to examine the effect of corn on barnyardgrass (Echinochloa crus-galli), common lambsquarters ( Chenopodium album), common ragweed (Ambrosia artemisiifolia ), fall panicum (Panicum dichotomiflorum), giant foxtail, (Setaria faberi), large crabgrass (Digitaria sanguinalis), redroot pigweed (Amaranthus retroflexus), and velvetleaf (Abutilon theophrasti). A second study was conducted during the same time period to determine the effect of common lambsquarters, velvetleaf and giant foxtail on corn yield. Weeds were established at four different times relative to corn growth; at corn planting, at corn emergence, when corn reached V1, and when corn reached V3.; Weeds had no effect on corn development or corn height. Weeds established prior to corn emergence generally grew larger, produced more seed and had a greater effect on corn yield than weeds established after corn emergence. Common lambsquarters, common ragweed and velvetleaf generally produced a larger biomass and volume relative to the other weeds. Giant foxtail volume and biomass production was similar to common lambsquarters, common ragweed and velvetleaf and was generally equal to or greater than the other grass weed species. Redroot pigweed volume and biomass production was more variable between years than the other weed species. In one year redroot pigweed volume and biomass production was greater than the other weed species. In the other two years, redroot pigweed volume and biomass production was less relative to the other weed species. Fall panicum and large crabgrass volume and biomass production were generally less than the volume and biomass production of the other weed species when established at or before corn emergence. Weed volume was more variable when weeds were established after corn emergence. Velvetleaf, common lambsquarters and common ragweed volume and biomass production were generally equal to and greater than the other weeds when established after corn emergence.; Weeds with smaller seed sizes generally produced the most seed. Common lambsquarters, redroot pigweed and large crabgrass produced more seed than the other weed species regardless of when weeds were established relative to corn establishment. Common lambsquarters produced more seed than redroot pigweed and large crabgrass.; Weather conditions, weed species and weed establishment time affected corn yield loss due to weeds. In cooler growing seasons, common lambsquarters and velvetleaf reduced corn yield more than giant foxtail. When established at corn planting, common lambsquarters and velvetleaf reduced corn yield in 2 of 3 years where as giant foxtail reduced corn yield in I of 3 years. Common lambsquarters reduced corn yield when established at corn emergence 1 of 2 years. Velvetleaf reduced corn yield when established at V3 corn 1 of 3 years.