Soil profile distribution of a single simulated seed dispersal event after tillage followed a nonlinear model. Approximately 40% of recovered simulated seed were found within 4 cm of the surface following chisel plowing and disking, and density declined steadily with depth to 20 cm. Moldboard plowing placed 50 to 60% of simulated seed to a depth of 11 to 16 cm. Simulated seed were evenly distributed to 8 cm depth by disking and did not differ regardless of whether plots were chisel or moldboard plowed prior to seed dispersal. More than 90% of seed remained within 2 cm of the surface with no-tillage. Simulated seed distribution was the same after a tillage rotation of chisel plowing, disking, moldboard plowing, and disking regardless if the dispersal event occurred prior to chisel or moldboard plowing. Two years of the tillage rotation and two dispersal events resulted in a distribution pattern greatly influenced by the most recent major tillage of chisel or moldboard plowing. Seedling emergence of common milkweed averaged 80% for seed buried 0.5 to 4 cm deep and emergence was negligible for seed on the surface or buried 7 cm in soil in pots in a growth chamber.

A random mail survey of Ohio growers was conducted to determine the geographic distribution of weeds across Ohio and the influence of production practices on the severity of agronomic weed problems. Statewide, the ten most severe weed problems, in descending order, were Canada thistle > foxtail spp. > velvetleaf = common ragweed > common cocklebur > giant ragweed = annual morningglory spp. > quackgrass = common lambsquarters = Pennsylvania smartweed. Distribution of most weeds varied geographically. Infestations of common and honeyvine milkweeds, hemp dogbane, and tree seedlings increased as tillage was reduced. Infestations of common cocklebur and common ragweed decreased as tillage was reduced. As crop rotation became more diverse, infestations of velvetleaf, common cocklebur, giant ragweed, Pennsylvania smartweed, and jimsonweed decreased. Where rotations included forage or hay crops, infestations of large crabgrass, common chickweed, wild carrot, and common dandelion increased.