The objectives of this study were to determine how the timing of weed management treatments in winter wheat stubble affects weed control the following season and to determine if spring herbicide rates in corn can be reduced with appropriately timed stubble management practices. Field studies were conducted at two sites in Ohio between 1993 and 1995. Wheat stubble treatments consisted of glyphosate (0.84 kg ae/ha) plus 2,4-D (0.48 kg ae/ha) applied in July, August, or September, or at all three timings, and a nontreated control. In the following season, spring herbicide treatments consisted of a full rate of atrazine (1.7 kg ai/ha) plus alachlor (2.8 kg ai/ha) preemergence, a half rate of these herbicides, or no spring herbicide treatment. Across all locations, a postharvest treatment of glyphosate plus 2,4-D followed by alachlor plus atrazine at half or full rates in the spring controlled all broadleaf weeds, except giant ragweed, at least 88%. Giant foxtail control at three locations was at least 83% when a postharvest glyphosate plus 2,4-D treatment was followed by spring applications of alachlor plus atrazine at half or full rates. Weed control in treatments without alachlor plus atrazine was variable, although broadleaf control from July and August glyphosate plus 2,4-D applications was greater than from September applications. Where alachlor and atrazine were not applied, August was generally the best timing of herbicide applications to wheat stubble for reducing weed populations the following season.

Alfalfa–orchardgrass hay is popular in the Western United States because of an expanding horse-hay market. However, weed control in mixed alfalfa–orchardgrass stands is problematic, as herbicides must be safe for both species. Most growers rely solely on the competitiveness of the crop for weed control, which is often insufficient, especially in older stands. Field experiments were established in northern California to determine the efficacy and crop safety of several herbicides for winter annual weed control in established alfalfa–orchardgrass. Metribuzin at 560 or 840 g/ha and hexazinone at 420 g/ha applied in late fall provided at least 95% control of shepherd's purse and at least 80% control of downy brome without crop injury. Imazethapyr at 70 g/ha applied shortly after crop green-up provided more than 85% control of emerged mustards without crop injury. Paraquat at 560 g/ha applied shortly after crop green-up gave 50 to 82% weed control and caused significant injury to orchardgrass, which was still noticeable at first cutting.

Tall ironweed is a troublesome perennial weed that infests cool-season grass pastures in Kentucky. Field experiments were conducted in 2000 through 2003 to evaluate the efficacy of fall-applied herbicides on established tall ironweed following a midsummer mowing. Triclopyr-containing treatments showed the greatest suppression of tall ironweed 12 mo after treatment (MAT), across all years. With triclopyr at 0.56 and 0.63 kg/ha, tall ironweed control was 80% or greater in 2 of the 3 yr. Dicamba initially provided 87% control 8 MAT in 2 of 3 yr and declined to less than 60% 12 MAT. Tall ironweed shoot density was also reduced 66% or more 12 MAT with fall-applied triclopyr-containing treatments. In contrast, tall ironweed density increased approximately twofold in dicamba-treated plots between 8 to 12 MAT in all 3 yr. The impact of herbicide treatment on dry matter (DM) yield of spring-seeded red clover (Trifolium pratense L.), tall ironweed, and forage grasses was also evaluated. Red clover DM yield in the herbicide-treated plots in 2002 showed no significant differences from the untreated control. However, red clover DM yield in 2003 was lowest for the two triclopyr + clopyralid treatments, indicating a decrease in DM production compared with that of the nontreated control. Results indicated that fall-applied triclopyr-containing herbicides following a midsummer mowing is an effective program for removing tall ironweed from grass pastures, but further research is needed to evaluate the establishment of red clover following herbicide treatment.

Field experiments were conducted from 1996 to 2000 near Manhattan, KS, to determine the effects of application timing on atrazine loss in surface water runoff. In addition, Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) was run to compare simulated loss with actual loss in the field. Atrazine treatments were fall plus preemergence (FALL + PRE), early preplant plus PRE (EPP + PRE), PRE at a low rate (PRE-LOW), and PRE at a full (recommended) rate (PRE-FULL). Ridge-till furrows served as mini watersheds for the collection of surface water runoff. Water runoff volumes and herbicide concentrations were determined for each runoff event. Across four sampling years, mean atrazine runoff loss was 1.7, 4.3, and 1.7% of applied for FALL + PRE, EPP + PRE, and the mean of the PRE treatments, respectively. Thus, actual average losses from FALL + PRE and EPP + PRE treatments were somewhat higher than that predicted by GLEAMS. For PRE treatments, actual average losses were significantly lower than that predicted by GLEAMS, with measured losses falling below the bottom of the graph in 3 of 4 yr. These findings suggest that in certain parts of the Great Plains, FALL + PRE split applications of atrazine offer acceptably low atrazine runoff loss potential; EPP + PRE is more vulnerable to loss than FALL + PRE; and the GLEAMS model may overestimate atrazine runoff potential for PRE applications.