Field trials were initiated at three Missouri locations in the fall of 2004 and 2005 to compare the efficacy of fall and early spring herbicide applications on winter and summer annual weed populations in no-till soybean. All three experiments received applications of chlorimuron plus sulfentrazone plus 2,4-D; chlorimuron plus tribenuron plus 2,4-D; and glyphosate plus 2,4-D in the fall, 60 d prior to planting (60 PP), 30 days prior to planting (30 PP), and 7 d prior to planting (7 PP). Good control of all winter annual weeds, except for common chickweed, was observed at planting from fall applications of chlorimuron plus sulfentrazone plus 2,4-D and chlorimuron plus tribenuron plus 2,4-D. Fall, 60 PP, and 30 PP applications of chlorimuron plus sulfentrazone plus 2,4-D provided relatively poor control of common chickweed. Glyphosate plus 2,4-D applied in the fall and 60 PP provided adequate control of early fall germinating winter annuals, such as common chickweed and henbit. However, these treatments provided poor control of winter annual species that exhibited some degree of spring germination. Control of summer annual weed species 7 wk after planting (WAP) was highly variable. Relatively poor control of common waterhemp was obtained from all treatments except chlorimuron plus sulfentrazone plus 2,4-D applied at all three spring timings. Giant foxtail control was highly variable ranging from 0 to 95%. Measurements of weed biomass collected 7 WAP revealed larger amounts of biomass present in the fall application timing of each herbicide treatment. Emergence of winter and summer annual weed species from early March to 7 WAP varied by herbicide treatment. Emergence of total winter and summer annual weed species was reduced with both residual herbicide treatments when compared with glyphosate plus 2,4-D and the untreated control.

Two field studies evaluating horsenettle control were conducted from 1997 to 1999 to examine the efficacy of various fall-applied herbicides and rates and to evaluate the effect of the stage of horsenettle senescence on the effectiveness of fall glyphosate applications. The herbicides and rates evaluated in the fall herbicide efficacy study included 1.1, 2.2, or 3.4 kg ai/ha glyphosate, 1.7, 2.2, or 3.4 kg ai/ha glyphosate-trimesium, 0.6, 1.1, or 2.2 kg ai/ha dicamba, 0.06 plus 0.16, 0.09 plus 0.2, or 0.17 plus 0.44 kg ai/ha BAS 654 plus dicamba, respectively, or 2.2 kg ai/ha glyphosate plus 0.6 kg ai/ha dicamba. The highest horsenettle control in the following spring was observed with all rates of glyphosate or glyphosate-trimesium, the highest rate of BAS 654 plus dicamba, or glyphosate plus dicamba. In the study on the horsenettle stage of senescence, 2.2 kg ai/ha glyphosate was applied at stages of senescence in the fall. The presenescence stage reduced horsenettle shoot density from fall to spring and provided the highest level of control in June and July of the following year compared with plants that had already begun leaf color change and leaf drop.

Field experiments were conducted in Missouri in 2004 through 2006 to compare the efficacy of fall and spring herbicide treatments for control of winter and summer annual weeds in no-tillage corn. Applications in the fall and 45 d before planting (45 PP) of 2,4-D and simazine; rimsulfuron, thifensulfuron, and 2,4-D; or glyphosate and 2,4-D controlled at least 90% of all winter annual weeds through 1 wk after corn planting (WAP), with a few exceptions. Applications made 30 d before planting (30 PP) of 2,4-D and glyphosate or rimsulfuron, thifensulfuron, and 2,4-D provided greater than 90% control of most winter annual weeds 1 WAP. Winter annual weed control was reduced with herbicide treatments applied 7 d before planting (7 PP), compared with earlier application timings. Summer annual weed control 5 WAP increased as the time between application and planting decreased. Fall applications resulted in greater weed biomass 5 WAP, compared with spring applications.

Volunteer horseradish plants that emerged from root segments remaining after harvest can reduce yields of rotational crops as well as provide a host for pathogens and insects, thus reducing the benefits of crop rotation. POST applications of halosulfuron in corn can be an effective component to improve management of volunteer horseradish, but the replant interval from application to safe planting of commercial horseradish has not been determined. Fall herbicide applications are another possible volunteer horseradish management strategy than can be implemented once crops are harvested. Therefore, field experiments were conducted to evaluate the safe replant interval of horseradish following halosulfuron applications and to determine the efficacy of fall herbicide applications for volunteer horseradish control. Visual estimates of horseradish injury were greatest (85%) in plantings made zero months after halosulfuron applied at two times the approved rate; moreover, for all rates, injury decreased as the time after halosulfuron application increased. No herbicide injury or root biomass reduction occurred on horseradish at any halosulfuron rate from replanting beyond 4 mo after halosulfuron application. Control of volunteer horseradish was 91% or greater for all fall herbicide applications that included 2,4-D. Furthermore, volunteer horseradish shoot density was the lowest following combinations of 2,4-D tank-mixed with halosulfuron or rimsulfuron : thifensulfuron (0.2 and 0.4 shoots m−2, respectively) compared with the nontreated control (5.1 shoots m−2). This research demonstrates the effectiveness of both halosulfuron and 2,4-D as components of an integrated management strategy for volunteer horseradish control and the potential for halosulfuron applications without soil persistence beyond 4 mo affecting subsequent commercial horseradish production.

Field studies were established at two Missouri locations in 2004 and 2005 to evaluate the effects of fall and early spring herbicide applications on soil temperature, soil moisture content, and insect injury in no-till corn production systems. Both experiments received applications of simazine plus 2,4-D, rimsulfuron plus thifensulfuron plus 2,4-D, and glyphosate plus 2,4-D in the fall, 45 d prior to planting (45 d EPP), 30 d prior to planting (30 d EPP), and 7 d prior to planting (7 d EPP). During a period from April 1 to April 14, simazine plus 2,4-D applied 45 d EPP resulted in higher soil temperatures at a 5-cm depth compared to the untreated control. However, there were few differences in soil temperature present from April 15 to May 1. Soil moisture readings taken during this same time period correlated with soil temperature readings. Measurements of soil moisture taken at 1 and 3 wk after planting (WAP) revealed significantly lower soil moisture readings in the untreated compared to herbicide treated plots. This lower soil moisture content allowed untreated plots to warm up more rapidly and thereby eliminated any negative impacts that dense stands of winter annual weeds may have had on soil temperature. Evaluations of corn flea beetle and lepidopteron injury taken at the V2, V4, and V6 corn leaf stages revealed significant differences in injury as a result of these treatments. When dense stands of winter and summer annual weeds were left uncontrolled, corn flea beetle injury was significantly lower than in plots treated with a herbicide. However, when a post herbicide application was made to remove all weed species prior to the V6 sampling date, differences in corn flea beetle injury between the untreated and herbicide treated plots were eliminated. Additionally, removal of all weed species led to higher lepidopteron injury in the untreated.