Junglerice has become a major weed in Tennessee cotton and soybean fields. Glyphosate has been relied upon to control these accessions over the past two decades but in recent years cotton and soybean producers have reported junglerice escapes after glyphosate + dicamba and/or clethodim applications. In the growing seasons of 2018 and 2019, a survey was conducted of weed escapes in dicamba-resistant crops. Junglerice was the most prevalent weed escape in these dicamba-resistant (Roundup Ready Xtend®) cotton and soybean fields in both years of the study. In 2018 and 2019, junglerice was found 76% and 64% of the time in dicamba-resistant cotton and soybean fields, respectively. Progeny from junglerice seeds collected during this survey was screened for glyphosate and clethodim resistance. Seventy percent of the junglerice accessions tested had an effective relative resistance factor (RRF) of 3.1 to 8.5 to glyphosate. In all, 13% of the junglerice accessions could no longer be effectively controlled with glyphosate. This research also showed that all sampled accessions could still be controlled with clethodim in a greenhouse environment but less control was observed in the field. These data would also suggest that another cause for the poor junglerice control is dicamba antagonizing the glyphosate and clethodim activity.

Field studies were conducted in 2018 and 2019 in Arkansas, Indiana, Illinois, Missouri, and Tennessee to determine if cover crop residue interfered with herbicides that provide residual control of Palmer amaranth and waterhemp in no−till soybean. The experiments were established in the fall with planting of cover crops (cereal rye plus hairy vetch). Herbicide treatments consisted of a nontreated or no residual, acetochlor, dimethenamid−P, flumioxazin, −pyroxasulfone + flumioxazin, pendimethalin, metribuzin and pyroxasulfone and S−metolachlor. Palmer amaranth took 18 d and waterhemp took 24 d in the cover crop alone (nontreated) treatment to reach a height of 10 cm. Compared with this treatment, all herbicides except metribuzin increased the number of days (d) until 10 cm Palmer amaranth was present. Flumioxazin applied alone or in a mixture with pyroxasulfone were the best at delaying Palmer amaranth growing to a height of 10 cm (35 and 33 d). The herbicides that resulted in the lowest Palmer amaranth density (1.5 to 4x less) integrated with a cover crop were pyroxasulfone + flumioxazin, flumioxazin, pyroxasulfone, and acetochlor. Those four herbicide treatments also delayed Palmer amaranth emergence for the longest period (27 to 34 d). Waterhemp density was 7 to 14 times less with acetochlor than all the other herbicides present. Yield differences were observed for locations with waterhemp. This research agrees with previous research that utilizing soil residual herbicides along with cover crop benefits control of Palmer amaranth and/or waterhemp.

Junglerice has become a major weed in Mid-south US and other areas. Glyphosate resistance has been documented in junglerice populations and is part of the reason for the increase in its prevalence. However, reduced junglerice control with glyphosate + dicamba and clethodim + dicamba mixtures has been observed in many production fields where glyphosate resistance has not yet evolved. Therefore, research was conducted assessing reduced junglerice control with glyphosate and clethodim when applied with dicamba. Adding dicamba to the spray tank with glyphosate reduced junglerice control by 27%. Adding dicamba to the spray tank with clethodim reduced junglerice control by 11%. The use of TTI nozzles reduced junglerice control an additional 8% compared to applications with an AIXR nozzle. When a drift reduction agent (DRA) was added to dicamba mixtures with glyphosate or clethodim, junglerice control was reduced 36%. Junglerice control was similar with the glyphosate + dicamba treatment compared to the glyphosate + 2,4-D mixture. There was no interaction between nozzles and herbicide treatment. Regardless of herbicide treatment junglerice control was always lower when applied with the ultra-course TTI nozzle. Many applicators in Tennessee prefer to make one application of glyphosate + dicamba in a mixture to save time (Authors personal experience). These results show that the addition of dicamba to glyphosate or clethodim applied with labeled nozzles and a DRA results in reduced junglerice control and should be avoided.

Junglerice is becoming more prevalent in Tennessee, Arkansas and Mississippi row crop fields. The evolution of glyphosate-resistant junglerice populations is one reason for the increase. Another possible explanation is that glyphosate and clethodim grass activity is being antagonized by dicamba. This question has led to research to examine if sequential applications alleviate antagonism observed with dicamba plus glyphosate and/or clethodim mixtures and determine if 24 h, 72 h or 168 h sequential treatments of those herbicides can improve junglerice control. Glyphosate + clethodim applications provided >90% junglerice control. The observed levels of antagonism varied by whether the location of the test was in the greenhouse or the field and the timing of applications. In the greenhouse, clethodim + dicamba provided excellent control while in the field the same treatment showed over a 30% reduction in junglerice control compared with clethodim alone. However, control was restored by using a mixture of glyphosate + clethodim without dicamba. The environment at the time of application and relative glyphosate-resistance (GR) level of the junglerice influenced the overall control of these sequential applications. Clethodim applied first followed by dicamba at 72 or 168 h, better control was observed compared with applying dicamba followed by clethodim. Overall, mixing glyphosate + clethodim provided the most complete junglerice control regardless of timing. These data confirm that leaving dicamba out of the spray tank will mitigate herbicide antagonism on junglerice control. These data would also indicate that avoiding dicamba and glyphosate mixtures will also improve the consistency of control with glyphosate-susceptible junglerice.

Several species of aphids (Hemiptera: Aphididae) infesting wheat may reduce yield by the transmission of barley yellow dwarf (BYD). Neonicotinoid seed treatments and foliar application of insecticides are two common methods to control aphid infestations and reduce BYD. An analysis was carried out across 33 insecticide efficacy tests performed in west Tennessee during the last 11 yr to determine how insecticide seed treatments and/or a late-winter foliar insecticide application affected aphid populations, incidence of BYD, and yield. A significant decrease in springtime aphid populations and incidence of BYD was observed when using a seed treatment, a foliar insecticide application, or both. Average wheat yields were increased by 280–381 kg/ha (5.3–7.2%) if an insecticide seed treatment was used or when a foliar insecticide application was made. Compared with insecticide seed treatments, average springtime aphid populations and the incidence of BYD were lower when a foliar insecticide was applied. A foliar insecticide application made in addition to insecticide seed treatments increased yield by an average of 196 kg/ha (3.4%). The yield increases over the nontreated control suggest that wheat growers in west Tennessee can use insecticides to manage aphids and prevent transmission of BYD. Consideration of environmental conditions, whether or not insecticide seed treatments were used, and scouting can be used to help make decisions on when or if to apply foliar insecticides.