The sugarcane aphid, Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae), has become a major pest of grain sorghum, Sorghum bicolor (L.) Moench, in the United States in recent years. Feeding by large densities of sugarcane aphids causes severe damage, which can lead to a total loss of yield in extreme cases. Our objective was to determine the effect of grain sorghum planting date on sugarcane aphid population dynamics and their potential to reduce yields. We conducted field experiments from 2015 to 2017 in which an aphid-susceptible grain sorghum hybrid was planted at four different dates, which encompassed the typical range of planting dates used in Arkansas production systems. Plots were either protected from sugarcane aphid feeding using foliar insecticide sprays, or left untreated to allow natural populations of sugarcane aphids to colonize and reproduce freely. Planting date impacted both the magnitude and severity of sugarcane aphid infestations, with the highest population densities (and subsequent reductions in sorghum yield) generally occurring on plots that were planted in May or June. Sugarcane aphid feeding reduced yields in the untreated plots in two of the four planting date categories we tested. Earlier planting generally resulted in less sugarcane aphid damage and improved yields compared with later planting dates. While the effect of planting date on sugarcane aphid populations is likely to vary by region, sorghum producers should consider grain sorghum planting date as a potential cultural tactic to reduce the impact of sugarcane aphid.

Sixteen field experiments were conducted across Oklahoma to evaluate the effects of MON 37500 time of application on cheat control, and winter wheat injury and yield. Winter wheat injury from MON 37500 applied preemergence (PRE) was slight and was influenced by cumulative precipitation for 10 d after application. Winter wheat injury was more frequent with early vs. late postemergence (POST) applications and was influenced by wheat growth stage and mean, high, and low air temperatures before and after application. Cheat control averaged 75% (n = 16 treatments with four to six replicates) when applied PRE and 88% (n = 126 treatments with four to six replicates) when applied POST. Cheat control from MON 37500 applied POST declined with increasing cheat growth stage at application and with decreasing mean diurnal low temperatures 0 to 14 d and 0 to 21 d before application. MON 37500 applied PRE increased yields 52 and 66% compared with the untreated control in Year 1 and Year 2, averaged over eight experiments each year. MON 37500 applied POST increased wheat yields 68 to 69% compared with the untreated check in Year 1 and Year 2, when averaged over all applications in eight experiments each year. Wheat yields were greater from fall POST applications than from late-winter applications.

The corn stalk nitrate test (CSNT) and ear-leaf N concentration (ELNC) are used to determine the adequacy of corn (Zea mays L.) N management programs and is used most extensively in the Midwest and northeastern United States. Information on the utility of both the CSNT and ELNC for irrigated corn produced in the mid-South is lacking. Twenty-four N rate trials were conducted in Arkansas between 2013 and 2016 to evaluate the utility of the ELNC and CSNT in a furrow-irrigated corn production system. An ELNC of 30 g kg -1 has been determined to differentiate between N-adequate and N-deficient corn plants at the R1 growth stage. The optimal CSNT concentration ranged from 170 to 1000 mg nitrate N kg -1 at maturity, indicating that adequate N was available to the corn crop to produce near-maximum grain yield. The N rate needed to achieve 95% relative grain yield (RGY) was consistently identified near the N rate where nitrate N began to accumulate in the corn stalk. A CSNT values of <170 mg nitrate N kg -1 was found to represent the low category, suggesting that N was limiting corn grain yield, whereas N availability was found to exceed the amount needed to maximize grain yield when CSNT values were >1000 mg nitrate N kg -1 . The ELNC and CSNT can be used to adequately determine the N status of corn produced within a furrow-irrigated mid-South corn production system.

Corn (Zea mays L.) yield under irrigated production systems is influenced by N rate and timing of application. This study was conducted to determine how current N application strategies (two‐way vs. three‐way split application) and N rate (optimal vs. suboptimal) influence fertilizer‐nitrogen recovery efficiency (FNRE) for furrow‐irrigated corn production in the mid‐South. The effects of N rate and application timing on corn FNRE were investigated in Rohwer, AR, on a Herbert silt loam (fine‐silty, mixed, active, thermic Aeric Epiaqualf). Corn grain yield and total‐N uptake were both influenced by the interaction of N treatment and year (p < 0.0001). Corn grain yields were maximized when an optimal‐N rate of 235 kg N ha−1 was applied in a two‐way split application with 50 kg N ha−1 pre‐plant and 185 kg N ha−1 sidedressed at the V6 stage. The ANOVA for FNRE indicated that N treatment was the only significant factor (p < 0.0001) and varied based on N rate and time of application. The lowest FNRE was 61% and occurred when 50 kg N ha−1 was applied pre‐plant. The highest overall FNRE was 91% when 50 kg N ha−1 was applied pre‐tassel in the suboptimal‐N rate treatment. The FNRE of N sidedressed at V6 ranged from 81 to 91% and was influenced by N rate with the suboptimal‐N rate treatments tending to have significantly higher FNRE values. The results presented in this paper highlight the high FNRE that can be achieved in furrow‐irrigated corn production.Core Ideas Fertilizer N recovery efficiency ranged from 61 to 91%. Fertilizer N recovery efficiency influenced by rate and application timing. High fertilizer N recovery efficiency can be achieved in irrgated corn production systems.