A non-GMO trait called Inzen™ was recently commercialized in grain sorghum to combat weedy grasses, allowing the use of nicosulfuron POST in the crop. Inzen™ grain sorghum carries a double mutation in the acetolactate synthase (ALS) gene Val560Ile and Trp574Leu, which potentially results in cross-resistance to a wide assortment of ALS-inhibiting herbicides. To evaluate the scope of cross-resistance to Weed Science Society of America Group 2 herbicides in addition to nicosulfuron, tests were conducted in 2016 and 2017 at the Lon Mann Cotton Research Station near Marianna, AR, the Arkansas Agricultural Research and Extension Center in Fayetteville, AR, and in 2016 at the Pine Tree Research Station near Colt, AR. The tests included ALS-inhibiting herbicides from all five families: sulfonylureas, imidazolinones, pyrimidinylthiobenzoics, triazolinones, and triazolopyrimidines. Treatments were made PRE or POST to grain sorghum at a 1X rate for crops in which each herbicide is labeled. Grain sorghum planted in the PRE trial included Inzen™ and a conventional cultivar. Visible estimates of injury and sorghum heights were recorded at 2 and 4 weeks after herbicide application and yield data were collected at crop maturity. In the PRE trial, there was no visible injury, sorghum height reduction, or yield loss in plots containing the Inzen™ cultivar. Applications made POST to the Inzen™ grain sorghum caused visible injury, sorghum height reduction, and yield loss of 20%, 13%, and 35%, respectively, only in plots where bispyribac-Na was applied. There was no impact on the crop from other POST-applied ALS-inhibiting herbicides. These results demonstrate that the Inzen™ trait confers cross-resistance to most ALS-inhibiting herbicides and could offer promising new alternatives for weed control and protection from carryover of residual ALS-inhbiting herbicides in grain sorghum.

Previous research has shown that glufosinate and nicosulfuron at low rates can cause yield loss to grain sorghum. However, research has not been conducted to pinpoint the growth stage at which these herbicides are most injurious to grain sorghum. Therefore, field tests were conducted in 2016 and 2017 to determine the most sensitive growth stage for grain sorghum exposure to both glufosinate and nicosulfuron. Field test were designed with factor A being the herbicide applied (glufosinate or nicosulfuron) and, factor B consisted of timing of herbicide application including V3, V8, flagleaf, heading, and soft dough stages. Factor C was glufosinate or nicosulfuron rate where a proportional rate of 656 g ai ha-1 of glufosinate and 35 g ai ha-1 of nicosulfuron was applied at 1/10X, 1/50X, and 1/250X. Visible injury, crop canopy heights (cm), and yield were reported as a percent of the non-treated. At the V3 growth stage visible injury of 32% from the 1/10X rate of glufosinate and 51% from the 1/10X rate of nicosulfuron was observed. This injury was reduced by 4 WAA and no yield loss occurred. Nicosulfuron was more injurious than glufosinate at a 1/10X and 1/50X rate when applied at the V8 and flagleaf growth stages resulting in death of the shoot, reduced heading and yield. Yield losses from the 1/10X rate of nicosulfuron were observed from V8 through early heading and ranged from 41-96%. Yield losses from the 1/50X rate of nicosulfuron were 14-16% at the flagleaf and V8 growth stages respectively. The 1/10X rate of glufosinate caused 36% visible injury 2 WAA when applied at the flagleaf stage, which resulted in a 16% yield reduction. By 4 WAA visible injury from either herbicide at less than 1/10X rate was not greater than 4%. Results indicate that injury can occur, but yield losses are more probable from low rates of nicosulfuron at V8 and flagleaf growth stages.

A field study was conducted in 2015 and 2016 in Stoneville, MS, to evaluate the influence of cytokinin products on soybean injury and weed control when combined with common POST soybean herbicide treatments. Cytokinin treatments included no cytokinin mixture and two formulated cytokinin mixtures (kinetin-1 and kinetin-2) applied at 0.000227 kg ai ha−1. Herbicide treatments were no herbicide, glyphosate at 1.37 kg ae ha−1 alone and in combination with S-metolachlor at 1.42 kg ai ha−1 or fomesafen 0.395 kg ai ha−1. The addition of cytokinin treatments had no impact on soybean injury, plant height, or yield. Glyphosate plus fomesafen provided the greatest level of Palmer amaranth control, between 84 and 67%., 7 days and 28 days after treatment, respectively. Barnyardgrass control with glyphosate plus fomesafen was antagonized by one of two cytokinin products. To prevent possible reductions in herbicide efficacy, tank mixtures with cytokinin products should not be applied to soybean in POST herbicide applications.