Evaluation of fall and spring applied herbicide treatments for weed control in dry peas at Hettinger, ND

A trial was conducted to evaluate fall and spring herbicide treatments for weed control in dry peas. In the fall, on November, 15, 2023, herbicides were applied to a field with a known infestation of downy brome. Fall applied herbicides included glyphosate alone (Roundup PowerMax 3 at 22 oz/A) and tank-mixed with Anthem Flex (carfentrazone plus pyroxasulfone) at 4 oz/A, and Fierce (flumioxazin plus pyroxasulfone) at 6, 7.5, and 9 oz/A (Table 1 and 2). Dry peas were planted using a no-till drill on May 1, 2024 at a depth of 2 inches. The prior crop was spring wheat. Spring herbicide treatments were applied on the same day after planting. Spring herbicide treatments included glyphosate alone and tank-mixed with Anthem Flex (4 oz/A), and Spartan Elite (sulfentrazone plus s-metolachlor) at 32 oz/A. There were also treatments with combined fall and spring applications. These included fall application of Anthem Flex (2.5 oz/A) followed by spring application of Anthem Flex (2 oz/A), and fall Anthem Flex (4 oz/A) followed in spring with Spartan Charge (sulfentrazone plus carfentrazone) (5 oz/A). All treatments were applied with AMS (8.5 LB/100gal) and an HSMOC (1% v/v).

A fall application of glyphosate alone controlled downy brome at 96%, but did not control any other spring emerging weeds. A spring application of glyphosate controlled downy brome at 86% and controlled some of the broadleaf weeds that had emerged prior to application. Fall application of Anthem Flex plus glyphosate controlled downy brome at 100% at either 4 or 2.5 oz/A. At 34 DAT, fall application of Anthem Flex provided better control of both kochia and green foxtail, but not common lambsquarters, when compared with spring application of glyphosate alone. A spring application of Anthem Flex resulted in better control of kochia, common lambsquarters, and green foxtail compared with fall application. The winter of 2023-24 had little snow cover and may have resulted in increased degradation of Anthem Flex applied in the fall which reduced weed control with this timing. The sequential application of Anthem Flex in fall and spring resulted in similar weed control when compared with the spring application. The sequential application of fall Anthem Flex followed by spring Spartan Charge resulted in similar weed control to the spring Anthem Flex treatment. Spring application of Spartan Elite resulted in the best weed control for all three spring annual weeds evaluated in this trial, along with 95% control of downy brome. Fall application of Fierce plus glyphosate controlled downy brome 96 to 100%. Control of spring weeds was generally similar to the fall application of Anthem Flex for kochia and green foxtail, but control was greater for common lambsquarters when Fierce was applied at 9 oz/A. Weed competition reduced dry pea stand in the untreated and fall glyphosate alone treatments compared with other treatments. Pea height was also reduced in the untreated control and in fall and spring glyphosate alone treatments. It was also less in treatments applied only in the spring, likely due to competition with downy brome that was present at time of planting. This was also evident when looking at pea yields. The highest yielding treatments included a combination of fall and spring applied herbicides. Fall application, by them self, had slightly reduced yield comped with the combination treatments likely due to reduced control on spring weeds. Spring applications alone also yielded slightly less than the combination treatments likely due to the competition from downy brome at time of planting, even though spring treatments were all effective at controlling downy brome. Downy brome was able to remove water and nutrient resources prior to treatment, which reduced access of these resources for the pea crop. This shows the importance of controlling downy brome in the fall.