Fields Not Treated Yet for No-Till Soybeans

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Due to the rains a number of fields that will be planted to soybeans have not been burned down or need to be retreated. A few things to consider if the fields have not been treated yet: 1.) coverage is important due to dense vegetation, keeping gallons per acre in the 20 gallons per acre range is important; 2.) while 2,4-D can help with some highly sensitive species (primrose), replanting intervals and proximity to sensitive crops will limit its use now; 3.) don’t try cutting rates, weeds are large and often reduced rates will not effectively control them, even higher rates may not provide 100% control; 4.) choose your herbicides carefully; if multiple species are present more than one herbicide will be needed and be sure they are compatible with one another, and that they are going to provide benefit to your situation; and 5.) be realistic in your expectations, controlling large dense populations of weeds is difficult, prioritize those species that are of the biggest concern and be sure to address them first and remember a follow up in-crop application may be needed sooner than usual after planting to help control some species not killed by burndown treatments.

Some fields have been treated and horseweed was not effectively controlled, but the fields have not been planted yet. First, a few scattered plants will not reduce final yield, so determine if a treatment is needed in the first place. The two options are Ignite 280 or a product with chlorimuron (Canopy, Canopy EX, or Synchrony). If the chlorimuron products have been used in this spring, a second application is not advisable due to both concerns with crop safety and reports of inconsistent horseweed control with these products. Ignite 280 at 29 to 36 oz/A or chlorimuron products at a rate providing 1.7 oz wt of Classic (Canopy 4 oz; Canopy EX, 1.8 oz; Envive at 4.1 oz; or Synchrony at 2 oz). We do not have much experience with side by side comparison of these options, but both should provide over 75% control.

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