By: Mike Hunter, CCE-North Country Regional Ag Team
A very popular question has been “What can I spray on my soybeans to control large weeds that weren’t controlled earlier in the season?”. Let me start out by saying that if you have waist high weeds in your soybeans the damage is done and most, if not all, herbicide applications will be a form of “revenge spraying”. Spraying very tall weeds usually provides unsatisfactory weed control. If you still have some weeds that are 6 inches tall or less there is a better chance to control them.
Roundup or glyphosate can be applied through the R2 (full flowering) growth stage on Roundup Ready or glyphosate tolerant soybeans. Enlist One and Enlist Duo can also be applied throughout the R2 growth stage in Enlist or E3 soybeans. Once the soybeans have reached the R3 (beginning pod) growth stage these products are no longer an option.
If the soybeans are at R3 (a pod 3/16” long found at one of the first four uppermost nodes) Cobra, Resource and Basagran are the options that are left. Cobra can be applied through R6 (full seed) or 45 days before harvest, Resource 60 days before harvest and Basagran 30 days before harvest. These are all selective, contact broadleaf herbicides. Unfortunately, none of these are very good at controlling common lambsquarters.
If you have any additional questions about late season soybean weed control, contact your local Cornell Cooperative Extension office.