There are many no till fields across Indiana that have either not been burned down or have had failed burndowns. The wet weather of the last two weeks has kept sprayers out of the field and allowed winter annuals to continue to grow and the majority to go into reproductive growth.
Those fields that did receive a burndown, may need to be scouted and readdressed as many of the burndowns were applied just prior to the latest cold snap thus the herbicides were not effective in killing all the vegetation.
Farmers will need to have a plan as we approach any possible dry spell in which sprayers will be able to get back into the fields to make late burndowns. Winter annuals that are in reproductive stages and larger in growth are tougher to control and will require an increased rate of glyphosate for effective control.
Rates of 1.25 to 1.5 lb. ae glyphosate (35-42 fl. oz. Roundup Powermax) will be needed to effectively control winter annuals in fields that have yet to receive any burndown applications.
It is also recommended that farmers include 2,4-D and/or a saflufenacil product (Sharpen, Optill, Optill PRO, or Verdict) into the tank to improve control of the larger broadleaf weeds. Farmers may be inclined to remove these products from the tank due to plant back restrictions in a time when our planting season has become more compressed.
Purdue weed scientists encourage farmers to NOT remove these products and to wait the 7-14 days in order to not only to achieve an improved burndown, but to assure that the field is clean as we always discourage planting into dirty/weedy fields as herbicide options become much more limited once the crop emerges.
There will also be fields that need a second burndown application to clean up weeds that were not controlled by a previous burndown applied just prior to the early May cold spell. In these fields, remember that plants need to be actively growing to achieve an effective cleanup burndown with a glyphosate based program.
Farmers need to make sure that partially controlled or injured weeds have begun to regrow to assure that the second burndown application is effective. Similar to what was mentioned above we encourage the use of at least 1.25 lb ae glyphosate and the inclusion of 2,4-D and/or Sharpen in the tank mix to improve burndown control.
Paraquat based burndown programs will be less effective for late spring burndowns if weeds are large, because effective spray coverage can be very difficult to achieve. If the wet weather prevented planting of a field that had been sprayed effectively in April, a paraquat based program can be effective on small, summer annual weeds.
We would still encourage the use of metribuzin (soybean), atrazine (corn), saflufenacil (corn or beans) or 2,4-D with paraquat to broaden the spectrum of activity if you are going after small, summer annual weeds.
Although if farmers do choose to use a paraquat based program, they need to make sure to have a spray volume of at least 15 to 20 gal/A and apply with fine to medium droplets to achieve proper herbicide coverage.