For several years now we have looked at numerous herbicides applied in the fall for residual weed control. Some of this has been for general winter annual weed control and some protocols have been specifically written for glyphosate-resistant horseweed management.
In general, I have always been skeptical of these treatments. Valor is one product that has led the charge for these applications.
In many cases, what we have observed is that even though fields are clean all winter, they would “break” prior to planting, requiring a spring burn-down prior to planting.
Often we could go out with similar treatments a few weeks prior to planting and end up with clean plots; so in many cases it seemed that money was wasted on fall treatments that merely keep the field clean all winter with no crop in the field, and then a follow-up treatment was needed.
This year we had a number of protocols that included not only Valor, but some longer residual chemistry such as Valor XLT, Gangster FR, Envive, Envoke, Resolve and Canopy EX. Due to heavy rainfall at all of our locations, many preplant timings have been missed — or at least those plots are very grown up. It is likely that once we get them out, they will not perform well.
Judging from some of the calls I have gotten, many of you may be in the same boat. There just is no chemical recommendation for controlling 2-foot horseweed or 3-foot winter annual junk weeds.
What has become very clear this year is that if you cannot get your spring burn-down out in a timely manor, you can get behind the eight ball in a hurry! So with all the options, what did we observe and what worked?
The untreated or no fall treatment plot would require glyphosate plus dicamba prior to planting for horseweed control. Due to wet weather, this has not gone out. This treatment has a minimum plant-back interval of 14 days after the accumulation of 1 inch of rain. So planting would be delayed.
For the most part, treatments that went out with no residual, such as glyphosate plus 2,4-D or dicamba, provided good initial control but quickly “broke” this spring with warmer temperatures and rainfall. Even treatments that contained glyphosate and Valor were not lasting until planting.
In my opinion, the heavy rainfall and length of time between application and planting are what resulted in weedy plots in April. Most of these fall and winter burn-downs in my trials went out between Nov. 15 and Jan. 15.
I was very impressed this year with treatments that included some ALS chemistry in them. This would include Canopy EX, Envive, Envoke, Valor XLT and others. Again, in the past I have not felt like these treatments were worth the money, but as the calls have come rolling in this year on grown up messes, I can definitely say that there was an advantage to going out some time in December or January with one of these fall/winter residual treatments.
In general, these plots (and some fields I have seen) are horseweed-free. They do have some weeds coming in them, but they are certainly closer to being ready to plant than those yet to be burned down or those that had a burn-down failure due to the size of the weeds and unfavorable spray conditions.
One consultant I talked to said that he was tired of fighting these weeds and had too many acres to get across to effectively burn-down everything at once in the spring. He is really pushing his growers to go out with Canopy Ex in the fall/winter in hopes of having fewer problems at planting time. In those fields where he did that this year, he hit a home run.
Fall/winter residual treatments may not be a fit for everyone, but on larger farms and horseweed acres and in years when weather does not permit timely, effective spring burn-downs, I am now a believer that they can pay.
We do not really address the need for these treatments in the Arkansas MP-44 “Recommended Chemicals for Weed and Brush Control,” but they will be discussed at our fall meeting this coming year.