By mid-April, we have usually applied our pre-emergent herbicides to control summer annual weeds. With the dry weather, many growers have not accomplished this spray for 2026. This is the driest spring since I have served the pecan industry in East Georgia. Rainfall is necessary for pre-emergent herbicides to activate. Many of us did not apply our burndown herbicides until after GPGA instead of early March. At this point, we need to give the burndown time to work, as dry weather inhibits herbicide movement in weeds. Your irrigation will, of course, help with this. And subsequently, we need to see rain in the forecast before applying pre-emergent. I can find no rain in any forecast for us at the time of this writing.
Which means, it may not be too late for me to share this for updated information. Mr. Bryan Wilkins in Fairhope, AL and I applied these herbicides at each respected orchard. The Vidalia Onion & Vegetable Research Center’s (VORC) low-input pecan orchard was in its 5th year. I’ve conducted these plots at the VOVRC for the past three years. Herbicide programs are under pressure from full sun. At Auburn, the pecans at the Gulf Coast Research Center (GCRC) are large. The GCRC shows the same program under more shade. We essentially put out the herbicide in replicated plots, then rate the plots every 30 days until they are grown over. The goal of this work is to determine how much residual effect each herbicide has at each location, and summarize its cost per application. Following the work, Mr. Guy Hancock of UGA Economics Department helped us determine fuel and labor per acre along with average chemical prices. All pre-emergent herbicide treatments included the cost of glyphosate at 2 quarts per acre + glufosinate at 24 oz per acre. The comparison is a post-emergent herbicide program of glyphosate and/or glufosinate through the same period.
We have a number of chemical mode of action with our pre-emergent herbicides. This provides easy rotation, which is always encouraged to reduce resistance. Some growers rotate during the season, and some growers rotate products year to year. Also, check label for tree age and pre-harvest interval before applying. (Ex. Alion can only be used on pecan 3-years of age, and it has a 14 day pre-harvest interval.)
*In previous years, I have compared a full rate of Alion (5 oz / acre) to a half rate (3.5 oz / acre) on virgin soil. Even at half rate, I have observed no significant difference. If it is your first year using Alion, it is encouraged to use 5 oz / acre, then come down to the half rate at second application. This comes from work done by Weed Scientists, Dr. Tim Grey of UGA, on the buildup of indaziflam in the soil. We are also doing the same thing with Chateau. In 2024 the 6 oz / acre rate of Chateau and full season rate of 12 oz / acre were not statistically different. In 2025, both Mr. Wilkins’s and my Chateau numbers may be statistically different if we had one more replication.
**This was the first year we used Mission. I received a recommendation of rate and combination from weed scientist at NC State. Keep in mind an herbicide will behave different in different soils. But since our numbers were much different and since it is already researched at NC State, I hope to look at this again this year.
Keep in mind that none of these herbicides are meant to last much longer than 60 days after treatment (DAT). Sunlight, rainfall, herbicide rate and soil type influence herbicide breakdown. At the VOVRC, the best treatments I have observed will make it 70 – 75 days before re-application. You cannot let weeds completely grow back before you re-apply a pre. These herbicides require soil contact (and subsequent rainfall/irrigation) to work properly.
