Recent rainfall across Louisiana restricted access to fields for burndown applications with ground equipment. At the time of this writing (early April), only a few cotton fields have received a burndown application, and cotton planting in Louisiana usually begins around April 15.
(1) Plant-back restrictions. The accompanying table shows the current labeled plant-back restrictions for burndown products in cotton. If wet weather continues and applications are delayed even further, then planting could also be delayed — depending on which burndown herbicides are chosen.
Pay close attention to the plant-back restrictions on the label.
|Herbicide||Days before cotton planting|
|* Consult label of individual products.|
|**An accumulation of 1 inch of rainfall or irrigation is required.|
(2) Weed species present. Paraquat and glyphosate have no plant-back restrictions. While they are the backbone of most burndown programs, they are only fair to poor on some winter weeds.
Some tank mixes may be required for adequate control. Know your weed species.
Weed species not adequately controlled by glyphosate alone include Carolina geranium, curly dock, henbit, cutleaf evening primrose, and smartweed spp.
Weeds not adequately controlled by paraquat alone include curly dock, cutleaf evening primrose, marestail, smartweed spp., and swinecress.
Tank mixes with Goal, Clarity, Valor, 2,4-D, and Aim will be needed in many fields for adequate control.
Weed size is important with Aim and Valor. Weeds greater than 4 inches tall or 3-inch rosettes are not controlled well. Therefore, pay close attention to the targeted weed species, weed size, and then the plant-back restrictions for various tank mixes. See the LSU AgCenter's burndown herbicide guide on the Internet and weed pictures at http://www.agctr.lsu.edu/cotton/WeedControl.htm.
(3) Acceptable planting dates. The window for planting cotton in Louisiana is generally from April 15 through the end of May. Historically, yields have declined when cotton is planted after May 15.
The overall yield decline that can be expected with late-planted cotton is different in every year and depends on the growing season. The main point is that all cotton does not need to be planted by May 1 or even May 5.
It is more important to properly burn down cotton land, adequately control cutworms, and plant in good conditions than to do a poor job of burndown and/or violate the plant-back restrictions risking injury. The wet weather has the potential to delay burndown and planting in some fields, but getting the crop off to a good start takes precedence over rushing burndown and planting by the end of April.
(4) Burndown by air. In wet conditions, applying burndown herbicides by air may be the best option. However, most burndown herbicides are more effective when applied with ground equipment.
Sandy Stewart, assistant professor and Extension cotton specialist; Steve Kelly, assistant professor and weed specialist; and P. Roy Vidrine, professor of weed science — all with LSU.
LSU AgCenter wheat field day April 17
THE LSU AGCENTER will host a wheat and oat field day April 17 at its Dean Lee Research Station at Alexandria, La.
The field day will include tours of research plots and reports on such topics as an update on the wheat situation, Roundup drift damage in wheat, Sencor tolerance of wheat varieties, wheat and oat variety trials, insect control, double-cropping wheat with cotton, sulphur fertilization, diseases and fungicide trials. The field day will begin at 9:30 a.m. and conclude following a sponsored lunch.
For additional information, contact LSU AgCenter faculty member Sandy Stewart at 318-473-6520 or [email protected].