Main: The Pros and Cons of Ignite, Widestrike Combo
March 18, 2011 By Dr. Chris Main
Cotton and Small Grains Specialist
University of Tennessee
Articles fill the pages of agriculture publications promoting the proactive management of crops to prevent the spread and establishment of glyphosate-resistant weeds and at the same time helping manage already established populations of these resistant weeds. While there are no magical cures for this problem, there are many options to help preserve crop yields. The use of multiple residual herbicides, timely applications, rotation of herbicide chemistries and crops are all tools available to producers.
Residual herbicides only work when ‘activated’ by rainfall or irrigation. Timely application can only be accomplished by actively scouting the crop and responding with appropriate tactics when weeds are present. Crop rotations can help by allowing the use of different herbicide chemistries, but as we have found in Tennessee, rotating to a corn crop can promote pigweed growth and seed production after an early harvest. Growers in Tennessee and other cotton growing areas have adopted a slightly different approach to managing glyphosate-resistant weeds in cotton.
If you have attended a crop production meeting this winter in the Mid-South or Southeast, you have heard discussion about using Bayer CropScience’s Ignite herbicide over-the-top of PhytoGen’s WideStrike cotton varieties to help control glyphosate-resistant weeds. While neither Bayer nor Dow AgroSciences warrant this use pattern, it is a legal application and is growing in popularity.
WideStrike cotton has only one gene, the pat gene, to detoxify Ignite in the plant. Liberty Link varieties have the pat gene and a second gene, the bar gene, that allows Liberty Link varieties to have complete tolerance to Ignite. This difference in gene composition is why we see different performance in the field for the two technologies in terms of tolerance to Ignite.
When using Ignite on WideStrike varieties, be wary. In situations where the cotton is under stress (cool-wet weather, insect damage, other herbicide damage, etc.) spraying Ignite over WideStrike cotton varieties can lead to yield reductions as has been reported by many University scientists this winter. However, research conducted at locations in Arkansas, Georgia, Mississippi, and Tennessee during 2010 demonstrate that two 29 oz applications of Ignite on WideStrike cotton varieties did not reduce yield.
In fact, we had to apply two applications of Ignite at 87 oz. per acre to statistically reduce yields. In these trials, Ignite was applied to 1-3 leaf and 6-8 leaf cotton, and plots were maintained weed-free so only the effect of Ignite would cause differences in yield. Additionally, yield reductions have been seen where Ignite is applied to WideStrike varieties that are blooming. While Ignite may be to blame for those reductions, the effect of competition from pigweed with cotton is much greater.
In Tennessee we do not promote Ignite use on WideStrike cotton as a system, but as a hedge against our other practices. Only 5% of Tennessee cotton acres are irrigated; therefore we rely on rainfall for activation of multiple residual herbicides. We hope that we never have to make an Ignite application over WideStrike cotton, but having that ability by planting a WideStrike variety is the difference between success and failure on many of our acres.
Finally, the driving principle behind this practice is the performance of PhytoGen’s 375 WRF variety as a top performing variety for the last three years. As new variety releases from FiberMax and Stoneville become available with stacked technology (Glytol and Liberty Link) Tennessee growers will be ready to adopt these varieties with a weed control program that is tested and proven effective.
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