Published on Friday, November 5, 2021
Replant is always a difficult decision to make, but what is the best option to terminate a failed corn stand? One option could be tillage, but depending on the type of tillage and the growth stage of the corn, it may take two passes to achieve 100% control. The benefits of tillage would be not having a plant-back restriction compared to some chemical options that require plant-back restrictions. One disadvantage of tillage would be the impact on the residual herbicide. Pre-emerge herbicides act as a blanket, reducing weed emergence, but tillage can destroy this barrier.
Products like Select Max® have a corn replant portion on the label. Select Max is a systemic grass her bicide that is very effective on corn and does not require the high carrier volume like a contact herbicide. However, when using lethal rates, Select Max has a plant-back restriction that will cause a replant delay. Gramoxone® SL 2.0 is another effective burndown herbicide and does not require a plant-back restriction. However, Gramoxone SL 2.0 is a contact herbicide that requires a greater carrier rate and is less effective than Select Max. Adding metribuzin to Gramoxone SL 2.0 can increase the effectiveness without increasing the plant-back restriction, depending on the rate of metribuzin. Another option without a plant-back restriction would be Liberty®. However, some hybrids may be tolerant to Liberty, thus making it an ineffective option. Just like applying Gramoxone SL 2.0 or Gramoxone SL 2.0 + metribuzin, coverage is king with Liberty. If a high (15+ Gal./A.) carrier volume is not used a r eduction in control can be expected.
Since Select Max is a systemic herbicide, it took the full 21 D AT to see the highest control with an 89% stand reduction. The contact herbicides saw the highest stand reductions early on and did not need the extra time like Select Max. With any herbicide, time is needed to work on the plant. Therefore, if we destroy the plant with a planter before the herbicide has enough time to work, we could see a r eduction in control. Group 1 herbicides work by killing the growing point; therefore, it takes more time to see the full efficacy of Select Max. Contact herbicide s like Gramoxone SL 2.0 and Liberty performed the worst with only a 66 and 62% stand reduction, respectively. However, tank-mixing metribuzin with Gramoxone SL 2.0 increased the stand reduction by 30% by 21 DAT vs. Gramoxone SL 2.0 alone. Gramoxone SL 2.0 + metribuzin had a more rapid kill vs. Select Max without the plant-back restriction. Proper coverage will be critical to ensure a successful Gramoxone SL 2.0 + metribuzin application. Using a field cultivator, we saw a 90% stand reduction by 21 DAT. Though tillage was effective, this was the first place we saw weeds start to emerge because we broke the residual barrier. We typically see more uniform control with a spray application vs. tillage if the application was made properly. With tillage, we had great control where we hit the corn plant, but some plants were missed. Finding a window to perform tillage in a wet spring may be a challenge vs. finding ideal s oil conditions to run a sprayer.
Though tillage controlled what plants it hit, some plants were missed. Tillage broke the residual barrier resulting in earlier flushes of weeds. Chemical treatments did not interfere with the residual barrier. Contact herbicides such as Gramoxone® SL 2.0 or Liberty® struggled. Tank-mixing Gramoxone SL 2.0 + metribuzin resulted in the greatest control and was more rapid vs. Select Max®. Select Max was effective but required a plant-back restriction and took the full 21 days to see the greatest control.
Author: Jim Schwartz
Categories: Agronomy, Agronomy Talk