Database Research Summaries2018 Evaluating Herbicide Incorporation Via Water Quality and Timing Under Different Tillage Strategies
Research Focus
The focus of this project is to evaluate common pre-emergent herbicide options that would be used in cases of glyphosate resistance under different environmental circumstances.
Objectives
- Measure the effectiveness of pre-emergent herbicides when rainfall is delayed or absent following herbicide application.
- Identify differences in herbicide activity based on tillage practices.
- Compare herbicide activation and residual duration between rain activated and incorporated products.
- Develop recommendations for an herbicide management plan when environmental conditions are not favorable for herbicide activation.
Results
- A study was conducted over the 2016 and 2017 growing season to determine the consequences of delayed herbicide activation of soybean herbicides (aka no rain). The study was conducted under a center pivot irrigation system to supply 0.5” of water to some of the treatments. The weeds present were redroot pigweed, common lambsquarters and kochia only in 2017. The herbicide treatments were metribuzin, Fierce, and Spartan, representing some of the most commonly used active ingredients in soybeans.
- Activation strategies included watering within 24 of herbicide treatment, watering 7 days after herbicide treatment, not watering at all, or using a rotary hoe to mechanically activate the products 7 days after application.
- A common understanding about PRE activation is that smaller rainfall events totaling ~0.25” or more are not sufficient to activate a herbicide. This study provides further evidence that this is the case. The products were not activated until the 0.79” rainfall 22 days after herbicide application.
- There was no decrease in herbicide activity with a 7 day delay in activation with any product. When averaged across herbicides, there was also no difference between mechanical incorporation and no activation strategy, except that mechanical incorporation decreased redroot pigweed control.
- With redroot pigweed and common lambsquarters, Fierce and Spartan were consistent performers except that Spartan control dropped after 7 days with no activation. Control of kochia dropped off with both products after 7 days without activation as well. Rotary hoeing typically did not improve weed control, except that it appeared to improve metribuzin’s effect on kochia.
- Overall, metribuzin performance decreased the quickest with delayed activation.
Importance
- A successful pre-emerge weed control program is the foundation of a glyphosate-resistant weed management strategy.
- This data will lead to information to direct decisions about subsequent weed management in a field or it may be used to determine when a product could effectively be applied in relation to a rain event, since it is not possible to put out all the PRE herbicide in the state the day or two before a rain.
For more information about this research project, please visit the National Soybean Checkoff Research Database.
Funded in part by the soybean checkoff.
