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Getting the Most From Your Grass Control Dollars

March 16, 2001
With increased nitrogen and fuel prices this year, many growers are wondering what are some ways to help reduce input costs. One option would be to maximize weed control by optimizing herbicide inputs. Currently, there are a number of growers and applicators considering early preplant (EPP) applications of acetamide herbicides for grass control in corn. These EPP applications have been widely used over a number of years. Many of these grass herbicides have labels that allow applications from fall to 45 days prior to planting as split applications, to 30 days prior to planting or planting as single applications, depending on the herbicide. However, in light of current economic considerations, when is the best time to apply these herbicides for optimal grass control in corn?

One reason EPP applications have become so popular is that they help spread out the workload for the herbicide applicator. Applying herbicides earlier in the spring gives the applicator more time to cover more acres. Another benefit to EPP applications is that they help reduce the risk of herbicide failure due to lack of precipitation following preemergence applications.

However, depending on application timing, many of these grass herbicides will need to be applied as split applications. These split applications would lead to another trip across the field, increasing herbicide application costs. Additionally, many of these herbicides need to be applied at higher rates the farther away from planting the application is made. These increases in herbicide rates lead to increased herbicide costs.

Another question is how EPP applications perform compared with applications closer to planting. Over the last several years many universities have examined the performance of these herbicides at different application timings. Some of the work conducted at the University of Illinois by Dan Parker and Dr. Bill Simmons has compared the performance of several grass herbicides at various application timings. The four application timings examined were fall (mid-November), 60 days prior to planting, 30 days prior to planting, and at planting. These research trials were conducted at three locations in Illinois for 2 years. Evaluations were made on giant foxtail control 30 and 60 days after corn planting.

By 30 days after planting (DAP, Figure 1), giant foxtail control was greater than 97%, with all herbicides applied at planting. When herbicide applications were made 30 days prior to planting, only three herbicides provided greater than 90% giant foxtail control, and when applied 60 days prior to planting, only one herbicide provided greater than 90% control. By 60 days after planting (DAP, Figure 2), only the at-planting herbicide applications provided greater than 90% giant foxtail control. The average giant foxtail control decreased the further away from planting time the herbicides were applied.

So how can you get the most out of these soil-applied herbicides in these tight input times? The simple answer: the closer these herbicides are applied to planting, the better the season-long grass control.--Christy Sprague and Aaron Hager

Author: Aaron Hager Christy Sprague


The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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