Three Key Midseason Weed Control Issues

July 17, 2011 10:09 PM

By Dwight Lingenfelter, Penn State Cooperative Extension Weed Science

As we proceed through the growing season, there are a few issues surrounding weed control and herbicide use. Below are some items to consider:
Rescue applications: We are receiving calls about and observing weeds breaking through pre herbicides. With all of the rainfall this spring and especially if reduced herbicide rates were used, a postemergence herbicide may be necessary to clean up some of the escaped weeds. However, keep in mind there are crop height restrictions on many of the post herbicides. Application restrictions can be found in the PSU Agronomy Guide or online (corn).
Be cautious of herbicide drift: With the many weather setbacks this spring, some are cutting some corners to get all the work done including spraying in less than ideal conditions.
We have received calls recently about spray drift onto residential gardens and subsequent damage. Some of this could have easily been avoided if drift reducing nozzles were used. To help reduce drift, use drift reducing nozzles such as venturi or air-inductions (AI) style tips. Most manufactures now make these tips as extended range models in order to reduce the spray pressure down to 15 psi. Although these drift reducing nozzles cost a little more than standard flat fan tips, it could potentially save a lot of money and hassle if a neighbor decides to take legal action.
Certain herbicides especially, glyphosate and the PGR herbicides (dicamba, 2,4–D, etc.) can cause problems outside the field boundaries. Also consider the difference between particle drift and vapor drift. Particle drift occurs when small droplets actually move and deposit onto leaf surfaces (this can be prevented by choice of nozzle, pressure, spray volume, application time, etc.). Vapor drift is related to the function of the herbicide formulation (e.g., ester vs. amine) and does not matter what kind of tip or pressure is used. It is impacted by temperature and relative humidity. For a more detailed discussion on spray drift and ways to reduce it.
However, keep in mind, if using herbicides that require good spray coverage (e.g., Ignite, Gramoxone, Aim, Cadet, etc.), AI tips may not be the best option unless certain adjustments are made to allow for better coverage including, higher spray volume, pressure, and boom height.
Sprayer cleanout: Proper sprayer cleanout is important especially when moving from one crop to another. There are still many reports of PGR herbicide injury on soybeans when applicators don’t properly clean out the sprayer after a corn application.
Dicamba residues left in the sprayer still pose one of the biggest threats to soybean (and certain vegetable crops) when not thoroughly cleaned out. Dicamba-containing products include: Banvel, Clarity, Status, Sterling, Marksman, NorthStar, Yukon and others. To get the most effective sprayer cleanout, simply rinsing with water will not work especially with plastic tanks and rubber hoses. Usually it requires a few steps with inclusion of ammonia and/or tank cleaner. For more details on sprayer cleanout.
For More Information 
Let Farm Journal Media prepare you for the battle against weeds. Visit the Weed Warriors section.



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