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What You Need to Know About Pesticide Use on the Farm

Pesticides serve many functions and come in many forms, including herbicides, insecticides, and fungicides. The ultimate goal in all cases is to increase crop yields by reducing competitive environmental factors.

Weeds, bugs, and disease steal a plant’s health and nutrients, reducing its productivity. Pesticides can help, if used properly.

Applying herbicides for weed control

Herbicides reduce weed competition. The products on the market are many and varied. One of the more popular herbicides is dicamba. Dicamba kills annual and perennial broadleaf weeds by increasing plant growth rate until it outgrows its supply of nutrients and dies.

Use of dicamba has increased with the introduction of Monsanto’s genetically modified dicamba resistant plants.

Older formulas of the herbicide have been known to create problems with drift onto other plants. Newer, less drift prone versions are now available. New EPA-approved labels for the 2019-2020 growing seasons offer revised instructions for use.

When applying dicamba, there are steps farmers can take to increase effectiveness and reduce environmental impact, beginning with selecting the right product for the right crop. For Round-up Ready soybeans, use only approved formulas, and make sure the applicator is properly certified. Most state extension services offer the necessary annual pesticide applicator training.

With the new label comes adjusted wind direction restrictions and buffer requirements. Be sure the wind is blowing in the opposite direction of any nearby sensitive crops, and keep at least a one-half mile buffer between those crops and where you are spraying. Also beware protected species buffer requirements. And pay attention to timing. Dicamba can be volatile for up to three days, and the wind can shift and gust.

There are time of day restrictions on dicamba application. The label states product should be applied within one hour after sunrise and two hours before sunset when temperature inversions are less likely.

Be sure to use the right application equipment, and check product information for acceptable additives and tank-mix partners.

Some farmers choose to apply a burndown herbicide before planting in the spring. This is especially crucial for no till planting. Most products have plantback restrictions of 7-30 days. Some burndown herbicides have residual activity, killing plants that overwinter crop pests such as the soybean cyst nematode.

How to manage Palmer amaranth

Despite the ag science community’s quest to manage Mother Nature, she often has other ideas. A new challenge to farmers appearing in recent years is palmer amaranth. The weed can grow 10 feet tall, has stems as thick as a baseball bat, and if tossed into a field, can reroot itself. Purdue University research has shown a 78% soybean yield loss due to infestation, 91% for corn.

Palmer amaranth grows quickly, making timely herbicide treatment crucial. Other measures, such as reducing soybean row width, keeping the plants from going to seed, and planting cover crops can help reduce the pest’s impact.

Palmer amaranth is on the move from the South into the Midwest and scientists at Kansas State University have confirmed a variety resistant to dicamba and 2,4-D. The Group 4 products have worked in the past, but are proving less effective in recent years. The research is ongoing.

How to manage Waterhemp

Waterhemp is another unwanted plant that can do serious damage to yields. University of Missouri researchers have now identified a population with resistance to six herbicides. Dicamba and glufosinate were the only two of eight herbicides applied that produced weed control.

Experts recommend a blend of biological, mechanical, and cultural measures to attack the weed. Identification, timely treatment, layering herbicides, planting narrower rows, and using new technologies, all while keeping an eye on other weeds may help.

Herbicide resistant waterhemp has also been identified in Illinois, the first broadleaf species to show Group 15 resistance.

Scientists chalk the resistance up to evolution. Farmers have traditionally applied pre-emergence residual herbicides, but now experts are rethinking the year-over-year practice and the changes in plant biology that result.

Using insecticides

Resistance is also a problem for insect control. Corn rootworms adapt to control programs, including hybrid corn varieties developed with pest control in mind. Luckily, rootworms don’t travel far, and resistance is often contained to the field where it developed.

Rotating crops can help; even a one-year soybean break can disrupt the rootworm life cycle and lower population density. Some have found using foliar insecticides that kill adult beetles can help, but products are becoming more restricted.

New insecticides are in the development stage, but it may be some time before they hit the market.

Bt traits in corn may not be as effective against rootworms as they were before the rootworms caught on, but the science does protect against European corn borer (EBC). Near eradication of the pest has caused some farmers to plant hybrids without corn borer protection.

For those wanting to use less expensive seed, ECB can be controlled via other means, but fields will require diligent scouting and immediate action.


Safe and effective use of fungicide, like any other pest control product, requires strict adherence to label directions. There are various classes of fungicides, some are curative and some are preventative. All work best before disease is present by preventing spores from germinating.

Again, ardent scouting and timing are crucial.

Beware pesticide drift

Safe pesticide application also includes awareness of pesticide drift. Both you and your neighbors will suffer if the product goes astray. Not only can yields be reduced, but in some cases, applicators may be liable legally.

Pesticide drifting to unsuspecting plants in the crossfire can cause environmental damage, including destruction of pollinator and wildlife habitat. So, make sure you are using the right product, at the right time, with the right equipment, under the right weather conditions. Generally you will want wind speeds of less than 10 mph.

Talk to you insurance agent about coverage against damage to yours or your neighbor’s crops. Know your coverage and your limits.

And always, always, always treat any pesticide with the utmost care. Used incorrectly, they can become an environmental hazard. Used correctly, they can protect your crop and your farm’s profitability.

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