The 2021 planting season is finally coming to an end, but that doesn’t mean everything else on the farm has come to a stop. On many farms there is plenty to do and many other issues to address throughout the farming landscape of Clinton County.

This week let’s look at post-emergent weed control.

Weeds compete with crops for water, nutrients, and light, leading to reductions in crop yield.

Weather, herbicide-resistant weeds, optimal size to control troublesome weeds, crop growth stage restrictions for post-emergence herbicide application and options to control mid- to late-season weed escapes are very important.

But remember, paying close attention to key principles of spraying is likely to result in achieving your goal: maximum net return on expensive pesticides sprayed.

First, let us start by identifying 6 key elements of successful spray application. According to Erdal Ozkan, Ohio State University Sprayer Technology specialist, when applying pesticides, certain tasks are required for maximum biological efficacy. These include:

• Uniform mixing of pesticides (especially dry products) in the sprayer tank. This can be accomplished only if the agitation system in the tank has sufficient capacity for its size and is operating properly.

• Choosing a pump with sufficient capacity to deliver the required gallonage (gal/acre) to the nozzles.

• Ensuring hoses and fittings between the pump and nozzles are properly sized to minimize pressure losses.

• Ensuring minimum loss of pesticides as they are delivered from the nozzles to the target.

• Attaining maximum retention of droplets on the target (minimum rebound).

• Providing thorough and uniform coverage of the target with droplets carrying active ingredients.

Ozkan recommends several best spraying practices to get the most out of the pesticides sprayed:

• Carefully read and follow the specific recommendations provided on the pesticide label, in nozzle manufacturer’s catalogs, and sprayer operator’s manuals.

• Calibrate the sprayer to ensure the amount recommended on the label is applied.

• Check the sprayer set up to ensure the amount applied is distributed evenly across the spray swath.

• If more than one type of chemical is added to the sprayer tank, check product labels to ensure the mixing is done in the appropriate order.

• Conduct calibration of the sprayer, mixing, and loading of chemicals in areas without risk of ground/surface water pollution.

• Operate the nozzles at a pressure that allows them to produce the spray quality (droplet size) recommended on the product label.

• To achieve the best coverage on the target, select the appropriate types of nozzles, and if applicable (not restricted by the label) keep the spray volume (carrier application rate) above 15 GPA for ground and 5 GPA for aerial applications.

• Pay special attention to the selection of nozzles when applying pesticides containing 2,4-D and Dicamba. Check the labels of these products for specific requirements for nozzles and operating pressure ranges.

• Follow recommendations to reduce spray drift to a minimum. The probability of spray drift is much greater with some nozzles than others.

• Slow down when spraying. Spray coverage is usually improved at slower speeds. The higher the travel speed, the greater likelihood of spray drift.

• For herbicide applications, flat-fan nozzles are better than cone nozzles which tend to produce a much smaller proportion of extremely small, drift-prone droplets.

• Good coverage of just the top of the canopy may be sufficient for adequate pest control with some products. However, both horizontal and vertical coverage of the plant may be necessary for other situations, such as disease and insects that may be hidden in lower parts of canopies.

• Air-assisted sprayers usually provide better coverage and droplet penetration into the canopy, than conventional sprayers when there is a full, dense canopy, such as soybeans sprayed in the late season.

• Be careful when using twin nozzle/pattern technology for the application of fungicides. Two nozzles or spray patterns angled (one forward, one backward), work better when the canopy is not dense and tall, or when the target is the upper part of the canopy, such as with a wheat head scab. Use single flow pattern nozzles under dense canopy conditions when penetration of droplets into the lower parts of the spray canopy is desired.

• Take advantage of technological advancements in spray technology.

• Be safe. Wear protective clothing, goggles and rubber gloves, and respirators if required on the label, when calibrating the sprayer, doing the actual spraying, and cleaning the equipment.

Of course, there are equally important topics not mentioned here, such as proper product agitation in the sprayer tank, adequate size hoses and fittings, determining sprayer setup for acceptable application rate, selecting proper boom height, cleanliness, and pH of water used to mix the products in the tank, proper cleaning of the sprayer tank, spray additives that can enhance product performance, and handling pesticide waste and empty containers.

Speaking of empty containers, there will be a Pesticide Container Recycling Collection again on Thursday, August 19 from 8:30 a.m. to noon at Nutrien Ag Solutions, 6704 E. US 22 & 3, Wilmington (Melvin location). For more info, check out our Clinton County Extension website at or call 937-382-0901.

Tony Nye is the state coordinator for the Ohio State University Extension Small Farm Program and has been an OSU Extension Educator for agriculture and natural resources for over 30 years, currently serving Clinton County and the Miami Valley EERA.

Tony Nye

OSU Extension