Dr. Karly Regan, Penn State Extension, has some tips for growers planning pesticide applications for the upcoming season.

“If something goes wrong with your application, it can result in losing those plants and lost profits,” said Regan. “A lot of wasted time was spent mixing product, getting it into the tank and to the field, then it didn’t do what you expected it to do.”

Regan listed some of the most common reasons for failed pesticide applications including faulty timing, unfavorable environmental conditions, incorrect dosage, not reaching the target pest and resistance.

“In some cases, a pesticide application failed due to improper pest ID,” said Regan. “The product used didn’t control the pest. It could be the wrong choice of pesticides for the crop.”

Not following label instructions is another reason for failure. “Labels can be tricky to read, but they have a lot of useful information, so take the time to read them,” said Regan. “Make sure you’re applying the product as intended so it works the way you need it to.”

Incorrect pest identification can mean the product (or the way it’s applied) will not work. The result is an unnecessary application along with wasted money and time. Growers should be able to correctly identify beneficial insects and avoid making them the target of pesticide applications.

Regan noted some harmful insects look similar to beneficials, which may hamper correct ID.

Become familiar with the physical features of insect pests for more efficient and accurate scouting. In cases in which a definitive identification is difficult, growers should be able provide accurate information to an Extension educator. A couple of good photos of an insect and damage can help an Extension educator identify the pest.

Consider whether the presence of an insect equates to crop damage. Some insects cause more damage than others, so determine which portions of the crop are threatened and use that information to make application decisions. Growers should be able to distinguish pests and disease from nutrient deficiencies or weather damage.

Reading the product label is the first key to successful applications. Know whether the product is for pre-emergent or post-emergent use for correct application timing, and whether it’s selective or non-selective. Understand the mode of action of the product, and whether the action is systemic or contact. Consider the life stages of insects and when products are most effective.

Product labels include dose and application rates. “One dose and one rate doesn’t fit all situations,” said Regan. “It depends on which pest you’re seeing to implement how much product to use.”

Labels also include critical details about product stability. Regan said a label may state that the product is stable for up to 21 days but must be incorporated with moisture to be effective.

“If you put the product out and don’t get any rainfall or irrigating,” she said, “you’re not going to get the same efficacy as if the moisture was present.”

The label will provide information regarding whether a surfactant is necessary and which surfactant should be used for best control. “The label will also indicate whether agitation is required,” said Regan. “The label might say to start agitation before adding the product to the tank and continue agitation as the tank is filling. If you don’t do that, it may not mix correctly.”

Vegetables with waxy leaves (such as brassicas and alliums) can be difficult to cover efficiently without a surfactant. Hairy leaves (like on eggplant and tomato) are also challenging to spray. Using the correct nozzle for the optimum droplet size will help with efficient coverage.

Application timing is important. Most pests aren’t equally controlled over their lifecycle, and in many cases, the youngest stages (larvae or nymph) are the easiest to control.

“Knowing what time of year to treat is important,” said Regan. “If a pest is only controlled in its larval stage, the product may not work on adults.”

Some target pests can be difficult to reach, depending on which part of the plant they prefer. Grubs in the soil, boring grubs inside plant tissue or pests on the undersides of leaves are often more challenging to reach.

Environmental conditions can affect coverage. Plants often develop thicker cuticles in certain weather which can prevent good systemic coverage. Spray droplets evaporate faster in hot, dry conditions. Recent or upcoming rainfall can affect efficiency – even if the rain has stopped, the root zone may still be flooded.

“Many products should not be applied before or during rain,” said Regan. “There are some exceptions, such as products that need water to incorporate to be more effective. But if it doesn’t need the moisture and the product can be easily washed off, don’t put on before rain. Again, labels will indicate how moisture may indicate efficacy.”

Some products have specific temperature requirements for storage. “If they’re stored somewhere excessively hot and the product will break down above a certain temperature, they aren’t going to work well,” said Regan.

Use an accurate measuring device to measure product rather than guessing on amounts, and  remember that dry and wet products are measured differently. “Nine ounces of liquid by volume is not the same as nine ounces of dry product,” said Regan. “If you’re working with a dry product, measure by weight and not by volume.”

Make sure spray equipment is properly serviced and calibrated prior to use. Even with proper mixing, if the equipment isn’t functioning correctly, there’s a good chance the product will not be effective. Calibrate equipment regularly throughout the season to ensure the product is being applied at the proper pressure.

Factors that influence calibration include consistent pressure settings, tractor speed or walking speed. Walking speeds vary among individuals, so be sure to calibrate equipment for each worker. Pay attention to the area being covered and calibrate for the equipment being used.

Pesticide resistance is another reason for failure and is different from other failure factors – it isn’t influenced by equipment, storage, mixing, weather or technique. Regan explained that over time, some fully susceptible insects become resistant. As the product is continually used, insects that are not susceptible remain alive and continue to reproduce. Over time, more pests are fully resistant to a product.

“You’ve done it the same way for many years and put it out correctly, and it doesn’t work the way it used to,” said Regan, explaining resistance. “This is because efficacy has changed over time. Continuing to use products with the same mode of action repeatedly for many years can result in the product no longer working to control the pest. The speed at which this happens depends on characteristics of the target pest and how frequently a product is applied.”

by Sally Colby