Month: June 2021

Here are some commonsense practices for effective spraying of pesticides

This article was posted on behalf of Dr. Erdal Ozkan, Department of Food, Agricultural and Biological Engineering.

June is the start of a busy spraying season for vegetable growers. Paying attention to some key principles of spraying is likely to result in achieving your goal: maximum net return on expensive pesticides sprayed. Before giving you some specific recommendations on how to achieve the best results from pesticides sprayed, I want to remind you 6 key elements of successful spray application.  When applying pesticides, certain tasks are required for maximum biological efficacy. These include:

  1. 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.
  2. Choosing a pump with sufficient capacity to deliver the required gallonage (gal/acre) to the nozzles.
  3. Ensuring hoses and fittings between the pump and nozzles are properly sized to minimize pressure losses.
  4. Ensuring minimum loss of pesticides as they are delivered from the nozzles to the target.
  5. Attaining maximum retention of droplets on the target (minimum rebound).
  6. Providing thorough and uniform coverage of the target with droplets carrying active ingredients.

Sprayer traveling over a vegetable field.

Here are just a few of the best spraying practices you may want to pay attention to get the most out of the pesticides sprayed:

  • Carefully read and follow the specific recommendations provided on the pesticide label, in nozzle manufacturers’ catalogs, and sprayer operator’s manuals.
  • Calibrate the sprayer to ensure the amount recommended on the label is applied.
  • Check the sprayer setup 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 mixing is done in the appropriate order.
  • Conduct calibration of 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 best coverage on the target, select the appropriate types of nozzles for the product, and if applicable (not restricted by the label) keep the spray volume (carrier application rate) above 15 gpa.
  • Follow recommendations to reduce spray drift to minimum. Probability of spray drift is much greater with some nozzles than others, and when nozzles are operated at a much higher pressure than they are designed for which forces them to increase the number of drift-prone small droplets discharged.
    • Slow down when spraying. Spray coverage is usually improved at slower speeds. Also, 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. However, for fungicide and insecticide applications, you may still stick to cone nozzles, or flat-fan nozzles that generally produce no larger than medium size droplets (nozzle manufacturers provide droplet size data).
  • 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.
  • Be careful when using twin nozzle/pattern technology for 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. Use single flow pattern nozzles under dense canopy conditions when penetration of droplets into the lower parts of the spray canopy is desired.
  • If you are a large-scale vegetable grower, take advantage of technological advancements in spray technology, such as GPS, Pulse Width Modulation nozzles for selective and variable-rate spraying, and auto guidance systems.
  • 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.

Inspect all parts of the sprayer periodically throughout the season.

Of course there are equally important topics I did not mention here, including: general inspection of the sprayer, importance of proper product agitation in the sprayer tank, adequate size hoses and fittings, determining sprayer setup for acceptable application rate, selecting proper boom height based on nozzle angle and spray overlap, 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. I will cover some of these topics in more detail in my future articles throughout the summer. However, as we get into the busy spraying season, I highly recommend you check two OSU extension publications for detailed discussions on the topics I covered and not covered in this article:

-FABE-527, “Best Management Practices for Boom Spraying” (https://ohioline.osu.edu/factsheet/fabe-527) -FABE-532, “Best Practices for Effective and Efficient Pesticide Application” (https://ohioline.osu.edu/factsheet/fabe-532).

Another excellent source of information on a wide range of topics related to pesticide application technology is http://sprayers101.com.

Staking Tomatoes and Peppers – Can Stakes be Reused?

We often get questions from growers about reusing wooden or other stakes for tomato and pepper production, particularly if diseases like Phytophthora blight, Pythium root rot or bacterial canker were present where the stakes were used the previous year. The pathogens that cause these and other diseases can survive over the winter in soil and plant debris on stakes. We recommend power-washing or brushing stakes to remove all of the soil and plant sap, followed by disinfecting. This may be a big logistical headache for growers with a lot of stakes. In the Midwest Vegetable Production Guide for Commercial Growers (pages 80-81), we recommend soaking stakes in 10% bleach or quaternary ammonium disinfectants, followed by rinsing and drying.  

There is more information on disinfecting stakes in the Mid-Atlantic Commercial Vegetable Recommendations (page 12): “The preferred (and most expensive) method of stake disinfestation is heat treatment. Pathogens are completely eliminated from wooden stakes with exposure to ≥ 220°F for ≥ 15 minutes. This can be accomplished in a large capacity autoclave, or seed dryer. It is unlikely that most growers will have access to such equipment. Alternatively, therefore, stakes may be exposed to disinfectants such as commercial chlorine solutions (sodium hypochlorite) or Oxidate® (hydrogen dioxide; see below). Research has shown that a 20-minute soak in a solution made of 5 to 20 parts by volume sodium hypochlorite (commercial bleach) to 80 to 95 parts by volume water is effective in eliminating pathogens only from the surface of wooden stakes. It is crucial to maintain the pH of the bleach solution within the 6.0 to 6.5 range, as effectiveness decreases at lower and higher pH levels.”

“Studies on stakes treated with bleach solutions show that pathogens may still be present beneath the surface at depths ≥ 1/16th inch. Pathogens embedded within the stake may be able to migrate back to the surface and re-infest plants, although this has not yet been demonstrated. To improve the effectiveness of procedures for removing microbial pathogens from stakes, consider the following: Add a non-ionic surfactant to the disinfesting solution; increase the soaking time to ≥ 1 h; apply a vacuum during the stake soak; use a higher concentration or more potent source of hypochlorite (such as “heavy duty” or swimming pool grade chlorine); or use stakes comprised of nonabsorbent stake materials (such as plastic or metal). Many growers have successfully used the commercial product Oxidate® or chlorine dioxide to disinfest stakes. Oxidate® is OMRI certified and had been demonstrated to be an effective control agent for several important plant pathogens. However, data on the efficacy of this treatment as compared to using heat or commercial chlorine solutions are not available.”

All disinfectants are quickly inactivated by organic matter, so getting as much of the soil off the stakes as possible before sanitizing would improve the results.