It’s no secret that in modern crop production, pesticides are necessary tools of the trade to manage insects and diseases or to prevent infestations, even with advanced integrated pest management practices. But for these pesticides to be effective, they must be applied correctly. So, you’ve purchased the newest pesticide, you sprayed your crop, seemingly getting adequate coverage, but still seen low yield and produce loss due to pest infestation at harvest. Why?
If your product is not working, it's likely due to poor spray coverage. Pesticides developed in a controlled lab environment advertise high rates of effectiveness for pest eradication, but in the open environment of a field with uncontrollable factors like weather fluctuations, equipment malfunctions and variances in migrating insect timelines, the situation is infinitely more complicated. The number one determining factor for how well a pesticide works is how well the product is administered. Coverage is therefore key. Furthermore, some sprays are expensive, so proper coverage is necessary for the highest economic benefit.
Here are our six essential tips to follow for farmers and growers to improve pesticide effectiveness by maximizing spray coverage
While pesticides may once have been “one size fits all,” science has made great leaps and pesticides are now more targeted than ever. Before choosing a pesticide to apply, know the ins and outs of your operation.
What are you planning to spray?
· Are you growing organic or conventional crops? To be certified organic and OMRI listed, pesticides must be carefully chosen. Conventional crops have a more comprehensive range of options.
· Is the crop fruit-bearing and, if so, does it have a harvest timeline? Regulations require pesticides to have been last sprayed a specific number of days or weeks prior to harvesting to ensure the pesticide has disseminated before being consumed.
· What is the crop density and height? A crop growing knee-high will have different sprayer needs than orchard crops, as the sprayer will have to be taller, for example.
Where are you planning to spray?
· Is your operation indoor or outdoor? Indoor operations require different sprayers than outdoor operations; outdoor operation sprayers must be calibrated to compensate for weather conditions.
· Does your area have restrictions? Operations near certain roads, public spaces, protected wildlife areas, residential communities, schools or protected neighboring fields are legally restricted to when and how they can spray. Aerial spraying specific pesticides are prohibited in many of these situations.
· Where is your operation located? Pesticides work differently in areas of the Midwest where it is very humid, and the temperature fluctuates seasonally than in California where it is dry and sunny, and freeze doesn’t occur. Microclimates also must be considered; on a large tract of cropland, a small downhill area can trap moisture and cause pockets of fog with high humidity or temperature inversion that can cause sprays drift.
For maximum effectiveness, a grower must know as much as possible about their intended target.
How does it travel?
· Is it a flying pest? Flying pests can be further categorized into strong and weak flyers. Strong flyers will quickly move to stagnant crops where the pesticide is not being sprayed; specific equipment that minimizes air displacement or sits closer to the crop allows less time for the pest to flee. Weak flyers can be conventionally sprayed; furthermore, they might only be present in one area of the field due to their smaller travel radius, minimizing the need to spray the entire field, cutting down costs.
· If it doesn’t fly, how does it move? Non-flying pests can move above ground or below ground within the soil. Below ground pests will not be killed by spraying on top of the crops, so this knowledge is vital.
How does it eat? Knowing the feeding habits of the targeted pest can help you focus your attack. For example, caterpillars eat whole leaves, while aphids go straight to the stems. Pesticides that are taken up through the soil may not make it into the leaves in high enough concentration, but they do make it into the stem and are thus viable for killing aphids, but not caterpillars.
What is the pest life cycle? Knowledge is power for determining a timeline of when to spray. Knowing when the pest is migrating up, laying eggs, or in various steps in its life cycle is vital. Again, spray too soon, you miss the pest; spray too late and there’s no undoing the damage.
Are you trying to affect multiple pests? If so, consider that the lifecycles of each one must be scheduled out, and overlap periods determined for maximum effectiveness.
Knowing what crop is being sprayed and what pest is being targeted, it’s time to choose your pesticide to fit your specific needs. But, don’t let re-application become an afterthought. If you’re using a pesticide with residual activity, you know that new growth will be susceptible to pests, as the pesticide hasn’t been applied to that part of the crop. If you’re using a systemic approach, remember that pesticides taken up by the plant have a degradation timeline and won’t be fully effective after a while, so re-application is necessary.
How will the pesticide reach your pest?
· By Contact: The simplest form of interaction, contact pesticides must touch the pest to eradicate it. Considerations for contact pesticides include migration timelines (the spray must hit the bug, the bug must be present when you spray) and whether the pest is a strong or weak flyer (and can thus escape contact by flying away).
· Ingestion: These pesticides must be taken into the pest’s system through feeding. Knowledge of the pest’s feeding habits is crucial: Does the pest typically eat the leaves, stem, or root of the crop? Special spray considerations must be made to ensure full coverage of the area the pest will ingest.
· Systemic: These pesticides are a subset of ingested pesticides, but instead of being sprayed onto the plant, they are taken up by the plant, and the crop becomes toxic to the pest. The pest then feeds on the crop and dies from the systemic pesticide. Some systemic pesticides can be taken up by the plant all the way into its leaves, while others make it only to the stem, so knowledge of what part of the plant is being ingested is necessary.
· Translaminar: Either a subset of contact or ingestion varieties, these pesticides are sprayed onto a crop and soak through the leaf to create toxicity on both sides of the leaf.
These solve the problem of pests that tend to hide out on the bottom side of the leaves and are thus not reached by standard spray coverage.
Know the pesticide restrictions and limitations. Read and follow the pesticide label directions very carefully for information about:
· Rate restrictions: The label gives directions on how many times the pesticide must be applied for maximum effectiveness. A pesticide expert once summarized: “Just because a little bit works well, doesn’t mean a lot works great.” Pesticide developers have done years of research to determine where the line is.
· Geographical limitations: In fact, some pesticides are banned within a certain area; be aware of where you need to spray and with what.
· Temperature regulations: Indicates what range of temperature the product is most effective within.
· Stage limitations: Pesticide needs to be sprayed within a certain growth stage of the crop and of the pest. Therefore, growers should adhere to this timeline.
Does your pesticide need a little help? Adjuvants are additives that, when mixed with a pesticide, can increase the effectiveness of the product for several reasons.
· Emulsifier: Oil-based concentrate pest control foliar sprays require an emulsifying agent to mix the oil with water at dilution, helping to mix the two immiscible compounds together and ensuring the even distribution of the product throughout the plant.
· pH Buffer: is an additive that changes the pH of the pesticide solution; often the water used to mix, or dilute pesticides is too alkaline, lowering the absorption rate of the product. A buffer can correct this.
· Stickers: are adjuvants that can increase the “stickiness” of a product, causing it to remain on the crop for longer, and thus be better absorbed.
· Wetting agents: are adjuvant that breaks the surface tension of a liquid; if your crop has waxy leaves, you’re likely familiar with the big drops of liquid that form and collect on the leaves, causing inferior coverage. A wetting agent can force those droplets into smaller droplets, increasing coverage and effectiveness.
Once you’ve decided on a pesticide that suits your pest in the best interest of your crop, you’re ready to start thinking about what equipment to use for an application. Again, there are situational considerations.
· Can your equipment handle the volume of pesticide needed to be applied? Some products require an incredibly high volume to be administered for maximum effectiveness.
· Are there heat limitations? A thermal fogger, for example, might not be the correct choice for the application of a fungal biopesticide, as high temperatures can kill the spores.
· Are there pressure limitations? Pesticide products that are micro-encapsulated (for slow release) can’t be pushed through a high-pressure sprayer, or the encapsulation will break and the slow release effect will be lost.
· Are there pairing limitations? Sometimes, a pesticide manufacturer might make it easy on you and eliminate an application option. Read the label for instructions such as “no aerial application.”
· What are the minimum and maximum rates of application? Recommended rates of application are posted on pesticide labels and can help you narrow down a range of application rates, thus narrowing your application selection as well.
Sprayers must be calibrated periodically to ensure they are working correctly. Even small differences in the state of the equipment can make large changes to the effectiveness of a sprayer, costing you time and money when you have to re-apply or when you don’t get the spray coverage you need to eradicate your pests.
Preparation is nine tenths of the battle when it comes to pesticide application. Now that you’ve chosen the right pesticide and application equipment for your crop and pest situation, it’s always smart to double-check your work. You want to know that what you’re spraying is actually getting out onto the crop and reaching your pest.
● Check with a water-sensitive spray card: Placing these water-sensitive cards periodically throughout your field and collecting them after you’ve sprayed can tell you a lot. The card turns blue where water has touched it, so a blank card is a good indicator that you’re not getting the spray coverage that you want. Re-adjusting boom height and checking your nozzles are the next step when you’re not seeing adequate coverage. If you’re looking for full leaf penetration, try placing the cards on the undersides of the leaves to check.
● Check with surveyor tape: Spray cards are great, but if you can’t reach them to check (for example, if you’re spraying an orchard instead of a field of crops), they’re useless. Consider using colorful surveyor tape that can be placed higher and looked at from a distance. The tape will move as air moves, indicating that the product is reaching the target area. This is not a conclusive coverage check, as air might be moving even if the spray is not being well-distributed, but it’s an easy check for malfunctions if the tape is stagnant.