Understanding Greenhouse Pesticides
What is a pesticide and how do you use pesticides in a greenhouse?
Greenhouse IPM Tips for Preventing Pests
- Look for regular opportunities to monitor plants closely like when pruning or transplanting
- Keep relative humidity below 55%
- Good airflow from fans prevents fungus and helps plant development
- Clean clothes, gloves, hairnets, and shoe covers should be worn in the growing area
- Have an effective integrated pest management program for your greenhouse
Pesticide Product Categories
Biofungicides, Biopesticides, and Predaceous Insects
Tips for Effective Pesticide Application
- Be sure to apply pesticides at the right time in the insect’s life cycle
- Pests can develop resistance to pesticides, so they need to be rotated
- Rotation of pesticides should include different classes of pesticides and pesticides with different modes of action
- Always follow the label and instructions for use
- Store and handle pesticides safely
Mixing Pesticides: pH and Growth Regulators
If a pesticide seems to be ineffective, the case may be that it was not used at the correct strength or frequency, that the pest is resistant to the particular product, the product may have degraded from exposure to heat or light, or it may be improperly mixed. Many of these factors are eliminated with good chemical hygiene like proper storage and ordering products as-needed instead of stockpiling. Improper mixing can be inadvertent for even the most cautious users.
Many pesticide users are unaware that the pH and alkalinity of their water can lower the effectiveness of some types of pesticides, and even deactivate them completely. Even water that has been tested and/or treated to be suitable for irrigation can be unsuitable for use with pesticides and growth regulators. Depending on the type of pesticide, it may work better or worse with differing levels of pH. Few pesticides perform best with neutral to basic water, slightly acidic water is more commonly ideal.
Example: Organophosphates, synthetic pyrethroids, carbamates, chlorinated hydrocarbons, and the growth regulator ethephon among others break down (hydrolyze) in water with a pH over 7. For each increment of pH over 7, they will break down 10x faster. Hydrolysis can happen fast, even instantly in water with a high pH, and also it can happen over time. After mixing, the solution should be used immediately to prevent it from becoming inactive.
Read the labeling on a pesticide carefully to check for guidance on the pH of water that it should be mixed with. If you need to correct the pH of your water, a buffering agent can be used. Most buffering agents will change color as the pH changes. Water should be tested with a pH meter before mixing with pesticides since the pH of water can change depending on season and rainfall. Some buffering agents do not work well with particular pesticides, so check with the manufacturer if that is a concern.
Spray Pesticide Application
Proper greenhouse pesticide and herbicide application are important to ensure that the product is effective and to avoid overuse that can lead to groundwater contamination and product waste. Most commonly, products are applied with a sprayer. Hydraulic sprayers use a pump to mix the product with water that carries it to the spraying target under pressure. Hydraulic sprayers may be booms or handheld “gun” systems. Low-volume sprayers use a water or oil carrier that is injected into an airstream.
he air stream in the pump is created by a fan, blower, or air compressor. Low-volume sprayers create a smaller droplet size than hydraulic sprayers so less product can be used to achieve good coverage. However, these smaller droplets do evaporate more quickly. Most pesticide labels give mixing instructions per 100-gallon dilution. This will differ from the concentration applied per acre or per 10,000 square feet. The ratio has to be adjusted for the additional water introduced through the sprayer. Another precaution to be mindful of is that some sprayers need to be calibrated to ensure proper function. Be sure to calibrate if needed before spraying.
Pesticide Impact Beyond Consumers
Pesticide use is a growing concern for the environment as it is for consumers. Improperly managed agriculture can lead to water depletion and damage to the surrounding environment were significant. Aquatic wildlife, land wildlife, and water sources, and other plant life are threatened by harm from pesticides and herbicides. Risks of pesticide exposure are important to workers as well. Growers must do their part to be sure that they are using safe procedures, mixing and using products correctly, and applying them properly. Safe pesticide and herbicide use is just as important as effective pesticide and herbicide use.
Recordkeeping for Pesticide Use
Keeping records of regular greenhouse pest monitoring and greenhouse pest control measures is an important step in integrated pest management. Records allow trends to be tracked and the effectiveness of control measures can be evaluated. At the end of each growing season, the greenhouse management should look over records to identify trends and evaluate the effectiveness of the treatments, and the effectiveness of their monitoring program as a whole. In addition to personal use, pest control records are also a requirement for compliance with FDA, EPA, and USDA codes for use of restricted pesticides. The USDA publishes a free guidance for what information must be kept in records.