Nine tips to improve the effectiveness of your spray program

Cannabis growers are prohibited from using most of the chemical pest control products that ornamental flower and vegetable growers rely on to protect their crops.

But cannabis growers should always exercise caution when applying wet sprays of organic-based products. Spray damage is common, but in most cases can be avoided with good agricultural practices and common sense.

If you are responsible for the health and profitability of your cannabis crop, keep these nine tips in mind as you plan and execute your spraying strategy:

1. Read the label

Don’t apply a product for the first time based on information you gleaned from an online cannabis discussion forum. Instead, read the label. Product manufacturers want you to succeed with their products, and reputable companies take significant steps to determine ideal application rates. Once you go “off label” you risk crop damage and, worse, non-compliance.

2. Try first

A common misconception about bio-based pest control products is that they are harmless. Most are highly refined natural oils or extracts from seeds or flowers, but they still have the potential to harm plants under certain conditions. It is best to try new products on a few plants first. If no phytotoxicity occurs after 48-72 hours, it should be safe to apply to the entire crop.

3. Irrigate before spraying

Do not apply wet sprays to dry or wilting plants. This can lead to leaf burns which not only compromise a plant’s productivity but, in the case of ornamentals, can render them unsaleable. The plants should be turgid and the soil should be moist. Prepare your plants for spray application by irrigating the crop a few hours to a day before spraying.

4. Be aware of the temperature

Whether applying an insecticide to kill aphids or a fungicide to control powdery mildew, the longer a product stays on the plant, the more effective it will be. Schedule spray applications for the coolest time of day to extend the length of time a wet spray stays on a plant. In greenhouses, spray early in the morning or late in the afternoon. Indoors, turn off circulation fans during application and for up to one hour after.

5. Avoid full sun and strong grow lights

Like high temperatures, bright light and wet sprays don’t mix. Water droplets can act as mini magnifying glasses that focus light and burn leaves. Although more of a cosmetic issue than a health risk, burn spots look like nutrient issues and can lead novice growers to unnecessarily solve a nutrient deficiency that doesn’t exist. . Avoid this scenario by always spraying in low light conditions.

6. Be aware of compatibility

Tank mixing is the simultaneous application of two or more different chemicals. For example, when a fungicide is mixed with an insecticide and applied to a crop. Tank mixing can save time and labor for multiple applications, but growers should keep in mind that many products don’t work well together. Incompatibility can lead to solubility problems in the spray tank and phytotoxicity in the crop. If in any doubt, do a jar test by mixing a little of both in a jar, shaking it, and seeing if they fall out of suspension. If so, apply separately.

7. Become a Certified Pesticide Applicator

Growers of ornamental flowers and vegetables must have on their staff a person who holds a pesticide applicator’s permit. This helps ensure good record keeping and the safety of greenhouse employees. Yet many cannabis operations aren’t even aware of the existence of pesticide certification, let alone of the need to keep certificates current with current credits. Preparatory courses and exam dates are scheduled throughout the year; contact your local agricultural extension officer and register today.

8. Don’t spray your beneficial insects

Wet sprays can negatively affect the effectiveness of beneficial insects. For example, growers who apply sulfur to repel mold and mildew will kill beneficial insects in the process. Growers dependent on predatory insects must carefully plan their wet spray applications. To avoid working against yourself and wasting money, coordinate with your beneficial insect supplier to establish a compatible IPM program.

9. Increase accuracy with automation

Using electrostatic sprayers and ultra-low volume (ULV) sprayers can help you save labor, use fewer pesticides, and improve the efficiency of your wet spray program. Electrostatic sprayers positively charge the spray droplets, so they are attracted to negatively charged plant surfaces. This is especially important for covering hard-to-reach areas of the crop. ULV sprayers are “set it and forget it” units that fill an enclosed space with a pest control product. Both are effective ways to achieve full crop coverage while saving money on labor and inputs.

When it comes to wet spray applications, cannabis is no different than any other commercial crop. If you read the product label, make sure your plants are well irrigated, and avoid intense light and temperatures, you’ll have peace of mind knowing your spray schedule is working as hard as you do.


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