By Blake Jackson
Frequent rainfall throughout Pennsylvania this growing season has created added challenges for vegetable and berry growers working to protect crops from foliar diseases.
According to Leah Fronk, Extension Educator with Penn State Extension, many areas of the state received significant precipitation, increasing the importance of timely fungicide applications as harvest continues for many crops.
One of the most common questions growers face during wet weather is whether fungicides should be applied before or after a rain event.
In most situations, applying a fungicide before rainfall is the better option because preventative treatments provide stronger protection than applications made after disease has become established.
For the best results, fungicides should be applied when foliage is dry. Wet leaves can dilute spray materials and reduce coverage. Growers should also allow sufficient drying time before rain occurs, as most fungicides require several hours to bind to plant surfaces and become effective.
Using recommended adjuvants, such as sticker-spreaders, can improve fungicide adherence and help products remain effective during rain events.
During prolonged wet periods, shorter spray intervals may also be necessary because rainfall can wash away residues while rapid plant growth creates new, unprotected foliage.
Experts also encourage growers to diversify their disease-management programs by incorporating systemic fungicides alongside traditional protectant products such as captan, mancozeb, chlorothalonil, and thiram. This approach can improve disease control and provide greater rainfastness.
Research has shown that rainfall can remove fungicide residues, although the amount varies by product and weather conditions. In general, about one inch of rain may remove roughly half of a fungicide residue, while two inches or more can significantly reduce protection. Older residues are often more vulnerable to weathering and wash-off.
The key takeaway for growers is to stay proactive. Applying fungicides before expected rainfall, maintaining proper spray intervals, and monitoring crop growth and disease pressure can help preserve crop quality and maximize returns throughout the growing season.
FAQs
- Should fungicides be applied before or after rain?
Usually before rain, as preventative protection is more effective.
- Why should fungicides be sprayed on dry leaves?
Dry foliage improves coverage and reduces product runoff.
- How long should fungicides dry before rainfall?
Most products need at least four hours, depending on the label.
- Does rain wash away fungicides?
Yes, heavy rainfall can remove residues and reduce protection.
- Why might spray intervals need to be shortened during wet weather?
Frequent rain and new plant growth can reduce fungicide coverage more quickly.
Photo Credit: gettyimages-kotenko-a
Categories: Pennsylvania, Crops, Fruits and Vegetables