Pyrimethanil phytotoxicity and rescue measures
Pyrimethanil is a highly effective fungicide against gray mold, which has led to its widespread use in agriculture. However, improper application can result in phytotoxicity, causing damage to crops. To help farmers avoid such issues, the **Chinese Pesticide Network** has compiled key safety guidelines for using pyrimethanil.
As an anilinopyrimidine fungicide, pyrimethanil exhibits strong systemic activity, allowing it to quickly move through the plant and reach areas that are hard to access, such as flowers and young fruits. This makes it particularly effective in controlling gray mold. Additionally, its efficacy is not significantly affected by temperature, making it suitable for use in cooler conditions without compromising its performance.
**I. Phytotoxicity on Potatoes and Eggplants**
Although pyrimethanil is effective, it can cause phytotoxic effects on certain crops. For example, eggplants may develop dark brown spots on leaves, or experience yellowing and irregular leaf damage. Some farmers might mistake these symptoms for "spotted leaf disease," leading them to apply more pesticide and worsening the problem. It's important to differentiate between pyrimethanil-induced phytotoxicity and other diseases.
Similarly, beans (such as canola, cowpeas, and others) can suffer from severe yellowing, browning, and even leaf drop when exposed to high concentrations of pyrimethanil. While this compound is not entirely unsuitable for these crops, it must be used with caution. The recommended concentration should not exceed 6g ai per mu. For instance, if using a 40% suspension containing 15% pyrimethanil, only 40g per acre should be applied to eggplants and beans.
**II. Phytotoxicity on Cucumbers**
When applied to cucumbers, pyrimethanil can cause chlorotic yellow spots, especially on young fruits and blossoms. Under high humidity and temperature conditions, the leaves may show yellow-green spots, burning, or whitening. In some cases, the leaves may turn into a light yellow halo, which can be mistaken for nutrient deficiency. Therefore, it is advisable to avoid using this product on cucumbers unless absolutely necessary.
**III. Phytotoxicity on Tomatoes**
Tomatoes generally respond well to pyrimethanil for gray mold control. However, the risk of phytotoxicity varies depending on the variety and environmental conditions. For example, large red tomatoes grown in early spring at around 26°C are usually safe, but under high heat and humidity, they may show rim yellowing, which could be misdiagnosed as magnesium deficiency. Farmers are advised to exercise caution in such conditions.
**IV. Phytotoxicity on Melons**
When used on melons, pyrimethanil is relatively safe when diluted properly. A dilution ratio of 700–1000 times is considered safe and effective for preventing diseases. This makes it a useful tool for protecting melon crops during pollination and growth stages.
In conclusion, while pyrimethanil is a powerful tool in managing gray mold, it requires careful handling to prevent crop damage. Following the recommended application rates and being aware of crop sensitivity can ensure its safe and effective use. Always read the label carefully and consult local agricultural experts if unsure.
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