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Biological pesticides - BT use "four look" to ensure control
Biopesticide - BT is a broad-spectrum, highly effective, and safe insecticide that has gained significant attention due to its ability to control a wide range of pests without harming humans, livestock, poultry, or natural predators. However, improper use can reduce its effectiveness. Therefore, it's essential to understand its characteristics and proper application methods before using it.
First, mastering the timing and concentration of BT application is crucial. BT is primarily used for controlling pests in various crops, such as cotton bollworms, red bollworms, cutworms, tobacco budworms, and others in economic crops; stem borers, rice borers, leafhoppers, and similar pests in food crops; cabbage caterpillars, diamondback moths, and other pests in vegetables; and pine caterpillars, peach fruit worms, scales, and leaf rollers in fruit trees.
For cotton bollworms, the best time to apply is during peak egg-laying, when egg counts reach around 100 per plant. Apply every 3–4 days, repeating 2–3 times per generation. For pests like cabbage caterpillars, tobacco budworms, bean cutworms, corn borers, pine caterpillars, and fruit tree pests, applications should be made during the peak of egg-laying or early larval stages.
Regarding concentration, BT with 10 billion spores per gram can be diluted at 2,000 times for 667 m² to control rice mites, aphids, small bollworms, thrips, and cabbage caterpillars. For cabbage caterpillars, use a 1,000-fold solution of 10 billion spores/g or a 300-fold solution of BT emulsion. For rice leaf rollers, locusts, and sweet potato cutworms, a 400–600-fold dilution of BT emulsion works well. To manage Helicoverpa armigera, Pieris rapae, and Plutella xylostella, use a 1,000-fold dilution of BT emulsion. For corn borers, 50g of 10 billion spores/g powder per 667m², diluted 2,000 times, or 100–200-fold BT emulsion mixed with 3.5–5kg of fine sand to make granules and place them in the corn whorl.
Second, when applying BT, follow the "four look" principle to maximize its effectiveness:
1. Look at the temperature: BT works best between 25°C and 30°C. Its efficacy is 10 times higher than at 10°C–15°C, so avoid using it below 20°C.
2. Look at humidity: Higher humidity improves performance, especially for powdered BT.
3. Look at the sun: Avoid direct sunlight, as UV rays can damage spores. It’s best to spray in the late afternoon or on cloudy days.
4. Look at the rain: Heavy rain may wash away the sprayed solution, reducing effectiveness. Light drizzle after spraying can enhance control, but heavy rain requires reapplication.
BT is slower than chemical pesticides. After application, pests stop feeding within 30 minutes, die within 24 hours, reach peak mortality at 48 hours, and achieve over 75% mortality by 72 hours. Even if they don’t die immediately, they won’t cause further damage, so no additional pesticides are needed.
Tip from China Pesticide Network: BT should not be mixed with organophosphorus insecticides or fungicides. Always read the label carefully and follow the manufacturer's instructions for best results.