Biological pesticides are highly sensitive to environmental conditions, and their effectiveness can be significantly influenced by temperature, humidity, wind, rain, sunlight, and the presence of chemical pesticides. Understanding these factors is crucial for maximizing the performance of these eco-friendly pest control solutions.
Temperature plays a key role in the activity of biological pesticides. For example, *Beauveria bassiana*, commonly used to control lepidopteran pests, performs best at 23–26°C. Similarly, when targeting underground pests like cockroaches, the optimal temperature range is 22–25°C, with control efficacy exceeding 80%. *Bacillus thuringiensis* (Bt), another widely used bio-pesticide, works most effectively at 25–28°C. Plant-based preparations such as nicotine and alizarin also show high efficacy within a temperature range of 20–33°C, achieving more than 85% effectiveness. Therefore, during winter, it's important to adjust the water temperature to above 20°C when applying plant-based pesticides to ensure their effectiveness.
Humidity is equally important, as low humidity can hinder the germination of spores in biological pesticides. A study on the natural parasitic effects of *Nomura’s wild mushroom* showed that two adjacent vegetable plots were compared—one was watered regularly, while the other was not. The caterpillars and armyworms in the watered plot were almost entirely infected by the wild bacterium, whereas the non-watered plot had a natural parasitic rate of less than 25%. This highlights the importance of maintaining adequate moisture when using fungal or bacterial bio-pesticides. It's recommended to spray water before application or after rainfall to improve coverage and effectiveness.
Wind and rain can also impact the performance of biological pesticides. Strong winds can cause granules and droplets to be blown away, reducing the chances of contact with target pests. Rain can wash away the active ingredients, leading to lower efficacy. As a result, it's advisable to avoid applying biological pesticides during windy or rainy weather, especially in open fields where they are more likely to be dispersed.
Sunlight, particularly ultraviolet rays, can degrade microbial pesticides such as bacteria and fungi. To prevent this, it's best to apply biological pesticides in the late afternoon, ideally between 3–4 pm, and continue until dew forms. This reduces exposure to direct sunlight and helps maintain the viability of the active organisms.
Chemical pesticides can interfere with the performance of biological pesticides. Many chemical insecticides, such as organophosphates, inhibit the growth of fungal mycelium and spore development. For instance, dichlorvos has been shown to completely suppress spore formation. Therefore, it's recommended to avoid mixing chemical and biological pesticides together. If a sprayer has previously been used for chemicals, it should be thoroughly cleaned before being refilled with bio-pesticides to prevent contamination.
Lastly, the quality of water used for dilution matters. Using clean river water or distilled water is preferable for preparing biological pesticides, as it helps maintain their stability and effectiveness. Tap water may contain impurities or chlorine that could negatively affect the microorganisms in the product.
By considering these environmental and application factors, farmers and users can optimize the use of biological pesticides, ensuring both safety and effectiveness in pest management.
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