Weather conditions can play a major role in pest occurrence:
- Weather fronts can assist migratory pests (such as helicoverpa, mirids, and armyworm) to move into regions
- Heavy or excessive rainfall may dislodge or drown some pests.
- Above average rainfall encourages slugs and snails.
- Abnormally high or low temperatures may result in a decline or absence of some pests.
- Cold conditions can make crops more susceptible to pest damage (slower to compensate).
- Weather conditions that favour plant growth will also favour growth of weeds, including those that are hosts for insect pests.
- The speed of insect development is often temperature-related. Under warm conditions, pests may develop to damaging sizes more rapidly and/or cycle through additional generations within a season.
Weather conditions should also be taken into consideration when planning control measures:
- Rain can reduce effectiveness of applied sprays.
- Temperatures that reduce pest activity are also likely to reduce the effectiveness of chemicals that rely on ingestion or direct contact (e.g. insects will not get a lethal dose if they stop feeding/moving due to cold weather).
- Lower temperatures may reduce the activity/effectiveness of some beneficials.
- Fungal pathogens work best under higher humidities.