What farmers need to know about pesticide weather considerations

There is a limited amount of time to control plant pests and diseases. As the time window opportunity might be even shorter due to unsuitable weather conditions, applicators need to be able to identify and plan accordingly. Pesticide weather considerations play a huge role in pesticide application timing. It can significantly impact the amount of pesticides that are sprayed, their effectiveness, and the risk of causing harm to the plants and the environment. We provide a hassle-free ‘Delta T spraying scheduler’ designed to simplify your decision-making process.

The four key pesticide weather considerations for pesticide application success

The four key weather factors that affect pesticides are temperature, wind, precipitation, and humidity. The worst weather conditions for applying pesticides are strong wind, high temperature, intensive rain, and low humidity. The wind is a crucial factor because it affects how pesticides move through the air; The wind can carry agricultural pesticides far away from where they were sprayed, making them drift onto other people’s property. This decreases the effectiveness of the spraying and increases the risk of polluting the environment and harming people living in nearby areas. This is why farmers must take into account wind direction and speed when spraying their fields with agricultural pesticides in order to reduce spray drift.

Precipitation and humidity can also change how pesticides are distributed, but it has a more minor effect than wind. Temperatures of air and surfaces are important factors in the efficacy of pesticides. Different chemical compounds have different temperature ranges at which they are most effective. For example, the insecticide pyrethroid is most effective at temperatures higher than 50°F.

Spraying pesticides outside is not recommended when there is more risk for a high evaporation rate, degradation, and extended droplet lifetime. The degradation of pesticides can increase when the humidity is high. High humidity also decreases evaporation, resulting in extended droplet lifetime and increased drift risk. These also play an essential role in safety. Higher concentrations of pesticides in the air can lead to potential health risks for workers and nearby residents. Some pesticides are more sensitive to temperature changes than others. In warm weather, humidity should allow good evaporation conditions. This will ensure that the pesticides have less time to break down into toxic compounds while contacting the plants. Decisions on spraying in such cases become challenging as high temperatures make plants more vulnerable to pests and diseases. Their natural defense systems break down and become more susceptible to pests and diseases like fungi and insects. Therefore, applicators need to carefully choose the timing of spraying to protect plants in such weather conditions.

A better way of telling how quickly pesticide droplets evaporate is the Delta T spraying indicator. Delta T is the difference between wet and dry bulb temperatures, which can be calculated by combining the effect of temperature and relative humidity.

Delta T spraying model shows the preferred spraying conditions
Delta T spraying model shows the preferred spraying conditions

Growers should also pay attention to the inversion phenomena. Inversion happens when the temperature increases with the distance from the ground. Spraying should be avoided in this case as the risk of drifting pesticides long distances is high. The inversion hazard is often highest from dusk to a few hours after sunset and weak at sunrise.

Rainfall can have a significant effect on the efficacy of pesticides. Rain has been shown to reduce pesticide washout in some instances and increase pesticide washout in others. The primary function of systemic pesticides is to be taken in by the roots, but the rain needs to be relatively light for this to happen without the effect of washing the active material away from the plant surrounding. In general, the plant will absorb most of the systematic pesticide solution within about 2-4 hours. Therefore, it is essential to know how long you need to spray before the rain starts in order to get an acceptable level of control. In the case of contact pesticides, rains can wash out the active ingredient and damage the protective and curative effect that was intended.

Pesticides can be applied as a liquid, powder, or gas. The pesticide used depends on the crop and pest to be controlled. The method of application should be added to the set of considerations when weather conditions are considered. For example, herbicides can evaporate at a greater rate when sprayed under high temperatures, while fungicides can freeze at lower temperatures.

Generally speaking, the best time to spray is early morning or late evening when there is little wind, and the temperature is cool. In the case of insecticide, the evening is preferred as the interference with bees is minimized.

How technology can help you with timing spraying

Agrio allows you to use hyper-local weather monitoring to obtain more precise information about the climate in your fields. It is the practice of collecting and analyzing weather data at a very specific and localized location. This is in contrast to traditional weather monitoring, which typically involves collecting data from large weather stations. Hyper-local weather monitoring is useful because it provides much more detailed and accurate information about the weather at a specific location than can be obtained from larger-scale weather monitoring systems.

With constant hyper-local weather monitoring and forecasting, we can show you the best spraying opportunities in the Agrio app. We save you time and present you with this information when you decide on a spraying application. In addition, our weather forecasts update every hour, so you can stay updated when forecasts are changing.

Intervention scheduling. Red - don't spray | Yellow - Spraying conditions are not optimal | Green - Good conditions for spraying
Intervention scheduling. Red – don’t spray | Yellow – Spraying conditions are not optimal | Green – Good conditions for spraying

Once a spraying strategy is planned, we help you keep a record and send you reminders in due time.

Track field Interventions
Track field Interventions


Pesticide weather considerations should be taken seriously before planning spraying applications. Using weather predictions to optimize treatment timings is an essential tool that will help you to optimize pest and disease control in your fields. We look forward to seeing you leveraging this technology for intelligent and effective pest management in your field. 

In the meantime, as always, we wish you an abundant harvest.