Heat stress is more likely to occur when there are high temperatures, high humidity and direct sunlight. If the workload is heavy, this will only increase the chances for it. Any time you can, use fans and as much ventilation as possible. Shade your work area for example. Take several days to adjust to working in hot conditions. Build your endurance by working for short periods each day then eventually extending the work periods. Take frequent breaks.
If you are able and do work during early morning or late evening hours, be sure there is someone who can check on you.
Also keep in mind that the precautions necessary to keep you from harmful pesticide effects are the same precautions that can cause you to overheat. Layers of clothing keep your body from cooling properly; therefore you should choose equipment that is as cool as possible. Also increase your shade and cooling by using fans, air conditioners, etc.
The loss of water from your body is also a concern during warm working conditions. Your body needs water to keep from overheating. If you have a heavy workload, are working in warm temperatures in direct sunlight, you could lose as much as one gallon of water per hour.
Be sure to drink plenty of water or sports drinks. Do not rely on a feeling of thirst; it can be deceiving. Drink plenty of water before and after work.
Take all of these necessary precautions and adjust work schedules as needed to prevent heat stress. If you must, adjust work and rest cycles. Schedule heaviest workloads during cooler times of day and stop work completely if necessary.