Some insect sprays are long lasting, so be careful about using them on crops near those you want to harvest soon. Keep a logbook on all your pest control activities. Your spray equipment should always be in good working condition. With some chemicals, it's safer to spray only at certain hours of the day. Sevin, for example, should be used very early in the morning or late in the evening because it is toxic to bees.
Dusts are more effective when applied early in the day while the dew is still on the plants.
Chemical control for diseases is usually recommended on a season-long basis. These are used every 7 to 10 days through the season, usually starting within a week or two of planting and not just when disease is evident. As with other substances, fungicides must be handled and applied carefully. Pesticides, used only when necessary and with caution, common sense and consideration for the environment, are available as a last resort. If the insect situation warrants chemical control, choose the weakest chemical remedy to control the insect.