During the dog days of summer, pests and diseases are frequent. When is the best time to spray pesticides?
The dog days of summer are the hottest time of summer and also the peak period for pests and diseases affecting various crops. Many farmers choose to spray pesticides on their crops. The effectiveness of most pesticides tends to increase as the temperature rises, so when is the most suitable time to spray pesticides during the dog days?
I. When is the best time to spray pesticides during the dog days?
1. Avoid the midday heat
Some farmers take advantage of the high temperatures to spray pesticides, thinking that the pesticide works better in the heat. The actual situation is quite the opposite. During high temperatures, pests do not come out to be active either, so spraying pesticides usually has relatively little effect on pests. In addition, in a high-temperature environment, pesticides evaporate quickly, which actually leads to poor effectiveness.
Whether it is plants, insects or pathogens, 20~30°C, especially 25°C, is the temperature at which they are most active. Spraying pesticides at this time is most effective against pests and diseases and also safer for crops. In the hot summer season, pesticide spraying should be done before 10 a.m. and after 4 p.m.
2. Do not spray pesticides in the early morning
The weather during the dog days is extremely hot, and many farmers take advantage of the coolest time in the early morning to spray pesticides. In fact, the effect is not very good either. If the time is too early and the dew has not yet evaporated, the pesticide will be diluted by the dew on the plants, reducing the pesticide concentration and making the spraying less effective.
When spraying pesticides in summer, choose an overcast day or a sunny day from 8 a.m. (after the dew has dried) to 10 a.m., and from 5 p.m. to 7 p.m. Spray during these two time periods when pests are most active. To prevent pesticide damage, the amount of water for dilution should be appropriately increased. When spraying, be sure to wear a mask and long-sleeved protective clothing, and take a shower promptly after spraying to prevent poisoning.
II. Common misunderstandings about spraying pesticides during the dog days
1. The concentration of the mixed pesticide is too high
Under high-temperature conditions, the temperature of the prepared pesticide should not be too high. In a high-temperature environment, the water in the pesticide solution evaporates relatively quickly, which is equivalent to increasing the concentration of the pesticide solution, and crops are prone to pesticide damage. Therefore, when spraying pesticides in summer, farmers should strictly follow the spraying concentration when mixing the pesticide, and must not increase the concentration without authorization.
2. The nozzle is too close
After the pesticide solution is sprayed from the nozzle, it collides with the air and breaks into smaller droplets. That is to say, within a certain distance range, the farther from the nozzle, the smaller the droplets. Small droplets are more likely to settle and spread on crops, so it is not the case that the pesticide will be more effective if the nozzle is pressed tightly against the plant.
Generally speaking, the nozzle of a knapsack electric sprayer should be kept at a distance of 30~50 cm from the target, while a motorized sprayer should be kept at a distance of about 1 m. According to the performance of the sprayer and nozzle, swing the nozzle so that the pesticide mist falls onto the crops, and the effectiveness will be better.
3. The smaller the droplets, the better the effect
In fact, the sprayed droplets are not necessarily better the smaller they are. The size of the droplets is related to whether they can be better distributed, deposited and spread on crops. If the droplets are too small, they will float in the air and be difficult to deposit on the target, which will certainly cause waste. If the droplets are too large, the amount of pesticide solution rolling onto the ground will also increase, which is also waste.
Choose appropriate spraying equipment and nozzles according to the target of control and the space environment in which it is located. When controlling diseases and tiny pests such as whiteflies and aphids in relatively enclosed greenhouses, a fogging machine can be chosen. When controlling these pests and diseases in open fields, equipment and nozzles that produce larger droplets must be chosen.
When spraying pesticides during the high-temperature weather of the dog days, farmers need to pay attention to taking protective measures to avoid pesticide volatilizing and drifting onto the skin, otherwise poisoning may occur.