Why are the leaves of the green beans curling even though no pesticide was sprayed?
Judging from the appearance of the green beans in the photo, it is likely a problem of green bean leaf roller (bean leafroller) or herbicide contamination. The specific cause can be determined according to local conditions. For example, check whether there are leaf rollers or eggs on the back of the leaves, and then check whether other neighbors around the green bean field have recently sprayed herbicide, then make a further diagnosis and take specific measures accordingly!
The measures are introduced in detail below.
Control of the leaf roller
The leaf roller generally wraps itself inside the curled leaf and spins a spider-web-like protection on the back of the leaf to avoid being pecked by other beneficial insects. Therefore, controlling it is relatively difficult; if you spray pesticide, the pesticide may not be able to penetrate to the back and thus cannot take effect. Although manual capture is also a method, it is still quite difficult, and if the pest outbreak is severe, this measure is obviously not feasible.
Generally speaking, for the control of this type of pest, strong insecticides are still used: 2.5% cypermethrin emulsifiable concentrate at 3000 times dilution, 10% beta-cypermethrin emulsifiable concentrate at 2500 times dilution, 20% fenvalerate at 1500 times dilution, 48% chlorpyrifos emulsifiable concentrate at 1000 times dilution, or 30% acephate emulsifiable concentrate at 1000-1500 times dilution, etc., sprayed for control.
During the stage when pests and diseases are rampant, spray once a week, and two consecutive sprays can basically eliminate the pests.
Herbicide damage
As for herbicide damage, in the Huang-Huai-Hai region it basically occurs during the corn sowing period after the wheat harvest, usually because herbicide sprayed on corn in adjacent plots drifts onto the green beans and causes phytotoxicity.
First, if the green beans have just been harmed by the herbicide or are in the early stage of harm, you can rinse with clean water to reduce the herbicide damage. However, the effect of this method is still relatively small. From the photo, it has already been harmed for some time, so even if you choose to spray clean water to dilute the herbicide, it is hard to achieve a very good effect. Moreover, current herbicides basically take effect within 24 hours.
Second, after suffering herbicide phytotoxicity, you can actively apply fertilizer and water to promote the growth of the green beans and improve their resistance to phytotoxicity.
However, although the above methods can have some effect, it is still relatively mild. The best method is still to spray the plants with some humic acid or brassinolide, diluted 7500 times, supplemented with some foliar fertilizer, spraying once a week after the phytotoxicity, and 2-3 consecutive sprays can basically relieve the phytotoxicity.
The above is some of the views shared by Science Xingnong about green bean leaf curling, and I hope it is helpful to you.