The top leaf curl of corn is the cause
Herbicide Damage
Mainly caused by 2,4-D and acetochlor, the occurrence time is earlier, generally can be seen in mid-June. The symptoms of 2,4-D injury were leaf-like curling on the heart, crispy brittle stems, dark green leaves, difficult to extract tassels, rooting abnormalities, severe yellow leaves, no ears. Acetochlor caused excessive use or improperly caused the corn leaf sheath can not normally hold the volume, the heart leaves deformed into a whip-shaped seedlings, swollen stem sections. The leaf curl caused by the herbicide injury is very hard when you touch the twisted part of the whip (onion) leaf.
Soft and hard intersections. Excessive use of herbicides, excessive application of pesticides, excessive precipitation after application, and poor site preparation, improper repression, excessive sowing, and herbicide transport are the main causes of phytotoxicity. At the same concentration, the sensitivity of herbicides among maize varieties is also different. At the same concentration, sensitive varieties and some varieties with weak seedlings are often phytotoxic. In addition, 2,4-D drift can cause varying degrees of damage to sensitive corn varieties that are not using herbicides. This is why some plots do not use herbicides and still exhibit symptoms of phytotoxicity.
Smut
The field performance symptoms of corn head smut are more complicated, and the upper leaf curl of corn is only one type of many symptoms, which usually occurs in the middle and early July. Some showed that the top leaf was curled upright along the side of the midrib, and the tassels were deformed and swollen. After splitting, there was white powder in the white film, and yellow and white stripes appeared on the leaves. Some showed loose curls and the tassel could be pulled out, but the flower was deformed and the leaves had yellow stripes. The incidence of disease-causing varieties and the coating of unused active ingredients and high sowing time are high.
Top rot disease
Corn rot causes infections during the entire growth period of the corn and shows different symptoms. Generally, 10-15 days before tasselling, the leaves curled like oxtails, the plants appeared dwarfed in different degrees, and the top leaves also appeared short and small.
Incomplete or wrinkled distortion. In the middle and late stages of corn growth, the base of the leaf rots, leaving only the main veins. The middle and upper parts are complete but often malformed. The newly generated leaves rot at the top, causing the leaves to be short, the tips of the leaves are dead or incomplete, and the edges of the leaves often appear to be cut-like. Nick and yellow stripes. Infection at the seedling stage shows slow growth of the plants, chlorotic chlorosis of leaves, yellow streaks, and deformed, shriveled or distorted leaves, with severe disease plants withering or dead. Some symptoms of maize top rot have similarities with the seedling symptoms of maize smut and other diseases, which are easy to confuse and distinguish between different corn varieties.
other reasons
Some individual plants of some maize varieties had a tusk-tail curled around the upper leaflet before tasseling, but they did not have other typical symptoms of top rot, especially on the stems of the plants, and there were no decaying plaques or pests. Cracks, no abnormal growth at seedling stage. By observing that most of the curled leaves can self-open during the tasseling period, but the upper leaves are stiff, easy to fold, and dark in color, and their yield is not significantly different from that of the plants without curling leaves. There is a significant difference in the degree of morbidity among different breeds. It is currently known that more than 20 corn varieties have such symptoms. Through field observation, it is possible to rule out the symptoms of this suspected top rot caused by light, and whether the real cause of curling is caused by top rot pathogens remains to be investigated.
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