In recent years, from June to July, before the corn jointing to the tasseling, it is often seen that the upper leaves of the corn are curled, and some are oxtail-shaped, and some of the leaves are stalk-shaped or whip-shaped, and the average plant rate is 10 - 30%, a serious 40-50%, poses a serious threat to corn production. Leading experts have summarized several common causes of corn leaf curl through field surveys of different corn leaf mass plots.

Several common causes of corn leaf curls

1. Corn herbicide phytotoxicity

It is mainly caused by 2,4-D and acetochlor. It occurs earlier and is usually seen in mid-June.

The symptoms of 2,4-D phytotoxicity are leafy curls with onion-like leaves, the stems are brittle and easy to fold, the leaves are dark green, the tassels are difficult to extract, and the aerial roots are deformed. In severe cases, the leaves are yellow and no ears;

If the acetochlor is used excessively or improperly, the corn leaf sheath can not be properly curled, the heart leaf deformation is twisted into a whip-like seedling, and the stem section is swollen. The leaf curl caused by the herbicide remedy is very hard to feel the twisted part of the whip (onion-like) by hand, and the soft and hard intersecting part is in the lower part.

The excessive use of herbicides, the late application time, the precipitation after application, and the poor quality of the soil preparation, improper suppression and deep sowing, herbicide drift are the main causes of phytotoxicity. At the same concentration, the sensitivity of the maize varieties to herbicides was also different. At the same concentration, sensitive varieties and some varieties with weaker seedlings were often phytotoxic, and in the survey, 2,4-D drift was also found. It can cause different degrees of damage to sensitive corn varieties that are not using herbicides. This is why some plots do not use herbicides themselves and exhibit symptoms of phytotoxicity.

2, corn smut

The symptoms of corn smut are more complicated in the field. The leaf curl in the upper part of corn is only one type of many symptoms, which usually occurs in mid-July. Some manifestations are that the top blade curls upright along the midrib side, and the tassel is deformed and expanded to reveal black powder in the white film, and the leaves appear yellow and white stripes. Some show that the curl is loose, the tassel can be pulled out, but the flower is deformed and the leaves have yellow stripes. The incidence of early planting time is high with the planting of susceptible varieties and coating agents without active ingredients.

3, corn top rot

Corn top rot can occur in the whole growth period of corn, showing different symptoms. Generally, 10-15 days before tasseling, the leaves are curled and oxtail-shaped, and the plants appear dwarf in different degrees, and the top leaves may also appear short, tissue defects or wrinkles.

In the middle and late stages of corn growth, the base of the leaves rots, only the main veins are present, and the middle and upper parts are intact but many deformed; the tops of the new leaves that are born later rot, resulting in short leaves, dead leaves or incomplete leaves, and the edges of the leaves often appear like knives. Nicks and yellow stripes.

Infested in seedling stage, the plant grows slowly, the leaves are chlorotic, yellow streaks appear, the leaves are deformed, shrunken or distorted, and the severely ill plants wither or die. Some symptom characteristics of corn top rot have similarities with seedling symptoms of corn smut and other diseases, which are easy to be confused and pay attention to distinguish. The degree of disease among different varieties of corn is significantly different.

4, the reason is to be determined

Some of the individual varieties of maize varieties are in the big bell stage - before the tasseling, the upper leaves are curled and entwined in the shape of a oxtail, but there are no other typical symptoms of top rot, especially on the stems of the plants, no rot plaques and pests. There is no abnormality in the growth of the seedling stage. After 2 years of observation, most of the curled leaves can open themselves during the tasseling period, but the upper leaves are stiff, easy to fold, and the leaves are dark, and the yield is not significantly different from that of the plants without the leaf curl.

There is a significant difference in the degree of disease among different varieties. It is known that more than 20 corn varieties in production have such symptoms. Through three years of field observation by leading experts, it is possible to rule out the symptoms of suspected top rot caused by light, and whether the real cause of curling is caused by top rot pathogens remains to be further investigated.

In addition, according to the data, corn madness and Swedish stalk flies, thrips and other pests can also cause different degrees of curl in the upper leaves of corn, but currently not found in the corn production in the region due to the above two reasons Rolling leaf phenomenon.

Suggest

1. When applying corn herbicides, we must strictly control the application period, spraying time and dosage according to the specific conditions of soil quality, variety, precipitation, temperature, wind speed, etc. After the occurrence of phytotoxicity, it should be taken according to the specific conditions. Remedy. According to the severity of the phytotoxicity, a large amount of water or a full-nutrient foliar fertilizer (Bao Tianxi) should be sprayed appropriately to improve the resistance of the corn.

2. If the leaf rolling phenomenon caused by suspected top rot or head smut is found in the field, 300g/L benzalkonazole or oxazol can be used for prevention and treatment.

3. Select varieties with strong disease resistance and adopt different cultivation management measures for different varieties. Cold and cold areas should be planted in a timely manner, and coated with a good anti-disease seed coating agent.

4. Strengthen field observation and find out that if the problem is serious, it should be promptly consulted and resolved by relevant departments or experts.