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In recent weeks, some farmers have raised concerns about the abnormal development of summer corn in certain areas. They've noticed that the tassels and leaves are not unfolding properly, often appearing as "cow tails" or "big whips." This has led to questions about how to address the issue. To provide clarity, we spoke with Shao Lixia, a senior agronomist from the Longyin County Bureau of Agriculture, who conducted an investigation and field trials in the affected regions. Here’s what she had to say.
Currently, summer corn in central and southern provinces is entering the critical "big bell mouth" stage. However, some fields are showing unusual symptoms where the heart and leaves are twisted, deformed, or even completely stuck together. These issues are commonly referred to as "cow tails" or "big whips," which can significantly impact yield and plant health.
**Main Causes**
1. **Thrips and Swedish Fly Damage**
Farmers have observed that the outer leaves are often peeled back, revealing shriveled bases with holes. The main symptoms include twisted leaves, damaged foliage, and visible holes on the leaf surface. Some leaves show a transparent film, while the heart may be covered in mucus or even broken. This is typically caused by thrips or Swedish fly infestations during the 5–6 leaf stage of corn growth. According to our survey between July 8th and 11th, some plots had up to 500–1,000 thrips per plant, leading to yellowing and severe twisting of the leaves. In some cases, the leaves were deformed, broke, or formed long, twisted "cow tail" shapes. The problem tends to be more severe in fields with lighter seed treatments, lower fertilizer use, and fewer pesticide applications. Thrips and Swedish flies damage the heart tissue, causing it to fail to unfold and resulting in the characteristic twisted appearance.
2. **Herbicide Injury**
Another major cause is post-emergence herbicide damage, particularly from products containing nicosulfuron. This leads to twisted leaves, stunted growth, and distorted hearts that cannot open properly. According to a survey conducted on July 20th, about 20% of corn fields showed signs of phytotoxicity. Symptoms include dwarfed plants, rotten hearts, and yellowing leaves. Some plants also experienced leaf rolling, with up to 10% of the crop affected. One reason for this issue is the low purity of domestically produced nicosulfuron, which can cause chemical burns. Spraying at high temperatures or repeated applications can also lead to injury. Additionally, if herbicides are applied when the corn has more than five leaves, the liquid may accumulate in the heart, causing further damage. Some hybrid varieties are especially sensitive to these chemicals, leading to improper tassel development and reduced yields.
**Control Measures**
1. **Manual Intervention and Foliar Treatments**
For affected plants, it's recommended to cut off the top 1/4 of the leaves using scissors or manually remove the twisted heart. Afterward, apply foliar fertilizers and growth regulators. You can spray 1 gram of gibberellin (90%) in 15–30 kg of water, or use "Tianfengsu" (brassica lactone) diluted at 1:1,000. Alternatively, mix "Double Effect King" (40 ml per 30–45 kg of water), or a solution of 6,000 times Love more + 0.2%–0.3% potassium dihydrogen phosphate + 1% urea + zinc fertilizer. Repeat this every 5–7 days, and consider applying it twice for best results.
2. **Pest Control**
If the issue is due to insect pests, focus on controlling thrips and Swedish flies during the 5–6 leaf stage. Spray with a mixture of 10% imidacloprid (1,000x dilution) or 5% acetamiprid (1,500x dilution) combined with agricultural streptomycin (500–800x). Adding gibberellin or a high-efficiency foliar fertilizer will help recovery. Apply every 5–7 days, and repeat the treatment twice for maximum effectiveness.
3. **Herbicide Management**
To prevent herbicide-related damage, use high-quality post-emergence herbicides and avoid spraying during hot periods. Ensure that herbicides are applied at the correct time to avoid late application, which can cause significant injury. Always follow label instructions carefully to minimize risks.
By addressing these issues promptly, farmers can reduce the impact of these problems and improve the health and productivity of their corn crops.