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In the process of rice cultivation, one common issue that farmers face is "dry heart" — a condition where the central part of the rice plant dries up and dies. This can be caused by various factors such as pests, diseases, or environmental stress. Accurately identifying the cause of the dry heart is crucial for taking timely and effective measures to prevent further damage and ensure high and stable rice yields.
First, let's look at how to identify the causes of "dry heart" in rice.
1. **Dry Heart Caused by Insect Pests**
Several types of pests can lead to dry heart, including stem borers, rice planthoppers, and even earthworms. Each has distinct signs that help differentiate them. For example, the larvae of the rice stem borer feed inside the leaf sheaths, causing water-soaked spots that eventually turn yellow and die. As they grow, they move into the rice stem, leading to the yellowing of the flag leaf and, in severe cases, the death of the heart leaves. You might also notice small holes in the stems with some insect droppings outside.
The Sanhuai cricket (a type of locust) can also cause dry heart. These insects feed on the inner parts of the rice leaves, causing dehydration. The affected area may appear curled and dry, resembling a "false dry heart." If the infestation continues, the growing point can be damaged, resulting in complete drying of the heart leaves.
Another type of pest, the earthworm stem borer, tends to affect japonica rice more. Their damage often shows as small holes in the stems, with white, fine droppings inside. Unlike other pests, there are usually no visible droppings outside the holes.
2. **Dry Heart Caused by Drought**
When rice experiences prolonged drought, the base of the stalks may dry out, leading to yellowing and eventual death of the leaves. The plants become easy to pull up, and there are no wormholes or insect droppings present. This type of dry heart is commonly seen in fields with poor irrigation or during dry spells.
3. **Dry Heart Caused by Diseases**
Two major diseases that can cause dry heart are rice virus disease and bacterial leaf blight. Virus-induced dry heart often resembles the damage caused by certain pests, but there are no wormholes or insect excrement. The heart leaves are difficult to pull out, and when pressed between two glass slides, they release a milky, sterile fluid.
Bacterial leaf blight typically starts at the tillering stage. Affected plants show water-soaked, curled, and necrotic leaves, which gradually turn blue and dry. When a fresh diseased leaf is squeezed on a slide, a yellow bacterial ooze can be seen along the veins. This is a clear sign of bacterial infection.
**Prevention and Control Measures**
To manage dry heart caused by insect pests, farmers can use targeted insecticides such as Ruijint, which effectively controls both larvae and adult pests. For earthworm-related damage, poison baits like wheat bran mixed with trichlorfon can be used when the rice is flooded.
For dry heart caused by viral infections, it's important to soak rice seeds in strong chlorine before planting. Controlling insect vectors like planthoppers and leafhoppers is also essential to reduce the spread of viruses.
When dealing with bacterial leaf blight, seed disinfection is key. Early application of bactericides like Shibaoling and Yekuning can help prevent the disease from spreading and minimize crop losses.
By understanding the different causes of dry heart and applying appropriate management strategies, farmers can significantly improve rice yield and quality. Regular field monitoring and timely intervention are essential for maintaining healthy crops.