After a cold snap, avoid applying too much nitrogen fertilizer, and be on guard against a major outbreak of rice blast.

Text / Tainan District Agricultural Research and Extension Station

With a strong cold air mass moving in, nighttime temperatures often drop below 10 degrees C. Farmers are in the habit of applying nitrogen fertilizer to help rice withstand the cold, but when the temperature is too low, rice roots cannot absorb the nitrogen fertilizer in the soil. This easily leads to excessive nitrogen fertilizer accumulating in the field, and when temperatures rise again later, the rice absorbs too much nitrogen fertilizer, increasing the probability of rice blast infection. Farmers are therefore urged to control fertilizer application carefully to avoid severe rice blast later that requires more spending on control, or losses in subsequent yield.

The rice blast pathogen can damage leaves, rice panicles, stem nodes and leaf sheaths. In the early stage of the disease, brown or dark green small spots form on the leaf surface. If environmental conditions favor disease progression, they expand into a spindle shape, with the lesion surrounded by yellow and grayish-brown in the center. In severe cases the leaves wither, and if the panicles are infected, the grains do not fill out properly. Rice blast is likely to occur when relative humidity is high; when temperatures fluctuate sharply, the resistance of the rice decreases, making the disease more severe.

Rice blast is more likely to occur in the first crop season. Generally speaking, rice is most susceptible to infection from 35 to 50 days after transplanting, especially in fields with high nitrogen fertilizer application, dense planting and poor ventilation. Farmers are therefore urged to pay close attention to the occurrence of rice blast in the field. Once disease progression is found, pesticide should be applied for control immediately to prevent the disease from spreading and expanding.

In conjunction with rational fertilization, do not apply too much nitrogen fertilizer. If there are problems with control, you can contact researchers at the Tainan District Agricultural Research and Extension Station.

Contacts: Lin Guo-ci, Wu Ya-fang, Zheng An-xiu
Chiayi Branch Station Phone: 06-5912901 ext. 305, 310, 301, 05-5371574