Common density of the insect ranges from 1,000 to 2,000 per sq.m but in worst hit areas, located mostly in northern provinces, the concentration of brown hoppers can be as high as 10,000 per one square metre.

According to The Plant Protection Department, rice fields infested by the pest in the north total more than 79,000ha, of which 16,000ha have been completely ruined, affecting mostly winter-spring crops.

About 32,000ha of rice fields in Thai Binh Province have been attacked by the pests, concentrated in the districts of Thai Thuy, Tien Hai and Kien Xuong with a popular density of 2,000-3,000 pests per sq.m.

For Hai Phong port city, nearly 6,000ha of rice fields have been heavily affected in the districts of Thuy Nguyen, Vinh Bao and Kien Thuy.

Khuong Quang Viet, head of Plant Protection Office attributes the surge in brown hoppers to the amount of intermittent rain and sunshine Viet Nam has seen this year. This combination of wet and sun is considered by experts as favourable breeding conditions for the insect.

"This is in addition to inappropriate use of pesticide sprays," Viet added.

To counteract the infestation, the Plant Protection Department has requested farmers spray pesticide only if there are 3,000 or more pests per sq.m and to rely on natural methods for lower density of the insect. In addition, rice seedlings should be planted more sparsely.

For its part, the Ministry of Agriculture and Rural Development have asked relevant departments to closely supervise and speed up the elimination of brown hoppers, while controlling an increase in the price of plant protection chemicals and the circulation of low quality pesticides.

Viet warned that the brown hoppers problem was a long-term one that wouldn’t abate unless action was taken immediately.