Weather condition these days is perfect for an outbreak
Pests: National Plant Protection Centre has alerted extensions officials in the dzongkhags to watch out for a possible armyworm outbreak.
The centre’s programme director Yeshey Dema said prolonged dry spells followed by heavy rains like the present weather pattern, and presence of many alternate hosts such as grassy weeds create conducive environment for an outbreak.
“So all extension officials are instructed to carry out regular monitoring of the pests particularly in maize fields and paddy nurseries,” she said.
Monitoring is key to get rid of the problem before it becomes a major threat to crops. Officials said awareness among farmers and extension officials has increased over the years.
Farmers have to look out for removal of leaves from seedlings of paddy, maize or any seedlings belonging to the grass species. Typical armyworm attack feeds on leaf tips and along its margins, leaving only the midribs.
Armyworm cut young seedlings at the plant’s base. They also cut off rice and maize panicles from base. They can devastate paddy nurseries if not detected early.
NPPC officials said that the pest becomes so destructive that it damages the host plant in a short period of time.
In 2013, paddy nurseries and maize fields in 18 dzongkhags were almost wiped out in an outbreak that troubled farmers across the country.
Between April 5 and May 6, paddy and maize seedlings in 11gewogs of Punakha reported armyworm outbreaks.
Thedtsho and Nahi gewogs of Wangdue, and some areas in Thimphu reported outbreaks of the pest.
The outbreaks occur in April and May.
The caterpillar damaging crops in Bhutan belongs to Mythimna separata. As moth, they lay eggs in clusters and each consisting up to 300 eggs. They hatch in two-five days to become caterpillars commonly known as armyworm.
The caterpillar that moves in masses is nocturnal. The larvae usually feeds on the upper portion of the rice and maize canopy on cloudy days or at night; while the adult feeds, mates, and migrates at night and during daytime take shelter at the base of the plant or under the soil clods.
Farmers have to remove grass weeds from adjacent fields and remove weeds regularly to reduce breeding sites and shelter for the worm.
NPPC officials said if farmers see the worms, flooding seedbed is the best defence.
There are numerous measures against armyworms.
A deep ditch filled with water can prevent the pest from infesting other fields.
Another method, although more painstaking, is to dig deep ditches with vertical sides to trap the larvae.
“If there is high infestation of armyworm chemical spray is necessary but it is the last option,” Yeshey Dema said.
The best time to spray is in the evening.
NPPC has asked dzongkhag agriculture officials to collect pheromone traps that helps to monitor the pest population levels and is used for early warning.
“If a trap catches between 25-30 moths, it indicates, an outbreak,” an official said.
The centre also maintains stock of chemicals should there be an outbreak.