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June 2016. An article on the Plantwise blog about an outbreak of armyworms in Cambodia and the method of removal caught members’ attention and here are some of the comments.
A member who is working in Cambodia wrote the following:
I am working on a NZAID project in the three NW provinces in Cambodia (CODES project executed by IDE). Yes, we are witnessing this issue in Oddar Meanchey, and also Banteay Meanchey. This armyworm outbreak is due to the hot weather but also the lack of natural enemies that are not able to sustain themselves in the long dry period (lack of nectar sources for parasitoids, etc.). Many corn crops are also being heavily damaged.
BUT the heavy rains that have now started will cause major mortality of caterpillar pests, including armyworm in these crops, so I expect the problems to reduce. The caterpillars can also be drowned in rice fields, but this control strategy (flood the fields and knock off the caterpillars) does not work in the upland rice growing areas.
Spodoptera mauritia is damaging the rice and corn crops, while S. litura and S. exigua are damaging the vegetable crops. S. mauritia looks similar to S. litura so I am sure there is some confusion in identification. S. mauritia is only a pest on the ‘grasses’ and most of the rice crops I have seen may compensate with their excess of plants, but most of the corn crops will be almost completely lost. Our advice to farmers to scout their corn and vegetable crops twice a week would have meant they would have seen the egg masses and small caterpillars and picked them off the plant or spot sprayed the vegetable crops before the caterpillars got big and caused major damage.
All these species have similar life cycles, so regular crop scouting and targeted use of selective insecticides should be effective. Where farmers have been applying selective insects such as Bt and chlorantraniliprole we are seeing good parasitoid activity in some seasons and crops, and spiders are great generalist predators on small plants.
Rice is more problematic because the area is so large (to scout?) and hard to see the caterpillars because they can hide during the day. Also, Bt is not effective on large caterpillars so they need to use different Mode of Action insecticides if the large caterpillars are out of control?
Another member asked if S. mauritia on rice in Cambodia is the same as species causing damage to lettuce, beans and corn each year? In response, the following was provided from Cambodia: I described which species we are finding on some of these crops in my earlier email on Pestnet. But this was for the 3 NW provinces, so possibly different in other provinces? For Oddar Meanchey, Banteay Meanchey and Siem Reap, from our surveys, at present in the NW, it is S. mauritia on rice and corn. Through the year, however, S. litura is the most common species on the other vegetable crops, although S. exigua is the most common armyworm we find on solanum crops.
A member from Thailand said in his country Spodoptera sp. attacking rice seedlings is the rice armyworm, S. mauritia. Other Spodoptera spp. reported on other crops are:
S. litura (common cutworm) attacking asparagus, castor bean, chili, cocoa, cotton, crucifers, cucumber, eggplant, jute, mungbean, okra, peanut, safflower, sesame, sorghum, soybean, and strawberry. S. exigua (beet armyworm) attacking asparagus, crucifers, cucumber, grape, peanut, and sunflower. And it is likely that the same situation occurs in Cambodia.
The article by Plantwise.
Thanks to Plantwise
https://blog.plantwise.org/2016/06/22/update-plant-health-news-22-jun-16/
 Farmers use a net in an attempt to clear army worms off a rice crop in Tbong Khmum earlier this week. Photo supplied
Army worm outbreak plagues rice crop in five provinces
Thu, 16 June 2016 Sen David
An outbreak of army worms – brought on by recent rains – is attacking crops in five provinces, according to the Ministry of Agriculture.
A statement released by the ministry on Tuesday identified the provinces affected as Kampong Cham, Prey Veng, Tbong Khmum, Preah Vihear and Oddar Meanchey
Army worms are common in Asia, and each year they damage Cambodian crops such as lettuce, beans and corn.
The statement said that this year, because of the drought, rice crops were also affected. The hot weather acted like an incubator for theworms, and following the rains, the growing rice provided a source of food.
“The impact hasn’t been serious yet, because the outbreak is just beginning,” said Keam Makardy, field operation program manager for agricultural NGO CEDAC.
“But if farmers don’t take care of the pests, it could turn into a big problem.”
Makardy recommended farmers dig canals around their rice fields and line them with ash, which would kill the worms.
Kampong Cham agriculture department director Kim Savoern said farmers could clear vegetation, release ducks into the field to eat the army worms or use pesticide.
The latter, however, worked only one time and would not eliminate future outbreaks, he warned.
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