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Worm outbreaks threaten food security

Armyworms are caterpillars that develop into nocturnal moths and can migrate thousands of kilometres. They attack cereals, grazing land and sugar cane.

At least 30 districts in central and eastern Kenya have reported cases of armyworm and bollworm infestation, raising concerns over damage to crops in affected areas after a prolonged drought.

"The infestation may be attributable to climatic change. The rains have led to a quick multiplication of the pests," the deputy director of agriculture in the plant protection services division of the Ministry of Agriculture, Joseph Ngetich, told IRIN.

"Intermittent periods of rainfall provide good conditions for the hatching of the pests' eggs," Ngetich said. "If after a dry spell it rains continuously, we will not see [an outbreak] as conditions will not be conducive for hatching."

This has been the case since October when heavy rains after the drought concentrated egg-laying moths and provided grass/cereals for newly hatched caterpillars. Dry, sunny periods, as experienced in November, during the caterpillar development, promoted their survival and rapid development.

The first armyworm outbreak was reported in the Tana Delta area along the coast in November, "but it was repressed and did not cause major infestations", noted Ngetich.

"Overall the armyworms have affected about 2,474ha of pasture and 386ha of maize," he said. "By December though, most of the maize was beyond knee-high, beyond the vulnerable stage."

The larva of the armyworm feeds on young grasses (pasture) and cereal crops.

About 10 districts, mainly in the Ukambani area of Eastern Province, have been affected; a bumper harvest is expected in parts of the province.

Outbreak forecasting

Trapping armyworm moths is useful for the prediction of an outbreak. Light and pheromone traps with an insecticide cube may be used. “If we see catches of up to 20 [moths] a night, we know there will be an outbreak because of mating, laying of eggs and hatching.”

There are at least 400 surveillance traps in Kenya.

Outbreak patterns elsewhere are also useful. "For example, if there are reports in Malawi, then in Tanzania, we know the next region to be hit will be Kenya," he said.

He said the armyworm outbreak is under control although there are still pockets of infestation in areas such as Kajiado, south of Nairobi. Armyworms are among notifiable migratory pests in Kenya.

African bollworm

The bollworm has also infested fields in central and eastern Kenya.

"Bollworms are usually a minor pest but this year they have become a major pest. People are not prepared for [them]," noted Ngetich, adding that control efforts and damage assessment were ongoing.

Unlike the armyworms, the bollworms feed on 35 food crops and about 25 wild crops, making their control difficult. "Even if you deal with the ones in the fields, others remain in the bush. You might spray on the farm yet on the roadside they are everywhere," he said.

"Bollworms also feed at many stages of crop development. They are attacking maize at various stages; they cut the silk in maize, in some instances preventing grain setting... Once inside the ear of the maize, if you spray you could end up poisoning the food."

The bollworms have been reported in almost all districts in Eastern Province. "Attacks on bean pods have been reported, causing an outcry from farmers,” he said adding that alerts have been issued for controls, including pesticides, cultural (field hygiene) and mechanical measures.

The central parts of Kieni West and Muranga and the eastern area of Kangundo are still reporting bollworm infestation first reported in Ukambani.

Control measures

"Pasture is a food security issue, [thus the] need for [armyworm] control. If we do not [implement] controls on pasture, we also risk a bigger secondary infestation," he said.

"In secondary infestations there is rapid multiplication; one moth can lay about 1,000 eggs and hatch almost a similar number."

However, controls over pasture were tricky, he said, adding that there was a need to sensitize herders because they could graze livestock on pesticide-treated pasture.

Other challenges included inadequate equipment and personnel for large-scale outbreaks; difficulty identifying pests and the time-lag between the flow of information about an outbreak and implementation of control measures.


This article was produced by IRIN News while it was part of the United Nations Office for the Coordination of Humanitarian Affairs. Please send queries on copyright or liability to the UN. For more information:

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