Many coconut-growing areas in Thien Nghiep Municipality are in the period when fruits are damaged by blackhead worms. Typically, more than 40 Siamese coconut trees belonging to Mr. Le Van Loi’s family were eaten by leafworms, causing the tree to die. Mr. Loi said this worm was about 1.5 to 2 cm long, had a hard head, and was brown and ivory white. They lie in the nest, the worm nest hides in the coconut leaves and then eats the leaves, causing the tree to become exhausted and die. In addition, worms form cocoons and roll leaves when they cause damage to leaves, making it very difficult for farmers to detect and prevent.
Many coconut areas in Thien Nghiep Municipality are being damaged by blackheads, which cause leaf burns. Picture: AH.
According to the Phan Thiet Agricultural Technical and Service Center report, as of July 12, nearly 11 hectares of coconuts in Thien Nghiep township were damaged by blackheads, especially in Thien Trung and Thien Binh villages.
Mr. Do Van Bao, director of Binh Thuan Plantation and Crop Protection Subdepartment said that the coconut blackhead, scientifically known as Opisina arenosella Walker, was first detected in Ben Tre in July 2020.
A member of the night moth family, the scaleworm is a dangerous exotic pest of coconut palms native to Sri Lanka and India. When the coconut palm is damaged by blackheadworms, it dries up from the old leaves at the bottom, then gradually to the top leaves and the young leaves at the top. Caterpillars scrape the underside of the leaflets, excrete feces and release silk to form nests for shelter. In the passive state, they hide in the nest or shed silk on the ground, the larvae attack the fruit peel.
“When the coconut tree is severely damaged by the blackhead, the entire leaves of the tree are burned, the tree is gradually exhausted, the yield is completely reduced, and the tree may die,” said Mr. Do Van Bao.
Caterpillars scrape the underside of the leaflets, excrete feces and release silk to form nests for shelter. Picture: KS.
In order to prevent blackhead pests from damaging coconuts, according to the director of Binh Thuan Plant Protection and Cultivation Subdepartment, farmers need to take measures such as: pruning the leaves or leaves of coconut palm tree damaged by pests, and at the same time removing the bulbs by burning or soaking in water to reduce the pest population.
This is an important step, effective, safe for the environment and should be done immediately if harmful blackworms are discovered in the old leaves underneath.
In addition, farmers need to use balanced fertilization, divide coconut palm fertilizer into multiple batches, and limit the transportation of coconut seedlings, secondary host plants (areca, bananas, etc.), and blackhead-infected coconuts. to other regions to limit the spread.
For biological measures, farmers use the bioactive pesticide Bacillus thuringiensis (Bt). At the same time, release the pintail beetle Chelisoches variegatus in numbers of 10-20 individuals/tree and preserve the natural predators available in nature such as weaver ants, bait bugs and parasitic wasps to protect coconut gardens.
The young caterpillars attack the skin of the fruit. Picture: KS.
Regarding chemical measures, the head of Binh Thuan Plantation and Plant Protection Sub-department said that no pesticides are currently registered to prevent harmful blackhead insects from coconuts. However, according to the guidelines of the Department of Agriculture and Rural Development, temporarily use the active ingredients abamectin, azadirachtin, emamectin benzoate and spinosad to prevent blackhead pests.
However, note that if the coconut garden is severely damaged by blackheadworms, farmers must prune and destroy the leaves before spraying pesticides to reduce the pest population as well as increase exposure to the larvae and the effectiveness of the drug. For coconut gardens in combination with livestock, the use of one of two active ingredients that have been shown to be less harmful to shrimp, fish and livestock, such as spinetoram and flubendiamide, is recommended.
Binh Thuan’s plantation and crop protection department found out how to spray five coconut trees with a machine of about 25 liters, evenly wetting both sides of the leaves. Spray twice, 7 to 10 days apart, alternating the active ingredients. When using pesticides, it is necessary to follow the “4 rights” principle and do not use water with a salinity higher than 0.5‰ to mix the drugs, nor spray until no harmful symptoms are detected.