Why Do Chestnuts Have Worms in Them?

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Chestnuts (Castanea) are a large family of trees and shrubs native to the temperate regions in the Northern Hemisphere. Deciduous in nature, the trees in the group are long-lived and drought resistant and are cultivated both for shade and for their nuts. The 3/4- to 1 1/2-inch-wide, brown-colored nuts have a glossy skin and are encased in a green, spiny cover. Chestnuts are prone to infestation from a worm that eats inside the fruit.


Pest Identification

Chestnuts are susceptible to damage from the lesser chestnut weevil and the larger chestnut weevil. The lesser chestnut weevil is more frequently found on American and Chinese chestnuts and chinquapin, the exclusive hosts of the pests. The insects start to damage the developing nuts and usually go undetected until after harvest.


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Female adults lay eggs on the round side of the nut. The eggs hatch in eight days and the tiny worms eat their way inside the kernel. The majority of the eggs are laid when the covering on the nuts starts to crack. The lesser chestnut weevil female is 1/6 to 1/3 inch long while the larger chestnut weevil female measures 1/4 to 1/2 inch in length. The female has a 5/8-inch-long snout and the male has a 1/4-inch-long snout.



Though both the adults and the grubs damage the fruit, the small grubs or the larvae are the more destructive of the two. The pests start to hatch just at the time of nut ripening, anywhere between the middle of August to the start of September. Pest damage by feeding is likely to damage an entire harvest. Damage by adult feeding creates entry spots for disease-causing organisms such as fungi and yeasts. Damaged nuts fall to the ground with mature larvae that exit the nuts and burrow into the soil for hibernation.



Harvest all the fruit that is likely to be infested before the worms damage the fruit extensively. Infestation in the early stages is barely noticeable and the treated nuts are still fit for consumption. Soak the nuts in 120 degree Fahrenheit water for about 20 minutes to kill all eggs and worms. This process does not damage the nuts. Use insecticides when pest presence is established in 10 percent or more of the tree. The recommended insecticide is carbaryl. Start treatment by spraying the crown as soon as adult weevils are detected. The pests are most attracted to trees with fruit that is about to ripen.



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