Ask Your PCA: Why are farmers having more trouble with diamondback moths?

Issue Date: July 15, 2020
Kirk Ellis PCA, AG RX, Oxnard
Kirk Ellis PCA, AG RX, Oxnard

Heading into the summer months, growers saw heavy pressure from diamondback moths in Brassicas—cabbage, broccoli, cauliflower and Brussels sprouts.

Diamondback moth is becoming an increasing problem in Brassicas in the Central Coast and other areas, particularly with current chemistries. Resistance to these chemistries is making it increasingly difficult to control the pest.

The diamondback moth is a small worm that burrows into the head of the cabbage, leaving holes in it and making it unmarketable. In some cases, damage has resulted in complete crop failure.

Diamondback moth infestations are most serious when they damage the crowns or growing points of young plants or Brussels sprouts. The pest can severely stunt plant growth. Diamondback moth caterpillars can bore into the head of broccoli or cauliflower, or in the flower buds of stalks, causing economic loss.

The moths are very prolific breeders. The adult moth lays the eggs, and then the larvae damage the plants. This makes it important to control the adults. Many of the materials used kill the larvae but not the adults. Adults need to be controlled, too, to break the life cycle and prevent them from laying eggs.

Growers are using every tool available, including pheromone trapping, which would be used alongside chemicals rather than in place of a spray application.

Weather plays a role, too. The temperate climate in the coastal region allows populations to build, but they will slow in winter and become more manageable. The only time there's a break is with a cold, wet winter that helps slow down the adults and make them less active.

Brassicas are grown year-round in the Central Coast. Increased acreage of Brussels sprouts and cabbage has made it harder to break the life cycle of the moth; reducing Brassica acreage would help break the cycle of this pest.

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.




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