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I N S E C T C O N T R O L

Save Your Cruciferous Crops From DiamondbackMoths

By Bonnie C. Wellsbcwells@ufl.edu

The diamondback moth (DBM) is the most destructive pest of cab-bage and other cruciferous vegeta-

bles worldwide, and one of the planet’s worst agricultural pests, wreaking havoc for growers to the tune of $4 billion to $5 billion dollars annually.

The DBM is a perennial problem in the southern U.S. The caterpillars are extremely efficient at developing resis-tance to all classes of insecticides and are highly dispersive and adaptive to new environments, making outbreaks of the pest unpredictable. Insecticide resis-tance and the lack of natural enemies are believed to be the reasons why DBM is increasingly hard to control.

What Growers Can DoImplementing an integrated strategy

is critical to manage the DBM in cru-ciferous vegetable production systems. Pest management programs must focus not only on DBM, but also the entire crucifer pest complex, which includes numerous other caterpillar species, aphids, harlequin bugs, stinkbugs, and

leaf beetles. This is because the presence of other early season pests is generally the motivation for use of preventative sprays in cropping systems and can decrease the presence of natural enemies and favor insecticide resistance.

A truly integrated strategy will incor-porate several complementary tactics over large areas that work to suppress multiple pests. When used together, the following tactics can act synergistically to enhance pest suppression, reduce insecticide resis-tance, and improve the sustainability of the overall pest management program in crucifer cropping systems.

Crop RotationBecause DBM has a narrow host

range, feeding exclusively on cruciferous plants, crop rotation away from a host plant can significantly reduce the number of pests and subsequent damage in crop-ping systems. However, crop demand and price may dictate if crucifer-free periods are economically feasible for commercial vegetable producers.

Trap CroppingTrap cropping, or using highly pest-

attractive plants on field borders, can

be used to intercept and retain pests such as the DBM and other crucifer pests. Collards and Indian mustard are recommended trap crops for suppress-ing DBM. Because collards are highly attractive to DBM, they can be planted on the periphery of cabbage or broccoli fields for pest management.

Insecticide Knowledge and Resistance Awareness

Insecticides have been widely used on cruciferous crops for the control of numerous pests. Preventative applications have been historically used for the control of early season pests and has led to the use of protective applications for later season pests such as DBM. However, use patterns significantly vary between regions and change depending on resis-tance development and new products becoming available for use.

Because the control of the DBM has relied heavily on insecticide applica-tions, the pest has developed resistance

This � eld of collards at the UF/IFAS Cowpen Branch demonstration plot in Hastings is serving as testing grounds for researchers to look at the efficacy of several different insecticides for diamondback moth control. Scientists also are conducting the same experiments on cabbage.

Phot

o by

Bon

nie

C. W

ells

An integrated approach is key to managing this destructive pest.

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to nearly every class of insecticides. According to the arthropod pesticide resistance database, DBM has developed resistance to more than 80 active ingre-dients in more than 20 countries. DBM was one of the first agricultural pests to develop resistance to DDT in the 1950s and later to the microbial insecti-cide Bacillus thuringiensis (Bt).

In North America, DBM has devel-oped resistance to all pyrethroids, most carbamates and Bt; however, the resis-tance varies greatly by region. DBM is highly adaptable and has proven to devel-op high levels of resistance to insecticides after only a few years of use. When new insecticides hit the market, it is absolutely imperative they are used judiciously and combined with other management tactics for the control of DBM and other cru-ciferous pest species, so that insecticide resistance can be prevented.

Bonnie C. Wells is a Doctor of Plant Medicine and UF/IFAS Commercial Agriculture Extension Agent based in St. Augustine.

Get up close with the diamondback moth, from larval stage (left) to adult. Recognizing Host Plant Resistance

D iamondback moth (DBM) caterpillars feed exclusively on crucifers, or plants

in the Brassicaceae family. Plants in this family contain biochemicals called glucosin-olates that are used as egg-laying stimulants by the DBM. Although the moths are crucifer specialists, crop species are not equally preferred, and DBM has a strong preference for collard plants. Mustards, turnips, and kohlrabi are the least preferred.

Leaf color, wax content, head compact-ness, and levels of glucosinolates all affect a plant’s resistance to the DBM. Shiny green or glossy leaves reportedly cause DBM caterpillars to spend more time searching for food, and less time feeding, which also might improve predation of the pest by natu-ral enemies.

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