Protect your cabbage family crops
from the diamondback moth
(continued from page 1)

How can organic growers prevent damage from the diamondback moth?
The diamondback moth is a difficult pest to eliminate, but you may be able to outsmart it by using a combination of the following control strategies.

Biological controls and natural enemies.
First, conserve the natural enemies that already exist in your fields. Ground beetles, wasps, spiders and birds are just a few of the natural enemies that help to control most agricultural pests. Scientists in central Japan have identified some ground beetles (members of the insect family Carabidae) at the National Research Institute of Vegetables, Ornamental Plants and Tea, that may be important natural predators of diamondback moth caterpillars. In general, Ground beetles have a good appetite for the diamondback caterpillars. Ground beetle species that actually climb cabbage plants work best, since the caterpillars spend their entire lives on the plant. Some ground beetles climb and dine on both the worm-like immature stages and the adults. Other species of ground beetles are important natural enemies of many crop pests, and some eat weed seeds or crop seeds. Most ground beetles are dark, shiny, fast moving and difficult to identify. You can encourage ground beetles and other natural enemies in your fields by avoiding pesticides and by providing a cool, mulched and moist environment under plants and at the soil surface.

Secondly, you might be able to rely on tiny wasps called "parasitoids" that lay their eggs in diamondback eggs, caterpillars or cocoons. Scientists throughout Asia have conducted experiments to identify and release parasitoids that work best in local environments, since the wasps require specific temperatures for their development. In Taiwan, for example, the wasp named Diadegma semiclausum–an important natural enemy of the diamondback moth worldwide–became established when released by scientists in the highlands, but not in the lowlands. You should check with local agricultural experts to learn more about specific natural enemies in your area. Depending on regulations, you may be able to purchase and release the parasitoids in your own fields.

Get help from H2O. If possible, avoid planting crucifers in the dry season, since rain helps to control the moth. Likewise, overhead irrigation helps to wash the caterpillars from leaves. If you irrigate at dusk, it may prevent the moths from mating. However, avoid this tactic if plant diseases will be worsened.

Avoid multiple planting dates. Don’t make it easy for diamondback moths to move from old plants to new plants. Or, plant later crops in the direction of prevailing winds to make it harder for moths to fly into new plantings.

Start with clean plants and fields–then keep them clean. Screen-out pests in the greenhouse. Check cabbage seedlings for eggs and caterpillars before transplanting. Later, remove all unharvested plants from the field or plow them down. You can chop the residue and add it to a hot (at least 60 C) compost pile. Keep fields free of cabbage-related weeds such as mustard–unless using them as a trap crop.

Try trap cropping. Some farmers plant strips of crucifers such as collards or mustard, that are more attractive to the diamondback moth, among rows of cabbage. In India, for example, some growers alternate a row of mustard with every 15 to 20 rows of cabbage. Adult moths prefer to lay eggs on the trap crop of mustard, which means fewer caterpillars on your main crop. If sufficient numbers of natural enemies are present, all stages of diamondback moth within the trap crop should be controlled–thus sparing the main cabbage crop. If you find that natural enemies aren’t providing sufficient control within the trap crop, pull, mow, or chop the trap plants before the moths within have a chance to complete their life cycle.

Try inter-cropping. When farmers grow mixed plantings of several crop species, they are practicing inter-cropping. Diamondback moths may find it more difficult to locate the main cabbage crop when thus camouflaged. Unlike trap crops, intercrops do not attract a target pest. Try growing a tall crop, such as tomato or corn, as a physical barrier between blocks of crucifers. Some scientists have found that intercropping with sage (Salvia officinalis), thyme (Thymus vulgaris), or white clover (Trifolium repense) helped to reduce damage to Brussels sprouts from diamondback moth.