Ask Judy: Question of the Week
Many of you have voiced your annoyance over the small green worms that eat holes in your newly forming cabbage heads or hide themselves along the stems of your broccoli plants, often ending up in the cooking pot or on the dinner plate. If this has bothered you enough over the years that you are now ready to be proactive, then now is the time to spray. I rarely recommend any type of spraying to home gardeners. Spraying takes extra time, and, in order to be effective and safe, it requires following certain protocols and scheduling. However, in this case, effective and safe organic sprays are readily available and many would say their use is worth the effort.
For the past couple of weeks the cabbage butterfly, a daytime flyer, has been fluttering about in our gardens and laying on the leaves of the brassica plants. The eggs have been and will soon be hatching and releasing the imported cabbage worm caterpillar. These gray-green fuzzy worms feed and rest on the undersides of the leaves and grow to 1 1/4 inches in length. They eventually work their way into the center heads of the plants, where heavy feeding can occur.
BT is a naturally occurring bacteria that has been isolated and used against a variety of chewing larvae, and the kurstaki strain specifically is effective on all types of caterpillars, including cabbage worms. It is the active ingredient in several brands of spray products, and the one you should look for on the label when you want to control cabbage worms. In order for it to work, the worm (caterpillar, actually) needs to ingest a small portion of the sprayed leaf. It quickly stops eating, effectively due to an upset stomach, and usually within 24 hours is dead.
The spray is most effective when the worms are small, and if you time it so that they are killed while they are on the leaves (before the head forms), you will never know they were there! Since the white moths fly and lay eggs right through the summer, you will have to be vigilant, spraying roughly once a week, or when the small eggs have hatched and new feeding is evident.
You can scout for the eggs on the underside of the plants’ leaves. They appear singly, are light green or yellow in color, 1/8 inch in length and slightly elongated. You can also look for fresh feeding, which, if the worms are newly hatched, will appear first on the underside of the leaf. If you find this, it is an excellent time to spray.