Beneficial Insects: Not All Bugs are Bad
(Page 6 of 8)
April/May 1995
By John Vivian
The most destructive pests in my garden are "cabbage worms," the broccolistem-green larvae of small white and sulfur butterflies, especially the European cabbage butterfly, Pieris rapae. These are the yellowish-white butterflies that you see fluttering daintily in mating pairs above your broccoli and other crucifers. An accidental introduction dating from the 1860s, P. rapae has no native North American predator and can reduce any cabbage planting to a ruin in a week from the egg stage. Each year I purchase a large bottle of Bacillus thuringiensis, —another living critter—a bacterium that infects the digestive tract of moth and butterfly caterpillars. After a bite of sprayed foliage, the bug gets enough of a bellyache that it quits eating within a day or two and shrivels up in a week. BT is harmless to any other creature, so will do no damage to baby birds if a parent feeds them a BT-treated caterpillar or to your own kids if they eat just-BTed cabbage leaves right off the plant.
I mix BT according to directions and spray it on young crucifers when first set out, after every rain early in the growing season, and once a week or so till harvest. I use a long-handled backpack pressure sprayer and poke the spray head under leaves where the caterpillars hide out. Once in a while a caterpillar will survive inside a broccoli head, so I always bathe openheaded crucifers in salt water before cooking or blanching for freezing. But, it has been a long time since I went to the garden to find the leaves of my young, laboriously inside-raised cabbage plants all cheese-holed by cabbage worms.
BT is effective against all caterpillars. Occasionally my beans are threatened by the two-inch larvae of one of the little brown Skipper butterflies—called "bean leaf rollers" in the south. One shot of BT takes care of them. Any time our fruit or lawn trees or flowering plants are threatened by an outbreak of gypsy moths, tent caterpillars, or other moth or butterfly larvae, I put the high-pressure nozzle on the garden-hose sprayer and fire BT up into the leaves when forecasters have promised an extended period of dry weather. Spraying the insects directly does no good. But, one or two applications on the undersides of the leaves they are feeding on works wonders. One year, the kid's play area under a big maple was "all icky" with the long, sticky silks of dangling inch worms. One good spraying of BT up into the tree finished them off in short order.
BT is a good general-purpose bug preventative. I squirt concentrated solution down into new-sprouted sweet corn silks as a faster and better preventative against corn borers than the traditional mineral oil treatment. When the egg of the borer moth hatches and the little caterpillar takes its first chomp, it is infected and seldom lasts long enough to take another. BT also goes around the bases of cucumber vines and other cucurbits—hand-pumped hard enough to get into slits in the stems holding young squash borers. I also spray it according to bug-hatching schedules, on fruit trees, against codling moths, leaf miners, and other destructive caterpillars.
Nobody wants to kill butterflies. Thankfully, most butterfly caterpillars are picky and each species lives exclusively on wild things like sorrel, beech trees, and hairy vetch. You needn't worry about BTing monarchs; they lay their eggs and feed exclusively on milkweed. If you see a pretty, green caterpillar, with black bands and golden spot's, on your carrots or parsley, don't spray. It will develop into a gorgeous eastern black swallowtail ( Papilio polyxenes asterius). Transfer it to a wild carrot. (If you see a whole lot of them—too many to hand-pick—spray away; they can be a real nuisance in quantity. The species is not all that common, but is not at all threatened.)
Some moths are endangered due to pollution and widespread use of insecticides against forest tree pests and in agriculture. The large silkworm moths are never very plentiful and the lovely chartreuse luna moth ( Actias luna ), is an officially endangered species. You may find lone silkworm moth caterpillars—three-inchlong, bright green with yellow or red stripes or spots—in your lawn or orchard trees. Let them graze if you can. Or, transfer them to a wild, chokecherry tree.
Of course, many species can become abundant enough at times to pose a threat to plantings. The rosy maple moth has a twoinch wingspan and in small numbers is a pretty green with white stripes and a pink underbody. In quantity its larvae become thrice-cursed "green-striped maple worms" and a big hatch can strip your prized silver or red maple of all its leaves. BT to the rescue! We treat the banded woolly bear caterpillars ( Isia isabella ) as cute, fuzzy bug pets and forecasters of winter weather—the blacker the bug, the nastier the coming winter. They never bother the garden, but occasionally their cousin, the yellow woolly bear ( Diacrisia virginica ) will reproduce in huge numbers, overrun the garden, and call for BT.
RELATED CONTENT
Plant the right flowers to attract beneficial insects to your garden....
Ducks produce valuable meat and eggs, and they’re fun to watch. But their most valuable asset to a ...
Page:
<< Previous 1 |
2 |
3 |
4 |
5 | 6 |
7 |
8 |
Next >>
