In the Garden:
Coastal and Tropical South
July, 2009
Regional Report

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Tomato hornworms devastated the upper branches of this cherry tomato.

Hornworms, Whiteflies, and Plant Lice

Yikes! It's bug season around these parts, and the first step in control is to know your enemies. Just yesterday I saw ladybugs on a tomato plant recently defoliated by hornworms. Unfortunately they're too small to eat the hornworms that stripped the leaves.

Bug Damage Signs
It's important to recognize the kind of damage associated with common insect pests. Aphids, or plant lice as they're called in some places, look like pinhead-size bumps. When they're present, the plant dehydrates even if you water every day. Leaves don't expand fully, and fruit production may be compromised, too. Whiteflies do similar damage, but their presence is easier to detect since they fly away when you touch the plant. While aphid control can be done at any time, you'll find more whiteflies resting on the plant at dusk. Tiny spider mites (not truly insects, they are arachnids) also dehydrate green plant material, but their damage is even more discrete. You'll know they're around when leaves look stippled, as if someone pricked them with a pin. The leaves may discolor, too, and flowering usually stops.

Big Mouths
Insects with larger mouth parts do more obvious damage, more rapidly. Caterpillars and their ilk chew entire leaves in a few hours, leaving only their droppings to reveal their presence. Capturing these rapid growers is best done while they are small, as no control product is immediate and their feeding is nonstop. Slugs also chew, but leave a slimy trail to make their detection easier. Barrier products work best, but you should also look for their damp nests and disrupt them occasionally to hold down the population.

There are of course, beetles that chew neat holes in bean and cucumber leaves, and sawflies that turn hibiscus leaves into lacy skeletons. Fortunately, the beetles are usually late-risers. Lay a sheet under the affected plants early in the morning and shake the leaves. The drowsy beetles will drop onto the sheet for easy removal. The sawflies can be controlled if discovered at their first appearance, but once they've devoured a plant, they're gone in search of food. Squash plants collapse from borers eating them from the inside out. There is nothing to be done then, but early in the season you can usually spot the round brown eggs laid along the stem. Remove these, so they don't hatch and bore into the plants.

Control Factors
Some of the best things to have in your arsenal for the war on bugs aren't sprays or dusts. For example, the white cloth known as floating row cover works very well to exclude many insects such as the moth that lays the eggs of squash vine borers. Copper bands are popular in England to keep slugs away from precious plants like dahlias. Likewise, trellises and other structures that lift plants off the ground and increase air circulation around them assist in pest control.

Basic garden sanitation is your best ally to keep pests at bay. Clean up the plant debris when annuals finish their season, keep areas mowed, especially around vegetable plantings. Don't leave infested prunings around to become harbors for more insects. If your compost pile is only leaves, like mine, it will not heat up enough to kill most insects or eggs, so do not add infested materials to the pile. Dispose of them as your municipality allows, either in trash pick up or by burning.


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