Identifying Pest and Disease

Identifying the problem is the first step in finding an earth-friendly way to reduce or even eradicate the damage caused by garden foes. Check the list below for the most common causes of garden problems.

Keep in mind that the 95 percent of garden visitors are either helpful or harmless. Beneficial insects include ladybugs, lacewings and many others. Learn more in the article Most Bugs are Good Bugs.

Lets take a look at the pests and diseases and their control measures:

1. Armyworm

Although an infestation of armyworm caterpillars can rapidly decimate a commercial field crop, they rarely cause this degree of destruction in home gardens. Armyworms feed at night on plant foliage and grass blades; they hide under foliage and debris during the day. Severe feeding can result in dead areas of lawn and ragged-looking or defoliated crops.

Young armyworms are pale green; older larvae are brownish with stripes along their bodies. Several species attack a variety of garden crops, including corn, beets, tomatoes, peppers, potatoes, onions, and peas. Adults are gray-brown moths that lay eggs on host plants and in lawns.

In general, armyworms do not survive cold winters, but they can be a year-round pest in warm-winter climates, such as California and Florida.

Prevention and Control

• Encourage native beneficial insects such as parasitic wasps that prey on caterpillars.
• Weed out grassy weeds as well as pigweed, plantain, and lamb’s quarters, which are host plants for the beet armyworm.

2. Cabbage Looper

These green inchworms can make a mess of your broccoli and cabbage plants. They chew on foliage, bore holes into cabbage and broccoli heads, and leave behind unsightly black frass (droppings). Cabbage looper damage is annoying, but rarely causes severe crop loss (cabbageworms cause very similar damage). To remove caterpillars from a harvested head of broccoli or cauliflower, just immerse it in salted water. Loopers will feed on any cabbage-family crops, including cabbage, kale, collard, broccoli, and cauliflower.

Cabbage loopers have no legs in the middle of their body; they hump their bodies as they “inch” along. The adult form of this caterpillar is a gray moth that overwinters in warm climates and then migrates to lay eggs. Look for these white eggs on the underside of leaves near the leaf edge.

Prevention and Control

• Cover susceptible plants with garden fabric (row cover)  as a barrier to the egg-laying moths.
• Use Bt (Bacillus thuringiensis)
• If plants are not covered, inspect them frequently. Crush the eggs; handpick the loopers and drop them into a pail of soapy water.

Cabbage looper. Photos: Ann Whitman

Cabbage looper damage and frass.

 

 

 

 

 

 

 

Cabbage looper egg.

 

 

 

 

 

 

 

 

 

3. Cabbageworm

Large, ragged holes in the leaves of cabbage, broccoli, Brussels sprouts, collards, kale, or cauliflower plants are a sign that cabbageworms may have invaded your garden. The green caterpillars may also bore into the heads of these crops, leaving behind their dark green frass (droppings). Cabbage loopers cause similar damage. Plants can tolerate a moderate amount of damage without reduction in yield.

The cabbageworm is the larval form of a small white butterfly that has three to four black spots on its wings. The butterfly lays white eggs on the underside of leaves; eggs hatch within a week and the larvae feed for approximately two weeks. The larvae pupate in silken cocoons attached to the lower leaves.

Prevention and control

• Cover susceptible crops with garden fabric as a barrier to the egg-laying moths.
• If plants are not covered, inspect them frequently. Crush the eggs; handpick the cabbageworms and drop them into a pail of soapy water.

4. Codling Moth

One of the major pests on apples, the codling moth, is found in all areas where apples are grown. It attacks pears, apricots and quinces as well as apples. Small holes are found on the fruit, usually at or near the blossom end. Inside, pinkish-white worms with brown heads feed on the flesh, leaving tunnels full of sawdustlike frass (droppings). The feeding of larva inside the developing fruit often causes fruits to drop prematurely.

The codling moth larvae over winter in cocoons under loose bark on the trunk or under debris on the ground. In midspring they pupate, emerging as grayish-brown moths in late spring. The females lay eggs on leaves, twigs and fruits. The larvae feed briefly on the leaves before tunneling into the fruits. After feeding for three to five weeks, they emerge and crawl down the trunk in search of a spot to pupate. There may be up to three generations per year.

Controls

• Spray with the insecticide Bacillus thuringiensis (Bt). At least three sprayings are needed, and timing is critical: Make the first spray 15 days after petal fall begins, and subsequently at five-day intervals. Note when petal fall begins and mark the spray days on a calendar.
• Rake leaves and dropped fruit through the growing season and in autumn after all leaves have fallen.

Grasshopper

Grasshopper populations are cyclic, and when their numbers peak, these pests will eat nearly any plant they encounter, wiping out entire gardens and fields. In vegetable gardens, they particularly favor lettuce, carrots, beans, sweet corn and onions. Initial signs of feeding by young grasshoppers are jagged and tattered holes chewed in leaves.

All species and most stages of grasshoppers look essentially the same: Long narrow bodies, with angled back legs suited to jumping, and a head featuring large eyes and chewing mouth parts. Most grasshoppers over winter are eggs in the soil. In spring, wingless juveniles hatch and feed on tender foliage near the soil surface. They molt and reach the adult phase within a few weeks. Adults are winged and can travel great distances to feed. There are usually one or two generations per year.

Prevention and Control

• Cover plants with garden fabric to prevent nymphs and adults from feeding.
• Encourage natural enemies of grasshoppers including birds, ground beetles, and blister beetle larvae.