Garden Word of the Day
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Earworms. Those songs that get caught in our mind and play over and over and over… These are not those earworms, but they can be just as annoying.
You don’t grow corn, you say? Don’t think that your garden plants are off the hook, just yet. The larval form of the corn earworm (Helicoverpa zea) goes by several names, such as cotton bollworm and tomato fruitworm. Tomato?!!? Yes, this is the dreaded tomato fruitworm. And these innocuous-looking moths can migrate as far as 400 km (or nearly 250 miles) to get at many favorite garden plants, including melon, beans, spinach, soybeans, peas, okra, squash, and sweet potato.
Corn earworm description
Adult moths are a little more than an inch across, and pale tan to light brown. The front wings can have various markings, and the hind wings are dirty white with a dark gray band at the tip. These moths are often found early in the worming, crawling in the lawn, as they get warm enough to start moving. [If seen, stomp on them!]
Eggs are spherical and slightly flattened, with ribbed lines running from end to end. They look a lot like cabbage looper eggs.
Larva start out a creamy white color, with a dark head. They have distinct, sparse hairs (tubercles) with dark spots. As the larva feed, the color changes to greenish-yellow to nearly black, depending on the food supply. Fine white lines can be seen along the body. The hairs and the spots remain. On some individuals, stubby bristles or spines can be seen with a hand lens.
Corn earworm lifecycle
Tiny pale green eggs turn creamy white, and then yellowish or gray. They are laid singly on upper and lower surfaces of leaves, leaf hairs, and on corn silk. They develop a reddish-brown ring within 24 hours. Eggs darken in color just before hatching, usually less than 72 hours after being laid. Larvae go through 4 to 6 instars, or developmental stages, all the while feeding heavily. In fact, corn earworm larvae are a brutal bunch. In addition to attacking your tomatoes, they will also attack and feed on other insets, especially butterfly and moth larvae, including their own kind. After 12 to 16 days, the larvae enter a pupal stage. If the soil is moist enough and temperatures are warm enough, an adult moth will emerge to begin the cycle again. A single adult female corn earworm moth can lay up to 2,500 eggs in her lifetime.
Corn earworm damage
Adult moths feed on nectar and pollen, but they are not the problem. It is the larval stage that causes all the damage. Being polyphagous, corn earworm larva eat many different things. And you won’t even know they are there until it is too late, unless you look very closely. The larvae feed inside the fruit, so it’s not until you cut into it or take a bite that the pest is discovered. Yuck! Also, larvae may move from fruit to fruit, leaving behind a wake of squishy, watery digested insides filled with frass and shed skins.
Damaged fruit tends to ripen prematurely and the feeding action makes plants susceptible to other problems, including fungal diseases and mold growth. Because the larvae are inside the fruit, control is difficult.
Controlling corn earworms
Protected within fruit, corn earworms are tough to get rid of. Making matters worse, these pests have developed a resistance to our chemical arsenal. This means that integrated pest management must be used instead. Integrated pest management (IPM) is an approach that uses many sustainable methods to provide the least amount of damage. IPM practices that reduce the damage caused by corn earworms include:
Farmers also use commercially available parasites and deep ploughing to combat the corn earworm, but these methods are not relevant to the home gardener. The parasites (Trichogramma pretiosum) are not available over-the-counter, and deep ploughing damages the soil microorganisms that help our plants thrive.
Monitoring plants regularly for signs of eggs of young larvae can help you protect your tomato, corn and other garden plants.
Did you know that plants use the saliva of their attackers to figure out which defense chemicals to produce?
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