Tomato Diseases Part 3: Insects
As we wind down our look into tomato disease, it would be difficult to overlook the damage that is caused by pests in the tomato industry. Pests will inflict physical damage and also spread many of the diseases we’ve previously discussed. They can leave operations of all sizes decimated, so it is crucial to know how to handle them. Controlling pests can be difficult, but it’s certainly necessary, so we’ll discuss some of the more common pests and how their presence and activity can be curbed.
Aphids are among the easier insects to control. They move slowly, so they can often be contained. However, they also reproduce quickly with numerous generations hatching in one season. These insects have a soft, pear-shaped body with long antennas, and they can be green, white, black, gray, brown or yellow. Aphids are often found on the underside of leaves, and they can occur in large numbers.
Aphids affect both the fruit and foliage on tomato plants. When aphids are in a garden the leaves may curl, become yellow and stop growing. They also feed on the fruit itself, so physical damage will become apparent on the tomato. They will pass disease from plant to plant, so once they become known they need to be stopped. At times, simply spraying plants with cold water can be enough to get rid of them. Dish washing soap has also been found helpful, and using a mixture of water and one drop of dish soap may help. If this doesn’t work there are horticulture oils and insecticidal soaps that are available. Bringing insects that feed on aphids can also control their population. Lady bugs or parasitic wasps can be a good option, and these beneficials can be ordered online. There are also plants, like nasturtiums, that may attract some of these insects.
Flea beetles emerge when the weather settles around 50°F, so they are particularly harmful at the beginning of growing seasons. They are small, shiny and are usually black or tan. Flea beetles lay their eggs at the base of the stem and the larvae will feed on the roots, while adult beetles will eat the leaves and fruit.
The damage caused by flea beetles usually doesn’t kill tomato plants, but the diseases that they carry will. They frequently carry different forms of wilt and blight. To stop them, growers should consider delaying their planting schedule by a week or two. This will leave them with no food supply after hatching and ideally starve them out before the plants begin to grow. Insecticides used early in the season can stop flea beetles in their tracks, and many have found success using row covers. When using row covers, make sure they are completely sealed and applied to each row once the plants have been transplanted. At the end of the season, tilling the soil may limit their numbers for next season.
These green caterpillars are some of the more common insects on this list, as they’re found all over the United States. They feed consistently for about four to six weeks, and they can grow as long as five inches. They can destroy the leaves and fruit of the plant, and plants affected by hornworms can have dark-green droppings left behind, wilted leaves or missing leaves.
Hornworms get large enough to remove by hand, but their color can make them difficult to spot. When they are found, hand removing is the most effective way to get rid of them. When populations are out of control insecticides are an option. A good insecticide for hornworms is Bacillus thuringiensis, because it is poisonous to hornworms, but still safe for plants and animals. At the end of the season, tilling may prevent hornworms from overwintering.
Nematodes are small, round worms that thrive in soil temperatures ranging from 70°F to 80°F and attack the roots of tomato plants. They cause the plants to fail due to dysfunction in the root masses, and they can reduce the plant’s ability to nourish itself with water and nutrients. Determining whether nematodes are the source of agricultural troubles is difficult, because of their size. Root tissue and soil samples are usually needed to diagnose a nematode problem. The only other way is to uproot plants to see if they have developed abnormal growths, also called galls.
Nematodes will cause improper development in the plant. Growth will be stunted, premature wilting will usually occur and the leaves may also turn yellow. There isn’t much that can be done once nematodes have infected plants, so prevention is the best course of action. There are nematode-resistant varieties that will reduce their effects. Crop rotation can help, but in order for it to be effective, nematode-resistant crops must be in the rotation. Some crops that should be considered in rotations are iron clay cowpea, sunn hemp and hairy indigo. When battling nematodes, weeds must also be controlled, because they are able to host these worms. Adding compost material and other organic matter may also be helpful. Organic soil amendments can limit nematode populations and the damage that they can cause. Finally, keep plants in infested areas isolated. Don’t let runoff water from infested areas infiltrate non-infested areas, but still make sure that tomato plants get plenty of water.
Whiteflies are closely related to aphids, and they can be found in most regions. These flies are difficult to see, but they are white and cluster on the undersides of leaves, so the careful eye can spot them. A whitefly problem can be discovered by the honeydew that they leave behind, which can lead to a number of fungal infections and diseases.
Since whiteflies are so tiny and bunch together, many growers use vacuum cleaners to remove these pests from the leaves. Traps can also be found in garden stores, and these give growers not just the ability to remove whiteflies, but also to monitor their population. Some growers also use insecticides, while others introduce beneficial insects. Lady bugs and spiders both feed on whiteflies and can help to control their numbers.
Stink bugs are pests that generally affect tomato growers on the west coast, but they can be found in other regions as well. Their drum-shaped eggs begin to appear in March and April, and can be found on leaves. Once they mature, stink bugs are shield shaped and generally brown or green. Stink bugs leave markings on tomatoes that look like the fruit was stuck with numerous pins. The edges of these tiny holes turn yellow, and, besides the physical damage that stink bugs cause, they can also carry pathogens, like yeast, that can cause the plant to decay and breakdown.
Unfortunately, stink bugs tend to go unnoticed until they inflict damage. They move quickly and aren’t picky eaters, so at times they can be difficult to control. Using traps will help growers monitor and capture them, and row covers can also provide growing plants with protection. To find them, simply shake the plants that may be infected, and the bugs should fall to the ground. Stink bugs do have plenty of predators, but in many places these predators haven’t been able to keep up with the stink bug population. Ants, ladybugs and lacewings all eat stink bug eggs and may provide some help in controlling stink bug numbers.
So we’ve covered some of the most common diseases that affect tomato plants and the pests that can spread them and cause more damage to tomatoes. Of course there are more diseases and insects that can harm your harvest, so if you have any questions leave them in the comments section and we’ll get back to you.