Also called tomato hornworms, tomato worms (Manduca quinquemaculata) can quickly decimate a healthy tomato crop. These worms can be identified by their green bodies, ornamented with white V-shaped marks along the sides along with the prominent “horn” growing at the rear of their bodies. If you do not take action to kill or prevent these pests, they may defoliate your tomato plants and might also feed on the fruit. To protect your tomato crop, consider using a natural pest control method to kill tomato worms before they become a problem.
If you only have one tomato plant or if you only have a small number of tomato worms to deal with, handpicking may be sufficient to control them. To use this natural method of tomato worm control, all you have to do is go over the tomato plant by hand, picking off the worms as you find them. Go over the plant methodically, examining the stems as well as the underside of the leaves so you don’t miss any tomato worms. As you collect the worms, drop them in a can of water mixed with liquid dish detergent to kill them.
Bacillus thuringiensis, also called Bt, is a bacterial disease deadly to tomato worms and it is often sold as a biological control organism. These bacteria serve as the active ingredient in some pesticides, but they can also be used on their own to kill tomato worms without harming beneficial insects or putting other wildlife at risk. Bt works by producing proteins that paralyze the digestive system of tomato worms, preventing the worms from eating — infected worms typically die of starvation within several days. The main disadvantage associated with this type of treatment is that it is subject to degradation by the sun, and foliar applications typically do not last more than seven days.
Though it may not do much to control the tomato worm population affecting your tomato plants during the current year, rototilling the soil in your garden may help prevent an infestation the following year. Tomato worms in pupae form often inhabit the soil beneath tomato plants, staying there over the winter and emerging in the spring. Because the pupae tend to be large and are not often buried very deep in the soil, rototilling the soil in your garden can be effective in killing up to 90 percent of the pupae in the soil. For the best results, use this method soon after harvesting your tomatoes.
Many times Mother Nature will take care of tomato hornworms by sending in reinforcements in the way of lady beetles, green lacewings and braconid wasps, as well the common wasp (Polistes spp.). In the egg or larvae stage, lady beetles and green lacewings solve the problem by eating the immature hornworms. Once developed into mature caterpillars, braconid wasps lay eggs on the worm, which in turn eat the caterpillar as they develop. If you notice hornworms covered in white egg masses, there’s no need to remove the caterpillar, as the wasp larvae are doing the job for you. Common wasps kill and feed off tomato hornworms.