Malathion Damage to Tomato Plants

Tomatoes are warm-season annuals that produce one of the most widely used and adaptable fruits. Full sun, good soil, staking and pruning, food and plentiful water ensure plump fruits, but tomato plants are susceptible to several diseases and insect problems. Malathion is recommended by the University of Missouri Extension and Clemson University, among others, as a useful insecticide for tomatoes and other vegetable plants. Chemicals must be applied in the correct amount in order to avoid damaging the foliage and fruits of the tomato plant.

Tomato pests include chewing and sucking insects. Aphids, tomato hornworms, cutworms, flea beetles and spider mites are just a few of the damaging insects of tomato plants. Many cultural methods of control, including picking, can help you with small infestations. Integrated pest-management practices have some effectiveness; but, for persistent insects, you may have to resort to chemical control. Malathion must be part of a regular spray program in order to be effective, which means it should be applied at the first sign of pest problems during the growing season.

Malathion is an organophosphate insecticide. It is listed for use on almost every vegetable and fruit you can imagine as a pest control spray. It is also used to treat head lice and their eggs. The spray cannot be used around water as it is dangerous for aquatic animals and fish. You can use the product up to within one day of harvesting the tomatoes. Malathion is the active chemical ingredient in the spray and is oily and smelly but considered safe to use on edibles if applied according to the product specifications. Concentrated or undiluted application of the chemical will cause foliar damage.

The time of day, amount of dilution and method of application are all important when using a chemical spray. Malathion works best if applied in the morning after dew has dried but before the heat of the sun can reflect off the moisture that the spray leaves behind. Malathion is mixed at a rate of 3 tsp. per gallon of water for worms or 1 tbsp. for the other pests. Dilution is important to prevent foliar damage. Apply the spray as a foliar application once and then watch for more insects. You can reapply it as needed and only need to wait a day before you harvest and eat the fruit.

Overspraying with any chemical can be damaging to plants. Tomato leaves that receive too much chemical may become yellowed or bleached. The leaves crinkle and dry out where over-spray has contacted them. Severe chemical burns from Malathion will result in the entire leaf shriveling. Malathion is applied as a foliar insecticide which is why it has the potential to cause damage to the leaves. If the product is not properly diluted, the concentrated effect is too strong for the leaves, and they will get chemical burns.