Spider Mites on Tomato Plants – Identification and Treatment

Spider mites is unending problem in gardening. I came to know about them when I found what appeared to be cobwebs covering some of my tomato plants. In a few days, the entire bed was infested. This really scared me to the core, and I had to seek help from a pest specialist.

Understandably, spider mites feed by sucking sap, the lifeblood of a plant. They are very tiny pests that hide underneath the leaves. However, they can be seen all over during a heavy infestation. Their feeding site oftenly show numerous yellow spots or bronzing.

Severe infestations can significantly affect plant health and proportionally the yields. I kept wondering why my tomatoes were too small, and finally I got the answer. Spider mites deprive the plant of the nutrient-rich sap, which is important in fruit formation and the general health of the plant.

Description and identification of spider mites

Spider mites overwinter in non-crop and weedy areas such as bases of trees, along irrigation ditches, and on debris. Their populations increase in the mid-to-late summer. These pests can complete their life cycle in as quickly as one week, but generations tend to overlap.

Webbing produced by spider mites helps in hiding and protecting their eggs. Surprisingly, unfertilized eggs develop into males and fertilized eggs develop into females. Eggs hatch within 3 to 18 day,s depending on temperature, resulting in several generations within a year.

Adult mites have eight legs and an oval body. They appear like moving dots when placed on a white piece of paper. Both young and mature mites feed by sucking sap from stems and leaves of plants, causing stippling of light dots.

In small numbers, mites aren’t a concern. Their population should be high enough to show visible damage to the plants. Leaves may appear burnt on the upper surface when infestation is heavy. Tomato plant leaves turning yellow, drying, and falling off is majorly linked to this pest. 

Management of Spider Mites on Tomatoes 

Spider mites are very tiny and sometimes difficult to see with the naked eye. For this reason, most gardeners discover them when they have already caused massive damage to their plants. It’s recommended to thoroughly check the undersides of the discolored leaves for minute webbing.

Studies have shown that moisture-stressed plants are more susceptible to spider mites. Therefore, proper watering of your tomato plants can help in controlling. Tomatoes appreciate consistently moist soil, but make sure you are not overwatering as it can cause root rot and other fungal issues.

Spider mites use weeds as a hideout and alternate food sources. So, keep your tomato bed margins and irrigation ditches clear of weeds. I would also recommend frequent overhead irrigation if your beds are close to grassy areas or dusty roads.

Biological control is also a great option for tomatoes grown in humid greenhouses. Predatory mites feed on a wide array of mites, whiteflies, and scale insects. They look almost identical to and about the same size as spider mites, but are commercially available for pest control purposes.

Chemical control

While some gardeners might think that using insecticides is effective against spider mites, the opposite is true. According to the University of California Statewide Integrated Pest Management Program, spider mites frequently become a problem after applying insecticide.

This commonly occurs as a result of the insecticide killing off the biological enemies of spider mites. Mites also tend to reproduce faster when exposed to certain chemical agents like carbaryl (Sevin). If it’s really necessary to use a chemical treatment, use insecticidal soap or insecticidal oil.

Insecticidal oils and soaps must contact mites to kill them. Make sure you are spraying comprehensively, including the undersides of the leaves. These materials may burn your plants in temperatures exceeding 90°F. It’s also wise to test on a small portion of the plant several days before a full application.

Using neem oil on tomatoes

Neem oil in particular is one of the effective insecticidal oils for combating destructive insect species such as spider mites, caterpillars, thrips, and whiteflies, among others. It has earned this reputation for not killing beneficial insects like ladybugs, bees, and butterflies.

Additionally, neem oil is non-toxic to humans and pets. This means you can safely treat your tomatoes right before harvesting. However, incorrect use of neem oil can potentially burn your tomato plants. The oil should be diluted and applied as direct on the label instructions.

References

Utah State University Vegetable Production & Pest Management Guide, Spider Mites

Plant Pathology Department  University of Florida, SPIDER MITE DAMAGE

University of Ankansas Cooperative Extension Service, Tomato Spider Mite Damage