Master Gardener: How to keep spider mites off your tomato plants

Q: For the last few years, I have been having problems with spider mites on my tomato plants. I’ve tried hosing off the plants in the morning, but I think this has been causing blossom end rot on the tomatoes. I don’t want to spray anything that will harm the Monarch butterflies. Should I give up on tomatoes next year to see if that will make the spider mites go away?

A: Spider mites can be a major nuisance in dry climates. They will infest a wide variety of plants, including vegetables, ornamentals, vines, berries, and even houseplants. The presence of fine webbing on leaves and leaf petioles is the most obvious sign of an infestation. The mites themselves are barely visible without magnification, but they can be found on the undersides of leaves. They can overwinter in mild climates, hiding in leaf litter or other sheltered spots.

Once the weather becomes warmer, they will begin to reproduce quickly and can produce a new generation every week during the summer and early fall months.

They prefer dusty conditions, so rinsing leaves regularly with overhead watering is helpful. (Blossom end rot in tomatoes is caused by calcium deficiency in the soil and water stress, not overhead watering.) Spider mites also tend to appear on plants that are water-stressed, so regular irrigation is essential.

Fortunately, there are lots of predators that enjoy snacking on spider mites. Ladybugs, six-spotted thrips, pirate bugs, big-eyed bugs, lacewings, and some species of predatory mites all feast on spider mites. Avoid using broad-spectrum insecticides since you don’t want to kill off the predators. In fact, spider mite infestations are worst right after pesticide treatment for this reason.

If the infestation is really bad, insecticidal oils or soaps can be used sparingly. Always follow the label instructions when using any pesticide.

Q: Somewhere I heard that you can overwinter pepper plants if you protect them from frost. Is this true?

A: Pepper plants are perennial in their native tropical climates. In fact, they can grow to the size of a small tree. If you live where the winter temperatures don’t get too low, you might be able to overwinter them.

Once they have finished producing, trim them back to about 18 inches and clear the ground of any fallen debris such as dead leaves and old fruit. (You want the plant to survive the winter, not any hidden pests.) Cover them with a frost blanket or use Wall O’ Water plant protectors. When my children were younger, we would go through one or two gallons of milk per day, so I would just rinse out the plastic jugs, fill them with water, and set them around the plants. (We didn’t have money to buy frost blankets because we spent it on milk.)

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Once the weather warmed up, remove the frost protection and look for those cute little new leaves. Some of the branches might die, but if there’s new growth then you’ve got a head start on next year’s garden.

Looking for more gardening tips? Here’s how to contact the Master Gardener program in your area.

Los Angeles County; 626-586-1988;

Orange County; 949-809-9760;

Riverside County; 951-683-6491 ext. 231;

San Bernardino County; 909-387-2182;

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