Prevent Spider Mites on Tomato Plants

Spider mites are very little arachnids that are difficult to see without a magnifying glass unless they have multiplied so much as to be in colonies. When spider mites invade your tomato plants, they inflict small wounds on the plants that can eventually harm or kill them. The mites feed on the plant's sap, working from the bottom of the plant to the top, and on the underside of the plant's leaves. There is no particular season in which the mites are more prevalent; they are active all year. In addition, they change colors depending on their life stage, which makes them even more difficult to find when they are white or blend with the color of your plants. Keeping your tomato plants healthy and prevent infestation of spider mites takes regular attention and vigilant application of various control methods.

Steps

Detecting spider mites

  1. Check your plants on a regular basis for any signs of infestation. Look for signs such as movement, or clusters of eggs. It may help to use a magnifying glass.
  2. Ensure that any plants that you purchase are not already infected. Check them carefully before purchasing or bringing them home.

Preventing spider mites

  1. Space your plants fairly far apart. Provide enough space so that mites cannot easily move from plant to plant. A few inches or centimeters will be far enough.
  2. Keep plants misted (inside greenhouse and outside). Also, keep the humidity high (if using a greenhouse).
  3. Allow the air in your greenhouse (if applicable) to circulate.
  4. Install screening over any open windows (if applicable). This will prevent bugs and insects from entering.
  5. Remove any already infected plants. Discard or burn these plants; do not compost them as this will spread the disease.
  6. Prevent migration from plant to plant by using sticky paper strips. Place these around your pots.

Controlling spider mite infestations

Natural controls

  1. Use natural predators such as those that feed on spider mites ("Phytoseiulus persimilis," "Neoseiulus californicus" or "Mesoseiulus longipes"). It is important that you introduce them before there is a large infestation, so that they can adequately control it.
  2. Pick off any mites or eggs by hand. Destroy them by squishing or drowning. This works with only very mild cases of infestation.
  3. Spray plants using a stream of water to knock mites off the underside of leaves. Be careful to not spray them onto another plant.
  4. Spray hot pepper wax onto leaves (underside) to kill the mites. Repeat this application every few days. The spray will not destroy eggs so you must continue to apply to kill all the hatched mites.

Homemade solutions

  1. Smother the mites by spraying with a 1/2 cup (113.4 g) of flour and 1/2 cup (118.3 ml) of milk mixed with 1 gallon (3.8 l) of water. Repeat this application every 4 to 5 days.
  2. Spray plants with an insecticidal soap to kill the mites but not damage the plants.
    • You can make your own insecticidal soap as follows: Mix together 2 tablespoons of liquid dish soap, 4 oz. ethyl alcohol (use the cheapest vodka you can find) and 12-16 oz. water. Transfer the resulting solution to a spray bottle. Spray on the tomato plants. You'll find that it works on other insects too.
  3. Prepare a garlic mixture. Place 1 oz. (28.4 g) of garlic in a blender with 2 to 3 oz. (57 to 85 g) of onion, 1 oz. (28.4 g) of cloves, 1 oz. (28.4 g) of cayenne pepper and 1 cup (237 ml) of water. Blend to combine. Add this mixture to 1 gallon (3.79 l) of room-temperature water and spray 3 times over 5 days. This is a preventative measure but will also kill young mites.

Commercial controls

  1. Spray plants with a horticultural oil. This will suffocate the mites but won't damage the plants.
  2. Use any popular insecticide spray if necessary. Follow the directions on the label for safety measures.



Warnings

  • Be sure to always wear protective clothing when using any chemicals or insecticides, such as long sleeved shirts, gloves and protective eye wear. You may also want to avoid breathing any sprays by wearing a face mask.

Things You'll Need

  • Magnifying glass
  • Screening (if greenhouse tomatoes)
  • Natural spider mite predators
  • Sticky paper sheets, such as fly sheets
  • Insecticidal soap
  • Horticultural oil
  • Hot pepper wax
  • Flour
  • Milk
  • Water
  • Garlic
  • Onion
  • Cloves
  • Cayenne pepper
  • Chemical sprays (insecticides) specifically for the spider mite species
  • Protective clothing, gloves, eye wear and face mask

Related Articles

Sources and Citations

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