How to Treat Spider Mites on Corn in California

California produces the second-largest corn crop in the U.S. Most of the corn grown in California grows in three counties: San Joaquin, Fresno and Tulare, where most of the corn ends up as silage to feed dairy cows. Fresno County has the highest production of sweet corn, and the San Joaquin crops produce corn for grain. Spider mites cut into the corn harvest by sucking the juices from the corn leaves, which stunts the growth of the ears of corn along with reducing the quantity and quality of silage. Natural controls for spider mites include dust and weed control along with predatory insects.

Thrips, minute pirate bugs or bigeyed bugs
Spiromesifen or Propargite

Instructions

- 1
  Remove as many weeds as possible since weeds provide a habitat for spider mites until the corn emerges. Spider mites thrive in hot, dry, dusty weather. Keep the dust at a minimum around the corn stalks by irrigating sufficiently.
- 2
  Inspect the lower leaves of the corn plants. Look for spider mites on the tops of the leaves and inspect for damage on the lower side. Spider mites leave small brown or yellow dots on corn leaves. As the infestation grows stronger, the mites crawl up the stalks, eventually damaging the leaves of the corn near the maturing cobs.
- 3
  Introduce thrips, minute pirate bugs or bigeyed bugs if you have had or are having an infestation of spider mites. These bugs are natural predators of spider mites. If these predatory insects exist in or near where you grow corn, minimize the amount of insecticide you use since insecticides kill the spider mite predators.
- 4
  Spray the corn with chemical pesticides before it reaches four feet tall. Corn taller than four feet is difficult to spray. Spiromesifen and Propargite are insecticides developed for corn.

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