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Combat Top Insect Threats in Tree Nuts

April 22, 2019

Now is the time for tree nut growers to fight navel orangeworms and spider mites. These insect pests can lead to devastating yield losses, and infestations can carry over from one season to the next. It is important to identify these pests early so timely treatments prevent further infestation and damage.

This illustration shows a navel orangeworm.

Navel orangeworm

  • Larvae are about 13-19 mm in length.
  • Larvae are reddish orange and turn milky white to pink as they mature.
  • Potential for 3 to 4 generations per season.

The navel orangeworm is a pest of primary concern in tree nuts. The larvae feed on the nut meat, rendering it unmarketable, and can transmit fungal diseases. Nuts are most susceptible to damage during hull split, when the nut meat is exposed.


Spider mite

  • Adults are less than 1 mm in size.
  • Adults are reddish orange with dark spots on the sides of their bodies.
  • Potential for many generations per season.

There are 2 types of spider mites that impact tree nuts, Pacific spider mite and two-spotted spider mite. Both develop colonies on the underside of leaves, and sometimes on the top side when populations are high. Look out for clusters of brown leaves as a telltale sign of increasing mite population. Feeding causes stippling and browning of foliage. Early defoliation is possible, and can lead to a reduction in nut yield and quality. Late defoliation can make harvest more difficult as well.

Take the Insect IQ Quiz to test your knowledge of insect pests. Certified crop advisers (CCA), are eligible to receive continuing education units for completing the quiz.

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All photos are either the property of Syngenta or are used with permission.