Garden Word of the Day
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Even if you aren’t growing avocados, avocado thrips are pretty fascinating.
[Just a reminder, the word thrips is the same for one thrips or many thrips.]
Avocado thrips (Scirtothrips perseae) are native to Mexico and Guatemala. In 1971, a single female was stopped at the border. By 1996, avocado thrips were found throughout California and Hawaii. By 1999, it was estimated that avocado thrips infested 99% of California’s avocado trees.
Damage caused by avocado thrips
These pests may be tiny, but they can cause significant damage. Thrips populations explode rapidly in spring and autumn, leading to defoliation and premature leaf drop. This, in turn, reduces tree vitality and crop size. The biggest problem with avocado thrips is the scabby, brown scars on the fruit they create. These damaged areas don’t look very nice and they can create points of entry for rot and other diseases and pests.
Avocado thrips identification
These suckers are tiny. At 0.03 inches long (0.7 mm), you could put 23 adult avocado thrips end-to-end across a dime, making them one of the smaller thrips species. If you could see them up close, you would see that adult avocado thrips are straw-colored, with three red spots on the top of their heads, between their eyes. Those dots are called ocelli and they are light-sensitive organs. They also have yellow abdomens with brown stripes, but their bellies may look greenish because of all the chlorophyll they consume. [I was unable to find a free-to-use image of an avocado thrips, but they look enough like chili thrips that that’s what I used above.] Avocado thrips first instar larva are pale whitish-yellow, while second instar larvae are bigger and brighter yellow.
Avocado thrips lifecycle
Avocado thrips have six distinct life stages and adult females can lay eggs whether they have mated or not. Unfertilized eggs produce males and fertilized eggs produce females. How’s that for efficiency?
Eggs are laid on immature leaves and fruit. When they hatch, they begin feeding in the first larval stage. Then they enter a voracious second larval stage, followed by two non-feeding pupal stages. These pupae hide out in cracks and crevices in the bark and on branches, or in leaf litter (duff) under the tree. Flying adults emerge and begin feeding on leaves and fruit as they search for mates and good sites for egg-laying, and the cycle continues.
Avocado thrips management
Scorching summer heat seems to do a number on thrips, but the eggs they lay beforehand are waiting for conditions to improve. You can use yellow sticky sheets, mulch, and natural enemies to battle avocado thrips. Those natural enemies include various green lacewings and a fascinating predatory thrips called Franklinothrips. I can’t make this stuff up, but we will learn more about that pest later this week. Some predatory mites also like to feed on avocado thrips larvae. To help these predators succeed, avoid using spinosad and other insecticides.
Avocado thrips and several other pests are attracted to yellow sticky sheets. These are inexpensive and very effective, just keep them away from your hair. Also, studies have shown that mulching under (but not touching) trees can result in 50% fewer thrips making it to adulthood. This is because 78% of larvae drop from the tree to pupate on or in the soil. Apparently, a mulch of arborist chips or composted organic yard waste contains enough different predatory nematodes, fungi, bacteria, and other killers of thrips to put a serious dent in their population. Three cheers for biodiversity!
To reduce the chances of the problem in the first place, only buy certified pest- and disease-free rootstock. Of course, while they do it badly, thrips can fly, sort of, so a brisk breeze may be all they need to reach your avocado tree. Be on the lookout. Remember, they like to hide on the underside of avocado leaves.
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