Articles, Blog

Monitoring for Thrips in Avocado Orchards

December 5, 2019


Hi, I’m Ben Faber. I’m a Farm Advisor here in Ventura [and] Santa Barbara counties, and we’re going to be talking about thrips. Specifically, pest thrips—avocado thrips and greenhouse thrips. [On-screen text: Avocado thrips] This is a really good time of year to look for avocado thrips, because it’s in flowering and this is when fruit set occurs, and this is when we would be seeing damage starting to occur to young fruit. We’ll start monitoring when we start seeing new leaf flush. The leaf flush occurs usually slightly before the flowering, and the idea is to keep the thrips feeding on the leaves. We don’t want them to go onto the flowers, and the new fruit, like that. This feather flush that’s near the flowers— once that hardens off, the thrips go to the young fruit and start feeding on that, because they don’t like to feed off this old tissue. They want new tissue. The problem with avocados along the coast is that we can have this flushing going on from January, through February, into March, April, May, and June. So during this period, depending on what the weather’s like, a pest control advisor or the grower will be out here looking at this flush, and they should be out here once a week looking. Because once the thrips shows up here, there’s very little threshold between moving from this, to that young fruit. You’ve got about a week’s period in order to arrange for any sort of pest control that you’re going to do. When we’re monitoring for avocado thrips, a lot of times we’ll look on the south side of the tree. That’s where the most heat and usually the most activity [will be], and where you’ll see the first leaf flushes, as well as the first flower flushes. And so that’s typically where we see the first fruit set. Later on you can find them on the other side of the tree as well. They’re on the bottom of the leaf, the backside of the leaf. And they’ll feed right along the veins, usually the lateral veins, sometimes the midvein. And that’s where you’ll see the feeding damage on the older tissue. In an orchard, you’ve got fruit of different sizes. You’ve got the little fruit that’s very susceptible, and then you’ve got this larger fruit that’s out of harm’s way, and then you may have some that really big fruit that is not going to be affected at all. So this is the fruit—it’s just about at the stage where you’re not gonna have to worry about it. This is still susceptible. So, once it gets to be about a quarter’s size in diameter, it’s gonna be free from damage, but I know a grower would most likely spray if there were thrips on these leaves. And here’s an example of fruit that is older, it’s not subject to feeding damage at this point, but there’s a lot of scarring. And this is unlikely to clear up. A lot of times when the fruit is smaller, you can see some feeding damage, and if there’s no further feeding damage as the fruit grows out, the scarring disappears. So at this point, depending on what the market’s like, when this fruit is harvested, it’s going to be fruit that would be downgraded, and it might be half the price of fruit that is unscarred. When we do treat for avocado thrips, thrips moves fairly fast, so if you find one or two in one part of the orchard, You might really consider spraying the whole orchard. [On-screen text: Greenhouse thrips] Now, for greenhouse thrips, that is an insect pest that’s looking for harbor and refuge. And it’s not going to be out here, where it’s exposed to the elements. It wants to be inside. Especially it’s feeding off of older tissue, so it’s looking for the older fruit. So it’s going to be on the inside, because as the tree gets older, the fruit starts to hang, and that’s the kind of environment that the greenhouse thrips likes. It likes a more protected environment. And it likes to be where there’s clusters of fruit, where the fruit is touching, actually. And that will occur, you start looking for that later on— July, August, September. So, we’re looking for avocado thrips [in the] spring, we’re looking for greenhouse thrips later on in the summer. When we’re looking for greenhouse thrips damage, feeding damage for that will be inside the clusters. When the fruit is close to other fruit, you’ll get rubbing damage occurring as well, so you can get the same sort of scarring damage just from physical damage. To distinguish between physical damage and greenhouse thrips, well first of all, you look for the greenhouse thrips. If you can’t find those, you look for the excrement from the greenhouse thrips. Greenhouse thrips tend to be in one or two or three or five or ten trees in one part of the orchard, so you’ll want to do a spot spray for them if it becomes necessary. In the case of greenhouse thrips, they really do like that cluster of fruit. And if you can thin that fruit so that there’s not that ideal greenhouse environment in that cluster, it’s less likely that the greenhouse thrips will stay there. So you really want to do a select pick, a thinning, so that the clusters aren’t present for them to hide in. For more information, visit the Avocado Pest Management Guidelines. [Credits slide: Produced by the University of California Statewide Integrated Pest Management Program: Ben Faber, Stephanie Parreira, Petr Kosina, Tunyalee Martin, Ray Lucas]

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