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Vegetable IPM Updates Archive
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Thrips, Aphids and Worms in Late Produce Crops (March 2, 2016)
Thrips: Western flower thrips are now becoming quite abundant on produce crops throughout the area. Based on historical data, we can expect thrips numbers to reach high levels by the mid-March and into April. Another factor that influences thrips abundance is “bioconcentration" which occurs each year in March as lettuce acreage declines. Each time a lettuce field is harvested and disked, adult thrips populations disperse from these areas into the next available lettuce field. This is generally coincident with our seasonally warm temperatures that are suitable for thrips development. As the number of lettuce acres becomes reduced near the end of the season, this creates a bottleneck effect that concentrates high numbers of thrips adults on the remaining fields under production. This can often make chemical control very difficult, particularly in March, as thrips adults may continually re-infest fields following spray applications. See the Thrips Control Chart 2016 for more information.
Corn Earworm: Reports of corn earworm larvae showing up in head lettuce are starting to come in from local PCAs. We are also finding them in very low numbers at YAC and observed a spike in adult moth activity in our pheromone traps last week, particularly in the Roll, Wellton and Dome Valley areas. Since, March and April are historically the time when spring lettuce tends to be infested heaviest by earworms, PCAs should consider intensifying their scouting efforts and begin tightening their spray intervals on the last remaining head lettuce fields.
Aphids: Although aphids have been what I would consider light this season so far on the lettuce crops, we have noted a significant increase in winged aphids on our sticky traps (both green peach and cabbage aphid alates). We have also found few foxglove aphids on our lettuce at YAC , but the numbers remain very low. In contrast, our broccoli and cabbage plots are beginning to be heavily colonized by green peach aphids. An observation I’ve made over the past several years is that cole crops tend to be more heavily infested with aphids this time of the year. Not sure why, but might be a good idea to start watching those brassica seed crops a little more closely.

Remember, When in Doubt . . . . . “SCOUT”

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For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.

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