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Vegetable IPM Updates Archive
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Weather and Spring Insect Populations (Jan. 9, 2013)

Mark Twain once quipped that Climate is what we expect, Weather is what we get. I think those of you who work in the desert can relate to his sensibilities. I remember earlier this fall the NOAA predicted that the desert southwest would experience mild El Nino weather patterns this winter, but subsequently altered their forecast in November and suggested that El NiŮo conditions were not likely to develop. In many regards, we entomologists arenít much different. We can describe historical population trends for a particular pest as influenced by environmental conditions (see report: Historical Trends in Aphid Abundance in Desert Lettuce), or explain how temperature and humidity influence insect growth and reproduction, but weíre no better in predicting insect outbreaks this spring than the weatherman is in predicting how much itís going to rain next week. Having said that, because insects are poikilothermic, that is they are cold-blooded, most species are not very abundant in the cold weather we often experience during January. But keep in mind; some insect species actually are adapted to cooler temperatures. Examples would be aphids, seedcorn maggot, and to some extent, western flower thrips. Thus, when the daytime temperatures return to the high 60s-low 70s (sorry, canít exactly predict when thatíll occur), you can bet these pests will become active. How abundant these pests ultimately become is difficult to forecast. However, given that weíve had a fairly mild winter, except for the past week or so, one might anticipate that insect survival during December and early-January has been favorable. In fact, Iíve been noticing quite a few whitefly adults on cole crops and lettuce plants, at least more than I remember in the past couple of years. Does that mean they will be heavy on melon and cotton this spring/summer - you would think so, but Iíll wait until May or June to let you know for sure. One thing I am certain of though, based on historical trends and my knowledge of the biology and ecology of desert insect pests, you will experience above average insect pressure at some point this spring on some crops. Thatís my New Yearís Prediction for 2013. Happy New Yearís.


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