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Fall Pest Pressure on Desert Vegetable Crops (November 26, 2014)
It appears that the weather has finally broken, although it is forecasted to be in the 80’s later this week. Nonetheless, it should soon begin to feel like “winter” in the desert. With cooler temperatures, you can expect a steady decline in insect abundance until temperatures begin to warm up again in February. Of course last winter, we had no winter. I don’t expect that again but it is always interesting to look back over this past fall in anticipation of what we might experience this spring. A quick look at both recent and historic data on pest abundance recorded from our research plots here at YAC and from our Area Wide Trap Network
suggests that insect pressure this fall was heavier for some pests and lighter for others. First, whitefly adult numbers on fall melons and produce were quite a bit lower than we’ve seen the past two seasons. Unlike like last fall however, untreated melon plots on the Ag Center did not succumb to whitefly damage and we were actually able to harvest melons. Sticky trap captures of whiteflies near cantaloupe fields from Wellton to Texas Hill, were lower than last fall as well. Similarly, CYSDV incidence at harvest in cantaloupe fields in these areas was very high this fall. For some strange reason, CYSDV incidence was markedly lower in fields in the Wellton area, an area once thought to be ground central for the virus. In all cases, high traps catches were found in melon fields in close proximity to cotton fields, and virus incidence was highest in fields near where spring melons had been grown. On the other hand, beet armyworm, cabbage looper and corn earworm population abundance on untreated lettuce at the Yuma Ag Center this fall was the highest we’ve recorded in 10 years. Populations began infesting plots in early September, and remained steady throughout October and November. Egg deposition and larval development has only recently declined significantly. Our pheromone trap catches ( Area Wide Trap Network) also show that moths were much more active in October and November relative to last year. The warmer temperatures, particularly nighttime temps, are largely responsible for this. In fact based on our AZMET station here at YAC, the average ambient temperatures during October and November were highest we’ve experienced in the past ten years. Finally, Bagrada bug infestations were abundant in untreated broccoli plots at YAC for the 5th consecutive year, but at lower numbers than what we have seen in the past years. As expected, populations appeared in early September, increased at a low rate through September and peaking in early October. Overall, the peak numbers observed were not as high as last year, but were higher than in 2011. However, even with these lower numbers, infestation levels in our untreated broccoli plots this year remained at damaging levels throughout most of October. In contrast, similar to last fall, western flower thrips population numbers have been relatively low. We’ve not yet begun to pick up winged green peach aphids on sticky traps or colonies in untreated lettuce plots. How these aphid and thrips numbers will translate into potential population pressure in the spring is unknown, but you should anticipate their abundance as usual. If we have a wet winter (El Nino) experience suggests that aphids may be quite abundant, where in contrast thrips don’t do well in wet growing conditions. Nonetheless, graphics showing recent trends in Whitefly, CYSDV, Lep Larvae and Bagrada abundance and a weather summary can be found at Pest Abundance on Desert Produce and Melon Cops in 2014.
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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