Now that the temperatures have finally cooled down, it is beginning to feel like
“winter” in the desert. With the cooler temperatures, we’ve seen a steady decline
in insect abundance. However, if temperatures pick back up, we would anticipate
an increase in insect pressure. Remember: insects are poikilothermic (cold blooded).
With that, 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 YAC research plots and the (
Area Wide Trap Network) suggests that insect pressure this fall was much
lower for most pests compared to last fall. First, whitefly adult numbers collected
from our Areawide traps were considerably lower than last year. Furthermore, sticky
trap captures of whiteflies placed adjacent to cantaloupe fields from Wellton to
Texas Hill, were the lowest we’ve seen since 2008. CYSDV incidence estimated at
harvest in cantaloupe fields in these areas was significantly lower than we’ve seen
on fall crops in several years. Surprisingly virus incidence was also markedly lower
in fields in Wellton and Roll; growing areas that have typically had high rates
of virus infection. We’re not sure why our virus and whitefly pressure was so much
lighter this year but may be related to the decrease in cotton acreage last summer.
Similarly, Lepidopterous larvae (beet armyworm, cabbage looper and corn earworm)
population abundance on untreated lettuce at the Yuma Ag Center this fall was the
lowest we’ve recorded in 4 years. Populations began infesting plots in early September,
and remained steady throughout early October, but began to drop significantly in
late-October and through November. Our pheromone trap catches (
Area Wide Trap Network) also show that moths were much less active in October
and November relative to last year. The cooler temperatures, particularly nighttime
temps, are likely responsible for this. Based on our AZMET weather station here
at YAC, the average ambient temperatures this fall in November was, on average,
5° lower than November last year. Finally, Bagrada bug infestations sampled from
untreated broccoli plots at YAC were the lowest we’ve observed since the invasive
stink bug first showed up in 2010. As expected, populations appeared in mid- September,
but never increased to the high numbers we have typically seen during October. Since
mid-October, adults have been difficult to find in broccoli and cabbage plantings
here at YAC. Western flower thrips population numbers have been relatively high
in some areas, but have dropped recently with the cooler weather. We’ve picked up
winged green peach aphids on sticky traps, and can find an occasional colony untreated
plots. How these aphids 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 Crops in 2015.
I feel kind of POIKILOTHERMIC today...
