Good Planting Conditions Keep Desert Pests Moderate

Pest pressures were moderate as planting moved into high gear on fall vegetable crops in the desert region of southern California and southwestern Arizona. With temperatures in late September unseasonably cool, sources report few significant pest problems and good conditions for stand establishment.

“It’s going along pretty well — we haven’t had too much weather outside of a few monsoon rains, but those weren’t enough to put things off,” says Bill Fox, an independent PCA in Yuma, Ariz.

“We’re knocking on wood here, but armyworms and loopers are kind of slow in developing. We get local infestations, but for the entire area it doesn’t seem to be too bad.”

Dan Fox, a PCA for the Dune Co. of Yuma agrees.

“The weather has been great. Worm pressure is down a bit and overall the season seems to be starting out pretty well. Night temperatures have been a bit cooler than usual and worms are taking longer to hatch.”

Yuma Valley independent PCA Jeff Nigh says armyworms and loopers are sporadic, with pressure heavy in some fields, light in others.

“I was looking at some lettuce and all I could find was three percent of the plants with eggs. Then I went to cabbage and it was 300 percent. I had cabbage with multiple stages on each plant, so it can go from light to heavy in one area.”

With temperatures starting to top the usual 100-degree mark Sept. 26 and plants drying down after the monsoons — which in August brought two to three inches of rain to some regions — Nigh says he expects worm pressures will accelerate.

“I’ve just got a funny feeling we’re going to have worms this year.”

Whitefly numbers, which were reported heavy coming off summer cotton and melons in the desert, are beginning to wane, as expected, says Eric Natwick, entomology farm advisor with the UC Cooperative Extension in Imperial County.

“Vegetable crops planted in September, and at least through mid-October, need to be treated at planting with imidacloprid two inches below the seed line. For vegetable plantings after mid-October, if the temperature and whitefly numbers have dropped enough, a grower may escape the whitefly problem and use only foliar insecticide treatments,” Natwick says.

Along with sporadic worm pressures, seedling pests have been more of a problem for some PCAs in the desert.

In the Imperial Valley, independent PCA Rick Klicka says planting and thinning conditions have been good, although striped flea beetles, a common pest during stand establishment, are showing up in larger-than-usual numbers, particularly in his organically-grown fields.

Nigh agrees: “We have them every year, but infestations are heavier this year.”

Natwick says flea beetles are a particular concern in fields that have come out of alfalfa or are adjacent to fields where alfalfa has been terminated. He recommends pyrethroids through sprinklers to control flea beetles in conventional spray programs.

Meanwhile, cabbage loopers and beet armyworms are showing up in some lettuce and cole crop fields, but Natwick says selective insecticides such as Avaunt, Success, Proclaim, and Intrepid are providing good control.

Tomato horned worms are also reported to be a problem in some fields, as the pest moves off purselane and migrates to seedling crops as neighboring fields are being disked for planting.

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