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Weeds, diseases bigger threats this year

The pistachio bloom this spring in his clients’ orchards has been good, says consultant Bob Gaddie, Bakersfield, Calif., “But, with the variable weather we’ve been having, the big question is: How good has the pollination been? We won’t know that until next month.

His company, Robert L. Gaddie Crop Production Consultant, serves growers in Kern and southern Tulare counties.

For now, he’s been working with growers to manage higher weed pressure due to above average rainfall during the dormant period.

This follows a post-harvest application of paraquat plus oxyfluorfen last fall. With the El Niño pattern this year, his growers treated orchards with preemergence herbicides in January. Various combinations of pendimethalin, rimsulfuron, oxyfluorfen plus a contact herbicide were aimed at stopping fleabane, the main threat, as well as chickweed, cheeseweed, and foxtail.

Next will be contact herbicides where fleabane escaped the pre-emergent application, and in others to kill white horsenettle, which is not controlled well by preemergence herbicides, Gaddie says. In late May and again in late June or early July, growers will spray glyphosate in blocks where johnsongrass is a problem. This treatment will also be used in a few weeks for nutsedge, bermudagrass and barnyardgrass.

This year’s wet weather has also raised the threat level for fungal diseases, he says. This is the first time in four or five years that he’s had to treat newly leafed-out trees for botrytis, which is usually not a concern in dry years.

Alternaria could be a bigger challenge. “It can be worse in a wet year, but we’ve also been having more problems with it in some orchards during dry seasons,” Gaddie says. “It depends on the particular orchards; some seem to have more alternaria than others, and I don’t know why. If the weather stays humid, we’ll spray for it later this month, but if it becomes dry and warm, we may not.”

Gaddie is also keeping his eye on botryosphaeria. “Our growers don’t have much history of it in their orchards, but with the wet conditions this year, it could be a problem. We’ll decide in a week or two if we need to spray for it. If we do, I will recommend a fungicide that is active against both alternaria and botrysophaeria.”

TAGS: Management
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