Almond growers with significant spider mite pressure in their orchards may want to hold back on that next miticide application to give the beneficial Sixspotted thrips populations an opportunity to build and knock back the mites.
Kris Tollerup, area-wide integrated pest manager with the University of California Cooperative Extension, Kearney Ag Station in Parlier, Calif., says the high pressure some growers are seeing with spider mites can be well-controlled through biological, non-chemical means.
The crux of this approach will be in the comfort level growers and their PCAs have in tolerating some level of leaf injury from the mites as thrips establish themselves and consume the mite populations.
In addressing this approach Tollerup says it is important to survey and monitor orchards for Sixspotted thrips and other beneficial insects before embarking on a pesticide spray program.
“I’m not here as an IPM advisor to tell you that chemicals are not an important tool to your programs because I know they are,” Tollerup recently told an audience of over 200 growers and pest control advisors in Kerman, Calif.
Tollerup’s message was one of trying to convince growers and PCAs that some level of leaf injury could be tolerable, meaning that tree health will not suffer to the point of causing yield loss or permanent tree damage.
“I know that’s easy for me to say because I’m not a grower,” Tollerup told the group. “Still, I think there is some level of pest injury that can be tolerated and still not impact tree health or yields.”
The issue of spider mites is forefront with growers and their PCAs as, generally speaking, areas from Fresno to Kern counties are heavily impacted with Spider mites. Though other areas of the state, including the northern San Joaquin Valley and Sacramento Valley growing regions are generally not as impacted, Tollerup realizes there could be pockets of significant concern for growers in these regions.
Spider mites are often a problem in water-stressed orchards, according to the UC IPM website. Orchards that are properly irrigated usually do not require treatment for mites, with the possible exception of dry-down prior to harvest.
These mites feed on the leaves of trees causing physiological damage that can, in severe cases, lead to defoliation. Tollerup says it is not completely understood at what point tree injury from Spider mites cause a definite loss in yield, but he suspects the threshold is greater than growers think.
“Just how much injury a plant can sustain before yield loss and plant damage occurs is really the $64,000 question,” Tollerup says.
According to the University of California’s IPM website, Sixspotted thrips are a tiny insect less than 1/8 inch long that commonly feed on Spider mites and other mite species. They can rapidly reduce high mite populations but often do not become numerous until after mites have become abundant and damaging.
Tollerup is already seeing a spike in Sixspotted thrip and predator mite populations at an almond trial in the Lost Hills area of Kern County, suggesting that mite populations have risen sufficiently to draw a thrip response.
Natural enemies of the bad pests will generally follow in sync with their prey, Tollerup said.
Tollerup is confident that Sixspotted thrips can address Spider mite populations if not killed by pesticide sprays used in controlling mites and other pests.
Typically the mite problem in almonds centers on Spider mites, he said.
“There are other mite species, but usually the heat will take care of these,” Tollerup continued.
For the most part, Tollerup says Spider mite pressures are generally heaviest and troublesome this year from Fresno through Kern counties and are generally lighter in numbers elsewhere in the state, including the northern Sacramento Valley counties of Tehama, Butte and Glenn.
“That’s not to say some growers might not have a worse problem than others,” he said.
Part of the issue with mites, according to Tollerup, is how they can rob almond trees of next year’s crop by the damage they cause. More research is needed to fully understand these thresholds, he said.