Early lygus migration deemed light, adjacent host crops likely sources

When the weather has been as wet as it has this spring, California Central Valley farmers look to the foothills’ heavy vegetative growth as a possible source for lygus to move into the San Joaquin cotton crop

However, University of California area wide IPM specialist does not expect lygus to be a widespread early problem except for fields bordering weedy areas near creeks, sloughs and river by-passes. As in most years, it’s the host sources in close proximity to cotton that could create problems for the San Joaquin Valley’s cotton growers, according to Goodell.

However, Goodell says his survey show, lygus populations in the foothills are surprisingly low this spring as were weed hosts.

“Based on the rainfall we had, I expected to see a lot higher populations in the foothills, but it’s not there,” Goodell says. “We had a lot of tar weed last year which is an excellent host for lygus, and I would have thought with that seed bank out there we would have seen a lot more host material this year. For whatever reason, it’s not there. Overall, the temperatures were cool in early spring so the lygus populations are not too advanced. Then it warmed up quickly and the weeds died back. I don’t think we’re going to have a huge widespread problem moving out of the foothills into Valley crops.”

In spite of that good news, Goodell cautions growers to remain vigilant for lygus infestations that could threaten July fruiting positions. “Early lygus populations in the foothills are not a good predictor of what might show up in localized fields in July,” he says. “I think growers need to keep an eye out for potential infestations, particularly if their fields are situated adjacent to host crops such as safflower, alfalfa and along sloughs, canals and waterways where the native vegetation will likely remain greener much longer this season.”

Potential lygus infestations stem from either external valley sources or internal sources, according to Goodell. While external sources such as the foothills can be a fairly good indicator of early pressure, it’s the internal sources that often create problems in mid-season. Fortunately, they are somewhat predictable.

“Predicting mid-season lygus is more of a matter of looking at what’s upwind from you,” Goodell says. “Regular, twice-a-week scouting is the best defense against getting caught by surprise.”

The sweep net in conjunction with square/fruit retention data is still the standard for monitoring lygus in mid-season, according to UC specialists. Most PCAs utilize this method and make treatment decisions accordingly. Sweeping should start coinciding with first square and continue twice weekly until Acala reaches five NAWF (nodes above white flower) and Pima reaches 3.5 NAWF.

“If the field is close to safflower, harvested alfalfa, weeds that are dying down or other lygus hosts, just be aware that counts can rise quickly in cotton due to migration,” Goodell says.

Calculating square retention can help determine whether or not to pull the trigger on a foliar application. Higher retention levels may warrant a short “wait-and-see” approach even if lygus sweeps indicate higher than threshold levels. Threshold levels at early squaring are generally considered to be 2-4 lygus per 50 sweeps, 7-10 lygus at bloom, and more than 10 lygus at late bloom.

Pima vs. Acala

“We don’t have a good data set on differences between Pima and Acala when it comes to lygus thresholds,” Goodell says. “The university simply hasn’t had access to the same resources to study Pima as it has Acala.”

While Acala has driven the research dollars for many years, that could change as Pima acreage increases. In the meantime, sweep counts and Acala thresholds are probably the best bet for making treatment decisions, according to Goodell.

“I don’t think too many people are using retained squares to make a judgment in Pima,” he says. One theory is that that Pima has more fruiting points, albeit smaller bolls, so it is able to compensate better for lygus damage. That could be. We’re not sure right now. I think anyone who is applying Acala thresholds to Pima is certainly erring on the conservative side.”

Lygus management strategies run the gamut from “wait and see” to preemptive control measures. While the former approach is tempting in what appears to be shaping up to be a potentially light year, it may not be the best approach for all growers.

“If you’re in an area where you know you will likely have problems with lygus, I still think Temik at sidedress is the best defense,” says Vern Crawford, Pest Control Advisor with Wilbur-Ellis in Shafter, Calif.. “It takes care of lygus. It doesn’t affect your beneficials and it doesn’t create problems with secondary pests. I’ve always said that it is the perfect foundation for an IPM program.”

This year Crawford is timing sidedress Temik applications at pinhead square to activate the product with the first irrigation.

“That was my original strategy that I changed somewhat in the mid-90s when aphids became a problem,” he says. “That’s when I started delaying the sidedress application. However, we have good aphid materials now such as the neonicitinoids to handle aphids so I’m going back to the early sidedress application of Temik.”

As production costs continue to rise and margins continue to shrink, growers are reevaluating all expenses and scrutinizing their return on investment more closely than ever. Ultimately, it comes down to specific situations and trying to evaluate the risks and rewards.

“The best payback for these applications has probably been in areas where the timing and duration of lygus populations were well-suited to the time when growers can successfully do a sidedress application and then follow it up with an irrigation to move the material into the roots and plant tissue,” says Bob Hutmacher, UC Cotton Extension Specialist at the Shafter Research and Extension Station. “I believe that Temik at sidedress application timing still has a fit in cotton production based on current prices and the levels of pest pressure that occur sometimes in the remaining cotton production areas of the San Joaquin Valley. Pressure from pests such as lygus in some areas can be prolonged, and we have field trial information where Temik at sidedress timing has reliably improved yields in amounts more than enough to cover application and material costs.”

Leaving uncut alfalfa strips in June, July and August can also greatly reduce migration into nearby cotton fields. As always, vigilance is the key. Even though cotton got off to a late start in the San Joaquin Valley, it was a uniform and vigorous start which should work in growers’ favor.

“Just make sure you watch the crop and not the calendar,” Goodell says. “Cotton may have been delayed, but so was everything else.”

He also cautions growers to be realistic about how much their plants can really compensate for in a short season.

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