With almond prices expected to top $2 a pound this year, maintaining the vigor of every tree in an orchard takes on heightened interest. And while this year's crop still needs protection from navel orangeworm and spider mites, it's not too early to start working on the 2005 crop.
“You need to keep trees strong and healthy this season in case next year there are even better prices,” says Benny Fouche, University of California Cooperative Extension, San Joaquin County.
No single practice guarantees a good return crop but basic principles for keeping trees healthy do apply, says Fouche. “It's a combination of adequate irrigation — not allowing trees to water stress — and keeping spider mites from defoliating trees late into the season.” Fouche points out that spider mites in particular can reduce tree vigor enough to impact current year's foliage and root growth and reduce carbohydrate reserves needed for the following season.
Fouche believes that in some orchards, an early season miticide spray is justified, especially when there is a history of mite outbreaks or where navel orangeworm are likely to be treated with pyrethoid or organophosphate insecticides. “Sometimes an early spray can turn the corner on mite populations and it's enough to hold all year,” he says.
A new miticide recently labeled for almonds, Acramite, fits into an early-season control program for spider mites. Fouche was one of the first university researchers to perform field trials with Acramite in almonds and saw what he describes as “excellent control of Pacific spider mites.” He's especially encouraged to see another product available for almond growers.
“It's always good news to have a new miticide on the market,” says Fouche. “Growers need the diversity. Acramite is a low risk material that is less disruptive to beneficials so it fits well into an Integrated Pest Management program.”
While the principles of IPM suggest no spraying unless scouting indicates a problem is certain, Fouche believes that orchards with a high risk of mite outbreaks often benefit from preventive treatments in May. “Some call that a calendar spray and say it's a waste of money but I have seen it work too many times in almonds and other crops to disregard its ability to work.”
Performance of Acramite in other crops, especially strawberries and stone fruit, leads other university entomologists to anticipate similar successes in almonds. “We had great experiences with Acramite in strawberries for two-spotted spider mite,” says Frank Zalom, entomologist with University of California, Davis. In strawberries, Acramite has shown excellent mite control with little impact on predacious mites.
In late April 2004, Zalom and other UC farm advisors in Kern County initiated a field trial sponsored by the Almond Board of California comparing Acramite and several other miticides. Hot temperatures in April in the Central Valley pushed ahead mite population development in the South Valley so treatments were applied earlier than usual.
Acramite lends itself to tank mixing with hull split sprays earlier in the season, says Curtis Sandberg, product development representative for Crompton/Uniroyal Chemical, makers of Acramite. “Field trails have shown excellent performance coming in early and holding populations through the season.”
Fouche points out that if a grower is on his toes or has a crop advisor closely following beneficial mite levels in an orchard, a late season outbreak is less likely. “Typically we have more success turning around a population as soon as it starts rather than trying to hammer it back.”
Choosing a hull split spray material that is easier on beneficials also can eliminate or lessen the severity of a late season mite outbreak, Fouche says. “Try for the least disruptive worm sprays and use good sanitation so worm problems can be kept to a minimum.”
If the stage is set for mites to defoliate trees, it's often better to pull the trigger and treat. “I don't think it is ever wiser to let pests overrun your trees because of the cost of control and the impact on its vigor. You really shouldn't cut costs and skip a mite spray if it threatens the long term health of the tree,” Fouche concludes.