Guthion has been one of the first lines of defenses against Navel Orangeworm (NOW) in pistachios, but it is scheduled to be phased out within the next two seasons, according to the University of California.
NOW is a menace and can destroy tree nuts, but for pistachio growers it also poses a marketing problem because NOW has been implicated in aflatoxin, which can be found in the popular in-shell nuts. This is an important issue to the pistachio industry because export customers for California pistachios have set aflatoxin levels for imported pistachios and there are safety standards in the U.S. as well.
Bob Klein, director of research for the California Pistachio Commission, said the alternatives to Guthion have been difficult to time for effective control.
At the recent California Pistachio Industry annual conference in Monterey, Klein reported that good progress has been made using pheromones in a mating disruption control program is showing progress toward effective control.
One of the problems in disrupting mating with NOW pheromones is that the products available have not been effective, but in a study funded by the commission, a University of Riverside, California entomologist Jocelyn Millar and a USDA/ARS research entomologist L.P.S. Kuenen have discovered a trace element that may make the NOW pheromone more attractive.
They found it by studying a related species, the meal moth, which is reported to cross attract NOW males.
The scientists extracted meal moth pheromone glands and analyzed the extracts using live antennae from both meal moth and NOW males.
These analyses identified a new trace component that produced “strong responses” from meal moths and weaker responses from NOW. This trace compound “may be a critical minor component in the complete pheromone blend of both species.”
The scientists say the compound was missed in previous analyses because it was present in trace amounts; stimulated only weak responses from NOW antennae and its chemical and physical properties are different from other pheromone components.
Analyses are under way to see if this compound enhances the attraction of male NOW to existing pheromone formulations.
Millar and Kuenen say their discovery “may have provided a key breakthrough” in increasing the efficacy of mating disruption.
“From the limited information that we have so far, it appears to be a compound new to science. This the most solid lead that we have obtained in years of attempts to identify the problem with NOW pheromone as an effective attractant for traps,” reported the two scientists.
Botryosphaeria panicle and shoot blight have become the most serious above-ground disease problem of California pistachios. Within 10 years it has become a potential problem in all California pistachio orchards, except those on the West Side of the San Joaquin Valley.
Last spring's wet weather and later thunderstorms exasperated the problem.
There is not much growers can do about the rain, but they can prevent the disease from causing too many problems with effective fungicides.
Klein said growers can also help their cause by using drip irrigation rather than flood irrigation; use the lowest trajectory possible for sprinklers and use run foggers at low pressure.
Keeping weeds down also reduces humidity.
Pruning blighted areas of the orchards and shredding or burning the infected wood also could prevent the spread during a rain or other high moisture situations, he added.
Last season under heavy pressure from latent infections, researchers found three strobilurin fungicides, Abound, Flint and Cabrio and a premix called Pristine were very effective in controlling Botryosphaeria blight. Flint and Abound also provided curative activity, especially in the leaves.
Scala, a pyramidine fungicide, also was effective against the blight.
Scientist cautioned growers about using strobilurins as curatives because they could exacerbate the risk of resistance. There has been one isolate of the disease that has been identified as resistant to Abound, one of the strobilurin fungicides.
The scientists conducting these trials recommend using these fungicides as protectants to reduce the risk of resistance.
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