LBAM likes high humidity and cool summers, Varela says. The pest has been tracked from Los Angeles to Hillsburg in Sonoma County and inwards into the Valley, around Mantica. It has been found primarily in coastal ranges, with the highest infestations in San Francisco and Santa Cruz. “We can argue that the coastal climate of high humidity and cool summers is the preferred climate or that that is where the infestation started,” she says. “My opinion is that populations are so high probably because it did enter there, but also because it is a high altitude and a preferred climate — very foggy and cold.”
The same integrated pest management methods that New Zealand growers are using to combat LBAM are also being used in the U.S., according to Varela. These IPM tactics include mating disruption, reduced risk insecticides including diamides and many new chemistries, insect growth regulators, Bacillus thuringiensis (Bt), and native parasitoids.
“With a strategic commitment to biological control within an IPM contest, California may ultimately achieve the same levels of light brown apple moth control as obtained in New Zealand,” she says. “Many fruit crops in California already receive control measures for native and introduced leafrollers, and these tactics may prove to be effective for light brown apple moth without a great deal of modification.”
In New Zealand, implementation of IPM programs in the mid- to late 1990s practically eliminated the use of broad-spectrum organophosphate insecticides, enhancing natural control. Varela says the combination of introducing parasitoids that attack LBAM and switching to reduced risk pesticides caused LBAM populations to dramatically decrease.
“If the New Zealand experience is any indication, adequate control of this leafroller can be achieved more effectively through a vigorous program of biological control and the use of selective insecticides for other pest species. That approach identified a need to introduce natural enemies to attack light brown apple moth through all stages of development. The focus on introductions to address parasitism gaps, especially those targeting the late larval and pupal stages, proved to be highly effective.”
Nick Mills, a biological controls professor at the University of California-Berkeley, is studying parasitoids that are native to California and the impact of those parasitoids on attacking LBAM, Varela says. Mills has trial plots in San Francisco and Santa Cruz, and has found at least 13 species are attacking LBAM, with three very important species.
“He is seeing a higher impact in San Francisco; on average he can get 50% control in San Francisco and 20% in Santa Cruz,” Varela says. “He is also studying parasitoids native to Australia, which is a long process because he needs to make sure that these parasitoids, if brought to the U.S., would not affect the fauna of California. All of these studies have to be done before that occurs.”
Mills’ studies began in 2007 and after three years of research, it is clear that it could take many more years to find an important species that is safe to introduce into the U.S. for control of LBAM, Varela says.