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ARS Home » Pacific West Area » Parlier, California » San Joaquin Valley Agricultural Sciences Center » Commodity Protection and Quality Research » Research » Publications at this Location » Publication #232532
Title: Navel Orangeworm (Amyelois transitella) (Walker) and Obliquebanded Leafroller (Choristoneura rosaceana)(Harris) as Pests of Pistachio

Author
item BENTLEY, WALT - UC
item Siegel, Joel
item HOLTZ, BRENT - UCCE
item DAANE, KENT - UC

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 10/15/2008
Publication Date: 10/30/2008
Citation: Bentley, W., Siegel, J.P., Holtz, B., Daane, K. 2008. Navel Orangeworm (Amyelois transitella) (Walker) and Obliquebanded Leafroller (Choristoneura rosaceana)(Harris) as Pests of Pistachio. Pistachio Production Manual 5th Edition. University of California Agriculture and Natural Resources. Oakland, CA. p. 179-191.

Interpretive Summary: The navel orangeworm moved into California in 1942 and by 1949 was present throughout the state. This moth is the primary pest of pistachios in California and causes direct damage to the kernel. Infestation reduces yield, increases aflatoxin contamination and increases processing costs. Methods used to calculate degree-days in order to optimize insecticide timing are discussed. Development rate is variable and depends on food quality as well as nut variety. This insect survives the winter in unharvested nuts (mummies). In emergence studies conducted between 2003-2008, peak emergence of the spring flight corresponded to the period April 21-May 15. Overall, spring emergence is prolonged and can stretch from February through June. The bulk of this flight lays eggs on mummy nuts but recent studies demonstrated that in the new crop, small pea split nuts and deformed nuts that may be present from late June throughout the summer serve as hosts long before mature nuts are available. Monitoring navel orangeworm should begin by early March in southern counties and by late March in northern counties although these dates may need to be adjusted in warm years. Mummy nuts play a key role in navel orangeworm population dynamics because they both shelter overwintering larvae and serve as a resource when the adults oviposit. Their prevalence is dynamic and decreases throughout the year although they are more numerous in dry winters. Currently, mummmies are blown into the drive rows and destroyed by disking them, but this method has varying success and several problems as well as solutions are discussed. The primary in-season control strategy for navel orangeworm is insecticide application. The advantages of traditional timing and suggested novel spray times in late April and late July are briefly discussed.

Technical Abstract: The navel orangeworm moved into California in 1942 from Mexico and by 1949 was present throughout the state. This moth is the primary pest of pistachios and almonds in California and causes direct damage by feeding on the kernel. Infestation reduces yield, increases aflatoxin contamination, primarily aflatoxin B1, and increases processing costs. Navel orangeworm develops between 55°F and 94°F and methods to calculate degree-days using the UC IPM website in order to optimize insecticide timing are discussed. Development rate is variable and depends on food quality as well as nut variety. There can be an average difference of 40% between development on new crop and old crop nuts and navel orangeworm can develop as fast as 350 DD on new crop pistachios. This pyralid moth overwinters in unharvested nuts (mummies) and its survival is dependent on winter rain; it is unaffected by winter temperatures. In emergence studies conducted in Madera County between 2003-2008 utilizing almost one million field - collected mummies, peak emergence of the spring flight occurred 400-500 DD°F after January 1, corresponding to the period April 21-May 15. Peak emergence will vary in other counties based on degree-day accumulation. Overall, spring emergence is prolonged and stretches from February through June in Madera County, and in Kern County newly laid eggs were observed as early as mid January. The bulk of this first flight lays eggs on mummy nuts but recent studies demonstrated that in the new crop, small pea split and deformed pistachios that may be present from late June throughout the summer serve as hosts long before mature nuts are available. Navel orangeworm development on these nuts may be as much as 50% faster than on mummies and survival is higher in the canopy than on the ground. Monitoring navel orangeworm should begin by early March in southern counties and by late March in northern counties, although these dates may need to be adjusted in warm years because emergence is driven by degree-day accumulation. Mummy nuts play a key role in navel orangeworm population dynamics because they both shelter overwintering larvae and serve as a resource when the adults of the first flight oviposit. Mummy availability decreases throughout the year although they are more numerous following dry winters. Currently, mummies are blown into the drive rows and destroyed by disking them, but this method has varying success. In a study conducted in Madera County, as few as 50% of the mummies were blown from the berm. Several problems contributing to mummies remaining on the berm, as well as solutions to this problem are discussed. It has been long established that navel orangeworm damage increases over time by as much as 1.1% per week, and that early harvest can reduce damage. In 2007 a study was conducted using processor damage data and several factors in addition to harvest date including percent split nuts, percent dark stained nuts, and percent blank nuts were identified that contribute to pistachio damage. The primary in-season control strategy for navel orangeworm is insecticide application. The advantages of traditional timing and suggested novel spray times in late April and late July using the new persistent insecticides are discussed.