A five-year navel orangeworm (NOW) research project funded by USDA-ARS and established last year is already offering key insights to NOW management in almonds, such as efficacy of mating disruption, refining winter sanitation and harvest guidelines, and reinforcing the link between NOW and aflatoxin. The Area-wide Pest Management Project for Navel Orangeworm in Almonds, Walnuts and Pistachios is a comprehensive and truly integrated program that involves personnel with a wide breadth of expertise: USDA-ARS and UC research and Extension personnel, and researchers at Paramount Farming.
• “Raising the Bar” on NOW management
Through the years, the almond industry has been successful in substantially reducing rejects caused by navel orangeworm. This has largely been accomplished by adoption of Almond Board-funded research findings. Most notable are the critical cultural controls of orchard sanitation coupled with early harvest. As a result, industry-wide NOW damage has been reduced from a high of 8.8 percent in 1978 to less than 4 percent in the 1980s, and has been reduced further over the last 10 years to an average of less than 2 percent.
However, a prime justification for USDA support of this five-year effort is current concerns about aflatoxin contamination in shipments to the EU, which is our largest export market. Aflatoxin contamination is highly associated with the navel orangeworm and its damage. Thus the almond industry is currently focused on improved NOW management and reducing the potential for aflatoxin contamination. USDA area-wide projects are geared toward adoption and implementation of promising research findings, and the initial findings from this project are offering avenues and insights for improvement.
• Mating disruption showing promise
For several years, the Almond Board has funded research aimed at developing mating disruption techniques for NOW. Earlier research by USDA Entomologist Chuck Burks and Paramount Farms Entomologist Brad Higbee looked at pheromone formulation and puffer density. This work showed that NOW damage could be reduced with mating disruption.
The current effort is using existing technology – the major component of navel orangeworm pheromone dispensed by “puffers” – across significant acreages in different growing areas. Again, disruption in this area-wide approach spanning significant acreage demonstrates disruption is effective in reducing damage.
One of the large-scale studies is under the direction of Paramount Entomologist Higbee in the southern Central Valley. On one ranch with very thorough tree and ground mummy sanitation, disruption has yielded control comparable to or slightly better than a program of two in-season sprays. This comparison has spanned three seasons and the highest damage recorded across all plots during the three years was 1.5 percent, which was the two-spray insecticide program.
A key to adoption is the economics of mating disruption, which will be evaluated in relation to and in conjunction with current control practices by UC Extension economist Karen Klonsky.
• Winter sanitation and harvest guidelines
Recently, Paramount’s Higbee and Joel Siegel, USDA-ARS, Parlier, have developed a field-oriented spreadsheet model that predicts navel orangeworm damage based on different winter sanitation and harvest timing scenarios. The model serves to illustrate the risks and benefits of different management scenarios, and provides a tool that growers and pest control advisers can use to assess expected results and project the outcome of different options in order to take appropriate action.
The model has been developed initially by extensive data sets from the southern Central Valley and it needs to be validated for the more northern growing regions. UC Davis Entomologist Frank Zalom is leading this validation effort, which is also being funded by the Almond Board.
The model, coupled with field experience and research, demonstrates that the current guideline to clean down to an average threshold of two mummies per tree by Feb. 1, needs to be tailored to growing regions based on the amount of rainfall, which is a dominant orangeworm mortality factor. For instance, in the drier southern region, the model and field experience show the mummy threshold is less than the current standard, while in the Chico area, this threshold could be revised higher.
• Understanding the NOW-aflatoxin link
Another initiative under the USDA Area-wide Project and also Almond Board-funded is led by Themis Michailides, UC plant pathologist, with USDA’s Siegel. Their work demonstrates under field conditions both NOW larvae and adults vector or carry spores of Aspergillus – the fungus that produces aflatoxin – and introduces it into the hulls, shells and kernels.
This field work corroborates recent lab studies led by Jeffrey Palumbo and others at USDA-ARS in Albany that show NOW larvae vector Aspergillus spores, increasing fungal colonization and resulting aflatoxin.
Other ABC-funded research led by May Barenbaum and Guodong Niu, both with the University of Illinois, demonstrates NOW larvae can tolerate high concentrations of aflatoxin, which helps to explain why there is such a strong link between navel orangeworm activity and aflatoxin.
For instance, orangeworm larvae can survive aflatoxin concentrations 100 times higher than doses that kill corn earworm larvae. This work shows NOW has an enzyme that breaks down aflatoxin, making it tolerant and well-adapted as a carrier.
• A multi-crop integrated effort
While the above focuses on almonds, this grant is the first coordinated approach to managing navel orangeworm across the three major California nut crops: almonds, walnuts and pistachios. This coordinated effort is looking at such important issues as movement of NOW among these crops and the implications for damage in each.
Also, in keeping with integrated pest management principles, entomologists Siegel and Zalom are looking at the role and “fit” of newer biorational pesticides, while Kent Daane, UC Extension biological control specialist, is looking at the dynamics of the natural enemy complex and secondary insect pests under mating disruption.