Great Lakes Fruit Workers – Update from the Tortricid Working Group

Ontario was well-represented by OMAFRA staff and several private consultants at the recent Great Lakes Fruit Workers Tortricid Working Group (TWG), held in Ithaca, NY, November 8^th, 2006. The TWG consists primarily of researchers, extension workers and private consultants from Ontario, New York, and Michigan. It was originally established to discuss the management of obliquebanded leafroller (OBLR) in apple, but has since evolved to include other tortricid pests of tree fruit such as oriental fruit moth (OFM) and codling moth (CM).

The multi-state / provincial nature of the working group allows for timely transfer of information on potential issues (resistance, new pests), discussions on pest alternative management strategies (insecticide rotations, models, trapping and monitoring techniques, new products, advances in sprayer application technologies, etc) and potential collaborations between production regions. Pest incidence and population development patterns from each region are also discussed, allowing for a pro-active approach in dealing with potential new pest management problems.

While it is difficult to present all of the information covered at the TWG meeting in a short article, there are a few trends and highlights that are definitely worth sharing.

Research has demonstrated resistance in OBLR populations in some apple growing regions to organophosphate (OP) insecticides, such as Guthion (azinphosmethyl) and Imidan (phosmet), and pyrethroids. Cross-resistance between OP insecticides and insect growth regulators like Confirm (tebufenozide) and Intrepid (methoxyfenozide) has also been documented. While there are other products available for managing OBLR in Ontario, these have short residuals, must be applied when larvae are small, and with consideration of appropriate pH levels (which differ) in the spray solution. Good timing is essential. Some problems associated with management of OBLR by growers in the Great Lakes region may be attributed to inappropriate product use.

Codling moth resistance to OP insecticides is widespread in Michigan and must be addressed in Ontario. Trials conducted by Dr. Larry Gut and Dr. John Wise have detected CM populations in the Northwest, Southwest, West Central and Fruit Ridge production areas that are highly resistant to Guthion. Preliminary trials using topical bioassays were initiated in Ontario this past season, and these should be expanded in 2007. Vigilance in managing potentially resistant CM populations, using existing alternative strategies, is required. It is important to note that lack of control can be attributed to several different factors including poor timing, inadequate coverage, rates, or a reduction in susceptibility (resistance) to insecticides.

Mating disruption for CM has been successfully used by growers in New York, Michigan, and has been demonstrated in Ontario. However, mating disruption does not appear to be a stand-alone strategy for management of this insect pest. Trials in the US have incorporated other products, such as CM granulosis virus and the neonicotinoids Assail (acetamiprid) and Calypso (thiacloprid), to help manage CM populations and keep damage below economic thresholds. Isomate C-Plus Codling Moth Pheromone is registered for use in Canada.

Researchers in the US have developed improved strategies for using CM granulosis virus. The virus is target specific (kills only CM) and breaks down quickly in the environment. It must be ingested by the larva, which is not immediately killed. The virus is quite lethal to CM, however, and the larva only needs to consume a single virus particle. The optimal use of the virus targets eggs just before hatch, so that it is present when the larvae hatch and before they enter the fruit. Research conducted in the US indicates that weekly applications at a low rate are a better approach than high dose sprays applied at wider intervals (low dose, frequent applications); the strategy is intended to ensure an adequate residual during the target pests’ activity period. What is particularly interesting is that the virus appears to be “vertically transmitted” within the population – in other words, it is passed from one generation to the next via infected females. Virosoft is a CM granulovirus product registered for use in Canada; however, the label makes no reference to the aforementioned low dose frequent application nor has this strategy been evaluated in Ontario. Granulosis virus should be used in conjunction with mating disruption for CM or other control measures.

Mating disruption for OFM in tree fruit (apples, tender fruit) is a highly effective pest management strategy, as repeatedly demonstrated in fruit production areas within the Great Lakes region. However, with the exception of apple growers in a few areas, rates of adoption have been limited in Ontario. There are new mechanical application technologies for mating disruption being evaluated by researchers in New York, using modified tractor-mounted spray equipment to apply pheromone-impregnated wax to the canopy. One application per generation appears to provide excellent control. Other pheromone dispensers are also being tested, each with the goal of reducing the application time. It is anticipated that the level of adoption will increase in the Great Lakes region and that mating disruption will become a standard pest management tool for OFM. Insecticides recommended for management of OFM include the neonicotinoids Assail and Calypso, and the insect growth regulator Rimon (novaluron). Assail is already registered in Canada; Calypso and Rimon are in the Canadian regulatory system and will hopefully be available to growers in 2007.