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Fruit Tree Production and Management

Management of apple diseases in Virginia.

Relevance: Annually, 10 or more fungal diseases impact the $235 million value of Virginia's apple industry. To prevent their deleterious effects on fruit quality, yield, and tree survival, they are typically managed with timely applications of fungicides. Field and laboratory fungicide evaluations are essential to disease management practices in view of the development of resistance to current materials and the potential loss of older, useful materials through withdrawal of registration.

Apple diseases

For example, the sterol-inhibiting (SI) fungicides have been valued for after-infection control of scab, powdery mildew, cedar-apple rust, and quince rust. However, the relative commercial value of the SIs is being compromised by the development of resistance in the scab and powdery mildew fungi in some areas of Virginia. The potential for resistance to multiple fungicide classes by several important diseases, the need for control of numerous diseases, and the variations in annual disease pressure underscore the need for ongoing testing of new materials and novel approaches for economical, environmentally sensitive, disease management. Resistance to fungicides brings shifts in usage patterns and changes in disease prominence. Although disease pressure may vary depending on weather conditions from year to year, since 2005 we have generally seen increased potential losses due to scab and mildew.

Our response: Since 2007, we have explored approximately 25 new products and mixtures for disease-control spectrum, economics, compatibility, and suitability as mixing partners in the commercial spray program. This involved 18 experimental compounds for broad-spectrum fungal disease control and resistance management on apples.

Scab fungus population-monitoring plots involving several at-risk fungicide classes have been established where resistance to the SI fungicides was first found. Testing of scab isolates on agar — conducted by S. C. Marine, a graduate student co-advised by David Schmale, assistant professor of plant pathology, physiology, and weed science — confirmed that isolates from SI-treated trees were less inhibited than those collected from nontreated trees. Under moderate scab pressure, the strobilurin compound trifloxystrobin performed better than myclobutanil for scab control, but the strobilurin class of fungicides is also at risk for developing resistance. We are now testing scab isolates for sensitivity to strobilurins, as well.

Results and expected outcomes: Several combination products and tank mixes show promise for management of SI-resistant scab and mildew and broaden the spectrum of control to other important diseases. Four new package-mix products combine compounds from different chemical classes to help manage most of the array of apple diseases. Some of these have shown outstanding reduction of overwintering mildew inoculum.

Test results also confirm potential for improved control of postharvest rot problems: Some package-mix products applied in the orchard late in the season improve postharvest control of bitter, white, and Alternaria rots, as well as Penicillium blue mold. A recently registered fungicide, applied after harvest, suppresses latent bitter rot and controls blue mold.

High levels of fungicide resistance in apple scab populations indicate that replacement programs must be considered. The potential for resistance by several important diseases to several fungicide classes, the need for economical management of 10 or more diseases, and varying disease pressure from year to year across fruit-growing regions of Virginia underscore the need for ongoing testing of new materials and novel approaches for economical, environmentally sensitive, tree fruit disease management.

Ongoing fungicide evaluations will underpin our apple disease management recommendations and offset development of resistance to current materials and compensate for the potential loss of older, useful materials through withdrawal of registration.

A long-term goal of our resistance-monitoring research, funded by the Virginia Apple Research Program and Virginia Agricultural Council, is to direct it toward methodologies that can more rapidly screen for resistance and more quickly employ the appropriate disease management strategies.

Extension specialists: Keith S. Yoder, Sasha C. Marine, Allen E. Cochran II, William Royston Jr., and Scott W. Kilmer.

Partnering with the Natural Resources Conservation Service to promote the adoption of Integrated Pest Management practices in Virginia fruit orchards.

Relevance: Ongoing regulatory changes following the Environmental Protection Agency’s Food Quality Protection Act of 1996 have necessitated a transition by Virginia’s tree fruit industry from its historical reliance on broad-spectrum insecticides to new tools and tactics that form the basis of a sustainable, integrated approach to insect and mite pest management. The Environmental Quality Incentives Program (EQIP) offered by the USDA’s Natural Resources Conservation Service (NRCS) provides assistance to growers who adopt Integrated Pest Management (IPM) practices, thereby promoting and facilitating their use of these tools.

Our response: A proposal titled “Proposal to Mitigate Resource Concerns in Virginia Tree Fruit Production through Revisions to 595 Component Techniques and Incentive Payment Rates” was submitted to NRCS in 2007. The proposal outlined a two-tier system involving “basic” and “advanced” IPM practices, including the use of reduced-risk and organophosphate-replacement insecticides, increased pest monitoring, the use of pest phenology models and thresholds, and mating disruption.

Incentive payments were based on a rate per acre under contract, with a higher rate for acreage that was managed using advanced practices. Provisions for comprehensive training for growers receiving contracts and in-season visits to their orchards by Virginia Cooperative Extension (VCE) personnel were included in the proposal to ensure correct and complete implementation of required practices over the contract term. The proposal was adopted by NRCS, and a Tree Fruit IPM program has been offered to Virginia growers under the EQIP since 2008.

Results: As of 2011, about 16 separate EQIP contracts have been awarded by NRCS to tree fruit growers in Northern, Central and Southwest Virginia. These contracts ranged in duration from one to three years and have included both the basic and advanced practice programs.

Several growers began with single year basic contracts and were subsequently issued contracts for implementation of advanced practices, including the use of mating disruption. The total value of contracts awarded through 2010 was about $360,000. NRCS has also allocated $20,000 as remuneration for technical services provided by VCE personnel.

The EQIP program has had positive impacts on tree fruit pest management practices in Virginia by increasing the number of acres treated with mating disruption and reduced-risk insecticides and by demonstrating to growers the utility and effectiveness of using decision tools based on pest monitoring and developmental models.

Extension specialist: J. Christopher Bergh