Could "Green" Approaches for Scab
Reprinted from Southern Tier Produce News; March 2005
The title for this presentation may have raised expectations that will prove impossible to meet. What one envisions as a "green" approach to scab control is probably dependent on prior experiences with apple scab, on the company that one keeps, and to some extent, on one's religion. This presentation will focus on the science of scab control as it relates to measures that can complement or substitute for traditional fungicide programs. I will not attempt to weigh various options based on their acceptability to groups with widely divergent philosophical perspectives.
Scab control with new "biorational" fungicides and nutrient sprays
This approach to scab control requires the least discussion: "biorational," "green" or "soft" fungicides introduced to date are uniformly ineffective for controlling apple scab. I have personally evaluated Serenade, Oxidate and Messenger and found them less effective than sulfur. Other scientists have evaluated some of the other oils and natural products with similar results. These "green" products may be profitable for the manufacturers, but none of those tested to date will improve profitability for apple growers!
Scab-resistant cultivars provide the ultimate solution for low-cost scab control, but they will prove profitable only if they can be marketed. Producers of scab-resistant apples will face several significant problems. First, organic production from the desert areas of Washington State is creating a very low floor for pricing of organic apples. Producers in non-desert regions will have higher costs for organic production because of greater pressure from diseases and insects. Second, many scab-resistant apple cultivars lack the taste and quality characteristics that consumers have come to expect in their apples, so finding an acceptable scab-resistant cultivar for your niche-market consumers may
prove difficult. Finally, scab-resistant cultivars may still require fungicide protection during the summer to prevent sooty blotch, flyspeck and summer fruit rots. If the objective of growing scab-resistant cultivars is to supply an organic market, then all aspects of pest control must be carefully considered before making a large investment in new cultivars.