Powdery Mildew on Apple
At full pink to open cluster stage, the first mildew spray should be applied. Click here for powdery mildew options. At the same time, you can mix in nutrients, such as urea and zinc.
Fire Blight on Apple, Pear
During apple and pear bloom, fire blight infections are a risk when conditions are warm and wet. It is important to watch the fire blight predictions on Utah TRAPs. If the risk level for infection is HIGH or above, you have a 24-hour window in which to apply an antibiotic. Most areas (except much of Utah County, which has resistance) can use streptomycin, while areas that have resistance should use either Kasumin or oxytetracycline. Typically, the spray should be reapplied within 2 to 4 days, depending on the fire blight risk, and the bloom stage.
Codling Moth Mating Disruption on Apple, Pear
Mating disruption dispensers should be hung by full bloom.
If coryneum blight is a problem for you, one of the most important times to apply a fungicide is at or right after the shuck split stage.
This pathogen is spread primarily by rain, and optimal conditions for infection are when temperatures are from 70 to 80°F.
Commercial growers can find options by clicking here.
Peach Twig Borer for Organic Growers
Before shoots have started to elongate, and while larvae are exposed, trees can be treated to help reduce the population. Data out of University of California-Davis showed that one or two bloom-time treatments of the organic option, Bt (Bacillus thuringiensis), is as effective as a dormant oil+insecticide spray. If you already sprayed a dormant oil for PTB, you do not need to apply the Bt spray.
Bt is a bacterium that must be consumed by the insect to be effective. The material only lasts about 3-5 days, which is why a second treatment may need to be applied. Although Bt does not affect pollinators or other beneficials, it should be sprayed at night so as not to disrupt them.
Bt products can be stored for 2-3 years in a cool, dry location. Liquid formulations will not last quite as long. Once the concentrate is mixed with water, it should be used within 12 hours.