First apple scab spores of the 2020 season detected in Pennsylvania

Growers throughout Pennsylvania are experiencing different stages of bud development. The southern half of the state is in some stage of green-tip, whereas the northern half is in silver-tip. Green-tip on Gala occurred on March 12, 2020, at the Penn State Fruit Research and Extension Center (FREC) in Biglerville, PA. Like clockwork, we detected the first mature apple scab spores shortly thereafter. The number of available scab spores is still very low; there is no need to panic.

March 18 – 20 is the first apple scab infection period of the season where trees have broken dormancy. For management if your trees are currently at green-tip through half-inch green-tip:

• If you applied your dormant copper spray within the last week, your trees are protected.
• If you applied your dormant copper spray more than a week ago, consider covering your trees with mancozeb, preferably a rainfast mancozeb (Manzate Pro-Stick, Roper Rainshield, etc.) at 3 lb/A. Depending on the scab history of the site, tank mix Syllit (1.5 pt/A) with mancozeb. Fungicides that are FRAC 3, 7 or 11 are not necessary at this point; save these for tight cluster through first cover.

For commercial fruit growers, please note: when controlling for disease, weather and tree growth conditions need to be monitored at a local level within one’s own orchard. Before chemical products are applied, be sure to comply by obtaining the current usage regulations and examining the product label. Product information can be easily obtained from CDMS.

Note to readers:

Sorry this Disease Update is a little late, folks. It’s been a crazy week at the Penn State Fruit Research and Extension Center (FREC) as we have been preparing to comply with the pandemic response directives of Penn State University and the Commonwealth of Pennsylvania. Although Penn State University has cancelled all face-to-face meetings because of the COVID-19 pandemic, we are still here to guide you.

Due to the emergency, the Penn State Fruit Research and Extension Center (FREC) is closed to visitors. FREC is still operating and continuing research; all faculty are accessible by phone or email. We have reduced our personnel numbers where teleworking is appropriate to ensure the safety of those who are essential and required to report to keep the farm and field research running.

– Kari A. Peter, associate research professor, tree fruit pathology, Penn State University

Any apple trees showing green tissue need to be protected from apple scab. Photo: Kari Peter