Peter offers latest news about tree fruit disease

SMITHSBURG, Md. — Penn State tree fruit pathologist Dr. Kari Peter shared her ‘nuggets of wisdom’ on the diseases of current concern with a crowd gathered at Barr Orchards for a twilight meeting.
Maryland has a higher instance of newly planted trees, four to five years old, that show fire blight. She instructed getting rid of it to avoid attracting other unsavory things such as beetles and aphids. If not, the infection will continue to spread. To mitigate shoot blight, she suggested using Apogee/Kudos for semi-dwarf and Cueva at two quartrs. per acre for cover sprays.
Noting the cool, wet conditions at that June 7 date, she predicted what will happen when the forecasted hot weather appears, “Bacteria will explode.” Sanitation and scouting is then even more critical.
The primary apple scab infection, typically ending in mid-June, still demands vigilance.
She reminded growers that two inches of rain washes off fungicides. Also, she advised shrinking spray intervals when conditions are favorable if using the alternate row middles technique.
With powdery mildew, since the tight cluster through terminal bud set is the most susceptible time, management should be active then. Considered a dry weather disease, spores germinate easily in high humidity and temperatures that range from 55 to 70 degrees Fahrenheit.
Peter suggested sterol inhibitors in the FRAC group 3, which includes numerous products, as well as Quintec and Vivando, in the FRAC groups 13 and U8 respectively. The latter two are only for stone fruit. Sulfur, too, can be used, but Peter cautioned against using it during hot weather.
Bacterial spot protection should begin at petal fall/shuck split. Peter advised the growers, “Be mindful of warm, humid and, or wet weather.” A rotation of copper and oxytetracyline (Mycoshield, Fireline) should give optimal control during those high disease pressure conditions.
Also, the growers should be careful when spraying copper during slow-drying conditions.
Alternatives for rotation include sulfur, Double Nickel, Regalia and Serenade Optimum. Keep in mind that products can be variety-dependent.
Peaches have been added to the Luna Sensation label, which was previously labeled for apple and cherry production. Also, Luna Experience can be used for all stone fruit crops. Its FRAC groups are 3 (DMI) and 7 (SDHI), which is tebuconazole + fluopyram.
Products for brown rot management for sweet cherry include Captan, sulfur, Ziram, Indar, Fontelis, Luna Sensation, Luna Experience, Merivon and Topsin M. Merivon was particularly useful in dry conditions.
Peter pointed out that Rutgers research showed that Captan cover sprays were enough for brown rot management spore management in peaches and nectarines. She added that single mode of action products such as Indar, Fontelis and Merivon could be saved for the pre-harvest sprays at 18, 9 and 1 days.
For cherry leaf spot management, two post-harvest sprays can include Captan, copper, sulfur, Fontelis, Luna Sensation, Merivon, Indar, Rally, Syllit, Topsin M and Ziram. Peter added that at least two sprays are likely necessary as symptoms are showing up in tart cherries.
Peter’s handout noted that for those who use NEWA (the Network for Environment and Weather Applications at Cornell), scab and fire blight pages have been updated. Plus, the fungicide resistance management tables for apples and peaches have been updated.
NEWA is accessible at newa.cornell.edu.
Peter has expanded the Mid-Atlantic guidelines for managing fungicide resistance for brown rot, apple and peach scab control, and powdery mildew.
She can provide growers with the latest information by contacting her at kap22@psu.edu.