Early season apple disease summary

Apple scab:
Scab ascospores were first trapped with rains March 22.
First primary scab infection period: Mar 28-29 (20 hr at 42-44º mean with 1.62 in. rain);
Scab lesions were observed on Golden Delicious Apr 12.
Primary or secondary scab infection periods:
Apr 13-14 (wet 22 hours at 44º with 0.07 inches of rain); Consider this likely to be an early secondary infection period where lesions were sporulating if 1/2" greentip-tight cluster growth was not protected for the Mar 28-29 infection period. This wetting period was too cold for rust infection.
Apr 25-27 (intermittent wetting approximately 28 hr at 53-63º with 1.3-in. rain total for event).
May 2-3 (11 hr at 72º with 0.4 in. rain).
All overwintering ascospores should be discharged by now, but it is important now to be sure that there are not lesions in the tree which would indicate potential for secondary infection of fruit.

Rusts:
Cedar-apple rust infection periods Apr 25-27 (28 hr at 53-63º with 1.3-in. rain total for event) and May 2-3 (11 hr at 72º with 0.4 in. rain); infection is not yet visible from either of these infection periods. Quince rust infection this year not too likely because most fruit would have become resistant by the time they reached thinning size and warmer wetting periods occurred.
Much cedar-apple rust inoculum remains to be discharged and inoculum may persist late into spring as it did several years ago. Heavy cedar rust infection can reduce return bloom. If the orchard is in a rust-prone location and residual protection is in doubt, it is best to supplement the next application with an SI fungicide for after-infection rust control.

Powdery mildew:
Mildew has been our most active disease this year. Spores were available on infected emerging buds by Mar 30.
Infection pressure has been almost ongoing with 29 dry weather “mildew days” since Mar 30.

Fire Blight:
Earliest bloom open at our AREC on Idareds Apr 5.
Infection events occurred at our AREC Apr 8 and Apr 16 (some local areas may also have had wetting of early bloom Apr 6). Blossom blight symptoms were predicted to start appearing Apr 30 from Apr 8 and May 2 from Apr 16. (Blossom blight symptoms have been reported from Frederick County). Canker blight symptoms were predicted for May 1, and trauma blight symptoms were predicted to appear May 4 from blight due to hail damage Apr 25. Temperatures favored infection with wetting where late bloom was still Apr 30-May 5. Wetting from a spray application is adequate for infection on an otherwise dry day.