Summary of early season fungal disease activity on apple and peach at Winchester.

Apple scab ascospores were first trapped Mar 10. Scab infection periods occurred on Mar 26-27: wet 15 hr at 46-60°, 0.23 in. rain. (also rust infection); Mar 27-28: wet 23 hr at 53-62°, 0.36 in. rain. (also rust infection); Mar 31-Apr 1: wet 23 hr at 41-48° with 0.95 in rain; Apr 3-4: wet 15 hr at 52-63° with 0.03 in rain. (also rust infection); Apr 6-7: wet 14 hr at 50-55° with 0.53 in rain. (also rust infection).

Apple scab pressure has been significant, with five infection periods in the past three weeks. Lesions from the March infection periods will be expected to appear in the next week and conidia will then be produced for heavy secondary infection. These five infection periods from Mar 26 to Apr 7 came with enough total rainfall to challenge weathering capabilities of protective fungicides.

Cedar-apple rust and quince rust have been active for about two weeks. Pink to petal fall is the peak time for susceptibility to quince rust. We suggest EBDC fungicides as routine protectants for rusts and scab, but always include an SI fungicide (Rally, Rhyme, Inspire Super, Indar) for after-infection rust control if there is any doubt about lack of protective residue.

Apple powdery mildew conidia were available Mar 27. The image of mildew below illustrates heavy sporulation of a primary infection source of inoculum. Any mild “dry weather “ day above 53° is suitable for mildew infection. From Mar 27 to Apr 14 we have had at least nine mildew infection days.

Primary powdery mildew infection on Ginger Gold apple.
Note heavy sporulation on Apr 14, 2017.

Early peach leaf curl symptoms were observed at our AREC Apr 14 (below). This infection occurs with extended wetting soon after bud swell. In our test plots, a protective fungicide applied Feb 28 gave excellent control, but the same fungicide applied Mar 9 was less effective.

Leaf curl symptoms on Redhaven peach Apr 14, 2017.

Peach scab overwinters in lesions on peach shoots (below). Lesions are now producing spores, and it is important to maintain a protective fungicide residue to prevent infection during extended wetting periods over the next 4-6 weeks. Infection can require as much as 7 weeks to appear on fruit.

Peach scab lesion on a Redhaven twig Apr 14,2017.
Close proximity to the young fruit makes it a challenge to protect against infection.