More of the same...

We have had several more extended wetting periods this week, favorable for both scab and cedar-apple rust and early summer disease development: May 23-24, wet 11 hr at 54° with 0.48 in. rain; May 24-25, wet 15 hr at 55° with 0.96 in. rain; . May 25-26 wet more than 9 hr at 56° with 0.56 in. rain.

Apple scab pressure has been significant this year, with five infection periods Mar 27- Apr 7 and enough rainfall to cause weathering of protectant fungicides during that time. Lesions from those infection periods were present to cause secondary infection Apr 22-26 and during later infection periods May 4-6, May 11-13, May 21-22, and the recent ones this week. Combinations of fungicides with protective action and after-infection activity for scab are suggested for control during repeated conditions with 1-2 inches of rainfall followed by extended wetting that favors additional infection.

Cedar-apple rust: Rusts have been active for 8 weeks and cedar rust galls were still active May 25-26. Cedar-apple rust lesions and some quince rust lesions are present from the Apr 24-26 and May 4-6 infection periods and more foliar infection is appearing from the more recent ones. Considering continued cedar gall activity and infection conditions this week, it would still be prudent to include an SI fungicide for after-infection rust control in the next application if there is any doubt about lack of protective residue. The recent wetting will add to the accumulated wetting hour totals for development of sooty blotch and flyspeck which will be updated early next week.

Stone fruits: Continue to protect peaches against peach scab which is also favored by the above conditions described for apple scab. Also, protect ripening cherries against brown rot and Alternaria rot which are favored by these wet conditions during the pre-ripening period.

Cherry rots

Sweet cherries are now ripe, or nearly so. The fruit on the right looks good; the one on the left not so good. Rains such as we had yesterday lead to cracking of ripening fruit and increased susceptibility to rots. The fruit above left is a good example of two common rot fungi- the tan colored sporulation on the right side, characteristic of brown rot and the dark green sporulation of Alternaria rot in the center. The grayish area to the left side is probably a mixture of both of these fungi growing together. A pre-harvest application of a sterol-inhibiting fungicide such as fenbuconazole (Indar) should give excellent control of brown rot but will be weak on Alternaria unless it is supplemented with something with a broader spectrum of activity such as captan. Pristine (a mixture of pyraclostrobin and boscalid) should be excellent for control of both Alternaria and brown rot.

Brown rot pressure is often influenced by warm, rainy weather during the period immediately before harvest. Because cherries are the first stone fruit to ripen, a brown rot problem there may signal a potential inoculum source and problem to follow on adjacent stone fruits which ripen later, including peaches, plums, nectarines and apricots.