Recent extended wetting periods resulting in potential rot activity

Significant summer disease pressure continues with extended wetting periods occurring Aug 17-18 (16 hr with 0.16 in. of rain at 61°), Aug 21-22 (14 hr with 0.05 in. of rain at 66°) and a serious one for rot activity this week, Aug 28-29 (30 hr with 0.42 in. of rain at 71°).

As of Aug 26 accumulated wetting hours totaled 655, approximately equal to or more than that for seven of the past ten years.

Disease management and pre-harvest sprays in the orchard directly affect postharvest quality and storage rot problems. Maintain intervals of pre-harvest fungicides appropriate to disease pressures and the prevailing weather conditions, but allow flexibility in pre-harvest intervals for your intended fruit market.

Continued summer disease pressure

We are seeing continued summer disease pressure with extended wetting periods last week occurring Aug 5-6 (11 hr with 0.3 in. of rain at 63°), Aug 7-8 (18 hr with 0.34 in. of rain at 74°) and Aug 8-9 (16 hr with 0.12 in. of rain at 73°). Also, the 78 wetting hours last week brings our accumulated wetting hours since May 13 to 549.

So in the first two weeks of August we have had five extended wetting periods, with three of these at relatively warm temperatures (more than 73°), which has given significant pressures for apple rots, and sooty blotch and flyspeck, and possible leaf spot diseases, and certainly for brown rot on ripening peaches. 

Disease management and pre-harvest sprays in the orchard directly affect postharvest quality and storage rot problems. Maintain intervals of pre-harvest fungicides appropriate to disease pressures, the prevailing weather conditions, and the intended fruit market.

 

Our congratulations to Frederick County Virginia grower Cordell Watt, Timber Ridge Fruit Farm, on his selection by American Fruit Grower as 2013 Apple Grower of the Year!
 

Apple and peach disease update

Significant extended wetting periods in the past two weeks occurred July 31- Aug 1 (16 hr with 1.1 in. of rain at 66°) and Aug 3-4 (21 hr with 0.18 in. of rain at 72-60°). As of Aug 5, our accumulated wetting hours since May 13 stood at 471. This is well behind this date last year (729 hr), but comparable to six of the last ten years.

As indicated in our fungicide tests, and from comments coming in from commercial orchards in Frederick County and elsewhere, this weather pattern continues to be favorable for fungal disease development on apples and peaches. Where they were not adequately controlled early, there is scab, mildew and cedar-apple rust; sooty blotch/flyspeck symptoms were readily apparent on non-protected trees in our fungicide test blocks several weeks ago and are now appearing on weaker fungicide treatments.

In the past week I have received several questions and images about leaf spot/leaf blotch symptoms on Golden Delicious. In Frederick County the symptoms appear to be almost entirely related to Golden Delicious necrotic leaf blotch, a physiological problem that can be suppressed by including ziram in the mid-summer cover sprays. But from southern Virginia and North Carolina, I am getting comments and indications that Glomerella leaf spot and the associated bitter rot have been very active on Gala apples as well as on Golden Delicious. We will continue to watch for a repeat of that in Frederick county and surrounding areas.

This year bitter rot, and others, have been associated with fire blight strikes in many areas of Virginia including Frederick County. The shoots and twigs killed by fire blight are quickly colonized by the rot fungi, and fire-blight killed shoots should always be seen as a warning for potential rot problems on apples and pears.

On the positive side, apple fruit size is coming along nicely on well-thinned fruit, and red color is developing early, thanks to the relatively cool nights.

The intermittent rains and wet hours have been near ideal for spread of brown rot spores and incubation on ripening peaches (shown below on Redhaven).



As usual, any type of fruit injury contributes to brown rot problems. This year we are seeing the green June beetle and brown marmorated stink bug injury and fruit cracking as possible factors in brown rot severity.