Increasing bitter rot pressures

Two extended wetting events in the past ten days have brought an increase in summer disease pressure, especially bitter rot at our AREC in Winchester: Jul 22-23, wet 13 hr at 72° with 1.3 in. of rain and Jul 28-29, wet 17 hr at 73-63° with 2.25 in. of rain. Be aware that, as a general guideline, two inches of rain will deplete most protective fungicide residues. 

Bitter rot on Idared apple.

Same fruit as above, cut to show the diagnostic cone-shaped progression of the bitter rot fungus into the fruit.

As an indicator of the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours from rainfall or dew. As of Aug 1, accumulated wetting hours (ACW) since May 4 are: at 909 ft elevation, 524 hr (with the 250-hr threshold reached Jun 7; sooty blotch first observed Jul 7); at 932 ft (the AREC NEWA station), 363 hr, threshold reached Jul 5; and at the 983 ft elevation, 302 hr ACW, threshold reached Jul 21.  The significance of the 250-hr threshold is that it predicts the presence of the fungi causing SBFS symptoms on unprotected fruit.

Since July 1, rainfall has been scattered, with a total of 3.66 in. for the NEWA station at Gadino Cellars  in Rappahannock County, VA. Augusta County  Barren Ridge, Fishersville rainfall total was less with 1.98 in. in July, but an additional 1.17 in. on Aug 1. July total rainfall was was generally lighter for Albemarle County ranging from 1.89 in. at Batesville, to 0.57 in. at Carter Mt. 

As of Aug 1, accumulation of wetting hours since Apr 30 at Tyro, 941 ft elevation was 512 hr, with the 250-hr threshold reached on June 12. The NEWA station at Gadino Cellars (elev. 665 ft, in Washington, VA) passed the threshold of 250 ACW June 16, and has now recorded 394 wetting hours since May 1. The NEWA station at Fishersville also passed the 250-hr threshold June 16 and now has 390 ACW. Three Albemarle County NEWA stations have also passed the 250-hr threshold, listed with ACW as of Aug 1 and date the was threshold reached: Batesville (367 ACW, July 2); Crozet (309 ACW, July 5); Carter Mt. (292 ACW, July 6).

Wetting period, hail and trauma blight prediction, and sooty blotch/flyspeck wetting hours

Last night we recorded an apple scab infection period (8 hr wet, mean 67°F).

Last Tuesday afternoon, May 17, scattered hail occurred with 1.6” of rain in some areas of Frederick County. Tracking Maryblyt prediction for this single event with this week's highs in the mid-80s and lows in the mid-60s, indicates that trauma blight symptoms should begin to appear May 25. Typically trauma blight is more common in affected areas that also had some blossom blight from infection during bloom. The plant growth regulator, Apogee, applied at petal fall on king bloom, helps to reduce the amount of shoot tip infection (shoot blight) in these situations.

Since May 8 we now have accumulated 109 hr toward the 250 wetting hour threshold for specific treatment against the sooty blotch and flyspeck fungal complex.