Dry weather great for sweet ripening peaches

At our AREC we have recorded only 0.2 inch of rain and no extended wetting periods with rain in the past two weeks. Although it is starting to get pretty dry, this has been a welcome break for ripening peaches, producing sweeter fruit with less brown rot pressure.

Ripening Redhaven peach: Dry and bright sunny weather reduces brown rot pressure in the pre-harvest period

But the blemishes from scab lesions are an indicator of earlier season disease pressures. The incubation period for scab infection to appear can be as long as 6-7 weeks, sometimes leading to the question "Where did this come from?"

Earlier rot activity is showing up as bitter rot and other rots on Honeycrisp apples, and this brings reminders that anything that causes injury such as Japanese beetle, will increase the possibility of rot activity, especially as sugar levels increase.

As of the Monday morning, July 27, accumulated wetting hours (ACW) at the AREC are related to elevation: at 909 ft elevation, 687 hr; at 952 ft elevation, 486  hr; and at the 983 ft elevation 444 hr ACW. 

At Tyro, in Nelson County, total ACW as of Monday morning, July 27, were: at 941 ft elevation, 595 ACW; at 1165 ft, 311 ACW; and at 1465 ft, 354 (with the 250-hr threshold reached July 5). 

Summer disease update

Summer disease pressure continued this past week with several extended wetting events at relatively warm temperatures and some locally heavy rainfall.

At our AREC we recorded three such extended wetting periods with rainfall: July 11, 9 hr wet at 71-66° with 0.28 in. of rain; July 13, 9 hr wet at 70° with 0.13 in. of rain (but as much as 4 inches with flooding locally in the Woodstock area of Shenandoah County); July 14, 11 hr wet at 70° with 0.34 in. of rain; . These frequent infection periods with rain deplete fungicide residue and continue to favor development of rots such bitter rot and white rot, as well as Alternaria and Glomerella leaf spots.

As of the Thursday morning, July 15, accumulated wetting hours (ACW) at the AREC are related to elevation: at 909 ft elevation, 588 hr; at 952 ft elevation, 467 hr; and at the 983 ft elevation 423 hr ACW. Since accumulation of wetting hours began May 14, this represents an increase of 2.2 wetting hours per foot of elevation drop from 983 to 909 ft!

At Tyro, in Nelson County, total ACW as of Thursday morning, July 15, were: at 941 ft elevation, 531 ACW; at 1165 ft, 299 ACW; and at 1465 ft, 345 (with the 250-hr threshold reached July 5). The 250-hr ACW threshold reached at all sensor elevations at Tyro early last week, and this probably true for all orchards in the central Virginia region.

The recent frequent wetting periods also favor development of brown rot on ripening peaches and other stone fruits.

Continued summer disease pressure

Summer disease pressure continued this past week with a pattern of afternoon or evening showers followed by wetting through the night, all at relatively warm temperatures.

At our AREC we recorded five such extended wetting periods with rainfall: July 2, 10 hr wet at 64-73° with 0.16 in. of rain; July 3-4, 15 hr wet at 72-65° with 0.01 in. of rain; July 6, 9 hr wet at 70° with 0.14 in. of rain; July 6-7, 15 hr wet at 68° with 0.04 in. of rain; July 8-9, 15 hr wet at 68° with 0.05 in. of rain (but more than 1 inch in some local areas). These frequent infection periods all favored bitter rot and Glomerella leaf spot development, as well as other rots, and depleted much fungicide residue for sooty blotch and flyspeck control.

Accumulated wetting hours (ACW) at the AREC are related to elevation: at 909 ft elevation, 497 hr; at 952 ft elevation, 390 hr; and at the 983 ft elevation 347 hr ACW. 

At Tyro, in Nelson County, total ACW as of Monday, July 6 were: at 941 ft elevation, 449 ACW; at 1165 ft, 250 ACW; and at 1465 ft, 264 (with the 250-hr threshold reached July 5). Note that the threshold has now been reached at all sensor elevations at Tyro.

The recent frequent wetting periods also favor development of brown rot on ripening peaches.

Sooty blotch and flyspeck and other summer diseases

Early signs of sooty blotch and flyspeck were observed in lower elevation areas at our AREC Monday, June 29. At this elevation (909 ft) we had reached the 250-hour total accumulated wetting hour (ACW) action threshold June 10. At higher elevations, the dates that the 250-hr threshold was reached and ACW totals June 29 were: 952 ft elevation- June 13, 332 hr ACW; 983 ft elevation- June 21, 297 ACW. Note that the threshold had been reached by June 21 at all AREC locations ranging from 909 to 983 ft elevations.

At our AREC we had two more extended wetting periods that favored summer disease development: June 25-26, 14 hr wetting at 72-64° with 0.02 in. of rain; June 26-28, 32 hr wetting at 72-59° with 1.62 in. of rain. This latter volume of rainfall would have depleted most fungicide residue available for sooty blotch, flyspeck and rot control.

At Tyro in Nelson County, a sensor placed at at 941 ft elevation had already recorded the 250-hr ACW threshold by June 3 for a total of 384 hr by June 29. By June 29, the ones at higher elevations, 1465 ft and 1165 ft, had not yet reached the 250-hr threshold with only 216 and 212 wetting hours, respectively.