For purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours from rainfall or dew, starting 10 days after petal fall. As of this morning, June 24, we had accumulated 221 wetting hours toward the 250-hour threshold for specific treatment against the SBFS fungal complex. 

Production areas east of the Blue Ridge exceeded the 250-hr threshold for inclusion of a specific SBFS fungicide in the mix as early as two weeks ago. Another indicator of early summer disease activity was appearance of bitter rot on apple samples delivered last week.

In addition to the usual summer diseases, be alert for possible early indications of Alternaria leaf blotch on Red Delicious and Glomerella leaf spot on Gala, Golden Delicious and Cripps Pink (Pink Lady) apples.

An uncommon apple fruit disease

This week an apple sample from Frederick County Virginia was brought to our laboratory with a problem that is unusual but not unheard of: Phytophthora infection of low-hanging, green fruit. Phytophthora cactorum is a causal organism of collar rot of apple but also infects several other hosts. Note the zoned appearance of symptoms on some fruits, likely a result of the effects of light and dark on its growth pattern. 

It is likely that swimming "zoospores" splashed up from the soil surface with heavy wind-driven rains and caused this infection within the past two weeks. EBDC fungicides, applied in the early cover sprays, should have helped to suppress this occurrence, although the residues would wear off quickly with heavy rains.

Disease update, June 17

Extended wetting occurred June 12-13 with 11 hours wet at 68° and 0.41 in. rain. As of June 17, accumulated wetting hour total from rainfall or dew at our AREC since May 13 is now at 172 hours . Wetting hours have accumulated more rapidly east of the Blue Ridge. As of June 12 Washington, VA, in Rappahannock County had 286 hours of accumulated wetting since May 13. Other areas in central Virginia probably had as much or more during this time.

In areas with heavier disease pressure, watch for early indications of sooty blotch and flyspeck, fruit rots and Alternaria leaf blotch, the fungal disease that causes defoliation and poor fruit quality of Red Delicious apples, and Glomerella leaf spot, which tends to be more common on Gala, Golden Delicious, and Pink Lady. Maintain fungicide protection, as needed, to suppress the disease spectrum common to your orchard blocks.

Extended wetting June 10-11

Extended wetting from early yesterday morning through this morning (June 10-11) occurred as two separate periods of 12 and 16 hours, each at 65°; but with just four hours of drying between them, they might as well be added together, with total rainfall of 1 inch for both events. 

Extended wetting at mild temperatures- a preview of summer diseases?

We had an extended wetting period at our AREC June 6-8: 40 hours wetting with 1.1 inches of rain at 63°. Today's rain has added another 0.4 in. of rain and it may not be finished yet. Those rains combined to remove much of any fungicide residue applied earlier last week, leaving the trees possibly vulnerable to secondary apple scab and Brooks spot infection; also think of these wetting events as initiating early activity by the Alternaria and Glomerella leaf spot fungi. The rains may cause cracking of ripening sweet cherries and will increase the potential for fruit rots:  http://treefruitdisease.blogspot.com/2010/06/cherry-rots.html

For purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours, starting 10 days after petal fall. As of this morning, June 10, we had accumulated 145 wetting hours toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex. Because of an earlier petal fall date and more wetting, some areas east of the Blue Ridge may now be approaching the 250-hr threshold for inclusion of a specific SBFS fungicide in the mix.
 
As of today, June 10, we have had 40 dry weather apple powdery mildew days since spores were first released Apr 11, ranking this year among the higher mildew pressure years. The recent rains will promote continued tree growth and susceptibility to mildew infection. Maintain mildew suppression on susceptible cultivars until shoot growth ceases to prevent the bud infection which leads to overwintering and a recurrent problem next year.

I have received several reports of fire blight showing up, likely from infection that occurred at late bloom: 
http://treefruitdisease.blogspot.com/2013/05/fire-blight-threat-to-late-bloom.html

Disease update- apple scab, mildew and wetting hours

We recorded an apple scab and cedar-apple rust infection period at our AREC June 2-3: 18 hours wetting with 1.1 inches of rain at 74-62°. (Yes, the cedar-apple rust galls are still active).

As of today, June 3, we have had 38 dry weather apple powdery mildew days since spores were first released Apr 11. Today I see a flush of terminal shoot growth that is very susceptible to mildew under this year's heavy infection conditions. On susceptible cultivars, maintain mildew suppression until shoot growth ceases to prevent bud infection, which leads to overwintering and a recurrent problem next year.

For purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours, starting 10 days after petal fall. This year the start of wetting hour accumulation is from May 13. As of this morning, June 3, we had accumulated 86 wetting hours toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex. Last year we reached the 250-hr threshold May 25. Some areas east of the Blue Ridge may now be approaching the 200-hr mark for wetting hour accumulation.