Early summer disease activity

For purposes of predicting the 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. This year our petal fall date at Winchester was Apr 24, so the start of wetting hour accumulation was from May 4. As of Monday morning June 5, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 241 hr; at 932 ft (the AREC NEWA station), 180 hr; and at the 983 ft elevation, 143 hr ACW. In the past week most of the wetting hour accumulation was from dew and occurred more at lower elevations in the orchard. Note that at the lowest elevation, the ACW of 241 hr will probably reach the threshold level of 250 ACW this week.

For Nelson County in central Virginia the petal fall date was Apr 20, and accumulation of wetting hours from Apr 30 is recorded by three weather stations at different elevations at Tyro. Wetting hour accumulation in central Virginia was slow last week. As of June 5, a sensor placed at 1465 ft. elevation had accumulated only 76 wetting hours from Apr 30, while the one at 1165 ft. had accumulated 151 wetting hours, and the one placed at 941 ft elevation had accumulated 199 hr.

The NEWA station at Gadino Cellars (elev. 665 ft, in Washington, VA) will probably also reach the threshold level of 250 ACW this week, having recorded 238 wetting hours since May 1.

We have had several reports of other early summer disease activity: bitter rot mummies forming on fire-blighted shoots and early Glomerella leaf spot symptoms in central Virginia and Alternaria leaf blotch on Red Delicious in Rockingham County.

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.

Extended wetting for scab and summer diseases

An extended wetting period last week, still in progress at the time of the last post June 5, ended at 14 hr wetting at 60°with 0.04 in. of rain. 

For purposes of predicting the 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. This year we have chosen May 4 as our petal fall start date for Winchester, and the start of wetting hour accumulation is from May 14. Last week we also had two nights with wetting from dew, totaling 18 hr. With a total of 96 wetting hours last week, our total accumulated wetting hours (ACW) came to 195 hours as of Monday, June 8. The threshold for specific treatment against the SBFS fungal complex is 250 wetting hours. 

A note to those farther south and east of the Blue Ridge: Your petal fall date may have been a week or more ahead of ours and I have updated the start date for accumulation of wetting hours by weather stations at Tyro, VA to May 3. One of the purposes of having three weather stations at this location is to compare wetting hour accumulation at different elevations. As of June 8, a sensor placed at at 941 ft elevation had already greatly passed the 250-hr ACW threshold for a total of 315 hr while the ones at higher elevations, 1465 ft and 1165 ft, had nearly identical ACW of 144 and 140 wetting hours, respectively. 

Alternaria leaf blotch, confirmed on Red Delicious leaves from Rockingham County May 21, continued to advance, as expected, with the extended wetting last week.

Fruit scab still a serious concern with extended wetting this week

After wetting periods of 16 hr May 30-31(0.13 in. rain) and 20 hr June 1-2 (1.2 in. rain), we have recorded almost continuous wetting 47 of 56 hours since 10 PM June 2. (It is still wet at the time of this post).

As fruits enlarge, they become more resistant to scab than the youngest leaves, so that at five weeks after petal fall, they require about double the length of wetting period at a given temperature than growing shoot tip leaves. But the several extended wetting periods the past week have easily surpassed the requirement for fruit infection. It is important to maintain protective residue now, to prevent fruit scab infection as well as early sooty blotch/flyspeck SBFS development.

Lower elevation orchards in central Virginia have passed the 250-hr accumulated wetting for SBFS. Also, we have confirmed Alternaria leaf blotch symptoms on Red Delicious leaves in Rockingham County.

Spring and summer disease update

In the past five days we have had two more apple scab and cedar-apple rust infection periods at our AREC June 4-5: 23 hours wetting at 73-60°, and June 8-9 at 74-66°. Note that cedar rust galls are still actively producing spores.

In addition to developing activity by the usual summer diseases, with the recent warmer wetting periods, 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. This is also a critical time for protection against Brooks fruit spot.

For purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours (CWH) from rainfall or dew, starting 10 days after petal fall. As of this morning, June 8, we had accumulated 80 wetting hours toward the 250-hour threshold for specific treatment against the SBFS fungal complex. 

At Tyro, VA we selected May 11 as the start date for accumulation of wetting hours by weather stations at Tyro, VA. As of June 5, a sensor placed in an apple tree at 1165 ft. elevation had accumulated 62 wetting hours from May 11, while one placed at 941 ft elevation had accumulated 128 hr. It is interesting that the station at the highest elevation (1465 ft) registered more wetting hours than the intermediate one, 81 CWH.

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.

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

Extended wetting August 5-6.

Extended wetting occurred Aug 5-6 with 13 hours wet at 73° and 0.41 in. rain. Accumulated wetting hour total from rainfall or dew since Apr 18 is now at 729 hours, 277 hours ahead the total for this time last year. This is the third highest wetting hour total for this time of the year since 1994. At our AREC, total rainfall for last week was 2.86 inches.

Watch for increased disease pressure from sooty blotch and flyspeck, fruit rots and Alternaria leaf blotch, the fungal disease that causes defoliation and poor fruit quality of Red Delicious apples.

Extended wetting May 24-25

Last night's extended wetting came to 15 hours with 60-70° temperatures and 0.06 in. rain. This wetting favored scab and all summer diseases on apples and brown rot on ripening cherries and other stone fruits.

Infection period May 23-24

Last night's wetting (12 hr at 63° with 0.04 in. rain) qualified as a scab infection period. 

This wetting brought the accumulated wetting hours since Apr 18 to 234 hours. In the next couple days it is likely that we will reach the 250 wetting hour threshold for specific treatment against the sooty blotch/flyspeck fungal complex. This would be the second earliest week for reaching this predictive threshold since we began recording this in 1994. Only 2003 was earlier. This signals early summer disease pressure from the sooty blotch/flyspeck fungal complex as well as other "summer diseases" and Alternaria leaf blotch.

As expected, there are early indications of heavy brown rot pressure on ripening cherries.

Outlook for next week

This year is starting out reminiscent of last year when we caught some apple scab spores and then had an infection period several days later.  A protectant spray of copper, mancozeb, or ziram before that first infection period and later protectants would have greatly diminished the threat of scab through much of April, but a delayed application after the first infection period required something with some after-infection control to prevent the appearance of lesions and re-infection two weeks later.

A chance of showers from tomorrow evening (Sunday, Mar 20) through Monday evening at temperatures in the mid-40s and warmer could again lead to early infection, assuming that most blocks in the Frederick County are not yet covered with a fungicide. In case there is an infection period, remember that follow-up sprays of copper or an EBDC fungicide alone do not have after-infection control. We have found that Vangard can be tank-mixed with copper or mancozeb to improve after-infection control in these early season situations.

We have applied oil to most of our fungicide test blocks in anticipation of increased mite populations later in the season if we need to step up controls for Brown Marmorated Stink Bug (BMSB). Remember to leave 7-14 days between an oil spray and sprays of captan or sulfur. We did not apply oil to the Red Delicious fungicide blocks to see if increased mite populations will aggravate the Alternaria Leaf Blotch that causes defoliation of Red Delicious, that has been observed for several years and might reappear this year.