Several extended wetting periods at warm temperatures in the past 10 days strongly favored summer disease development: June 14-15, 22 hr wetting at 80-70° with 0.50 in. of rain; June 17-18, 19 hr wetting at 71° with 0.32 in. of rain; June 19-20, 15 hr wetting at 72°with 0.06 in. of rain; June 20-21, 12 hr wetting at 75° with 0.73 in. of rain. Note that all of these were above 70°, indicative of bitter rot and Glomerella leaf spot activity.
For the purpose 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. We are tracking this as we have for the past 21 years using a hygrothermograph located at 952 ft. elevation. The start of wetting hour accumulation was from May 14. At this elevation we reached the 250 total accumulated wetting hour (ACW) action threshold June 13. As of the morning of June 24, ACW at the 952 elevation was 288. We also have electronic recorders at 909 ft and 983 ft elevations. At 909 ft ACW was more rapid with the 250-hr threshold reached June 10 and total ACW at 368 hr. At 983 ft ACW was slower with the 250-hr threshold not reached until June 21; total ACW at 983 ft was 256 as of June 24 hr.
For the central Virginia areas, represented by three weather stations at different elevations at Tyro in Nelson County, we started accumulation May 13. A sensor placed at at 941 ft elevation had already greatly passed the 250-hr ACW threshold June 3 for a total of 335 hr by June 24. By June 24, the ones at higher elevations, 1465 ft and 1165 ft, had not yet reached the 250-hr threshold with only 175 and 183 wetting hours, respectively.
Thursday, June 25, 2015
Tuesday, June 9, 2015
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.
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.
Friday, June 5, 2015
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.
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.
Subscribe to:
Posts (Atom)