Wednesday, June 30, 2010

Wetting hours for sooty blotch and flyspeck

Above is a wild blackberry cane with sooty blotch and flyspeck colonies-a common inoculum source for primary infection of apple fruit. Accumulated wetting hours (starting April 29, 10 days after petal fall, Apr 19), as of June 28: Winchester AREC, 252 hr. Accumulation of wetting hours has been slow the past week, but we have just reached the 250-hr threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit. We have had no extended wetting periods since June 15. Washington, VA in Rappahannock county has had more wetting hours, with a total of 338 as of June 28. Hit-or-miss evening showers likely led to some of the difference in accumulated hours and would also make a difference in areas of Frederick county that received evening wetting in the past two weeks.

Tuesday, June 22, 2010

Sooty blotch / flyspeck wetting hour threshold

As of yesterday morning, June 21, we had 247 accumulated wetting hours (starting April 29, 10 days after petal fall, Apr 19). This is very near the 250-hour threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit.

Wednesday, June 16, 2010

Infection period for scab and summer diseases

June 14-15: Wet 12 hr at mean 73º- favorable for warm weather summer diseases such as bitter rot.

Monday, June 14, 2010

Wetting hours for summer diseases

Accumulated wetting hours (starting April 29, 10 days after petal fall, Apr 19): 218 hr. The wetting hour threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit is 250 hr. It is expected that we will reach that threshold in the next week. Update: Rappahannock county (Washington, VA) has surpassed the 250-hr threshold, with 282 wetting hours as of June 16.

June 9: Apple scab infection period; wet 11 hr at mean 61º.

This is a reminder of the breakfast meeting at our AREC Thursday, June 17 at 7 AM. The main purpose of this meeting is to further assess weather-related crop losses to tree fruit in our counties and the submission of a crop damage assessment to the state government. Bill Whittle will lead this assessment at the meeting on Thursday, with the intention of collecting updated information on crop damage that may be used to trigger some remedial actions at the state level. We encourage you to provide feedback regarding your crop loss situation. In addition to addressing this topic, Plant Pathology and Entomology updates will be given during breakfast.

Monday, June 7, 2010

Mildew days and wetting hours

As an indicator of relative annual mildew pressure, we note the number of days above 53º without rain as potential "mildew days". From March 30, when powdery mildew spores were first were available on infected emerging buds, until June 1, we had 45 mildew days this year. Since 1993, the number of such days from tight cluster to six weeks after petal fall (about third cover) has ranged from 24 (in '96 and '03) to 49 in '99. This year ranks as the second most frequent mildew weather in 18 years.

Accumulated wetting hours (starting April 29, 10 days after petal fall, Apr 19) now stand at 185 hr. The wetting hour threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit is 250 hr. Rappahannock county (Washington, VA) has logged 237 wetting hours, also as of June 7, using the Apr 19 petal fall and Apr 29 start accumulation date. Rappahannock's total will be updated every two weeks.

Friday, June 4, 2010

Cherry rots


Sweet cherries are now ripe, or nearly so. The fruit on the right looks good; the one on the left not so good. Rains such as we had yesterday lead to cracking of ripening fruit and increased susceptibility to rots. The fruit above left is a good example of two common rot fungi- the tan colored sporulation on the right side, characteristic of brown rot and the dark green sporulation of Alternaria rot in the center. The grayish area to the left side is probably a mixture of both of these fungi growing together. A pre-harvest application of a sterol-inhibiting fungicide such as fenbuconazole (Indar) should give excellent control of brown rot but will be weak on Alternaria unless it is supplemented with something with a broader spectrum of activity such as captan. Pristine (a mixture of pyraclostrobin and boscalid) should be excellent for control of both Alternaria and brown rot.

Brown rot pressure is often influenced by warm, rainy weather during the period immediately before harvest. Because cherries are the first stone fruit to ripen, a brown rot problem there may signal a potential inoculum source and problem to follow on adjacent stone fruits which ripen later, including peaches, plums, nectarines and apricots.

Tuesday, June 1, 2010

Summer disease outlook

Accumulated wetting hours (starting April 29, 10 days after petal fall, Apr 19): 165 hr. The threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit is 250 hr. As of May 25 a hygrothermograph in Rappahannock county (Washington, VA) had logged 163 wetting hours, also using the Apr 19 petal fall and Apr 29 start accumulation date.

For practical purposes, cedar-apple rust galls near our AREC have completed their sporulation for this year. Rust lesions are still showing up on apple leaves that were not protected two weeks ago.