Tree Fruit Pathology: 2009 Disease Development Notes

Summer | Late Spring | Early Season

Summer (June-September)

Sept. 23-24: Wet 14 hr split wetting at 70º with 0.11" of rain.

Sept. 21: Accumulated wetting hours since May 8: 927.

Sept. 16-18: Wet 33 hr split wetting at 60º with 0.26" of rain.

Sept. 14: Accumulated wetting hours since May 8: 884.

Sept. 7: Accumulated wetting hours since May 8: 866.

Aug. 31: Accumulated wetting hours since May 8: 808. This is the highest accumulated wetting hour total since 2003 and the 3rd highest total in 16 years.

Aug. 24: Accumulated wetting hours since May 8: 768.

Aug. 21-23: Wet 28 hr split wetting at 70º with 0.59" of rain.

Aug. 18-19: Wet 11 hr at 76º with 0.03" of rain.

Aug. 17: Accumulated wetting hours since May 8: 714. As should be expected for a "wet year", fruit rot pressure is generally high on early maturing apple cultivars.

Aug. 12-13: Wet 15 hr at 66º with 0.19" of rain.

Aug. 10: Accumulated wetting hours since May 8: 664. Golden Delicious leaf blotch, a physiological condition related to alternating wet-dry conditions and causing defoliation of the older leaves on shoots, has become prominent in the past week or two. Trees treated with ziram will be less affected by this problem, but note that ziram has a 14-day pre-harvest interval.

Aug. 5-6: Wet 12 hr at 69º with 0.36" of rain.

Aug. 3: Accumulated wetting hours since May 8: 634. (78 hr in past week).

Aug. 2: Wet 12 hr at 71º with 0.28" of rain.

July 29: Wet 14 hr at 73º with 0.17" of rain.

July 26-27: Wet 16 hr at 68º with 0.55" of rain. Some hail injury occurred at our AREC on July 26, resulting in some cuts and dents that are now showing as reddish spots. Also, strong winds did some damage in some of our younger blocks of trees. Accumulated wetting hours since May 8: 556. (96 hr in past week).

July 25-26: Wet 17 hr at 69º with 0.38" of rain.

July 24-25: Wet 14 hr at 66º with 0.01" of rain.

July 23-24: Wet 12 hr at 68º with 0.04" of rain.

July 22-23: Wet 20 hr at 73º with 0.06" of rain. The 10-day outlook indicates a pattern of scattered storms with the possibility of frequent overnight wetting and erosion of fungicide residues. Sooty blotch and flyspeck are common on non-protected apples. Where present, fire blight-killed shoots should be viewed as a potential fruit rot inoculum source. Brown rot is common on non-protected ripening peaches.

July 20-21: Wet 15 hr at 63º with 0.5" of rain.

July 20: Accumulated wetting hours since May 8: 460.

July 17-18: Wet 10.5 hr at 66º with 0.17" of rain.

July 13: Accumulated wetting hours since May 8: 437.

July 6: Accumulated wetting hours since May 8: 406.

July 1-2: Wet 15 hr at 64º with 0.62" of rain.

June 29: Accumulated wetting hours since May 8: 378. Watch for sooty blotch and flyspeck on lower elevation poorly protected trees.

June 26-27: Wet 13 hr at 70º with 0.18" of rain.

June 22: Accumulated wetting hours since May 8: 344. Sooty blotch and flyspeck observed on non-treated trees.

June 20-21: Wet 11 hr at 71º with 0.16" of rain.

June 19-20: Wet 18 hr at 71º with 0.64" of rain.

June 16-18: Wet 36 hr at 64º with 1.67" of rain.

June 15: Accumulated wetting hours since May 8: 273.

June 11-12: Wet 8.5 hr at 66º with 0.04" of rain.

June 10-11: Wet 15 hr at 66º with 1.1" of rain.

June 9-10: Wet 10 hr at 66º. This wetting brings us to a total of 256 accumulated wetting hours, beyond the 250-hr threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit.

June 8: Accumulated wetting hours toward 250-hr threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit: 229 hr.

June 3-6: Wet 62 hr at 58º with 2.4" of rain. This is the third time since May 3 that we got enough rain to totally deplete protective fungicide residue during an extended wetting period. The threat of secondary scab continues.

June 1: Accumulated wetting hours toward 250-hr threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit: 155 hr.

Late Spring (May-June)

In drier years, the early cover spray period a month after petal fall should be a time of transition from early season apple diseases, scab, the rusts and powdery mildew to summer diseases, sooty blotch, flyspeck and fruit rots. But this year we still have scab showing up from frequent infections in May. So continue to watch for unusual, damaging amounts of scab on leaves and fruit and for secondary mildew infection, and be prepared to react accordingly. With continuing active shoot growth, there is also a threat of secondary fire blight infection, especially if hail damage occurs. Where present, fire blight-killed shoots should be viewed as a potential fruit rot inoculum source.

June 3-6: Wet 62 hr at 58º with 2.4" of rain. This is the third time since May 3 that we got enough rain to totally deplete protective fungicide residue during an extended wetting period. The threat of secondary scab continues.

June 1: Accumulated wetting hours toward 250-hr threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit: 155 hr.

May 28-29: secondary apple scab (wet 16 hr at mean 68º, 1.25 in. rain).

May 25-27: Heavy secondary apple scab and early rot activity; wet more than 41 hr at 55-68º with 2.43" of rain, which eroded protective fungicide residue. Remember that longer wetting periods can cause infection on fruit which normally would have become more resistant to shorter ones by now.

May 25: Accumulated wetting hours (starting May 8, 10 days after petal fall, Apr 28): 64 hr.

May 24-25: secondary apple scab (wet 10 hr at mean 66º, <0.01 in. rain).

May 18: Accumulated wetting hours (starting May 8, 10 days after petal fall, Apr 28): 43 hr.

May 16-17: Apple scab infection. Wet 14 hr at 66º with 0.84" rain.

May 15-16: Apple scab infection. Wet 12 hr at 65º with 0.02" rain.

May 14-15: Wet 14 hr at mean 67º with 0.13 in. of rain, a scab and rust infection period. Check for rust inoculum on galls in your area. 22 days favorable for mildew infection since March 30.

May 11-12: Wet 15 hr at 44-63º with 0.39 in. of rain, a scab and rust infection period.

Earlier scab (and often rust) infection periods occurred every day from Apr 29-May 7.

Early Season (March-May)

May 14-15: Wet 14 hr at mean 67º with 0.13 in. of rain, a scab and rust infection period. Check for rust inoculum on galls in your area. 22 days favorable for mildew infection since March 30.

May 11-12: Wet 15 hr at 44-63º with 0.39 in. of rain, a scab and rust infection period.

May 6-7: Wet 16 hr at mean 59º with 0.42 in. of rain- another scab and rust infection period. Consider including an SI fungicide (such as Rally, Rubigan, Indar, Inspire) on unprotected cedar-apple and quince rust-prone blocks.

May 5-6: Wet 17 hr at 53º with 0.29 in. of rain, a scab and rust infection period.

May 3-5: Wet 54 hr at 59-52º with more 1.97 in. of rain- a heavy scab and rust infection period. Secondary mildew infection observed.

May 2: Wet 7 hr at mean 62º with 0.03 in. of rain. A secondary apple scab and cedar-apple and quince rust infection period.

Apr 30-May 1: Apple scab and cedar-apple and quince rust infection period. Wet for 16 hr at mean 62º with 0.08 in. of rain.

Apr 29-30: Apple scab and possible rust infection period. Split wetting for 23 hr at 48-62º (mean 53º). Heavy quince and cedar rust spore discharge. Apple scab lesions observed.

Apr 29: Most apple trees still with susceptible bloom; fire blight infection was possible with wetting last night and will again be possible with wetting May 1-2. Setting fruit are still susceptible to quince rust infection. 15 days mildew days in April.

Apr 27: Apples at full bloom. Forecasts show wetting Apr 29 as our greatest fire blight threat for the bloom period this year. 14 days favorable for powdery mildew infection since March 30.

April 24: Many apple cultivars at or near full bloom. With predicted warmer temperatures into next week, fire blight risk will quickly increase to a high level with infection possible with storms (or other wetting) tomorrow, Apr 25.

April 19-21: Wet 32 hr at 45-51º with 1.12 in. of rain. Heavy apple scab infection period; also heavy cedar-apple rust spore discharge and possible infection (temperature was less than optimum for heavy rust infection). Ten dry weather days favorable for powdery mildew infection since spores were first observed March 30.

April 17: For first bloom open Apr 13, fire blight infection is not likely with predicted temperatures and any wetting through at least Monday, April 20.

April 14-16: Wet 49 hr at 39-46º (mean 43º) with 0.44 in. of rain. A heavy apple scab infection period. Consider this likely to be an early secondary infection period where lesions might be starting to sporulate if 1/4-1/2" greentip growth was not protected during the March 25-29 infection periods.

April 11: Wet 10 hr at 46-51º with 0.73 in. of rain. Not an apple scab or rust infection period at our AREC. Earliest bloom open on Idareds Apr 13.

April 2-3: Apple scab and cedar-apple rust infection period. Wet 18 hr at 54-58º with 0.34 in. of rain. Wind was mostly from the east- note direction from possible cedar rust inoculum trees. Trees at tight cluster stage.

March 30: Apple mildew spores are being released from emerging leaves of Idareds nearing tight cluster.

March 27-29: Apple scab infection period. Wet 28 hr at 50º with 1.08 in. of rain.

March 25-27: Apple scab infection period March 25-27 with ascospores discharged by 9 AM March 26. Wet 26 hr at 44º mean with 0.56 in. of rain.

March 18: Apple scab ascospores trapped during wetting; not wet long enough to constitute an infection period. Cedar-apple rust gall spore horns will likely discharge some basidiospores with warm (55ºF+) wetting periods. Check for abundance of galls on cedar trees in your orchard area and plan your control strategy accordingly.

March 16: Peach buds have swelled and are showing enough green tissue for leaf curl infection with wetting March 14-16. Several apple cultivars at our AREC had green tip exposed March 13, but scab spores were not trapped and infection was not likely during this long wetting period.