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Keith Yoder

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Research Projects: Management of Diseases of Tree Fruits; Fire Blight; Mildew.
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2007 disease update archives

Summer disease development notes for the Winchester, VA area. September 21, 2007

Sept. 21: Alternaria leaf blotch observed on Red Delicious north of Winchester, the northern-most report for Virginia. If observed, this should be considered in disease management programs for next year.

Sept. 10: Accumulated wetting hours since May 13: 713. Watch for rots in ripening apple fruits.

Sept. 3: Accumulated wetting hours since May 13: 680; the current total is comparable to five of the past six years at this date. Rots following the hail injury Aug. 25 are sporulating and, if present, they should be considered an inoculum problem for healthy fruits.

Aug 27: Accumulated wetting hours since May 13: 632, more than the past two years at this date.

Aug 25-26: Wet 18 hr at 72 degrees with 0.79" rain and localized hail at and near AREC 4PM Aug. 25.

Aug 20-23: Almost continuous wetting from rain, fog, or dew since midnight Aug 20 to present -- now totaling more than 82 hours with approximately 1.5 in. rain, most of which occurred Aug 20-21. Accumulated wetting hours since May 13: 576

Aug 20: Accumulated wetting hours since May 13: 504, about same as the past two years at this date.

Aug 13: Accumulated wetting hours since May 13: 464.

Aug 9-10: Wet 15 hr at 74 degrees with 0.48" rain.

Aug 5-6: Wet 17 hr at 71 degrees with 0.26" rain. Accumulated wetting hours since May 13: 422.

July 29-30: Wet 11 hr at 70 degrees with 0.14" rain. Accumulated wetting hours since May 13: 402.

July 27-28: Wet 8 hr at 67 degrees with dew.

July 24-25: Wet 11 hr at 64 degrees with dew.

July 23: Accumulated wetting hours since May 13: 362.

July 18-19: Wet 7.5 hr,72 degrees with 0.04" rain.

July 16-17: Wet 10 hr at 67 degrees with 0.01 in. rain.

July 15-16: Wet 14 hr at 70 degrees with 0.39 in. rain. Accumulated wetting hours since May 13: 344. Flyspeck observed on nonprotected apples.

July 13-14: Wet 9 hr at 62 degrees with 0.04 in. rain.

July 11-12: Wet 10 hr at 68 degrees with 0.06 in. rain.

July 9: Accumulated wetting hours since May 13: 302. Sooty blotch symptoms observed on nonprotected apples.

July 5-6: Wet 10 hr at 69 degrees with 0.06 in. rain.

July 4-5: Wet 12 hr at 70 degrees with 0.37 in. rain.

July 2: Accumulated wetting hours since May 13: 250. This meets the wetting threshhold for presence of the sooty blotch and flyspeck fungi on nonprotected fruit. Symptoms may be visible on these fruit in 2-3 weeks. Last week's wetting periods were also favorable for early fruit rot activity and rapid Alternaria leaf blotch development on Red Delicious. Keep in mind that fire blight-killed shoots become a significant rot inoculum source.

June 28-29: Wet 19 hr at 72 degrees with 0.22 in. rain.

June 27-28: Wet 11 hr at 65 degrees with only 0.03 in. rain.

June 25-26: Wet 14 hr at 72 degrees with 0.15 in. rain.

June 25: Accumulated wetting hours since May 13: 202.

June 21-22: Wet 9 hr at 65 degrees with 0.18 in. rain. Peach scab lesions, developing from infection which occurred about 7 weeks ago, appearing on non-protected fruit. Alternaria leaf blotch reported on Red Delicious in Shenandoah county; had been present about 3 weeks.

June 19-20: Wet 14 hr at 70 degrees with 0.84 in. rain.

June 18: Accumulated wetting hours since May 13: 174.

June 13-14: Wet 19 hr at 59 degrees with 0.33 in. rain.

June 12-13: Wet 14 hr at 63 degrees with 0.35 in. rain.

June 11: Accumulated wetting hours since May 13: 124. More fire blight than we have seen for several years- evidence of weather to activate the problem. Fire blight-killed shoots can quickly become infested with rot fungi such as bitter rot and increase the amount of rot inoculum this summer.

June 3-4: Wet 20 hr at 64 degrees with 0.5 in. rain- an apple scab and cedar rust infection period. Accumulated wetting hours since May 13: 98.

May 28: Accumulated wetting hours since May 13: 50.

May 21: Accumulated wetting hours (starting May 13, 10 days after petal fall, May 3): 32.

Early season disease development notes for the Winchester, VA area:

June 3-4: Wet 20 hr at 64 degrees with 0.5 in. rain- an apple scab and cedar rust infection period.

May 31: 31 days favorable for mildew infection through May 31 (compared to 28 infection days through June 1 in '06, 36 in '05 and 22 in '04). Protect trees till shoot growth hardens off to prevent a recurrent problem next year.

May 18-19: Wet 22 hr at 47 degrees with 0.69 in. rain- an apple scab infection period.

May 16-17: Split wetting: Wet 5 hr, dry 4 hr, then wet 10 hr mostly from dew at 55 degrees with 0.65 in. rain. May have been a light apple scab infection period.

May 14: Cedar-apple rust and scab lesions appearing on trees which were not protected Apr 26-27.

May 12-13: Wet 12 hr at 50-65 degrees with 0.59 in. rain- an apple scab and cedar-apple rust infection period.

May 10-11: Wet 10 hr at 59-72 degrees- an apple scab and cedar-apple rust infection period. Fire blight infection possible on trees with late bloom. Most fruit not susceptible to quince rust.

May 3: Days favorable for secondary mildew infection in the month since spores were first observed: 12.

May 1-2: Fire blight infection is possible with overnight wetting which occurred last night (see MARYBLYT graphic and recommendation and blossom symptoms below).

Apr. 30: Fire blight risk can again reaches an infective level on susceptible blossoms with predicted wetting May 1-2 and May 4.

Apr. 28: Apple scab lesions observed on unprotected trees, probably from the infection period Apr 14-15.

Apr. 26-27: Wet 16 hr at 52-59 degrees- an apple scab, cedar-apple rust and quince rust infection period. Fire blight infection possible.

Apr. 25: Fire blight alert! Near full bloom. Fire blight infection is possible with wetting today.

Apr. 24: Fire blight infection possible with wetting by early morning showers.

Apr. 23: Many apple trees with susceptible bloom; infection would be possible with wetting any of the days, Apr 23-25.

Apr. 20: With apple trees coming into bloom, and based on predicted temperatures and first bloom open Apr 19, fire blight infection would be possible with wetting any of the days, Apr 22-25.

Apr 14-15: Wet 26 hr at 43-46 degrees- an apple scab infection period. Bud stages at our AREC now range from tight cluster on Romes to open cluster on Red Delicious and Idareds. Looks like poor spray weather at least the next two days.

Apr. 12: Apple scab lesions appearing this week from the infection period March 23-24 will be obscured by frost injury on the affected leaves but that does not diminish their potential role in later secondary infection.

Apr. 11: In spite of the low temperatures Apr. 6-8 (29, 27, and 26F) with apples beyond tight cluster, we still have the potential for a full crop of apples at our AREC. Our peach trees still have enough live flowers to make a full crop, but poor pollination/ fruit set conditions may be more questionable.

April 3: Apple mildew spores observed on emerging leaves. Some highly susceptible cultivars such as Idared and Ginger Gold are at tight cluster stage with rapidly expanding foliage. Dry, warm weather is favorable to early mildew development. Blossom infection, causing fruit russet, can occur at the pink stage.

March 23-24: Apple scab ascospores trapped March 23. Wet 25 hr at 54 degrees mean temp., a scab infection period. Susceptible green tip exposed on Red Delicious, Granny Smith, Idared, Fuji, Gala, Ramey York, and Jonagold.

March 16: Cedar-apple rust galls are plentiful in some Frederick county areas and less abundant in others. Check for galls on cedar trees in your orchard area and adjust your control strategy accordingly.

Because of frequent wetting by snow cover and rains in recent weeks leading up to green tip stage, expect some apple scab ascospores to be mature and discharged with rains near green tip.

Peach buds have swelled and are showing enough green tissue for leaf curl infection with wetting March 15-16.

Fire blight situation at Winchester, May 11, 2007

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

FIRE BLIGHT: Here is a graphic from the Maryblyt program. With most apple trees now at or beyond petal fall, but with susceptible blossoms still present on some trees, such as Rome, here is a prediction for trees with first bloom open Apr 19-22. The temperature and wetting data are current through Friday morning, May 11. Predicted weather conditions are shown for May 11-13. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). Based on predicted temperatures and wetting, Column R (risk), shows that fire blight infection (I) was possible had wetting occurred from rainfall or heavy dew any of the days, Apr 22-25, 27 and May 1-2. Wetting occurred at our AREC and other Frederick county areas Apr 24-25, Apr 27, May 1-2 and May 10-11. Infection remains possible for May 12 where late bloom is present and wetting occurs for May 12. Check high-risk blocks (late blooming susceptible cultivar / rootstock combinations) for susceptible late bloom and consider protecting high-risk blocks with streptomycin before predicted infection events. Column BBS is tracking the potential appearance of blossom blight symptoms where infection occurred April 24 (letter a), Apr 25, Apr 27 (b and c appear May 10), and May 1 (98d, to appear about May 13-14). BBS indicates that symptoms from infection Apr 24 were predicted to appear May 9 (when the number in this column reaches 100a or more). Symptoms from our experimental inoculations Apr 23 and 25 are now visible as small, darkening fruits and droplets of bacterial ooze on stems of infected fruits/flowers. The CBS column indicates that canker blight symptoms on new growth, due to extension of overwintering cankers from last year, should begin to appear May 13. Canker advancement cannot be prevented by chemical treatment at this time and the presence of symptoms indicates a build-up of inoculum which could become a factor in the event of a trauma blight situation due to hail injury, etc. Fire blight cankers should also be recognized as a warning for potential fruit rot problems later in the season; bitter rot (Colletotrichum sp.) spores can be produced on blight-killed twigs and spurs within six weeks after the initial fire blight infection. This will be the last Maryblyt graphic update for this season. The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from Skybit, Inc.

For your reference, this year's previous MaryBlyt graphics are archived below, with the most recent at the top and the earliest one at the bottom.

Idared blossom blight symptoms 5-2-07; inoculated 4-23-07.

On the left is a picture of an unprotected Idared flower cluster taken May 2 '07, less than 8 days after inoculation in the evening of Apr 23. Note the cream-colored droplet of bacterial ooze on the pedicel (stem) and the darkening flower parts and fruitlet. Such ooze droplets will typically be cream-colored when they are fully hydrated early in the morning (as this one was), then become amber-colored as they dry down during the day. These symptoms were evident a couple days before MaryBlyt had predicted them, likely because of the high inoculum dosage (1 million cells/ml) used in the experimental inoculation.