Scab and rust infection period; tracking sooty blotch and flyspeck development

We recorded another apple scab and cedar-apple rust infection period at our AREC May 26-27: 12 hours wetting with 0.4 inches of rain at 72-63°. Most cedar rust galls now seem to be depleted of inoculum.

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, so the start of wetting hour accumulation is from May 14. As of Friday, May 30, we had accumulated 74 wetting hours toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex. 

A caution to those further south and east of the Blue Ridge: Your petal fall date may have been a week or more ahead of ours and we have arbitrarily selected Apr 27 as the start date for accumulation of wetting hours by weather stations at Tyro, VA. One of the purposes of having three weather stations at this location was to compare wetting hour accumulation at different elevations. As of May 29, a sensor placed at 1465 ft. elevation had accumulated 50 wetting hours from Apr 27, the one at 1165 ft. elevation had accumulated 90 wetting hours from May 11, while one placed at 941 ft elevation had already accumulated 204 hr!

Recent scab and rust infection periods; rust galls still active

We have seen two recent significant scab and rust infection periods: May 16-17 (22 hr wet at 74-71° with 0.77 in. rain) and May 18-19, 16 hr at 72-64° with 0.88 in. of rain.These are important for secondary scab infection where primary infection was not well-controlled earlier and, at temperatures in the 70s and higher 60s, also could signal some early Glomerella leaf spot and bitter rot activity. Cedar-apple rust galls are still actively producing spores.

We have had 22 dry weather powdery mildew infection days since mildew spores were first available Apr 6.

Yesterday we had reports of fire blight symptoms in the region, probably from infection that occurred May 5-7, which Maryblyt predicted to appear May 11-14.

Continued fire blight risk; scab and rust infection May 5-7

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: Above is a cropped graphic from the Maryblyt 7 program. Many trees still have susceptible bloom. Here is the prediction for trees with first bloom open Apr 17-18, 2015. The temperature and rainfall data are current through Wednesday night, May 6. Predicted weather conditions are shown for May 7-11. 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 recorded temperatures and wetting, the risk column shows that fire blight infection was possible Apr 20 and would have been possible with slightly warmer average temperatures for Apr 19 and 21. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. 

Based on predicted temperatures, EIP will remain at an infective level through this  weekend, requiring only wetting to trigger infection conditions wherever susceptible bloom is present. Wetting from rain occurred at the AREC May 5 and 6. Other forms of wetting capable of triggering infection conditions include heavy dew, fog or routine spray applications-- anything that can splash the fire blight bacteria from the flower stigma into the nectaries in the base of the flower. Infection conditions remain possible with wetting wherever bloom is present May 7-11. This situation generally applies to other areas in the mid-Atlantic region well beyond Winchester. It is recommended that streptomycin be included with routine spray applications in high risk situations this week. Under the temperature conditions shown for this week, expect streptomycin to remain residually effective for only about 3 days.

The BBS column is tracking predicted appearance of blossom blight symptoms from infection that occurred Apr 20, and this is predicted for May 6. (Actually on May 4 we saw early symptoms from test inoculations Apr 20). Yesterday, May 6, blossom blight symptoms were observed in a Rappahannock County orchard, also likely from Apr 20 infection. The CBS column at the right in the graphic indicates progression toward the appearance of canker margin symptoms due to extension of overwintering cankers, with 100% of the degree-hour requirement May 1. Canker blight symptoms on new growth, due to extension of overwintering cankers are predicted for May 8. Canker advancement cannot be prevented by treatment and the presence of symptoms will signal build-up of inoculum which could become a factor in the event of a trauma blight situation due to hail injury, etc. 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. Be aware that risk can change quickly with unpredicted warmer temperatures and wetting.

Fungal diseases: Apple scab, quince rust, and cedar-apple rust infection periods occurred, with temperatures in the 60s, the nights of May 5 and 6. Blossoms are still susceptible to quince rust infection at petal fall.

Fire blight and fungal disease update

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 my intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

(Click image for larger view)

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Most cultivars still have much susceptible bloom. Here is the prediction for trees with first bloom open Apr 17-18, 2015. The temperature and rainfall data are current through Monday morning, May 4. Predicted weather conditions are shown for May 4-9. 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 recorded temperatures and wetting, the risk column shows that fire blight infection was possible Apr 20 and would have been possible with slightly warmer average temperatures for Apr 19 and 21. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. 

Based on predicted temperatures, EIP will remain at an infective level through this entire week, requiring only wetting to trigger infection conditions wherever susceptible bloom is present. Wetting from rain is shown as being predicted for May 5 and 6; other forms of wetting capable of triggering infection conditions include heavy dew, fog or routine spray applications-- any wetting event that will move the fire blight bacteria from the flower stigma into the nectaries in the base of the flower. It is recommended that streptomycin be included with any routine spray applications in high risk situations this week. Under the temperature conditions shown for this week, expect streptomycin to remain residually effective for only about 3 days.

The BBS column is tracking predicted appearance of blossom blight symptoms from infection that occurred Apr 20, and this is predicted for May 6. (Actually we are already seeing early symptoms from test inoculations Apr 20). The CBS column at the right in the graphic predicts the appearance of canker margin symptoms due to extension of overwintering cankers by Apr 30. Canker advancement cannot be prevented by treatment at this time and the presence of symptoms will signal build-up of inoculum which could become a factor in the event of a trauma blight situation due to hail injury, etc.

The weather conditions used in the predictive part of this graphic come from the WeatherChannel for Winchester, supplemented by site-specific data from SkyBit Inc. Be aware that risk can change quickly with unpredicted warmer temperatures and wetting.

FUNGAL DISEASES

We recorded our 7th apple scab infection period of the year May 1-2 (15 hr at 58-53° with 0.21 in. of rain). This also favored quince rust fruit infection and cedar-apple rust on foliage and flowers. Apple scab lesions were first observed at our AREC last week; now some leaves on unprotected trees have as many as six lesions per leaf. Also present are cedar-apple rust lesions, probably from infection that occurred April 14. 

Powdery mildew is our only "dry weather" fungal disease on apples. So far, we have had 13 “mildew infection days” since spores first became available Apr 6.

Scab and rust infection Apr 30-May 1

Last night's wetting (14 hr at 63-54° with 0.21 in. of rain) was favorable for scab, quince rust, and cedar-apple rust. The blossoms are now very susceptible to quince rust and, if protection was questionable, a follow-up including an SI fungicide for after-infection is advised.

This was our 6th apple scab infection period this year. Apple scab lesions were observed on unprotected trees at our AREC this week. Where protection was inadequate during early primary infection periods Apr 7-10, consider this and any additional infection periods in the Winchester area to be secondary ones, with high inoculum potential on very susceptible blossoms and leaves. 

Outlook for fire blight in the Winchester area remains similar to what was posted yesterday: with warming through the weekend and warmer temperatures predicted all of next week, essentially all of the components will be such that any wetting of susceptible, unprotected blossoms could trigger infection any day next week.