Heavy scab and rust infection period; fire blight risk moderate to low

Scab and rusts: Extended wetting began at our AREC, Winchester, at 3 PM Monday Apr 28 and will likely extend through the night to Thursday morning, May 1, a total of more than 60 hours. Temperatures for this heavy scab infection period ranged from 59 F to 46 and back up to the mid-50s. Because the beginning and ending temperatures also favored quince rust and cedar-apple rust infection at peak susceptibility of blossoms to quince rust, follow-up fungicide mixtures should be selected that include after-infection rust control. 

This extended wetting also favors peach scab infection.

Central Virginia has had similar conditions this week, with almost continuous wetting, starting at 2 PM Apr 28 and about 2.5 inches of rain recorded at Tyro.

Fire blight outlook: With cooler than predicted temperatures, the fire blight risk through this weekend remains moderate to low. But the 10-day forecast shows warmer temperatures toward the middle of next week, and with an extended bloom period, this will bring higher risk of fire blight to later bloom. The fire blight outlook will be updated May 3.

Powdery mildew: The 10-day forecast shows dry weather, favorable for mildew infection through the period. Earlier we had 13 dry weather mildew infection days since Apr 9, so secondary mildew pressure on susceptible cultivars will be heavy in the coming weeks, and tank mixes of fungicides should also include a material for mildew suppression. 

Fire blight 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. 

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Most apple cultivars at our AREC are near full bloom, but with delayed blossoms continuing to open over the next several days. Later cultivars such as Rome Beauty are just starting to bloom. This prediction is for trees with first bloom open Monday, April 20, 2014. The temperature and rainfall data are current through this morning,  April 28. Predicted weather conditions are shown for April 28-May 7. 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, the risk column shows that fire blight infection will be high for Apr 30-May 1. If the temperatures were five degrees warmer for those two days, infection would be predicted for May 1. Following the higher risk for Apr 30-May 1, the current forecast with cooler predicted temperatures holds the risk at a low to moderate rating through May 7. 

This graphic will be updated April 30. 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.

Scab and rust infection April 25-26

We recorded 12 hours of wetting at 53-62° at our AREC, Winchester April 25-26, an apple scab, quince rust and cedar-apple rust infection period. Where protection was not adequate, growers are advised to follow up with an SI fungicide to offset possible infection of blossoms, which are now very susceptible to quince rust. Extended wetting is likely tonight and during the next several days.

Fire blight and fungal disease update, April 25

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: The fire blight outlook has varied with a changing forecast the past several days. Above is a cropped graphic from the Maryblyt 7 program. Most apple cultivars at our AREC have bloom open, some are nearing full bloom and many flowers are expected to open over the next several days. This prediction is for trees with first bloom open April 20. The temperature and rainfall data are current through this morning,  April 25. Predicted weather conditions are shown for April 25-May 4. 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 current predicted temperatures and wetting, the risk column shows that fire blight infection will remain moderate until May 1. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. Following briefly higher risk on May 1, the current forecast shows cooler predicted temperatures which hold the risk at a low or moderate rating through May 4. These cool temperatures will also prolong the bloom period and increase the possibility of fire blight infection with warmer temperatures on late bloom.

This graphic will be updated April 28. 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.

Other diseases: Extended wetting at relatively warm temperatures tonight will likely result in apple scab and rust infection, and blossoms are now very susceptible to quince rust. Rain and shower activity next week Apr 28-30 will also favor rust and scab infection. Expect scab lesions from April 11-15 infection periods to be present during Apple Blossom Festival weekend.

Powdery mildew spores were available under favorable dry weather infection conditions by Apr 9, and we have had 12 dry weather “mildew infection days” since Apr 9.

Fire blight 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 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. Most apple cultivars at our AREC have bloom open, some like Idared, are approaching full bloom and many flowers are expected to open over the next several days. This prediction is for trees with first bloom open Monday, April 20, 2014. The temperature and rainfall data are current through this morning,  April 23. Predicted weather conditions are shown for April 24-May 2. 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, the risk column shows that fire blight infection will be high for Apr 25, but the temperatures would need to be warmer over the next two days for infection to be predicted for Apr 25. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. Following the higher risk on Apr 25, the current forecast with cooler predicted temperatures holds the risk at a low to moderate rating through May 2. 

This graphic will be updated April 25. 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.

Fire blight caution

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. With early cultivars with bloom open, and more bloom opening over the next several days, here is a prediction for trees with first bloom open yesterday, April 20, 2014. The temperature and rainfall data are current through this evening, April 21. Predicted weather conditions are shown for April 22-26. 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, the risk column shows that fire blight infection is high. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher.  Infection would be more likely in areas where bloom is more advanced, and temperatures are a couple degrees warmer than that shown for Apr 25 or 26, and if wetting occurs Apr 25-26. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. 

This graphic will be updated April 23, or sooner if significant change warrants it. 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.

Apple scab and rust infection April 14-15

Ginger Gold apple bud stage, April 16, 2014

As shown above, apples at our AREC were mostly in open cluster bud stage Wednesday morning, April 16.

Scab and rust infection period:  We had about 13 hr wetting in the 59-64° range Apr 14-15, followed by another 10 hr wet as the temperature dropped from 55 to 38. This was plenty enough for scab, quince rust and cedar-apple and infection.

As usual, we saw powdery mildew spores emerging from tight cluster stage buds last week, and mildew infection would have occurred with dry weather April 9-10 and 13-14, so we should now be spraying apples for scab, the rusts and mildew.

After-infection control of rusts: Quince rust and cedar-apple rust spores were released and likely found a susceptible target in apple blossoms at open cluster.  It is best to include an SI fungicide for after-infection control of rusts, especially quince rust, considering yesterday’s warm infection period. If an EBDC fungicide had been applied just before the rain, it may have weathered through with less than an inch of rain, but where rainfall was more an inch or the most recent fungicide application was more than a week earlier, applied more than a week ago, it is best to follow-up with a supplemental SI fungicide for after-infection control of rusts.

Fire blight?: The warm temperatures over the weekend to Apr 15 might have favored fire blight Apr 14-15 if bloom opened April 11-13, but fire blight infection was not likely where bloom first opened during the day April 14 or 15. Now it looks like it will remain relatively cool into next week, but with warmer temperatures and more bloom expected by the middle of next week. Of course the fire blight threat can change quickly if the temperatures are warmer than predicted.

TYRO, VA: Similar apple disease scenarios were expected for central Virginia, where the bud stage is more advanced with bloom open last week, temperatures generally several degrees warmer and rainfall reported to be as much as 2.4 inch.

Scab infection at Winchester Apr 11-12

At our AREC near Winchester, wetting which began at 6 PM Apr 11 and continued for 14 hours at 64-40° F was long enough for a scab infection period. Total rainfall during the infection period was only 0.01 inch.


Wetting during this event was not long enough for scab infection at Tyro, Apr 11-12.

Wetting April 7-8 Winchester and Tyro, VA

Apple buds at our AREC are now at 1/2-inch green-tip stage with some approaching tight cluster. 

With wetting starting at 6 AM yesterday, and starting to dry as of 8 AM this morning, we did not have enough wetting for a scab infection at 38-44° F.

Wetting in the Tyro area, central Virginia, began at 4 AM Apr 7 and continued for more than 26 hours at 42-47° F with 1.25 inch rain. This was more than adequate for a scab infection period. Tyro also was close to an infection period  Apr 3-4 with 11 hr wet with light rain and temperatures 51-59° F.

Expect the release of powdery mildew conidia as buds approach the tight cluster stage.