Apple scab and rust infection Apr 23-27; fire blight blossom symptoms reported on early blooming Asian pears in Clarke Co.

At Winchester, Red Delicious apple trees are near petal fall, but there is still much bloom on many apples, and later varieties such as Rome Beauty are now in full bloom. At the AREC we received two recent infection periods.  Apr 23-24: 21 hr wet at 50° with 0.41 in. rain (scab and rusts); Apr 25-27: 31 combined hr wet at 47° with 0.80 in. rain. Cedar-apple rust galls and quince rust cankers were in "full bloom" during these extended wetting events, and unprotected apple blossoms remain very susceptible to quince rust infection, so a follow-up application including an SI fungicide is suggested. On Apr 27 a few cedar rust lesions were evident on flower cluster leaves, from infection that occurred Mar 27-28.

The above conditions for Winchester were generally similar across most of the major commercial fruit production areas of Virginia. The greatest concerns for these events are where earlier infection periods occurred with inadequate fungicide protection, and scab lesions are now sporulating, leading to heavy secondary infection.

Apple powdery mildew infection occurs on days without rainfall above 53°, and we have had ten days favorable for infection since spores were available on Mar 29. Expect secondary powdery mildew symptoms to begin appearing in the next week or so.

Although fire blight pressure has been mostly low to moderate on apples that first bloomed Mar 30 in the Winchester area, fire blight blossom symptoms on early blooming Asian pears were reported Apr 27 in Clarke County. In that case, apparently the pear trees were in bloom by Mar 19 and infection likely occurred on Mar 20, before the first apple blossoms were open at our AREC.

Fire blight pressure low to moderate through April 25; secondary scab infection possible where control was inadequate Mar 27-28.

At Winchester apple trees are mostly at mid-bloom. 

Fire blight: With prevailing cool temperatures, current fire blight pressure remains low to moderate through Apr 25 in the Winchester area, the Shenandoah Valley, and across much of northern Virginia. Conditions through Apr 25 are not favorable for fire blight infection in the Roanoke and east of the Blue Ridge south of Charlottesville, however some of these areas had earlier potential infection Mar 28-31 and Apr 7-9.

Scab: At the AREC we received a marginal apple scab infection period Apr 17-18: 14 hr wet at 47° with 0.08 in. rain. Most of the scab ascospores have been discharged signalling the end of the primary infection, but where protection was inadequate during the Mar 27-28 infection period, expect lesions to be appearing, and secondary infection could be possible with predicted wetting events later this week.
   
At Winchester, we have had 12 days favorable for apple powdery mildew infection since spores were available.

This will be updated again Apr 28.

Apple scab and rust infection April 12-13; fire blight pressure low to moderate through April 19.

At Winchester apple trees are mostly at mid-bloom, with later cultivars coming into bloom. 

At the AREC we received an apple scab, quince rust and cedar-apple rust infection period Apr 12-13 with 15 hr wet at 57° with 0.74 in. rain. Earlier last week we also had a possible combined scab/rust infection period Apr 7-8 with 9 hr wetting at 57° with 0.94 in. rain.  More than 95% of the scab ascospores are now mature in the Winchester area. At Winchester, we have had 10 days favorable for apple powdery mildew infection since spores were available.

Most of the commercial fruit production areas in Virginia had similar scab and rust infection conditions Apr 12-13, but with more rainfall east of the Blue Ridge and southward. Rainfall ranged from 1.5 inches at Sperryville and 2.3 inches at Manassas to 3.36 inches at Lynchburg. Such volumes of rainfall deplete fungicide protection, calling for fungicides with after-infection control for scab and rusts, as well as something for protection against powdery mildew in mildew-susceptible cultivars..

FIRE BLIGHT: With most apples in bloom, the current fire blight threat remains moderate to low in the Winchester area. 

Graphic from Cougarblight, April 14, 2020. Click to enlarge.

Above is the graphic from the Cougarblight model as shown on our NEWA site. We selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 3/30/20. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is moderate or low through Apr 19. The Roanoke area and areas east of the Blue Ridge south of Charlottesville had possible infection Apr 7-9 (graphics not shown), and after high risk Apr 13, are now also showing moderate to low infection potential through Apr 19.

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. Be aware that risk can change quickly with unpredicted warmer temperatures and wetting. In high-risk situations.

This week's fire blight outlook for Winchester and beyond

NOTE: This year for fire blight risk assessment, I will post a graphic from the Cougarblight model as shown on our NEWA site. I will be using the same weather data from our NEWA station to make a comparison to Maryblyt 7 as in previous years, but not posting the MaryBlyt graphic. We thank Dr. Mizuho Nita for hosting the Maryblyt 7.1 download site at: http://grapepathology.org/maryblyt 

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.

Graphic from Cougarblight, April 6, 2020. Click to enlarge.

FIRE BLIGHT: Above is the graphic from the Cougarblight model as shown on our NEWA site. We selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 3/30/20. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is low or caution for this week Apr 7-11. The Roanoke area and areas east of the Blue Ridge south of Charlottesville have a potential for infection Apr 7-9 (graphics not shown). Setting the first bloom date to 3/25/20 instead of 3/30/20 did not make any difference in prediction of infection for this week. However, Roanoke and areas south of Charlottesville could have had earlier infection (March 27-31) if the first bloom date had been as early as March 20.

Be aware that risk can change quickly with unpredicted warmer temperatures and wetting. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection, which occurs with wetting. The fire blight outlook will be updated Apr 13.