Friday, April 28, 2017

Fire blight outlook April 28-May 3.


NOTE: This year for fire blight risk assessment, we are comparing graphics from Maryblyt 7 and from the Cougarblight model as shown on our NEWA site. We are using the same weather data from our NEWA station to make these comparisons in both predictive programs.

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.
Maryblyt graphic April 28, 2017
FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program, using Apr 5 as the date for first bloom open on Idared cultivar. Early-blooming cultivars still have scattered susceptible bloom, and later cultivars are at petal fall but with much susceptible bloom in the Winchester and central Virginia areas. Some recently planted trees still have much susceptible bloom. The temperature and rainfall data are current through Thursday evening, Apr 27. Predicted weather conditions are shown for April 28-May 3. 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). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. Based on recorded temperatures and wetting, the risk column shows high risk and possible infection with any wetting Apr 11-12, 15-18, 21 and, and if bloom persists, Apr 27-May 3. Infection was indicated for Apr 12, 15-17 and 21. Predicted warming temperatures have again increase risk wherever susceptible bloom remains Apr 26-May 1. Note that risk can change quickly with warmer than predicted temperatures and wetting. In situations where all other requirements for infection have been met except wetting (as for May 1-3, wetting from any spray application (fungicide, insecticide, or thinning spray) can provide the wetting trigger for infection to occur. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. Continue to protect late bloom and open bloom on recently planted trees as needed.

The BBS column is tracking predicted symptom development for the first infection Apr 12 and symptoms are predicted to appear Apr 27. Later infections are tracked with letters b-e, and symptoms for those are predicted to appear Apr 28-May 2. The CBS column indicates progression toward the appearance of canker margin symptoms due to extension of overwintering cankers from last year, which were predicted to Apr 22. Canker advancement cannot be prevented by chemical 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/shoot blight situation due to hail injury, etc. To offset the potential for shoot tip infection in an active fire blight year such as this one, apply the plant growth regulator, prohexadione-calcium (Apogee, Kudos), at late bloom. Shoot blight suppression results from hardening off of vegetative shoot growth starting about 10 days after the initial application. The fire blight outlook will be updated Monday, May 1.

Below is the graphic from the Cougarblight model as shown on our NEWA site. Note that we selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 4/5/2017. (This date must be re-set each time this site is accessed). Cougarblight shows color-coded risk as “high” for Apr 27 and “extreme” Apr 28-May 2. 
Cougarblight graphic April 28, 2017.