FIRE BLIGHT CAUTION: We are in late bloom on Winchester area apples, and this update applies to wherever there is susceptible bloom. New plantings, late-blooming cultivars, and young trees are especially vulnerable. Below are the fire blight risk assessments, comparing graphics from Maryblyt and also from the Cougarblight model as shown on our NEWA site, using the same weather data from our NEWA station to make these comparisons.
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| Graphic from Maryblyt 7, May 13, 2018. Click to enlarge. |
Above is a cropped graphic from the Maryblyt 7 program, with first bloom open Apr 14. The temperature and rainfall data are current through Sunday evening, May 13. Predicted weather conditions are shown for May 14-18. 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, dew or a spray application), 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, and this must coincide with an average daily temperature of 60°F or more. Based on recorded and predicted temperatures and wetting, the risk column shows that infection conditions occurred May 5, 7, 10, and 13, and are predicted for May 14-17 (or 18 with wetting). Thunderstorms are predicted for most days this week. High risks were shown for all of the other days between May 2 and May 11, except May 8, with only wetting lacking for infection May 2-4, 6, 9, 11, and 12. Because any spray application can serve as the wetting trigger, include streptomycin with spray applications through late bloom. Remember to protect young and recently planted trees, with flowers but considered to be "non-bearing".
The BBS column in the above graphic is tracking predicted blossom blight symptom development for the first infection May 5 (letter a), with 103% of the degree hours required for blossom symptom prediction by May 14. Letters b and c are tracking infections May 7 and 10 respectively, and predict appearance of symptoms from those on May 15 and 17. The CBS column indicates progression toward the appearance of canker margin/canker blight symptoms due to extension of overwintering cankers from last year, which was predicted for May 8. Canker blight symptoms are predicted for May 15. 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 petal fall on king bloom. Shoot blight suppression will begin about 10 days after the initial application.
Below 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 4/14/2017. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” risk is extreme for May 12-19, and EIP infection conditions are shown for May 12-18.
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| Graphic from Cougarblight, May 13, 2018. Click to enlarge. |
Similar fire blight threats remain throughout much of the region, wherever late bloom persists and wetting occurs.
