Thursday, May 28, 2015. Vol. 23:11 Maine Tree Fruit Newsletter Apple Scab.. Many Maine orchard locations received at least some rain on Thursday May 28. For some locations it was just a sprinkle but for others thunderstorms brought well above the 0.10 rain required for a full release of mature scab ascospores waiting for release. The forecast indicates a high probability that all Maine orchards will get rain on Saturday Sunday May 30 31. Finally getting rain moves us toward the end of primary scab infection potential. However, rain on May 31 will not be the last blast of apple scab however, especially for locations to the north and coastal of Highmoor Farm. Chart below if for Highmoor Farm in Monmouth.
If it rains on Sunday May 31 at Highmoor Farm, then there would still be about 10% of the season s primary scab infection potential remaining to release with subsequent rains. At Highmoor Farm, Sanford, and Limerick, the final primary scab infection period will occur with the first daytime soaking rain after Saturday, June 6. In Appleton, there would still be about 25% of the season s primary scab infection potential remaining after a soaking rain on May 31. The final primary scab infection period in Appleton will occur with the first daytime soaking rain after Friday, June 12. Cumulative primary apple scab potential at Appleton ME.
Fire Blight.. Where there was rain on Thursday there was risk of fire blight blossom infection wherever there were still open blossoms present. Cumulative heat units were especially high in Sanford. There were probably very few blossoms left on the trees by then, but some cultivars continue to have flowers long after most trees have lost all bloom. Check your orchard. If needed, those trees should receive antibiotic application within 24 hours after start of the rain if possible. That is especially true if there is any history of fire blight in the orchard. Risk varies directly with inoculum population, and the number of fire blight bacteria in an orchard with active fire blight is tremendously higher than in an orchard with no history of fire blight. Fire blight risk will continue through Saturday May 30 where is bloom is present. For orchards with temperatures similar to Appleton, on trees treated with antibiotic on Tuesday evening May 26, flowers that opened on May 27 would accumulate enough heat units for fire blight infection (assuming they were inoculated with fire blight bacteria soon after opening by visiting flies and bees) with rain late Saturday and Sunday. But flowers opening on or after Thursday May 28 would not accumulate enough heat units before the weekend rain. In this scenario, it is only flowers that opened the day after a May 26 antibiotic application that would need a new application of antibiotic to prevent risk of infection. That number of new opening blossoms this late into bloom might be small to none, or could be as much as 14% or more of the total orchard flower population. The number depends on how many trees of late blooming cultivars there are in the orchard. There is no need to base a respray decision on vague estimates. You can check your late blooming cultivars to see if and how many new blossoms are opening. If fire blight infection occurred, it would be obvious in about two weeks as blackened dead shoots, but close inspection infection will be apparent before then as water soaked softening fruit pedicels and collapsing shoot tips, possibly with bacterial ooze. Fruit cluster in the process of dying because of fire blight infection. ARS photo.
Thinning for Return Bloom.. Bloom is heavy this year, which has many of us concerned about return bloom next year. To get sufficient bloom next year, your best bet is to thin early and thin again. Thinning at bloom or petal fall is the most effective method of reducing the degree of biennial bearing. Honeycrisp is biennial and should be thinned by petal fall and again at the 10 12 mm stage. A specific thinning program for this variety can be found in the New England Pest Management Guide on page 181. Maxcel (6 BA) is reported to be better at promoting return bloom than other thinners, but also increases fruit size which in some cases is undesirable in Honeycrisp due to its ability to grow large fruit. However, if you feel that fruit set is going to be heavy this year on Honeycrisp, fruit size will be smaller than normal. The section on fruit thinning for apple begins on page 175 in the New England Pest Management Guide 2015 edition. Here is the Thursday afternoon update of the Sanford thinning weather chart.
Closing Words.. For beautiful eyes, look for the good in others; for beautiful lips, speak only words of kindness; and for poise, walk with the knowledge that you are never alone. ~ Audrey Hepburn Glen W. Koehler Associate Scientist IPM Email: glen.koehler@maine.edu Voice: 207 581 3882 (within Maine: 800 287 0279) Pest Management Office, 491 College Avenue Orono, ME 04473 1295 http://pmo.umext.maine.edu/apple/ Dr. Renae Moran Extension Tree Fruit Specialist Email: rmoran@maine.edu Voice: 207 933 2100 ext. 105 Highmoor Farm Ag. Exp. Station, P.O. Box 179 Monmouth ME 04259 0179 http://extension.umaine.edu/fruit/ Putting Knowledge to Work with the People of Maine Where brand names are used, no endorsement is implied nor is any discrimination intended against products with similar ingredients. Always consult product label for rates, application instructions, and safety precautions. Users of these products assume all associated risks. The University of Maine does not discriminate on the grounds of race, color, religion, sex, sexual orientation, including transgender status and gender expression, national origin, citizenship status, age, disability, genetic information or veteran status in employment, education, and all other programs and activities. The following person has been designated to handle inquiries regarding non discrimination policies: Director, Office of Equal Opportunity, 101 North Stevens Hall, 207.581.1226. If you are a person with a disability and need an accommodation to participate in a program described in this publication please call Glen Koehler at 207 581 3882 or glen.koehler@maine.edu to discuss your needs. Receiving requests for accommodations at least 10 days before the program provides a reasonable amount of time to meet the request, however all requests will be considered.