Vermont Apple IPM Alert
L.P.Berkett, IPM Specialist
May 16, 2000
Stage of Development: Full Bloom at the UVM Hort. Res. Center
Disease Management
Apple Scab -- The following chart contains the estimated DD accumulated as of 5/14/00:
2000 Estimated Degree-Day Accumulation (Base 32F,
from McIntosh Green Tip) and Cumulative Ascospore Maturity for Selected Sites
Date 5/14 |
So. Burlington (GT=4/08) |
Shoreham (GT=4/15) |
New Haven (GT=4/08) |
Bennington (GT=4/05) |
Saxtons River (GT=4/11) |
Franklin GT=5/2) |
DD |
592 |
577 |
601 |
618 |
537 |
310 |
% Mature |
75-90 |
75-90 |
75-90 |
75-90 |
50-75 |
12-25 |
We are still in the "accelerated phase" of ascospore maturity. Also, now is the time for rapid shoot development which can translate into tissue that is not protected during infection periods. This is a period of high risk in scab development.
Please note that lesions should begin to appear, if not already present, from the earliest infection periods of this season (e.g., April 22-24). Lesions from the infection period that occurred last week (e.g., over May 8-10) in some parts of the state should appear within the next week. Please see the section on "Conidia Suppression" on pages 17-18 of the 2000-2001 New England Apple Pest Management Guide for information on fungicide options once lesions are present to suppress conidia production.
Powdery Mildew -- The Petal Fall and 1st Cover sprays are particularly important in mildew management because they coincide with the period of active shoot growth. The SI fungicides (Bayleton, Nova, Procure and Rubigan) are effective against powdery mildew. They will provide good control when applied from bloom through the time when the apical bud sets on vegetative terminals (about 24 days past Petal Fall). Note that all of the SIs listed except Bayleton are effective against apple scab, so, if you are applying SIs for scab, you will be getting the added benefit of mildew management. The new strobilurin fungicides (i.e., Sovran, Flint) have activity against both powdery mildew and scab so the same would apply.
Please note that sulfur is an alternative mildew fungicide. It also is effective against powdery mildew but applications have to begin earlier (i.e., Tight Cluster) and, because of short residual activity, reapplied every 7 days for good results under high disease pressure. Benlate and Topsin-M have been used against powdery mildew but it has been reported that they have provided poor control in some orchards in recent years.
Fire Blight: The good news is that the cooler temperatures we are currently experiencing are less favorable for blossom infections. Using the Maryblyt model and estimated temperatures for a few sites around the state (e.g., UVM HRC, Shoreham, Bennington, Saxtons River) conditions so far were favorable for infection May 9 in Saxtons River and on May 6,8,9 in Bennington; at the other sites, according to the model, all the four factors necessary for infection have not occurred yet. Note that the model does assume inoculum is present. If infection did occur, blossom blight symptoms should appear after 103 Degree Days (base 55F) have accumulated from the date of infection.
Arthropod Management Update
2000 Estimated Degree-Day Accumulation
(Base 50F, from Jan. 1) for Selected Sites
| Date | So. Burlington |
Shoreham | New Haven |
Bennington | Saxtons River |
Franklin |
5/14 |
181 |
209 |
194 |
200 |
178 |
138 |
Based on estimated DD, Leafminers 1st generation adult flight should have peaked between 108-216 DD and, at the UVM HRC that is the situation. This week we saw a drop in the average number of male moths caught in pheromone traps from approx. 1,693 moths per trap down to 263 per trap. (Yes, pheromone traps really attract them !!) First LM sap-feeding mines should be present at 187-323 DD.
Note that Codling Moth first adult trap capture in pheromone traps should occur around 182-322 DD so if you are planning to monitor CM using pheromone traps to determine the biofix for running the DD model, you should have your traps in the orchard.
The Plum Curculio should be active soon in orchards around the state. First egg-laying scars on fruit can be expected at 249-323 DD. Last week there were reports of high activity of PC in some Massachusetts orchards.
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