Vermont Apple IPM Alert

L.P.Berkett, IPM Specialist

May 2, 2001

Reminder:        **Joint Twilight Meeting with UMass Fruit Team at Scott Farm in Dummerston, VT on Tuesday, May 8.   

**A second Twilight meeting with just the UVM Apple Team will be held at Champlain Orchards, Shoreham, VT on Thursday, May 10. 

Please see  the April issue of VT Apple Newsletter for directions and details.

Stage of Development:  Tight Cluster   to very early Pink on McIntosh at UVM Hort.Res.Center.

Disease Management

 Apple Scab –  Microscopic examination of approximately 15 pseudothecia dissected out of about five scabby, overwintered leaves collected today from underneath non-sprayed McIntosh trees at the UVM HRC revealed only 3% of the asci (sacs) containing “pre-mature” ascospores and no evidence of discharged ascospores.   By “pre-mature” I mean that the outline of the ascospores could be seen and they were yellow in color but had not reached the darker olive green color of mature ascospores.  One or two more days of warm weather should move these along.    Again, it must be remembered that this is a very, small sample.  What I saw under the microscope is less that what would be expected at the site using the degree day model to estimate ascospore maturity (see table).  Note that the southern part of the state is farther along in ascospore maturation, as would be expected.   You can see the difference elevation makes – the East Dorset orchard is at 408 meters elevation, whereas the Dummerston orchard is at 171 meter elevation.

2001 Estimated Degree-Day Accumulation (Base 32F, from McIntosh Green Tip) and

Cumulative % Ascospore Maturity for Selected Vermont Sites1

Date

5/01

SouthBurlington (GT=4/23)

Shoreham (GT=4/23)

South Hero

(GT=4/23)

East Dorset

(GT=4/30)

Dummerston

(GT=4/21)

Franklin

(GT= 4/25)

DD

168

174

139

182

235

110

Maturity

5-10%

5-10%

3-5%

0-1%

10-25%

3-5%

Predicted date to reach 300 DD (start of “accleration phase”

 

 

5/05

 

 

5/05

 

 

5/05

 

 

after 5/10

 

 

5/03

 

 

5/07

1Degree Days received from Skybit E-Weather Service: http://www.skybit.com/

2DD as of 4/30/01

 

Included in the chart is the predicted date on which 300 DD will have been accumulated.  This would be the start of the “accelerated phase” of ascospore maturity which is when a high percentage of this season’s ascospores will mature and will be released.    It will be interesting to see how the dry weather we have had will affect the overwintering inoculum.    One can hope that the lack of rain and the high temperatures will be detrimental to the developing ascospores causing some of them to abort.   Some orchards have not had an infection period yet but be prepared for when the rains come.

Fire Blight:  If the unusually warm, humid weather continues through bloom, we may see more fire blight this year than we want.  The 2000-2001 New England Apple Pest Management Guide, pages 22-24, gives a good overview of disease management including information on predictive models.  In general terms,  warm (65-85F), wet and humid weather during bloom favors blossom blight infections.

 

Arthropod Management Update:

2001  Estimated Degree-Day Accumulation (Base 50F, from Jan. 1)

for Selected  Vermont Sites 1

Date

So.Burlington

 

 Shoreham 

South Hero

East Dorset

Dummerston

Franklin 

05/01

64

76

65

54

95

57

1Degree Days received from Skybit E-Weather Service: http://www.skybit.com/

 

Running Out of Time to Apply Oil

 Oil remains the first defense in the management of European Red Mites.   It is not too late to apply oil at the early/tight Pink stage of bud development.  ERM egg hatch is estimated to begin at approximately 100 DD.  

Coming Events:

Early Pink - - Place EAS traps in orchard

Late Pink - -Check TPB and LM Red Sticky Traps to determine if thresholds have been reached

Bloom - -Place CM pheromone traps in orchard.  Begin to inspect fruit for PC injury during late bloom

 

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