IPMalert060701

Vermont Apple IPM Alert

June 7, 2001

L.P.Berkett, IPM Specialist

Disease Management

Apple Scab – As was mentioned in the last IPM Alert, the final scab ascospore release in commercial orchards can be assumed to have occurred when 900 scab DD have accumulated before a daytime rain of at least 0.1 inch and temperatures of at least 50F during the wetting period. The table below shows the estimated date when the various monitoring sites reached 900 DD. Note that it is expected that East Dorset (higher elevation) will reach that point on June 8. Again, it will take about 10-17 days after the final infection period to see if any lesions develop before sprays can be extended. However, this is all moot if there are scab lesions in the orchard pumping out conida. Check your orchard very carefully. Some of the newly emerging leaves at the time of previous infection periods may not have been covered and now may have lesions.

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

Cumulative % Ascospore Maturity for Selected Vermont Sites¹

South

Burlington (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)

Date reached 900 DD

5/29

5/30

5/29

***6/08***

5/27

6/04

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

Fire Blight: We have been using the Maryblytä computer model and weather estimates from Skybitä to predict when fire blight symptoms are most likely to appear if infection did take place in three of the sites where conditions were favorable for infection during bloom: Dummerston, Shoreham and So. Burlington. At all three sites, blossom blight symptoms should be evident by the end of this weekend according to the computer model. Next week would be a good time to check your orchard to see if you see any clusters that appear watersoaked, wilted, shriveled and/or brown. Page 23 of the 2000-2001 New England Apple Pest Management Guide describes the “ugly stub” method of pruning out infected areas.

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
06/05	378	379	381	300	386	356
¹Degree Days received from Skybit E-Weather Service: http://www.skybit.com/

Predicted Degree Days for Arthropod Pest “Events”:

OBLR - 1^st adult catch, 1^st summer brood 484-612

STLM – 2^nd gen. 1^st adult catch 558-750

AMF – 1^st capture 741-993

Plum Curculio: Yes, but another table with DD accumulation !!!! The following table shows the estimated DDs that have accumulated since 95% Petal Fall at six sites. As was mentioned in the May issue of the Vermont Apple Newsletter, insecticide residues to control PC should be maintained until 340 DD have accumulated since 95% Petal Fall. The last row of the table estimates how many degree days will have accumulated by the end of next week. It shows that insecticide residue should be maintained.

2001 Estimated Degree-Day Accumulation (Base 50F, from 95% McIntosh Petal Fall Date) for Selected Sites
	^{UVM Hort.Res.Center So. Burlington Chittenden Co. Elev. 71 M}	Shoreham Addison Co. Elev. 107 M	South Hero Grand Isle Co. Elev. 54M	East Dorset Bennington Co. Elev. 408 M	Dummerston Windham Co. Elev. 171 M	Franklin Franklin Co. Elev. 137 M
95% McIntosh Petal Fall Date	05/21	05/17	05/18	05/28	05/14	05/23
DD as of 06/02	110	132	134	26	124	81
Predicted DD accumulation by 06/15	272	293	299	149	278	237

Codling Moth: On Monday of this week, 119 DD had accumulated (base 50F) at the UVM Hort. Res. Center from May 17^th which was the biofix for pheromone trap captures at this site. This is less than halfway to the time of 3% egg hatch (see the last issue of IPM Alert for more details on effective times to manage CM based on DD).

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