Weathering Diseases With Pruning

The appearance of some real July weather should help considerably with the scab epidemic in the state. As growth stops, tender new leaves which are most susceptible to scab will no longer be available. As trees mature, they become more resistant to scab.

The situation can be improved more by summer pruning. Summer pruning does two things. It improves the "weather" in the tree canopy. Canopies retain humidity and moisture, and the thicker a canopy, the longer it will stay wet and humid following rain or heavy dew. Summer pruning also improves the spray coverage and penetration in trees. Both of these factors will help eliminate scab in a block.

We know that summer pruning will also help with flyspeck and sooty blotch. These diseases have started to appear on unsprayed trees to the south of us, in Connecticut and New York. Just this week, the first flyspecks appeared in one orchard in Massachusetts.

Of course, summer pruning may help fungicide coverage and reduce disease pressure, but fungicides will need to be applied frequently in most orchards. There are other fungicide options, but probably the best program for the next few weeks will be captan (1 lb. 50WP/100 gal or equivalent) at 14 day intervals or a benzimidazole (Benlate or Topsin M) plus captan at 21 day intervals. If scab is active, and needs more aggressive treatment, cut the interval in half and/or increase the captan rate.

Switch to Guthion or Imidan for Larger Invasions of Maggot Fly

For reasons laid out in the July 1 issue of Healthy Fruit, this season has the potential for development of a large population of apple maggot flies. Along with the potential for high populations, trap captures in late June suggested that AMF would be active very early compared to recent years. Samples taken this past week seem to indicate that the AMF population may in fact become quite large, while activity is certainly early.

Well developed ovipositions were observed last week in early, susceptible varieties such as Red Free and Jersey Mac, but no significant damage has been recorded in any mid- to late-season cultivars. Captures on unbaited monitoring spheres are consistent with threshold levels; growers who applied Guthion or Imidan in the last week of June would be wise to check trap captures to determine when the next application is necessary.

Some growers have chosen to use Lorsban for early-season AMF control. This material does offer some control of early, light populations, and has the secondary benefit of knocking down woolly apple aphids and leafhoppers. However, with the potential for large influxes of AMF, we recommend switching to Guthion or Imidan for effective AMF control.

Summer Mite Management

As has been the case for the past month, orchard blocks which received an early-season miticide treatment (Savey, Apollo or Agrimek) remain relatively clean, harboring ERM populations of 0 to .5 ERM per leaf. Blocks which received a double-oil program are beginning to show higher levels of ERM infestation, from 1 to 3 ERM per leaf. Logically, blocks which received no oil or miticide have the highest ERM populations (up to 20 per leaf) along with pockets of significant bronzing. This week will be a real test for the early-season miticide treatments, with forecasts of sustained hot, dry weather conditions which are ideal for rapid development of mite problems.

Last year, some orchards found that treatments of Kelthane against ERM were almost totally ineffective. This ineffectiveness is not particularly surprising, as similar reports are received each season. Even if a grower has not used Kelthane for many years, loss of effectiveness is generally attributed to development of resistance to the material, which chemicals of this nature (chlorinated hydrocarbons) are notoriously prone to.

Development of resistance was enhanced by widespread use of these chemicals in the past, and the trait for such resistance can be carried in the genome and passed from generation to generation over the course of decades. A grower should not expect optimal performance from a Kelthane treatment unless no related chemicals have been used in the past 40 years. If a mite problem develops which warrants treatment, we recommend an application of Pyramite, but the potential for development of resistance should be a consideration regardless of the material of choice.

ANNOUNCEMENT

UMASS EXTENSION STORAGE SCHOOL

THURSDAY, JULY 30, 1998 Horticultural Research Center, Belchertown

9:00 a.m. Registration/check in. Coffee will be available. Registration fee*: $20 for first farm/family member; $15 each for additional persons per farm/family.

9:30 a.m. Harvest and Storage Management for High Quality Fruit - Dr. Chris Watkins, Cornell University

10:30 a.m. Managing Storage Disorders - Dr. Bill Bramlage, UMass

11:00 a.m. Predicting Scald Susceptibility; and the Measures Necessary to Obtain Control - Dr. Sarah Weis, UMass

12:00 noon LUNCH - will be provided. (Cost is included in the meeting registration fee.)

1:00 p.m. Storage Construction and Operation - Dr. Jim Bartsch, Cornell University

2:15 p.m. Managing Postharvest Diseases - Dr. Dan Cooley, UMass

3:00 p.m. ADJOURN

*Fee includes luncheon, partial reimbursement of Cornell speakers costs' (UMass Tree Fruit Program will pay remainder of speaker fees), and a small contribution towards coffee and facilities.

DIRECTIONS TO THE UMASS HORTICULTURAL RESEARCH CENTER:

The UMass HRC is located on Sabin Street in Belchertown; accessible from Route 9 (just before the entrance to Quabbin Reservoir [MDC]); or from Route 181 (to Cold Spring Road to Sabin Street) between Belchertown Center and Palmer.

The HRC telephone number is 413 323-6647.

If you wish to attend this meeting, please either call Karen at 413 545-5304 with your name and number of persons who wish to attend OR COMPLETE AND RETURN THIS FORM (by July 27). Do Not send money. Please pay at the meeting.

Name: ______________________________________ No. of persons _____________

Karen I. Hauschild Extension Educator
(413) 545-5304
hauschild@umext.umass.edu

Healthy Fruit is written by Dan Cooley, Ron Prokopy, Starker Wright, Wes Autio, and Karen Hauschild except where other contributors are noted. Edited by Dan Cooley. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. Healthy Fruit is available on the Web at The Massachusetts Tree Fruit Advisor, (click here). A text version can be e-mailed to you if you contact me, at dcooley@microbio.umass.edu. Please cite this source if reprinting information.