Populations of Maggot Fly Building and Moving Into Orchards

Over the past week's sampling, trap captures of immigrating apple maggot flies have continued to mount, and the peak of AMF immigration may be just around the corner. One factor leading to such early, heavy immigration is the lack of fruit on unmanaged hosts; last year's unmanaged trees harbored a large population of AMF, and this year's adults have no choice but to move into commercial orchards in search of fruit.

At this time of year, growers should pay particular attention to non-baited monitoring trap captures and AMF damage in early-ripening varieties. Not surprisingly, AMF tend to cause the earliest damage in the earliest fruit, and have been known to cause serious damage in July in Paula Red, Jersey Mac and Red Free. Sprays of Guthion or Imidan are best triggered by trap captures, though most treated orchards reach the AMF treatment threshold in 2 to 3 weeks after application.

At this point, captures on non-baited monitoring spheres in treated orchards range from 0 to 10 AMF per sphere, with approximately 50% of blocks exceeding the treatment threshold of 2 AMF per sphere.

Mite Bronzing Where No Oil or Miticide Was Used

Orchard blocks receiving an early-season miticide treatment are still relatively mite-free. In blocks which received no oil or miticide, the hot weather of the past weeks has stimulated substantial population growth, as expected. Some orchards are experiencing significant bronzing already, and may find themselves in need of a summer rescue treatment.

Over the past several weeks, we have discussed the alternatives for summer miticides, generally concluding that Pyramite is the best available alternative, offering excellent control of pest mites with the least impact on predators. However, use of Pyramite is no long-term panacea. It is known to have a moderate negative effect on predaceous mites, and one can expect development of resistance within a few years if it is used on an annual basis.

It is not easy to see a way out of the mite management woods, as recent information tells us that neither Kelthane nor Carzol can be relied on for long-term control, possibly due in part to resistance. As discussed in recent issues, both Kelthane and Vendex are available for use either with or without summer oil. Use of either material with oil (the most effective method of delivery) is difficult to recommend when applications of Captan are being used against summer diseases. With Captan being the recommended backbone for summer disease management in Massachusetts orchards, we don't want to detract from a solid disease management program with recommendations for mite control.

In short, the current hot weather is very favorable to rapid mite development and increased risk of bronzing. Growers may very well see a need for a rescue treatment during the next couple of weeks. If this is the case, growers can try an application of Kelthane, Carzol, Vendex or Vydate, but it is impossible to predict the degree of success that will be realized.

Leafminers and Leafhoppers: The Next Generations

As is generally the case after the first generation, leafminer development has become extremely strung out. Third generation adult flight has begun, while roughly 50% of mines are still in the sap-feeding stage. Results of applications of Vydate, Lannate or Provado against the second generation are widely variable. This is not particularly unusual, especially with use of Provado; properly timing a treatment against the second generation is very difficult, as is proper coverage, due to increased foliar density. Thus, one could argue that treatment against the first generation is preferred over treatment against the second. Studies in New York suggest that little advantage is gained from treating the third generation, as the majority of damage leading to fruit drop and poor storage appears to be caused by feeding of second-generation miners.

The second generation of white apple and rose leafhoppers is progressing into the adult stage, the stage at which they are not particularly susceptible to chemical intervention. If, however, large numbers of adults are observed in the trees, then a treatment may be in order against the third-generation nymphs. Leafhoppers are often overlooked as a serious threat until harvest, when they have left their residue cemented to the fruit and can be a tremendous nuisance to pickers.

San Jose Scale Damage to Fruit

Some orchard that traditionally experience problems with San Jose scale are already showing SJS infestation on fruit. While SJS is only a minor player in most orchards, growers should make every effort to avoid problems, as it can become an annual nuisance. Growers who did have problems with SJS last year will benefit from a treatment of Lorsban against the second generation, ideally in early August.

Scab to Flyspeck

With help from the heat, scab is slowing or stopped in many orchards. That is stopped in the sense that new tissue isn't showing lesions. The old lesions also appear less active, and with drier, hotter weather, they should stay that way.

Just when one disease finally stops, the symptoms of the next one arrive. In surveys and casual observations this past week, flyspeck has appeared on a single fruit in a commercial block, and on another fruit in an abandoned block. Frankly it is surprising that it hasn't shown up sooner. Perhaps the constant captan and benzimidazole barrage has kept flyspeck in check. With scab under control, cut back on fungicide use. But be aware that some fungicide will need to be on fruit to keep sooty blotch and flyspeck in check.

Storage School Next Week

Don't forget next week's Apple Storage School at the Hort. Res. Ctr. in Belchertown. It's open to anyone, and will have Chris Watkins and Jim Bartsch from Cornell, as well as Bill Bramlage, Sarah Weiss and Dan Cooley from UMass. Registration is $20 for the first person from a farm, and $15 for each additional person, to cover lunch and expenses. It will run from 9 AM to 3 PM. Please call Karen Hauschild at 413-545-5304 for more information and to reserve a slot.

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.