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Most areas received at least some rainfall from storms moving across the state (6/28-6/29), and with these rains the soil has likely absorbed enough moisture to trigger emergence of apple maggot flies. From recent studies, it is clear that nearly all of the threat of AMF infestation in commercial orchards arises from immigrating flies: those which emerge from the soil beneath unmanaged trees nearby orchards and move into commercial blocks. Because AMF are emerging in and invading from the periphery, most flies are mature upon arrival; fruit damage from AMF egglaying can begin as soon as flies enter orchards.
As mentioned in the last several messages, we do not believe that this season holds much potential for heavy AMF infestation. However, in a season of light populations, regular monitoring of AMF abundance can gain importance, as growers may be able to save resources by reducing the number or intensity of chemical applications.
For monitoring of AMF, we consider red sticky-coated spheres as a superior tool to yellow rectangle traps or the more cumbersome sphere/rectangle combination. Regardless of the trap type being used, we suggest deployment during the first week of July, and proper placement is the key to accurate monitoring. When positioning traps in the canopy, it is critical that they be placed with abundant fruit and foliage beneath and to all sides. However, light is also a necessary component of effective placement as it enhances trap visibility to flies, so the most effective positioning is one-third of the distance into the canopy from the perimeter of the limbs. Dwarf trees are the exception to this rule as their small size allows light penetration throughout the canopy. Foliage and fruit should not be within 6" of traps in order to keep the sticky surface free of interference and scraping from limbs and leaves. Traps should be placed at least at head height, if not slightly higher.
Results from many years of data show that the capturing power of traps decreases for every week of exposure, so for accurate results traps should be examined at least once a week and should be cleaned of all flies every 3 weeks. Cleaning is best accomplished by picking the flies and debris off the traps with a small, sharpened twig, removing as little of the sticky as possible.
Traps should be placed in susceptible varieties in order to gauge the threat in areas where trouble will most likely arise. Common susceptible varieties are as follows:
Early-season: Early McIntosh, Gravenstein, Jersey Mac
Mid-season: Cortland
Late-season: Red and Golden Delicious
A farm of 10 acres should have 10 traps placed, while a farm of 100 acres should have 20 traps fairly evenly distributed. The treatment threshold for unbaited traps is a cumulative average of 2 AMF per sphere; when this threshold is reached, Guthion or Imidan should provide effective control. If the AMF population is low or moderate (as we expect in many areas this season), a half or partial rate of either material should be sufficient.
Early second-generation sap-feeding mines have been observed in some orchards, meaning that the ideal time to treat this generation is upon us. Growers who treated against the first generation (especially with Provado or Agri-Mek) should not have much need to re-apply—those who did not treat against the first generation would be well served to monitor the presence of the second generation to determine if application is necessary. For second-generation monitoring, samples should be drawn from middle-aged leaves of terminal shoots, and treatment should be considered if the population exceeds the thresholds listed in the June 22 issue of Healthy Fruit. When sampling, it is important to calculate only the presence of second-generation mines (not first-generation tissue-feeding mines), and treat with Provado, SpinTor, or Lannate if necessary.
With only spotty rain and high temperatures, we have had good weather over the past couple of weeks for rapid buildup of European red mites and two-spotted spider mites. Areas that have received only oil for mite control thus far may start to show some stress from the building mite population—we have seen little accumulation of ERM or TSM in blocks that received Savey, Apollo, or Agri-Mek. If treatment becomes necessary over the next couple of weeks, we recommend an application of Pyramite or Apollo, which should boost mite control through the season.
Green apple aphids have been observed on young foliage in relative abundance of late. This is not surprising this time of year, as most chemicals used to this point (such as Provado, Agri-Mek, and SpinTor) are locally systemic: they will control aphids on treated foliage, but are not known to migrate through the tree to the youngest foliage, where GAA are most likely to be found. Common predators of aphids are just starting to build as well, and in the past decades, the predators alone have been enough to control the GAA population.
Presence of liquid excrement (honeydew) on fruit and foliage is a common symptom of aphid infestation, but growers should not be alarmed. Honeydew itself does not damage the fruit and is regularly washed off by rainfall, though it may offer sites for development of sooty mold. If the pattern of the past can be used as a guide, GAA will be present in most orchards, but pose very little threat.
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Starker Wright, Wes Autio, and Duane Greene 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. A text version can be e-mailed to you if you contact Doreen York. Please cite this source if reprinting information.
