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Scab inoculum has continued to mature slowly. We estimate that in the eastern part of the state and in the southern sections of Western MA, by the weekend we will be at the 10% mature spore level. This is when infection periods need to be treated in orchards that were "clean" (no scab) last fall. This will coincide with tight cluster to very early pink. So, if temperatures aren’t warm enough to push trees, then they won’t cause spores to mature either. As in most years, look at tight cluster as the time when scab management needs to get serious.
If you had a bad scab year last year, then you should get serious earlier. Keep in mind that last year we had conditions that allowed a lot of scab to develop late in the season. Pin point scab on fruit indicates that there was a lot of scab inoculum at harvest. In these blocks, there will be a lot of scab inoculum this spring. Where you have a lot of overwintering scab, treat carefully, treat earlier rather than later, and make sure you get good coverage!
Keep in mind, if captan or one of the EBDC fungicides are used alone, then they need to be used earlier than the SI's (Rubigan, Nova or Procure). The SI fungicides have significant post-infection activity. Captan and the mancozeb fungicides do not. They will, at best, "kickback" 24 hrs from the start of the infection.
For the first time in a few years, we have new fungicides available for apples. Cost will probably determine whether or not growers use them. Here are a few general facts to consider beyond the money issue.
The strobilurines, Flint and Sovran, are very good scab fungicides. They have good protection and excellent post-infection activity, making their total efficacy period about 10 days. Some tests indicate that the time between applications could be up to 14 days, but it isn’t clear that this is always the case. While these are good materials, there are limits on the number of times they may be used in a season, and on the amount that can be used in the season. These are designed to limit development of resistance. Both Flint and Sovran are excellent flyspeck fungicides, and it may be that this summer use is even more important to growers than their use as scab fungicides.
Vangard is another new fungicide, not related to the strobilurines. It is most effective if applied as a protectant early in the season, when temperatures are cool. Later on, as days get warm, Vangard is less effective. The short story is that Vangard could serve as an early-season alternative to Syllit (dodine).
From 1997-1999, we conducted an exhaustive survey aimed at determining the optimal numbers of traps per orchard block (based on block size) needed to provide a reliable estimate of tarnished plant bug population levels. Through this work, a striking trend emerged—a dramatic, steady decline in numbers of TPB captured each season since 1995. This trend is holding true thus far in 2000, as all sampled orchards remain well below recommended thresholds.
Despite the fact that TPB numbers have been steadily below threshold, we still recommend that growers monitor abundance of this pest with white rectangle traps. It is pretty far along in the TPB season to consider placing traps now; these traps should be placed in orchards by green tip (though silver tip is ideal). For reference, traps should be hung at knee level, clear of waving branches and tall grass. Current thresholds for treatment are listed in the 2000 March Message.
Along with TPB, we have also monitored early-season populations of leafminer adults for many years, with a very different trend taking shape. In the last two years in particular, many orchards have been bombarded with emerging LM adults. In fact, in 1999 a great majority of Massachusetts orchards exceeded thresholds for treatment based on trap captures, thus requiring chemical intervention. Because so many orchards effectively used Provado against first- or second-generation mines last year, we had expected that the overwintering LM population might be fairly calm this season. Unexpectedly, the emergent population of LM adults seems quite heavy again—some blocks have already reached an average of 20-50 LM per trap, which is well above treatment threshold.
Prior experience has demonstrated that sticky red rectangle traps stapled to tree trunks offer a reasonable estimate (~80% accuracy) of apple blotch leafminer population density. Unfortunately, these traps may not be reliable for orchards whose principal species is spotted tentiform leafminer—the species that appears to be gaining quite a foothold in many Massachusetts commercial orchards. Species composition seems to play a significant role in establishing differences in each orchard’s LM population growth potential, though far more research is needed (and pending) to understand the dynamics of LM buildup and management in commercial orchards.
Samples of overwintering European red mite eggs have revealed that most (though not all) orchards are harboring a very light ERM egg load. Given appropriate weather for oil applications, this may be a season in which growers can achieve acceptable season-long control of ERM with use of oil alone.
As always, we are placing a strong emphasis on recommending use of early-season oil applications as the foundation for a sound mite management program. We remain firm in the belief that use of oil sets the stage for effective management of mites, particularly given the following observations:
1. Much evidence of resistance to Apollo and Savey has been demonstrated (in other countries) where these materials have been used for 3 or more consecutive seasons. Both materials are safe on beneficials, but are essentially interchangeable in development of resistance. Given the fact that use of both materials has become fairly widespread since registration several years ago, eventual resistance development is likely—leaving both as short-term solutions.
2. Studies in 1997-1999 in Massachusetts and New York have shown that Agri-Mek has a particularly destructive effect on the development of mite predator populations. Specifically, these destructive effects were seen on building populations of T. pyri, which holds the greatest potential to offer biological control of ERM in the Northeast.
With these factors, our philosophy at present remains: a pre-bloom oil program is the best start to successful long-term mite management. If wind, cold, and traction are favorable, we recommend use of a 2% oil spray at or near half-inch green, followed by a 1% oil spray as a supplemental treatment.
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Jon Clements, Starker Wright, Wes Autio, and Duane Greene except where other contributors are noted. 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.
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