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For the past 3 years, we have been placing and monitoring sticky white rectangle traps for tarnished plant bug in many orchards across the state. This has been done in an attempt to refine our threshold levels for treatment against TPB and to determine optimal numbers of traps per orchard block (by block size) needed to provide a reliable estimate of TPB population.
The most striking trend of this study thus far has been the relative lack of early-season TPB buildup in most orchards-few growers have needed to apply a pre-bloom insecticide targeting TPB. Although trap captures of tarnished plant bug have been below average statewide for the past 4 years, we highly recommend continuing to monitor for this pest with white rectangle traps. These traps should be placed in orchards by green tip (silver tip is ideal), and they should be hung at knee level, clear of waving branches and tall grass. Current thresholds for treatment are listed in the 1999 March Message, and will appear in next week's issue of Healthy Fruit.
Miner
Infractions
Along with early-season monitoring of TPB, we have been conducting a study aimed at refining trap-capture thresholds for leafminer. 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, a relative newcomer to Massachusetts orchards. Last year, we witnessed a very rapid rate of multiplication between first- and third-generation leafminers in many orchards where LM adults were essentially undetectable prior to bloom.
In order to address this shortcoming, we have expanded our leafminer monitoring project for 1999, and have brought aboard a visiting scientist from China to evaluate leafminer density, species composition, and leafminer parasitoid complex present in 24 commercial orchards. In addition to this project, we are evaluating 8 different combinations of trap style and placement for their effectiveness in capturing each LM species.
This year, as always, we are placing a strong accent on recommending use of early-season oil applications as the foundation for a sound mite management program (with the added benefit of San Jose scale suppression). 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 the development of resistance. Given the likelihood of eventual development of resistance in this country, we do not believe that either material can offer a long-term solution.
2. Recent studies in Massachusetts and New York have shown that Agrimek 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 is likely the best available species for biocontrol 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 agreeable, we recommend use of a 2% oil spray at or near half-inch green, and a 1% oil spray as a supplemental follow-on treatment.
Scab Prepared to
Strike
The heavy scab last year has left most orchards with a heavier-than-usual dose of inoculum ready for this spring. The maturation of ascospores appears to be about normal. There are only from 1 to 5% of the spores that are mature and ready for release. In most years, this wouldn't be cause to rush out and spray. That's because in most commercial orchards, 1 to 5% of a very small amount of inoculum is not a very big deal, and the leaf area is still relatively low.
This year, the leaves aren't growing any faster, but the spore load is larger, and so there are 1 to 5% of A LOT of spores available in many orchards. For that reason, growers should be ready to treat before or right after the next infection period.
In view of the recommendations for an early oil, if possible, it might be time to look again at oil plus a fungicide, such as Syllit or an EBDC, early. This program has been very successful in the past, and would deal with the early-season scab issue as well as the mite problem.
The most recent information on the EBDCs, Dithane, Penncozeb, Manzate and Polyram, indicates that with the 3 lbs./acre rate (usually around 1 lb./100 gal.) these materials are being stretched to the limit of their scab controlling power. On larger trees (around 300 gal. per acre dilute tree row volume), either boost the rate to the 6 lb/acre level and use fewer applications, or make sure that the interval isn't stretched beyond 7 days between sprays, the sprays cover well, and all else is right with the spraying method. On smaller trees, where the tree row volume drops down to 150 gal. dilute or less, then 3 lb. per acre should be fine, because essentially that is 2 lb./100 gal., a full rate.
Late for Leaf
Curl
It's probably beyond bud swell on peaches in most areas. That means it's too late to get good control with a spring leaf curl fungicide spray. Hopefully, most growers got something on either last fall or this spring before now.
The problem with treatments after the buds have swelled is that the fungus has already had a chance to infect. Once it's inside the leaf tissue, fungicides can't stop it. Fortunately, it hasn't rained much if at all this spring, and the fungus needs wet weather to grow well. If there was bad leaf curl in an orchard last season, and nothing has gone on yet this spring, probably an application of Bravo or a copper-based fungicide as soon as possible would still have some benefit.
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.