March 21, 2005 Volume 14 No. 1 Update on Pest Management and Crop Development
We were starting to worry that this might be one of those years marked by a series of memorable March blizzards, but about a week ago the jetstream parted to give way to a long stretch of nice, bright sunny (if chilly) days. This winter seems to have dragged on past everyone's "cranky" threshold, so even if the warmer temperatures are a bit late in arriving this spring, the sunshine alone is cause for some optimism (not to say preparedness) for the coming field season. This first issue of the year always seems to be looming on the calendar long before I'm ready to tackle it; this usually lasts until about the second issue, at which point I get worried that we were almost too late in starting.
Don't Delete Us with the Mortgage Offers
The mailing list for this newsletter is not unlike some reclusive living organism. As ever, if you're reading this issue, it's because our rendering of where you are and how you prefer to receive it coincides with your own. Currently, about four times as many subscribers are electing to get the e-mail version as opposed to the hard copy; this latter figure is something less than 20% of its original size when we started publishing in 1992. At a certain point, it may not be worth the effort and cost to print Scaffolds on real paper, so it's important for us to know with some accuracy how many readers have that preference. Delivery of the hard copy to subscribers failing to return the re-subscription card will cease after some famously arbitrary period of time. If you got the e-mail ASCII-text version last year, it's being sent to the address you last specified; if you're not receiving it, you must have forgotten to notify us that your Internet Service Provider got voted off the island. Let us know of any preferred modifications you wish to make in this general arrangement (to/from one form or another, address changes, start-up or stopping of subscriptions, etc.), and we'll do our best to accomodate you. If your mail server automatically strips out "extra" space characters in messages, which will make our carefully crafted tables look like spam subject lines, let us know and we'll send your issues as attached Word files. There is also a web version available from the NYSAES server, which is normally up by Tuesday or Wednesday each week, at: http://www.nysaes.cornell.edu/ent/scaffolds
As always, we are happy to consider contributions (particularly from N.Y. sources) in the form of articles on topics in any of the fruit crop protection or crop production areas, as well as N.Y. field observations, trap data, etc. We generally do not send the mailed version of this newsletter to growers, homeowners, or other private individuals not having some fruit extension, commercial, university or governmental affiliation, as the extension superstructure that pays the bills would rather that audience obtain this information through their local Cornell Cooperative Extension programs. Unless things get too out of hand, the e-mail version will still be sent to anyone who requests it. (Just don't ask how this squares with all that stuff in the previous sentence.)
Like the first robin of spring, the 2005 Pest Management Guidelines for Commercial Tree-Fruit Production has actually emerged into the cold light of day before the pear psylla's inaugural flight, so it should now be available from all the usual sources. Moreover, an online version of the new edition is available as a series of pdf files that can be selectively printed off, from:
We're once again updating the html-format version, which contains the appropriate interactive links to all of our other online resources and now more closely resembles the printed copy, for ease of navigation; a link to this version will appear at the above address when it's finished. Incidentally, these can all be accessed at the Cornell Fruit page: http://www.fruit.cornell.edu/
Fruits of the Label Tree
• Zeal - This is a new-chemistry miticide from Valent that acts much like an insect growth regulator by inhibiting molting, and has very good activity against European red mite and twospotted spider mite when applied preventively or at threshold. Good performance has been noted in a number of efficacy trials conducted recently in our region. Labeled on apples and pears; REI = 12 hrs, PHI = 28 days, 1 application permitted per season.
• PureSpray Green Horticultural Spray Oil - Another offering from Petro-Canada, this emulsified spray oil is labeled for dormant and delayed dormant use on all tree fruits against mites, psylla, scales, and various aphids, and is billed as the only spray oil that is both OMRI-approved and EPA organic-certified. Like the full-season PureSpray 10E Oil, its extremely high 'purity' or paraffinicity (otherwise expressed in terms of unsulfonated residue -- in this case, at least 99%, compared with 92 for some more commonly used oils) accords it a high safety factor in terms of avoiding phytotoxicity, and contributes to its efficacy.
• Isomate-OBLR/PLR Plus - This twist-tie dispenser contains the principal pheromone component of the obliquebanded and pandemis leafrollers (Z-11-acetate), and is recommended by the manufacturer (CBC America) at 200/acre as a supplement to leafroller pesticide control programs. This product has not been evaluated in N.Y.
• Assail - A new member of the neonicotinoid group of insecticides (which includes Provado and Actara) from Cerexagri, this selective product has activity on aphids, leafminers, leafhoppers, apple maggot and psylla, but more importantly, codling moth and oriental fruit moth are also susceptible. This product actually received its label (on apples and pears only) last spring, so its name may not be too familiar yet in the field; its versatility makes it a good choice for a number of pest management decisions. REI = 12 hrs; PHI = 7 days.
• Intrepid - This Dow product is the more-active successor to Confirm, which is due to be phased out of the tree fruit market. Also labeled on apples and pears in N.Y. last spring, this IGR is primarily active against OBLR, but additionally offers some activity against internal leps like oriental fruit moth, codling moth, and lesser appleworm. REI = 4 hrs; PHI = 14 days.
• Calypso - A new entry in the neonicotinoid category from Bayer, this may be one of the most active and promising ones in the stable, with activity against curulio, codling moth, oriental fruit moth, leafminers, leafhoppers, aphids, and apple maggot. It's not labeled in N.Y. yet, but appears to be very close, and may well be in place by the time the growing season gets under way.
• Pristine - A new stone fruit fungicide from BASF that combines a strobilurin with activity similar to that of Flint and Sovran, together with a carboxamid that is effective against Botrytis and brown rot. N.Y. registration is pending, expected this season.
• Penbotec/Scala - This fungicide is in the same chemical class as Vangard; Penbotec is intended for postharvest use (against decays) on pome fruits, and Scala is used for control of scab on pome fruits plus brown rot blossom blight, scab, and shot hole on all stone fruits except cherries. As with Pristine, N.Y. registration is pending, but expected this season.
• Maxcel is a 1.9% formulation of Benzyl Adenine growth regulator that induces fruit thinning when used between petal fall and 15 mm fruit size. Registration in N.Y. is expected in time for the fruit thinning period.
Scattered orchards throughout the eastern US developed severe scab problems during the 2004 growing season. Some problems were attributable to wet spring weather in 2004 that interfered with fungicide applications and favored scab development. In other cases, control failures occurred when growers continued to depend on the SI fungicides (Rubigan, Nova, Procure) in orchards where apple scab has developed resistance to this class of fungicides. In either case, regaining control of apple scab this year may be easier if sanitation measures are applied to reduce inoculum levels before apple trees begin to grow this spring.
The amount of overwintering scab inoculum in orchards can be significantly reduced either by applying a urea spray sometime before green tip or by shredding leaf litter with a flail mower. Urea works by stimulating microbial breakdown of overwintering leaves and by softening leaves so that they can be removed more quickly by earthworms that feed on the leaf litter. Urea may also directly suppress ascospore formation in the surviving leaf litter. Shredding leaf litter with a flail mower causes leaves to decay more quickly and also reorients much of the leaf litter so that ascospores released from those reoriented leaf pieces will discharge into the ground rather than into the air. In a recent study in New Hampshire, Sutton et al. (2000) found that either of these sanitation measures (spring urea sprays or flail chopping leaves in spring) could reduce ascospore production by 70-80%.
In using urea for inoculum reduction, the standard recommendation is to treat each acre of orchard with 40 lb of urea fertilizer dissolved in 100 gallons of water. Applications can be made either with air blast sprayers that have the upper nozzles turned off or with boom sprayers rigged to spray both the sodded row middles and the areas beneath the trees. The portion of the urea spray that falls within the herbicide strip beneath the tree canopy (or inside the drip-line) will ultimately contribute to nitrogen fertilization of the trees, whereas the portion of the spray that is applied to the sodded row middles will be utilized primarily by the ground cover. Nitrogen fertilizer rates should be adjusted accordingly for orchards where urea applications are used for scab control.
Effective leaf shredding can be accomplished only with a flail mower that is set low enough to contact leaf litter on the orchard floor. If the flail mower cannot be offset to reach most of area beneath trees, then leaf litter beneath trees should be blown or raked into the sodded row middles where it can be accessed with the flail mower. Mechanical brush rakes can remove leaf litter from beneath the tree if the orchard has a relatively clean herbicide strip. Flail mowers used to chop prunings should shred leaf litter at the same time if the flails are adjusted to cut low enough. However, low mowing in early spring can remove most of the overwintering sod cover, thereby increasing potential problems with mud and equipment traction at the time when early sprays will need to be applied.
Why are we promoting urea sprays or leaf shredding for high-inoculum orchards this spring? The primary reason is that we believe the SI fungicides are no longer effective in many of these high-inoculum orchards (more on that next week). Even conservative programs with protectant fungicides may provide less than 100% control of scab in high-inoculum orchards. In orchards where we no longer have any dependable method for arresting scab development after infections occur, just a few prebloom scab infections have the potential to cause season-long problems if the summer turns out to be cool and wet. Sovran and Flint may still be useful for stopping scab after infections appear in trees, but they are far less effective than the SI fungicides and using them to "burn out" scab will only contribute to further selection for resistance to the strobilurin fungicide group.
Sanitation measures applied to high-inoculum orchards will provide the following benefits:
1. Reducing inoculum reduces risks of getting green tip infections. These early infections begin sporulating as trees approach bloom, just at the time that terminal leaves and fruitlets are approaching peak susceptibility to scab. Only a small proportion of ascospores are usually mature enough for release at green tip, but that small proportion can still be a huge number in high-inoculum orchards. High-inoculum orchards subjected to urea sprays or leaf shredding will behave more like "normal" orchards vis-a-vis risks of green tip scab infections.
2. Protectant fungicides such as mancozeb and captan work better in low-inoculum than in high-inoculum orchards, especially if foul weather prevents perfect spray timing. Whereas the SI fungicides provided a "safety net" that eliminated infections that escaped prebloom sprays, the only option in orchards with SI-resistant scab will be to purchase that insurance up front by reducing inoculum levels before the season begins.
3. Reducing inoculum reduces selection pressure for resistance to the strobilurin fungicides (Sovran, Flint) and the anilinopyrimidine fungicides (Vangard, Scala) if those fungicides are used during the prebloom period.
Using a urea spray or leaf shredding prior to bud break will not eliminate the need for protectant sprays beginning at green tip. Where SI resistance is suspected, extra care will still be required to ensure that trees are protected with mancozeb, Polyram, and/or captan ahead of rains. Sanitation measures that reduce overwintering inoculum levels are therefore a supplement to, not a replacement for, effective spray programs during the prebloom period.
Literature cited: Sutton, D.K., Mac Hardy, W.E., and Lord, W.G. 2000. Effects of shredding or treating apple leaf litter with urea on ascospore dose of Venturia inaequalis and disease buildup. Plant Dis. 84:1319-1326.