March 22, 2004 Volume 13 No. 1 Update on Pest Management and Crop Development
(Art Agnello, Entomology, Geneva)
March is traditionally when we get snow storms, wind storms, rain storms, you name it, so we were starting to get a little worried over the relatively benign weather so far -- until last week's snowball express, which naturally coincided perfectly with a road trip we had to make to attend a research meeting. Good to know there's some constancy in the universe. With that, and the fact that we're officially into spring, we're assured that this first issue of the year is right on schedule.
Change Your Spam Filters
Sometimes it's hard to tell whether the mailing list for this newsletter is continually changing, or just ascending to a higher plane. As usual, if you're reading this issue, it's because our version of where you are and how you prefer to receive it coincides with your own. Currently, more than three times as many subscribers are electing to get the e-mail version than the hard copy; 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 is at some undisclosed secure location. 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 accommodate 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
I also post it to the CENET Tree Fruit Discussion Group
BB, a list-serve, at:
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 be sent to anyone who requests it; just don't ask how this squares with all that stuff in the previous sentence.
Book of the Month
The wizards at Cornell Media Services (or whatever they're called these days) have been honing their craft, and the 2004 Pest Management Guidelines for Commercial Tree-Fruit Production has actually emerged to see the light of day before the first psylla took wing, so this reference 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 printed off, from:http://www.nysaes.cornell.edu/ent/treefruit
We're once again updating the html-format version, which contains the appropriate interactive links to all of our other online resources and will now more closely resemble 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 web page: http://www.fruit.cornell.edu/
PRODUCT REGISTRATION UPDATE
(Art Agnello, Entomology, Geneva)
Old Faces, New Labels
It's always a useful exercise at this time of year to recap some of the recent or imminent pesticide registration changes in our fair state since the end of the last season:
• Asana - The apple label now also includes mullein plant bug, which we have found to be quite susceptible to pink bud applications.
• Dimethoate - EPA has cancelled its use on apples, following the registants' request, although existing stocks may be used through the 2004 season.
• Lorsban - Gowan has registered a new, low-odor, 75 WG (water dispersible granule) formulation on a number of crops, including all tree fruits except apricots. They describe it as an encapsulated "dry EC" that is a replacement for the old 50W formulation, which has been phased out, with better efficacy and rainfastness, and fewer phytotoxicity problems than the 50W or 4E formulations. Pre-bloom use only in apples is allowed against OBLR, rosy apple aphid, Lygus bugs (includes tarnished plant bug) and San Jose scale, along with some other minor species. Pests labeled in other tree fruits include pear psylla, San Jose scale, many borers (American plum, LPTB, PTB, shothole), leafrollers, lesser appleworm, scales, stink bug, tarnished plant bug, and climbing cutworms. See label for full details.
• Nexter - Pyramite is no longer being produced, but the same active ingredient (pyridaben) is now available and registered by BASF in NY under this new name, as a 75 WS formulation, which is slightly higher than the old Pyramite 60 WS. Looking at the use rates against ERM and TSSM, the range given is a higher a.i. for the minimum rate than Pyramite, but the maximum rates are generally comparable. Like Pyramite, Nexter may not be used on Long Island, and the PHI values remain the same (apples, 25; apricots and cherries, post-bloom; all other crops, 7). One important difference -- only ONE application per season now permitted on apples and pears.
• PureSpray Spray Oil 10E - This product was also labeled late last year, and probably not noticed by many growers because its registrant, Petro Canada, is less well known than are other oil manufacturers. This is a full season horticultural mineral oil whose claim to fame is 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). This accords it a high safety factor in terms of avoiding phytotoxicity, and helps its efficacy against mites and scale insects.
• Provado - A registration on stone fruits that came through last June might have escaped notice by some people, and we may have failed to give it proper attention at the time. Nevertheless, it can now be used in all NY stone fruit crops for the control of such pests as aphids, Japanese (and other) beetles, San Jose scale, tarnished plant bug, stink bugs (suppression), and leafhoppers.
Over the Rainbow
One of these days, we might start up a pool to predict when state registrations might come through for some of those elusive new products the rest of the country has had access to for at least a year before they appear in our distributors' warehouses.
• Assail - A new member of the neonicotinoid group of insecticides (which includes Provado and Actara), 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 is this product's second year on the Limbo List, although we have been informed that the registration package has been deemed 'complete' by the DEC, so presumably action of some sort and on some time schedule should be taken in 2004.
• Intrepid - We waited in vain for progress on this registration all last year. This is the more-active successor to Confirm, which is due to be phased out of the tree fruit market. Dow has been working diligently on the package with the DEC, and our most recent conversation with unnamed sources was uncharacteristically optimistic, so I guess we'll see if the magic is real this season.
• Calypso - A new entry in the neonicotinoid category from Bayer, it 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. Calypso was labeled federally last year, but is still doing the registration tango in NY this year and isn't likely to be seen in the 2004 season.
• Zeal - A very promising new miticide from Valent, this acts much like an insect growth regulator by inhibiting molting, and has very good activity against the major species when applied at threshold or preventively. Legal everywhere but NY; difficult to see it here earlier than late season, if then.
REVISING SCAB CONTROL STRATEGIES FOR 2004
Controlling apple scab in 2004 may be more difficult than at any time in the past 25 years because of the following factors:
• Most orchards have significant carry-over inoculum due to less-than-perfect scab control during the wet summer of 2003.
• Scab populations with multiple resistance to apple scab fungicides are present in some (perhaps many?) orchards, but there is currently no way to determine where resistant populations are lurking.
• Apple growers have become accustomed to limited-risk prebloom scab control strategies that may prove ineffective for managing scab in orchards where the scab population is resistant to dodine, Topsin M, and SI fungicides (Rubigan, Nova, and Procure).
The rest of this article address each of these issues and then provides specific recommendations for a conservative scab control program in 2004.
High inoculum contributes to more scab control failures than is generally recognized. In high-inoculum orchards, the first infections often occur earlier than in low-inoculum orchards, and the slightest gap in prebloom fungicide protection can result in economically significant scab infections. Orchards with visible scab on leaves at the end of last season are automatically considered high-inoculum orchards. However, there is increasing evidence that some symptomless leaves may also harbor overwintering inoculum. This may occur if infections were only suppressed by use of SI fungicides applied on a post-infection timing or if infections occur in autumn. The latter is of special concern for spring of 2004.
Exceptionally wet conditions persisted from August throughout September of 2003 in many parts of the Northeast. In the Hudson Valley, 9.1 inches of rain fell in September, with 4.2 inches in the first four days of September. In Geneva, 9.2 inches of rain fell in August and September with nearly 5 inches falling in the first 13 days of August. These rains removed all fungicide residues, thereby allowing ample opportunity for late-season infections to occur in any orchard that had visible scab lesions prior to the start of the rains and that were not resprayed with fungicides after the rains. Late-season infections may remain invisible or may be only faintly visible on the underside of the leaves, so the severity of late-season infections may be underestimated.
High inoculum alone increases the potential for severe scab infections at green tip, but the risk for infection skyrockets if high inoculum is combined with early ascospore maturity. Ascospore maturity is often advanced compared to tree phenology in years where continuous snow cover and cold wet spring weather combine to allow rapid advances in spore maturity. Prebloom temperatures between 32 and 40 F (assuming adequate moisture to keep leaf litter damp) favor advanced maturation of apple scab ascospores when trees reach the green tip bud stage. Even worse, pseudothecia that develop under cool temperatures produce more ascospores than those that develop under warm temperatures. In one study, pseudothecia incubated at 43 F produced 1000 spores per pseudothecium as compared with only 584 spores per pseudothecium when incubated at 54 F. Thus, a cool wet spring will make a bad year worse.
Fungicide resistance has been identified (via extensive lab testing) as the cause of high incidences of fruit scab in at least four NY orchards over the past year. We suspect that similar levels of resistance are present in many other orchards, but major scab epidemics were averted only because scab was held in check by the contact fungicides (mancozeb, Polyram, captan) that are used with SI fungicides. Low rates of contact fungicides tank-mixed with SI fungicides can control SI-resistant scab so long as inoculum levels remain low. With high inoculum levels anticipated for spring of 2004, more growers will probably see control failures if they omit green tip sprays and use SI+contact sprays at 10-day intervals.
There is no way (at this time) that we can test hundreds of orchard blocks to determine whether scab in those orchards is resistant to SI fungicides, dodine, or Topsin M. Thus, the only safe approach to scab control in 2004 is to assume that every orchard contains some level of resistance to all of the fungicides noted above.
Grower attitudes toward apple scab may adversely affect prospects for good scab control in 2004. Scab control strategies developed and adopted over the past 25 years were based on the assumption that growers could afford a small risk of less-than-perfect scab control during the prebloom period because fungicides applied starting at tight cluster or pink would eradicate any missed infections. These limited-risk strategies included delaying the first scab spray, spraying alternate rows without reducing the spray interval, and using low rates of contact fungicides (often <50% of the rates recommended in 1960). These strategies were cost effective thanks (in part) to the availability of fungicides with post-infection and pre-symptom activity (dodine, Benlate, Topsin M, SI fungicides). Success in controlling fungicide-resistant apple scab will largely depend on how quickly apple growers can react to the need for conservative scab control programs. For some large farms, an additional sprayer and sprayer operator may be required if trees are to be sprayed every 5-7 days rather than every 8-12 days.
No new fungicides are available to resolve the fungicide resistance problems. The strobilurin fungicides (Sovran, Flint) were originally promoted as substitutes for the SI fungicides, but we increasingly recognize that these fungicides are excellent protectants with only limited post-infection activity. Perhaps more importantly, the strobilurin fungicides do NOT have pre-symptom activity (activity from 72 hour after infection until scab lesions appear). It is precisely the pre-symptom activity of dodine, Benlate, Topsin M, and SI fungicides that made them so effective in eliminating the "misses" that occurred as we cut back on pre-bloom scab control. Using Sovran or Flint to arrest epidemics after scab lesions become visible in spring will only speed development of complete resistance to this class of fungicides.
Vangard, an anilinopyrimidine fungicide, is of questionable value for scab programs under New York conditions. Protection provided by Vangard is never better than that provided by 3 lb/A of mancozeb, and the 48-hr post-infection activity of Vangard is most reliable at low temperatures (<45 F). We do not expect that Vangard will ever match the qualities that dodine, Benlate, Topsin M or the SI's had before resistance compromised their activity against apple scab.
A conservative scab program for 2004 will include the following:
1. Apply a urea spray (40 lb/A) to the leaf litter before green tip in orchards that were clobbered with scab last year. A spring application of urea can significantly reduce inoculum production in the leaf litter, thereby reducing pressure on fungicides.
2. Apply a fungicide at green tip or at least before the first scab infection period. A copper spray applied at green tip to suppress fire blight will also control scab and will suppress the superficial bark cankers caused by Botryosphaeria species.
3. Follow up at 5-7-day intervals (or before rains) with applications of captan, mancozeb, or Polyram.
4. Use either a strobilurin fungicide or an SI+contact fungicide starting at pink or bloom to initiate mildew control and to enhance scab control during the period of peak risk for development of fruit scab. (The SI will help with scab control only where scab is still sensitive to SI fungicides).
5. After the first strobilurin or SI+contact spray, continue with additional strobilurin or SI+contact sprays through second cover. Alternating strobilurin with SI+contact sprays may be more effective than using two applications of one group followed by two applications of the other. Using the high label rates of strobilurin fungicides will slow development of resistance to these fungicides. Use the strobilurin and SI+contact fungicides with shorter spray intervals (i.e., 7-9 days rather than 8-12 days) if the season is highly favorable for apple scab, and maintain these short spray interval through second cover if scab lesions are visible on leaves at petal fall.
By using shorter spray intervals and depending primarily on contact fungicides, growers should be able to completely control prebloom scab infections even in orchards with high inoculum. Effective scab control from green tip to petal fall virtually eliminates risks of significant fruit infection, and more extended fungicide spray intervals can be employed after the supply of scab ascospores is depleted (usually around petal fall) so long as no scab lesions are evident on cluster leaves.
Fungicide resistance has eliminated the safety net that allowed for limited-risk prebloom fungicide strategies that were developed over the past 25 years. Any shortfall in prebloom scab protection now can explode into a serious fruit scab problem if weather conditions favor scab development. Even if resistance is not currently present in an orchard, using a conservative prebloom scab control program will prolong the effectiveness of those fungicides to which resistance has not yet developed.