Captan, EBDCs (Dithane, Manzate, Penncozeb, Polyram), Syllit and even sulfur have shown the ability to prevent scab infections when applied within 18-24 hours after an infection period begins.  The length of interval is temperature dependant.  Even though these fungicides work on the leaf surface, they can control scab after the ascospores land because it takes a while for the ascospore to produce a penetration peg that uses enzymes to enter leaf tissue.  These steps in the infection process that occur on the leaf surface can be interrupted by a surface (aka protectant) fungicide.  But that window is too short to be useful very often.

     Longer postinfection control is provided by sterol inhibitor (aka DMI or SI) fungicides (Nova, Rubigan, Procure) and strobilurin fungicides (Flint, Sovran).  When these products were introduced, they were thought to be able to reach back 96 hours to control scab.  These two groups share the characteristic of attacking scab at a very specific biochemical target.  That target differs between the groups, but it makes both of them vulnerable to development of resistance or lowered sensitivity in the scab population through single gene mutation and selection of less sensitive strains.  In contrast, captan and EBDCs attack scab in multiple ways, such that scab strains resistant to those materials have not developed despite decades of use.

     Wolfram Koeller, Dave Rosenberger, Alan Jones and other plant pathologists have studied the development of scab resistance to SI and strobilurin fungicides. The final word isn't in yet, but enough is known to provide guidance for continued use of these products. 

     An SI fungicide should always be used in combination with at least half rate of a surface fungicide such as captan, both to reduce the chance for resistance and to increase protection against fruit scab.  For strobilurins, the best investment may be to increase the rate of stroby used rather than to add a surface fungicide to the tankmix.  If you are going to use back to back postinfection applications, it may help reduce resistant scab strain selection to alternate between SI and strobilurin products.

     The recommendation for good coverage and adequate rates gets said so often that people may stop hearing it.  But with respect to postinfection fungicides it is especially important.  Marginal dosage, alternate row or applications at more than 6X (i.e. less than one sixth of the amount of water need for foliage to be saturated with spray such that additional spray would run off), alternate row spraying, and delayed applications share one characteristic.  They cause scab infections to be exposed to sub lethal doses. That seems to be the key factor that leads to resistance in the long term, and of course poor control from that particular application.

      Because of the general concern about resistance, it may now be prudent to not count on more than 72 hours postinfection activity from SI or strobilurin fungicides.  This is not just to insure good results from that particular application, but also to prevent sublethal exposures that select for tolerant strains.  If there is a site-specific concern about shift in the scab population towards lower susceptibility, then if these materials are used at all, the kickback window should be considered over at no more than 48 hours.    

      Curiously, even though SI and stroby fungicides have different modes of action, scab strains that are less susceptible to SIs also appear to be less sensitive to postinfection control by strobilurins.  The six day forward protection provided by strobilurin fungicides does not seem to be diminished for scab strains with reduced sensitivity to SI fungicides.  SI-tolerant scab strains also show a six-fold increase in tolerance of Vangard fungicide.

      If an SI or strobilurin application is made beyond the range of reliable postinfection control, then that application should be followed 7 days later by another postinfection fungicide application.  If an SI was used in the first treatment, then its best to switch to a stroby for the second.  If a stroby was used for the first, use an SI for the follow-up.

     Full rate captan is as good as anything for burning out scab lesions.  If the situation is drastic, you might consider combining it with Topsin M.  SIs are rated Fair to Good for eradication, but because of the resistance issue, their use in that situation is discouraged.  Strobilurins are not effective as an eradicant for existing scab lesions, and their use in that situation can greatly increase the chance for resistant strain selection.

Scab status report: 

     For Sanford, Friday was most likely the year's final important scab infection period.  But you should stay protected through the rain forecast for June 1 -3, and to be safe you should maintain protection at a near-primary scab level until scab control can be confirmed.  See below. 

     For Monmouth, what is probably the year's final important primary scab infection period is the one forecast to start Monday night and last into Wednesday.  While it's a tail end infection period, this one could carry a considerable amount of infection potential.  As above, protection beyond that infection period should be maintained until scab control can be verified by lesion scouting.

     Scab lesions are just now developing to the point where they are visible on leaves.  It won't be until June 10 - 12 when almost all the first generation lesions will have had time to appear in the Sanford and Monmouth areas, respectively.  It won't be until roughly (depends on future rain dates) June 20 - 22 before all second generation lesions will have had time to appear, allowing you to confirm that scab control was successful.

Fire blight

     No news is good news.  There does not appear to have been suitable conditions for fire blight in Maine this year, though it won't be until June 6 when we can confirm that the questionable infection period on May 15 in Sanford had no significant effect.  Growers in New York, West Virginia and other states are dealing with some of the most fire blight conditions in years.

*** = good or excellent, ** = fair, * = poor
0 = no effect.
" - " means not rated, presumably no effect.
P = preventative effect with continuous coverage from repeated applications.
? = no information or conflicting ratings.
L? = pest is member of group listed as target pests on Pyganic label, but no information on efficacy available. 

Pyganic 1.4 and 5.0 have 1.4% and 5% pyrethrin as the active ingredient, Pyrellin is a combination of 0.5% pyrethrin and 0.6% rotenone.

CM = codling moth, EAS = European apple sawfly, OBLR = Obliquebanded leafroller,
OFM = Oriental fruit moth, PC = Plum curculio, STLM = Spotted tentiform leafminer,
ERM = European red mite, PPs = Pear psylla.
BEN = Relative toxicity ratings for three beneficial species in this order:  Honeybees, Typhlodromus pyri (mite that feeds on ERM), and Aphidoletes aphidimyza (syrphid fly larvae that feed on aphids).  Toxicity to beneficials ratings are H = High, M = Moderate, L = Low.

Many apple insecticides are rated effective against leafminer moths.  Ratings in this table are for control of sap-feeding leafminer mines.  Some of the materials effective against moths may contribute to suppressing a summer leafminer problem, but only the materials with a two or three star rating displayed are recommended to suppress an over-threshold population of sap-feeding mines.

Aza-Direct/Neemix ratings against CM and PPs assume frequent applications at short intervals.  The same may also be required for Pyrellin applications to achieve the ratings shown.

Bt ratings assume earlier start and more frequent applications than might be used with other insecticides rated effective against the same pests.

Assail, Calypso and Intrepid require timing at beginning of egg hatch for best control of CM, OBLR, and OFM..  See Orchard Radar for timings.

I could not reconcile the Cornell and Penn State ratings of Esteem for OBLR because they are so different ("0" and "good", respectively).
 

Sources:

Ratings for all pests except EAS and OFM, and for all materials except for Assail and Calypso,  based on Cornell Cooperative Extension Pest Management Guidelines for Commercial Tree Fruit Production 2004, Entomology section by A. M. Agnello.  Alterations made to a few ratings for congruence with ratings from sources noted below.

Ratings for Assail and Calypso and for EAS and OFM ratings based on 2004-2005 Pennsylvania Tree Fruit Production Guide, Entomology section by G. Krawczyk and L. A. Hull.  Penn State ratings use a 4 point scale, whereas Cornell uses a three point scale.  This required some arbitrary assignments in translating Penn State values into a three point system.  Ratings within a column for EAS and OFM are consistent in how materials are ranked, but rankings across a row for Assail and Calypso may have slight discontinuity due to differences in rating systems.  Also, some ratings altered as noted below.

Ratings for Assail, Calypso, Avaunt, Esteem and Intrepid for CM, EAS and PC adjusted in accordance with spray trial results published in 26th Annual March Message to Massachusetts Tree Fruit Growers (2004) by Ronald Prokopy and Jon Clements.

     Weed competition in the tree row is most damaging to tree growth and productivity in the early postbloom period when foliage growth can exceed a tree's ability to transport water and nutrients.  This is especially true for trees whose roots and vascular system have been injured by low winter temperatures.  Young apple trees also benefit from not having to compete with weed growth during this critical period. 

     Postemergence herbicides are more effective and a lower dose can be used when weeds are small.  Label guidelines give the following recommendations for timing applications by weed height: Gramoxone < 6", Rely < 8", Roundup (and presumably other glyphosate products) < 12". 

    The optimum window for herbicide applications to control persistent weeds such as bindweed, morning glory, raspberry and other brambles, dandelions, goldenrod and vetch starts mid-June and lasts until mid-July.

     There is a typo on page 123 of the NEAPMG.  In the bottom row of the table, the E for 2,4,-D should be in the column for Broadleaf weeds, not grasses.
 

 Other stuff

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