A major scab infection period is forecast to start Saturday May 22, with warm temperatures and a chance that showers could continue into Monday.  The next infection period will account for about a quarter of the year's total primary scab infection pressure in the Sanford area, and will probably be the last significant scab ascospore release in the Sanford area for 2004.  But there is enough chance of leftover spores that Sanford area growers should plan on treating the next rain that occurs after May 22-24 as the final infection period. 

     Lesions from the first 20% of the seasons primary scab infection potential will have had time to produce second generation spores in the Sanford before the end of the upcoming infection period, thus increasing the risk.

     For Monmouth and other Maine locations, an infection period beginning May 22 will be the second huge infection period of the year and will account for about 40% of the year's total primary scab infection pressure, with at least two more significant infection periods likely to occur after this coming weekend.

     Fungicide protection should be renewed as close as possible before this rain arrives. 

     Organic growers relying on sulfur for scab protection may need to reapply sulfur in the middle of this infection period if it does stay wet for two or three days continuously.  Sulfur dust formulations are preferable to a wettable powder solution for application during drizzly conditions.

     Scab Lesion scouting:  By next Friday May 28, roughly 40-60% of the season's primary scab infection potential in central and southern Maine orchards will have had time to appear as lesions.  This is a good time to begin scab scouting.  If you find more than 5 - 10 leaves with one or more scab lesions on them out of 100 shoots, that is indication that back to back fungicide applications might be called for to prevent subsequent spread of the disease.  For information on materials, rates and timing for conidial suppression sprays, see page 16 of the 2003-2004 New England Apple Pest Management Guide. 

     The laminated apple pest scouting card is designed for field use and can helpful for identifying young scab lesions and other pest damage.  You can pick one up for $1 at Highmoor Farm or by mail from the Pest Management Office, 491 College Avenue, Orono, ME 04473.

 Fire blight

     Unlike southern New England and New York, which had some of the worst fire blight weather in recent years, Maine orchards seem to be at little risk of fire blight blossom infection last year, with one caveat.  There was a potential blossom blight infection period in the Sanford area, but only one of the two models called it an infection period.  The Cougarblight model called it a borderline high risk infection period, but the MaryBlyt model did not rank it as being warm enough.  In this case, the MaryBlyt model seems to be the more realistic as many of the heats unit counted in the Cougarblight estimate occurred on May 12.  But most of the blossoms that were open when the rain arrived on Saturday May 15 were probably not open on May 12. 

     Still, it would be prudent for Sanford area growers to be on the lookout for wilting fruit clusters starting around June 6.  If found, fire blight infections on young trees or small trees on M9 or M26 rootstock should be pruned out as soon as possible and removed from the orchard.  Time is critical because the longer the fire blight is allowed to develop in the tree, the greater the chance of systemic whole-tree damage.  The critical window may be as short as two or three days after symptoms become apparent. 

     On older established trees, pruning out infected shoots is both more time consuming and of less clear benefit, though it can prevent the spread of subsequent shoot blight.  Whether it is necessary to clean blades between cuts is still an open question, but tools used on fire blighted trees should certainly be sterilized with bleach or alcohol before being used to work on uninfected trees.  Applying oil to blades previously treated with bleach before storage will prevent corrosion damage.

     Sanford has reached Petal fall, and Monmouth area orchards will probably reach it this weekend.  Petal fall is a key time for insect and mite pest management. 

     Plum curculio weevils have already been found in borer traps at Highmoor, and will be ready to start laying eggs as soon as fruit start to swell.  European apple sawfly have already been laying eggs that begin hatching at petal fall.  EAS traps at Highmoor had already started catching adults by King Bloom at Highmoor on Friday May 14.

     Codling moth adults start flying around Petal fall.  Even though the best timing for codling moth control is against eggs as they start to hatch about 25 days after Petal fall, insecticide applications at Petal fall and First cover usually provide adequate protection, either by killing adults before they lay eggs, killing the eggs before they hatch, or through residual activity against newly hatched larvae.  Pheromone traps that help in timing applications for this pest aren't very good as population indicators because they only catch males.  But traps can be useful as a rough indicator, with weekly trap catches above 6-14 a week considered evidence of a high population requiring control.  You should never rely on data from a single trap, however, and an average from three traps is better than two. 

     Obliquebanded leafroller and Oriental fruit moth also usually do not require targeted management in Maine orchards, especially at Petal fall.  However, these and other caterpillar species have been problematic elsewhere in the Northeast in recent years.  Early reports are that their presence is already being noted in other Northeastern states this year.  Even if they do not drive spray decisions in Maine orchards at present, it is good to at least consider how your pest management program is likely to affect them (see table below).

     Prebloom leafminer trap counts varied between blocks at Highmoor.  The weather during bloom this year has been much more favorable for leafminers than it was last year.  The best time to monitor leafminers is to look for light colored sap-feeding mines in the first two weeks after petal fall.  Finding 10 or fewer mines on 40 middle-aged fruit cluster leaves indicates that leafminers will come under biological control before becoming a threat to the crop or to tree health.  Finding 29 or more mines on 40 leaves at this time is indication that chemical control will be needed.

      Rounding out the crowd of potential apple pest problems to be aware of in the two-weeks-after-Petal fall window is European red mite.  With some luck, 2004 will be the sixth year in a row where this formerly formidable pest will be much less of a problem than in years past.  The threshold from Petal fall until June 15 (when first generation starts dying off and before second generation is fully developed) is if living hatched mites (not eggs) are present on more than 30% of middle-aged fruit cluster leaves, or if those leaves have an average of more than 1 mite per leaf.  The scouting card includes sequential sampling stop points to minimize sampling time.

     For Pear growers, pear psylla is a major pest needing attention in this time frame.

     The range of Petal fall insecticide options has expanded in recent years with new options such as Assail, Calypso, Avaunt, Actara, and Warrior.  Here is how they rank in comparison to Imidan and other materials against key Petal fall pest species in Maine.

*** = 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.

Many materials are rated effective against leafminer moths.  Ratings here are for sap-feeding mines.  Some of the materials effective against moths may contribute to suppressing a summer leafminer problem by effect on moths, larvae in sap-feeding mines, or both.  However, only the materials with a two or three star rating displayed are recommended to suppress an over-threshold population of sap-feeding mines.

Danitol, Asana, Warrior and Sevin may cause the European red mite population to flare through disruption of biocontrol.

Danitol rating for ERM is for early season use, for late season use Danitol is less effective against ERM.

While Agri-Mek is not rated for EAS, anecdotal observations at Highmoor Farm suggest that Agri-Mek suppresses EAS.

Aza-Direct/Neemix ratings against CM and PPs assume frequent applications at short intervals.

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

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.

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     Tarnished plant bug activity at Highmoor was low to moderate between Tight cluster and Pink, indicating little need to consider need for tarnished plant control at Petal fall at that location.

     A problematic population of apple mealybug was observed in a Maine orchard this week.  Oil at Green Tip - Tight Cluster combined with insecticide at petal fall should bring this population under control.  Apple mealybug appears as white waxy spots on branches.  Honeydew excreted in the summer by the small insects the live under the waxy coverings gives rise to black sooty mold that stains branches and fruit.

     Green pug moth larvae are showing up in other New England locations, and have been found in backyard trees in Maine as well.  They larvae are distinguished by a dark red line down the back.  They can be controlled by petal fall insecticide application.  

     Bt or other spray applications should help keep Eastern Tent Caterpillar colonies from increasing, but for a greater immediate effect simply tear the nests out of the tree and discard them into a bucket for removal from the orchard.

     1) Winter damage has appeared in at least three southern Maine orchards.  The worst damage appears to have occurred on sandier soils.  Winter damage to roots and trunks that damages a tree's vascular system results in shoot growth and fruit clusters collapsing for lack of water supply during and shortly after bloom.  The degree of winter damage to buds has to be considered in thinning decisions.  Other than preventing additional stress by mites, drought or other causes to winter damaged trees, there isn't much you can do other than waiting to see if they will pull through.

    2)  Where a good response is needed from chemical thinner on unstressed trees, the thinning weather estimates can help choose the best day for application.  The current thinning forecast for Sanford shows intermediate conditions through May 26.

   3) With support from the Maine State Pomological Society, the Apple IPM Scouting Co-op offers either weekly or biweekly (depending on location) scouting visits free of charge to orchards of 1 acre or more.  Scouting visits will commence June 7 and will focus on mites, leafminer and scab.  The scout can also check grower-provided traps.  If you would like to sign up to be considered for a slot on the route, please send me an email stating your interest.  If you have not been in the scouting coop before, please include your town and size of orchard.  We accommodate as many growers as possible, but logistics and limited resources means we can't always visit everyone that signs up.

     Growers participating in the co-op must provide current Restricted Entry Interval information.  Co-op growers who will be applying captan, are encouraged to consider using the new Micro-Flo 80 WDG formulation that has a 24 REI instead of the previous 96 hour REI.

    4) There will be a twilight meeting on June 4 at 5:30 PM at Ken Sullivan's orchard at 356 PuddleDuck Road in Charleston.

     5) Figuring how much pesticide to mix in a small pump sprayer to spray a few backyard trees has come up repeatedly in the last two weeks.  The simplest way to deal with this situation is to mix according to the label directions and spray the trees until they are soaking wet, to the extent that any additional spray will just run off.  Gardeners who mix according to the label but then just mist the trees under-dose the pesticide application, which frequently leads to lack of control. 

     Low spray trees are showing signs of borer activity, the sooner you can remove borer infestations that started last year, the better.  Protection through trunk insecticide application, screening and latex paint/water application will be needed starting in a few weeks as this year's crop of adults takes flight.

     A sad note to end on.  Dr. Ron Prokopy passed away unexpectedly last week.  In addition to being an extremely insightful and productive world-renowned entomologist, Ron was a unique, inspiring and wonderful human being in many other ways.  He was brilliant and hard working, yet also kind, humble and gentle.  He will be sorely missed.  It doesn't even seem fitting to use past tense when talking about Ron.  A spirit that alive, a mind that intense, can't just go away.  It has to be somewhere.  The shock and grief of his passing are only tempered by the smiles and good thoughts that come to mind when thinking of him.  Our best acknowledgement of his gifts are to follow his example by treasuring each other and the time we share on this mysterious fascinating world.