Apple Pest Report:  Wednesday, May 21, 2003 
Vol. 11 No. 4

 Scab

Prime time for primary scab

Sunday night's prediction almost came true, but as the old saying goes, "close" only counts in horse shoes and hand grenades.       

The weather observation for Sanford, Monmouth and Morrill areas all show 0.02" rain on Wednesday afternoon with only 1 hour of leaf wetness.  Scab is too well engineered to fall for that trick, so it is likely that few if any ascospores released if there was that sparse of a rain at your location.

While it has been dry, it hasn't been dry long enough or hot enough to appreciably slow down ascospore maturation. That means we have gone since May 14 since any significant rain.  But wait, there's more!  We haven't had a soaking rain during daylight hours since May 6th in the Sanford and Morrill area, and May 9th in Monmouth.

That means a 'whole lotta' scab ascospore maturation has happened since the last release.  And that means the next daytime rain is going to be the major scab ascospore release of the year. 

Meanwhile tissue expansion has been proceeding rapidly.  Forgetting about ascospores for a moment, the risk from increase in susceptible leaf tissue has doubled in the last week.

Combine that with the latest forecast showing rain on Friday and Saturday, with a high chance of showers continuing into Wednesday, May 28.  Mix it all together and what you get is the season's most important scab infection period. 

Rain forecasts beyond 3-4 days are not all that accurate, but it is best foundation available for analyzing the situation.  More than 2 inches of rain is expected during Friday May 23 through Tuesday May 27, with continued risk of showers into Wednesday.

 

 

 OK, enough fear mongering.  What can you do?

The rule of thumb for Surface' (also called 'Protectant') fungicide such as captan, Polyram, Dithane, Manzate, Manex, or Penncozeb is to expect protection to be depleted by 2 inches of rain.  So even if you apply a surface fungicide just before the rain starts, there is some risk that ascospores released at the end of this wetting period could land on unprotected tissue.  I would not advise using Vangard against this infection period.  It's time of best is efficacy before Pink. 

If full dose - good coverage protectant fungicide coverage was applied on Thursday, May 22, then protection should be good enough assuming the amount of scab inoculum in the orchard is not too high.  This may also be true if the surface fungicide was applied Wednesday May 21.

Mature ascospores should release on Friday or Saturday when protection should still hold, with little additional maturation and release on Sunday - Tuesday. 

And if coverage does wear off before the infection period ends, the protection from a Wednesday or Thursday application should at least last long enough to allow follow-up application of a systemic post-infection fungicide to reach back and protect against any infections that started after the previous fungicide wore off.

If your fungicide protection going into the May 23-2X? wet period was applied between Sunday May 18 and Tuesday May 20, then it would be advisable to plan on coming back with a long-kickback post-infection fungicide (Flint, Sovran, Nova, Procure, Rubigan) at a high dose.

And if your fungicide coverage was applied on or before Saturday May 17, then you should consider a pair of high dose post-infection fungicide applications, the second being 7 days after the first.  

       

 

 

Of course, all this analysis is based on information that could change with the next weather forecast in 12 hours.  Keep an eye on the Monmouth hourly weather chart at

http://pmo.umext.maine.edu/apple/AllModels/MEmodel/ME-Monmouth-HourChart.htm

 

While I can only give live access to the Sanford and Morrill charts to those who signed up for the $10/month fee, if there is significant change in the forecast I will send the updated chart in an email.

 

Details about Highmoor infection periods are updated twice a day and posted on the web at:
http://pmo.umext.maine.edu/apple/AllModels/MEmodel/RadarME-Monmouth.htm

 

 

The Sanford scab risk forecast is shown below.

 

 

 

Chart interpretation

 

    The chart above shows that a large portion of the season's total primary scab infection risk in the Sanford area will occur May 23-25.  The situation in Monmouth and Morrill is not quite as extreme, but still shows about half of the season's primary scab infection risk occurring during that period. 

 

     These assessments do not account for additional risk posed by the fact that all of this year's earlier scab infection periods in the Sanford area will have had time to begin producing asexual conidial spores before the end of the forecast wetting period that starts Friday, May 23.  Though as  you can see from the chart above, only about 10% of the season's total scab infection risk had been expressed by those earlier infection periods.

 

       The report below is also for the Sanford area.  The Monmouth version is online at
http://pmo.umext.maine.edu/apple/AllModels/MEmodel/ME-Monmouth-ScabPrimaryInfPerDetail.htm

 

 
******   Primary  Infection  Period  7  Details   ****** 

   Begin: Friday, May 23 at 12 AM    --->     End: Saturday, May 31 at 10 AM.     
       Growth stage at start of period:  Between Full Bloom and Petal Fall
       Infection period conditions rating is 375.  This infection period accounts for roughly 86 % of the year's total primary scab risk.       
       178 leaf wet hours, with 55 F degrees average temperature during wet hours.  
       Cumulative scab ascospore release by end of this wetting period is roughly 95 %.       

       Reliable pre-infection protection during this period expected if full dose + good coverage captan or EBDC fungicide applied since Sunday, May 25,  6 AM, or if strobilurin fungicide applied since Friday, May 23,  6 AM.

       Infection period accompanied by daytime rain to release ascospores.  

       Opportunity for surface fungicide kickback ends Saturday, May 24, at 3 AM.   Counting from beginning of daytime ascospore release (low inoculum blocks), opportunity for surface fungicide kickback ends Saturday, May 24, at 12 PM.  
   
       Opportunity for sterol inhibitor or strobilurin kickback ends Tuesday, May 27, at 12 AM.   Counting from beginning of daytime ascospore release (low inoculum blocks),  kickback window ends Tuesday, May 27, at 8 AM
     
       First generation lesions arising from this infection period would start appearing by Tuesday, June 03.  

 

   

""- Fire blight
        The fire blight situation is edgy in the Sanford area.  Technically there was a potential infection period on Wednesday afternoon in Sanford, but I'm not that worried by it.  Assuming that the amount of rain and duration of wetness was as little as reported (0.02" and 1 hour), that reduces the real risk.  Also the major fire blight infection periods are ones that occur from Full bloom on, and Sanford was just hitting Full bloom on Wednesday.  And the rating of the infection period by the Cougarblight model saw it as a significant risk only in orchards that have had fire blight within the last two years.  If there were blossom infections by fire blight bacteria on May 21, then the symptoms of wilting clusters should be apparent by June 8.  Keep an eye out for it starting around June 1.  Young trees on M26 or M9 rootstock are the most likely to be affected, as are cultivars such as Paulared, Gala, GingerGold, Honeycrisp, and Golden Delicious.  

 

 


 

""

 

 INSECT and MITE PESTS

Tarnished plant bug (TPB) trap captures continued to be low at Highmoor Farm up through Tuesday, May 20, when McIntosh buds were at late Pink.  I use 4 traps per block in 4 blocks (16 traps total). 

       The cumulative average per trap from Green tip through Pink in the 4 blocks was: 0.75,  1.75,  1.75,  and 2.1.  The threshold at Pink for a retail apple crop is 8 per trap.  The wholesale crop threshold at that time is 5 per trap.  The bottom line is that I am not too worried about TPB damage in these blocks this year.

Leafminer captures in those same four blocks was a cumulative average per trap of:   0.8,  3.8,  15,  and... 149.

        Leafminer trap thresholds from Massachusetts are 9 leafminer moths per trap from silver tip to Pink for McIntosh or other trees prone to preharvest drop.  The threshold for other cultivars or non-stressed trees is 21 per trap.  While these numbers will not by themselves drive treatment decisions, they will certainly help prioritize where to do leaf mine counts shortly after Petal fall.

    



I could not find any European red mite eggs in three blocks checked at Highmoor on Tuesday, May 20.  The previous newsletter discussed options if treatment mites is needed shortly after Petal fall.  

Trees that received few insecticide sprays last year have noticeable Eastern tent caterpillar colonies this spring.  Hand removal is an effective option if the number of trees is not too large.

European apple sawflies are already showing up on traps at Highmoor, and at Pink had already exceed the Petal fall threshold in one block.  That block will certainly need EAS treatment at Petal fall and I expect at least several of the other monitored blocks to be over threshold also.
       

 

Into the Future

Here are estimated budstage dates for Monmouth (Highmoor) and Sanford-area McIntosh trees:

McIntosh Bud Stage  

Estimated date Sanford

Estimated date Monmouth

King Bloom

May 19

May 22

Full Bloom

May 21

May 26

95% Petal Fall           

Tue., May 27

Sat., May 31
100% Petal Fall May 30 June 2
Fruit Set Mon., June 2 Fri., June 6

 

 Twilight Meeting, Monday June 9

There will be an Orchard Twilight Meeting at Sweetser's Apple Barrel Orchard in Cumberland Center, which is about 8 miles due north of Portland.  The meeting will start at 5pm and is informal.  A large part of the value in attending is a chance to talk to other growers.

Agenda
5:00 - Apple pest update and scouting tips - Glen Koehler
5:30 - Thinning situation and recommendations - Renae Moran
6:00 - Growing and selling apples at Sweetser's Apple Barrel - Dick and Connie Sweetser

The orchard is at 19 Blanchard Road, near the intersection with Route 9 in Cumberland Center.

From I-95 South:

At I-95 Exit 16, turn RIGHT onto Ramp 0.3 < 1min
8: Turn LEFT (South) onto US-1 [Blue Star Memorial Hwy] 2.3 0:02
9: Turn RIGHT (West) onto Tuttle Rd 5.5 0:06
10: Road name changes to Blanchard Rd 0.3 < 1min


        Here is the Orchard Radar management calendar for Sanford as of Wednesday night, May 21.  The Morrill version is very similar to the Highmoor version, which is online at http://pmo.umext.maine.edu/apple/AllModels/MEmodel/ME-Monmouth-CalendarEarly.htm
 

 

Sincerely,                                            
Glen

 

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