July 16 Apple Talk Conference Call Summary

Apple Talk Conference Call Summary
Tuesday July 16th, 8:00 – 9:00
John Aue, Threshold IPM.
Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org.

July 16th Call download Here

Michigan State University Crop Advisory Team Alert: Imidacloprid labels need to be read closely prior to application.
Multiple insecticide products contain the active ingredient imidacloprid, and cherry growers should pay close attention to the label before applying these insecticides close to harvest. Read the full article Here.

Brown rot
Monitoring for brown rot diseases in stone fruits needs to be a priority in these crops.  These fruits are close to harvest and rapidly sizing up, this dilutes the fungicide coverage and brown rot infections could increase.  Even though we have not had a lot of rain, instances in fruit disease problems could increase in plums, peaches and cherries.

Sootyblotch and Flyspeck (SBFS)
The first incidences of flyspeck appeared in orchards the week of July 4th, however sootyblotch has not developed yet and there have been no reports of sootyblotch development.   Recent research suggests that relative humidity hours may have more relevance to infections for summer diseases than leaf-wetting hours.  When we have 90 to 95% humidity, then each hour is equivalent to one hour of leaf wetness re summer disease infection periods.  The current model is to apply materials for summer diseases when we have reached 175 leaf-wetting hours from petal fall.

Obliquebanded leafroller (OBLR)
OBLR are considered a secondary pest in many orchards in our region and have a wide host range that includes other plant species than apple.  We do not associate trap captures with a threshold for management and the level of infestation to growing terminals does not correlate with the number of OBLR adults caught in the traps.  Rather, we use our trap captures to begin monitoring for terminal or fruit injury seven days after the moths begin to fly.  In the spring we see overwintering larva feeding on the growing terminals of apple trees at petal fall.  The flight that recently ended is technically the first flight and a second generation will be active in mid-August.  John is advising not to ignore terminal feeding now because the final generation that hatches in August will feed directly on the fruit.  Growers observing OBLR now are much better to scout for terminal infestation and control this generation of OBLR will have an impact on controlling the next generation.  Due to the heat, egg viability may be reduced and many lay eggs in the canopy where relative humidity is higher so the eggs do not dry out.

If Delegate or Altacor were used for codling moth, these materials have excellent activity on OBLR.  Often enough sprays are applied for codling moth, that there is overlap with the OBLR flight.  For example, if Delegate was applied at 700 or more degree days from codling moth biofix, you may also be covering the emergence of OBLR larva in your orchard.  A good way to know is to compare your OBLR trap counts to the timing of your last spray of Delegate or Altacor or scout for terminal damage.  If Bacillus thuringiensis (Bt), Delegate or Altacor spray was applied seven to ten days after OBLR flight subsided, there is a good chance you covered the larva emergence with these materials.  Note: John also indicates that OBLR is resistant to many of the organophosphates and most of the neonicotinoids do not have activity on this generation of OBLR.

Redbanded leafroller (RBLR)
Similar to OBLR, the RBLR is considered a secondary pest that often does not require an insecticide.  However, this pest should still be monitored closely for damage that can occur to fruit in late-August.  The second flight of RBLR is happening and pheromones and liners should be current.  John thinks these are less critical because there is not a fall generation and are often suppressed in sprays targeting codling moth and apple maggot.

Codling moth
(See other notes from July 9 for information on spot treatments and conservation of natural enemies)

At this time in the season it can be hard to determine if we are at the end of first generation or the start of second generation.  The best way to differentiate is to use our degree days.  If you are at 800 to 900 degree days from biofix, we are still in first generation.  If you are approaching 1000 degree days from first generation biofix, then second generation is very close.  Normally by this time, trap counts will have declined dramatically.  However, there are instances where trap counts may not drop off, and this could be true where orchards were not managed for codling moth due to a poor crop in 2012.  Typically there are 1000 degree days between first and second generation codling moth.  If trap counts do not drop off in your orchard, use the accumulation of 1000 degree days from first generation biofix to begin timing sprays for second generation codling moth.

With persistent hot weather, the accumulation of 250 DD can move fast when we are accumulating 30 growing-degree days per day.  We need to not be complacent with the lures and liners.  If the liners are soggy, difficult to get them into traps or covered up, with other stuff, replace the liners.  We want to make sure we are accurately monitoring second generation CM.

We should remember there is an upper threshold of 86°F and a lower threshold of 50°F.  When temperatures are above the 86°F threshold, they are not going to register on the degree day model for codling moth and will not develop faster if above 86°F.  For example if we had a high of 90°F and a low of 72°F, conventional calculations for degree days would indicate that we accumulated 31 degree days.  When we replace the daily high with the upper threshold for codling moth our degree day accumulations change to 29 degree days (base 50°F).

European red mites (ERM)
The cool and wet spring really helped trees recover from the stress of the 2012 drought and has tempered many concerns about ERM.  Now that we have not had significant rainfall in the last several weeks, mites present a renewed concern.  The ground is starting to dry out, trees are sizing fruit and trees are beginning to prepare for dormancy, combined with bronzing from mites, this can prevent the apples from finishing correctly and will impact tree health going into the fall, and could impact fruit buds for next year.

Population growth of ERM and temperatures do not have a linear relationship.  ERM populations can actually accelerate their rate of growth exponentially as hot weather increases.  This can happen at a rate that will allow them to outgrow their predators, e.g., black hunter thrips or predatory mites.  This can allow us to go from having no mites to surprising populations of mites in just one or two weeks.

A summer oil will be the primary tool for organic growers and need to make sure a very light oil, e.g., JMS stylet oil at a 1% concentration is applied.  Right now, long drying times for a summer oil is okay.  Applying oil in the heat of the day will intensify drying and could burn leaves.  If you are still applying Captan, need to head the warning of not applying within 10 days of an oil application.

If conventional miticides are being used, make sure to rotate mode of action from a previous miticide application, even if this was last year.

San Jose scale (SJS)
See the July 9 call notes for additional details on SJS.  The first generation has ended and second generation crawlers could be just a few weeks off.  Tape used for monitoring crawlers should be replaced weekly through the remainder of the season. Unfortunately, I was unable to locate degree day information that could help us predict emergence of the next crawler generation.

Plant tissue nutrient analysis
Growers should be establishing tree nutrition needs for this fall and next year now that terminal buds are set.  Leaves from this year’s shoots should be collected along with a soil sample from the orchard and submitted for Nitrogen, Phosphorus, Potassium and other micro-nutrient needs .  See links from the University of Wisconsin for information on soil and foliar nutrient testing.  Right now there can be lots of differences in nutrient deficiencies across the orchard.

Spotted wing drosophila (SWD)
Spotted wing drosophila catches have been reported in the Wisconsin statewide monitoring program.  Additional, SWD traps in stone fruits have caught male flies in New York.  Growers with small fruits and stone fruits are advised to hang SWD traps, if this has not been completed already.  Visit the UW SWD website, http://labs.russell.wisc.edu/swd/.