August 8, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, August 8 2017, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,

August 8th Call Stream: CLICK HERE

Crop maturity and pre-harvest intervals
At this point many varieties are showing to be a week ahead of schedule and current temperatures are forecasted to remain cool.  John is predicting that sugars are developing well and quality may have been aided by this season’s cool spring and above average rainfall.  John tried a SweeTango last week that was pretty tasty, harvest for this variety is usually around the end of August/early September.  As we near harvest, remember to verify pre-harvest intervals (PHI) before making pesticide applications.  See last week’s call summary for a short list of PHI for popular pesticides.

Late season codling moth management
Many growers have set their second-generation biofix for the end of July or beginning of August and at current degree-day (DD) accumulations, it may take two weeks or more to accumulate 250 DD to time the first insecticide application.  If traps do not exceed threshold an insecticide application is not necessary.  Spot spraying blocks where traps exceed threshold may be a good option to avoid early varieties and PHIs.  Captures greater than 10 per week/trap could result in damage at harvest.  Granulosis virus, e.g., CYD-X, could be applied in scenarios that require a short PHI since it can be applied up to and including the day of harvest.  Granulosis virus is not fast acting and some injury can still be caused by infected larvae before they die.  Bt (Bacillus thuringiensis) products, e.g., Agree, Deliver, Dipel, do not work well on codling moth (CM) but can work well on obliquebanded leafroller (OBLR).  Depending on how long the OBLR flight is, larvae may hatch over an extended period of time and feeding can continue into September.  John has not used Bt to control late summer generation and is unsure of efficacy since larvae burrow into fruit rather than feeds on surface.

When scouting, continue to look for injury from first generation larvae.  Fruit that colors prematurely, likely have some sort of injury.  Another great place to look for codling moth injury is areas where two apples are growing together from the same cluster or where pesticide coverage was poor due to preexisting injury, e.g., scab lesion, hail.  While scouting and assessing injury, most injury that is observed needs to be at a 1% presence or greater to be easily detected.  Continue to monitoring CM pheromone traps through early September to time insecticides applications.

San Jose scale
Monitoring for second generation San Jose scale (SJS) crawlers should continue in blocks with known hotspots.  As harvest begins, or while hand thinning, look for first generation adults (black cap stage) on fruit and continue to check scale tape on infested limbs for crawlers.  Fruit injury should serve as the canary and John recommends to continue maintaining tapes on branches regardless of what you plan to do management wise.  Second generation adults appear from late July through early September and the live young ‘crawlers’ from this generation can be found until a hard frost in the fall.  When checking tapes it is important to note that low trap captures do not reflect overall pressure, i.e., false negative, rather may indicate the beginning of the hatch.  Catches of 10-15 crawlers in a couple of days or 10 crawlers on one tape with zero on all other tapes, may warrant application.  See the article below for more information managing summer generation and be aware of PHIs when selecting insecticides.

San Jose Scale: Crawler Emergence Begins Today, HVRL, Highland, N.Y., The Jentsch Lab, June 15 2017,

Oystershell scale
Oystershell scale (OSS) overwinters as eggs beneath the female scale and crawlers begin to hatch around petal fall and can continue to emerge through June; there is one generation per year.  Dormant or delayed-dormant (half-inch green to tight cluster) horticultural oil sprays that are often timed to manage mites or SJS are not as effective in managing this pest since the eggs are protected under the thick chitin layers of the female scale and do not need to respire like overwintering immature SJS do.  The scale is most vulnerable to insecticides when it is in the crawler stage.  If OSS is found on fruit during harvest or young branches while pruning, ample time can be dedicated to planning management for next spring.

Sara Ecker, Ecker’s Apple Farm (Trempealeau WI), shared her experience in managing OSS on today’s call.  Last season she found OSS on fruit while hand thinning, especially on fruit stems and pygmy fruit, and while pruning this winter spotted OSS encrusted branches throughout the orchard.  She divided the orchard into two management zones and a few notes on her tactics are below.  Oystershell scale has yet to be found on fruit in either treatments.

Treatment A (35 acres)

  • Dormant/ delayed dormant: two applications of oil (2% v/v)
  • Tight cluster: Esteem (pyriproxyfen) + oil (1% v/v)
  • Oystershell scale crawlers found May 18 (king fruit at 8-10 mm)
  • One week after first crawler emergence: Movento (@ 9 oz/A) + penetrant
  • Three weeks after first crawler emergence: Movento (@ 9 oz/A) + penetrant

Treatment B (5 acres)

  • Dormant/ delayed dormant: two applications of oil (2% v/v)
  • Tight cluster: Lorsban + oil (1% v/v)
  • Oystershell scale crawlers found, Danitol (fenpropathrin) + Diazinon (diazinon) applied that evening.

Apple maggot
Apple maggot activity has been light throughout the region with captures continuing to occur in blocks with historic pressure.  Some orchards are reporting that they have yet to capture a fly all season.  In blocks with attractive varieties that are almost ripe, e.g., Redfree, or with hand thinned or hail damaged fruit baiting a few red spheres or putting out additional traps may have utility to make sure trap are not showing false negatives.  Continue to monitor traps through the first week of September.  Clean traps 10-12 days after an insecticide application or one inch of rain to determine if a reapplication is necessary.

Neonicotinoids have limited lethal action on adult apple maggots, but provide strong curative activity on eggs and larvae.  It is recommended to apply neonicotinoids as full cover spray to blocks that exceed threshold.  Alternate-row-middle applications will not provide adequate control.  For more information visit:

Fruit sunburn
Fruit sunburn has been increasing over the last several seasons, especially as adoption of high-density plantings increase.  Sunburn can occur as early as mid-July and is still a threat through early September.  Anecdotal evidence suggests that fruit becomes more susceptible to heat/sunburn injury with increasing fruit maturity near harvest.  Damaged flesh is vulnerable to colonization by various fruit rots and fungicide programs may need to be modified if symptoms of rot are detected.  Sunburned fruit are also susceptible to changes in pigment, restricted coloring, and degraded internal-fruit quality.  Several types of sunburn can occur when shaded air temperatures are above 86°F and fruit temperatures are above 113°F.  Sunburn necrosis is caused by heat and when fruit-surface temperatures reach 126°F for 10 minutes.  Sunburn browning is the most common form and results in yellow, brown or dark tan patch on the sun-exposed side.  Threshold is 115 – 120°F for one hour.  Photo-oxidative sunburn (bleaching) occurs when shaded or partially-shaded apples are moved into strong or direct sunlight, e.g., most often occurs when weight of a heavy crop load moves branches and exposes previously shaded fruit to the sunlight.  It is independent of temperature and is caused by visible light.  Additional environmental factors that can result in sunburn include: intensity of solar radiation, cloud cover, humidity, wind; and growing conditions including canopy density, variety, fruit size and water stress.  Varieties at greatest risk of sunburn include Granny Smith, Royal Gala, Honeycrisp, Zestar, Jonagold, Braeburn, Golden Supreme, Ginger Gold and Fuji.  Implementation of the following strategies can help control sunburn on apples.

  1. We can mitigate the impacts of sunburn by scheduling frequent irrigation to avoid tree-water stress; avoiding excessive summer pruning, especially before or during hot weather; protecting picked fruit in bins from direct sunlight and improving air flow in the orchard to keep fruit cool.
  2. There are three primary types of protectants that can be applied directly to the fruit to mitigate sunburn. Generally, these all work under the principle of reflecting ultraviolet and infrared radiation which can damage the fruit skin or cause overheating.  These include:
    1. Clay based: kaolin clay, e.g., Surround WP
    2. Calcium carbonate-based: Purshade (62.5% calcium carbonate). Growers that have used Purshade do not usually apply after end of July because it is difficult to wash off harvested fruit.
  • Wax based: Raynox (water, carnauba wax, organically-modified clay, emulsifiers). Growers have noted that it is difficult to mix in the spray tank and there can be issues with the materials clogging nozzles.  For more information visit: Raynox Plus applications to prevent sunburn of Honeycrisp apples, Jon Clements, Sunday, December 6, 2015,
  1. Additional resource:
    1. Sun Protection for Fruit, A practical manual for preventing sunburn on fruit – 2011, Department of Primary Industries, Farm Services Victoria Division,
    2. Which Type of Apple Sunburn is in Your Orchard?, Washington State University – Decision Aid System, June 6 2017,

Bitter pit
Adapted from August 11 2015, AppleTalk Conference Call with guest speaker Dr. Amaya Atucha, University of Wisconsin- Madison

Calcium (Ca) is important for fruit quality and the majority of Ca is taken into the fruit during the cell expansion phase from petal fall to the end of July (~50 days after petal fall).  After this period, the xylem in the fruit losses efficiency especially in the calyx end.  Calcium does not easily move from the soil to the fruit and is relatively immobile within the tree.  Concentrations can vary between foliage, fruit and soil.  Note: Foliar Ca levels will be greater than what is in fruit since high transpiration rate in the leaves cause more Ca to accumulate.  The following factors can influence Ca levels and incidence of bitter pit: Nutrient imbalances with nitrogen (N), potassium (K) and boron (B), soil moisture levels and fruit size.

Keys to reducing bitter pit

  • Submit foliar, fruit and soil samples for nutrient and pH analysis. It is recommended to test samples for all available macro/micro nutrients as many complex interactions exist.  For example: an excess amount of magnesium (Mg) or potassium (K) will compete with Ca for uptake.
  • Keep soils adequately hydrated throughout entire growing season.
  • Reduce excessive vegetative growth; Apogee (prohexadione calcium) can be applied to curb vegetative growth. Reducing vegetative growth will redirect the transport of Ca from foliage to fruit.  The pre-harvest interval for Apogee is 45 days.
  • Lite crops or excessive thinning can result in large fruit. Calcium levels can be diluted in large fruit; Ca concentrations typically vary from stem to calyx end (location where bitter pit symptoms are most pronounced), excessively large fruit usually have exacerbated symptoms.
  • Calcium sprays can begin at petal fall and continue to end of August; up to six applications may be necessary. Coverage is important, Ca most contact fruit to be effective.  The recommended rate is 1-2 lb. Ca per 100 gallons of water. If visible symptoms are present it is not too late to apply Ca to prevent further injury.