July 31, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, July 31, 2018, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

July 31st Call Stream: CLICK HERE


Apple maggot
Baited or unbaited red spheres can be utilized to track emergence and population trends of apple maggot (AM). Monitoring should begin in early varieties and can determine the location and method of insecticide application. Organic suppression includes Surround WP (kaolin) and PyGanic (pyrethrins). Conventional control using old insecticides, e.g., Imidan (phosmet), may be achieved with lower insecticide rates and alternate-row-middle applications. Orchards using newer chemistries, including the neonicotinoids or diamides are advised to use the maximum labeled rate and apply to every row in the block.

In August, Assail (acetamiprid) is the best neonicotinoid option for combined management of apple maggot and codling moth. If a different insecticide is being used for second generation codling moth, then imidacloprid products may be used for apple maggot management.  The neonicotinoids have limited mortality on adult AM (two-to-three days) and increased mortality on eggs and their ability to hatch, plus repellency and avoidance of egg laying (up to 14 days). Rainfall following an application will impact efficacy. If Assail was applied with the dual purpose of controlling codling moth (CM), reference John Wise’s article below to determine when to reapply. Note: Since neonicotinoids do not perform well against adult flies, trap captures will not be impacted by an application, whereas they would have been if a broad-spectrum material, e.g., Imidan (phosmet), were used. If pressure is localized spot spraying may offer adequate control. Note: The fruit essence on baited traps is viable for one week and should be changed accordingly.

John Aue is resistant to the routine monitoring of AM populations with red spheres baited with apple-volatiles due to the increased need for insecticide applications as the clumped distribution of trap-count data suggests large numbers of pregnant females may be drawn in the orchard from external sources. John is also concerned for the use of baited red spheres because most growers are using neo-nicotinoid-based AM management, which largely allows females to survive. However, the level of AM-infested fruit has been insignificant regardless of the monitoring type employed, and both situations will still result in AM oviposition on fruit containing sub-lethal amounts of insecticide during harvest. The threshold for apple maggot management uses an average capture of one fly (unbaited) or five flies (baited), where three traps are hung per ten acre block.  This would suggest a minimum of 12 traps on a 40 acre orchard.  To mitigate the risk against false negatives, trap density with unbaited traps should increase beyond three per ten acres.  Exact trap density would vary based on surrounding habitat, e.g., woods vs. agronomic crops, variety and historical pressure.

Additional resources

Dogwood borer
During the 2018 season our focus on DWB has been driven by increased trap catches – which may or may not be due to a change in pheromone lure chemistry than to an actual increase in DWB populations. Additionally, reports of DWB infestation in the upper Mississippi River valley have also increased. With many orchards replanting or replacing thousands of older trees with new rootstocks and new cultivars over the last decade, there are large fractions of orchard trees that are currently young and more vulnerable to attack from borers. Growers should begin to more rigorously and regularly evaluate borer populations.

While scouting for borer activity, be on the lookout for pupae casings protruding from the trunk near feeding sites, cracked/scaly bark, or at the base of the tree. Pupae are brown and when fully intact are about 0.5 inch in length; if the adult moth has already emerged they may be half that size; see photos at link: Dogwood Borer, NC State Extension, https://content.ces.ncsu.edu/dogwood-borer

DWB are trending towards younger trees but have been found on M.7. Best luck is finding them below the trunk guards or on trees with burr knot or damaged bark. Injury is more a product of the planting trends, e.g., what have growers been planting the last three-to-five years, rather than specific to a specific cultivar or rootstock. Larvae have been found in tree that are in their second leaf and up to eight-to-ten years old.

Applications for DWB are based on scouting and finding larvae or injury rather than trap captures. If treatment is required, see notes below.

  • Assail 30 SG is currently the only labeled alternative to Lorsban for a trunk application targeting DWB. Efficacy trials very and Assail is not currently recommended for control.
  • Lorsban is not systemic and must be thoroughly applied to the lower four feet of the tree trunk. It needs to be investigated if spraying a smaller amount of the trunk (e.g., lower 2 feet) is suitable.
  • Lorsban can be applied early in the spring and will provide an active residue for one year. An application at this time would minimize contact of this insecticide with the fruit.
  • If fruit are present, do not apply using lower nozzles of an airblast sprayer; use a hand wand, shielded sprayer or other method where drift onto fruit can be avoided.
  • The application may also be made post-harvest, if other blocks are found to be infested during the growing season.
  • Some growers have reported using an herbicide sprayer that has been carefully cleaned prior to the trunk application. There are several issues that should be carefully considered before using this strategy, see http://extension.missouri.edu/p/G4852 for some of these.
  • Below is a good video showing one application method:

Extension research results indicate several benefits of adding compost or fixed-carbon materials to soils in mediating non-obligate soil-borne plant pathogens. These benefits derive from fixed-carbon sources’ ability to create soil microbiomes capable of limiting plant pathogen growth during stressful periods.

Recent results from a study by Dr. Amaya Atucha (UW-Madison, Dept of Horticulture) evaluating tree health, growth, and yield under several types of orchard-floors indicated mulch covers offered long-term advantages for tree health as well as limiting nutrient and pesticide leaching and run-off. Many of these benefits were attributed to improvements in measurements of soil health, including increased complexity and diversity in the soil microbiome.

Additional resources:

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 and sunburn injury fruit maturity increases near harvest. Damaged flesh is vulnerable to colonization by various fruit rots, requiring fungicide programs to be modified if symptoms of rot are detected. Sunburned fruit is also susceptible to changes in pigment, restricted coloring, and degradation of 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.
  • Sunburn bleaching is independent of temperature and is caused by visible light.

Additional environmental factors that may 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 Braeburn, Fuji, Honeycrisp, Jonagold, Gala, Ginger Gold, Golden Supreme, Granny Smith, Royal and Zestar.

The impacts of fruit sunburn can be mitigated 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 keeping fruit cool by improving orchard airflow.

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.
  3. 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, http://jmcextman.blogspot.com/

Additional resources:

Bitter Rot
Bitter rot has been an increasing problem for growers over the last decade, perhaps because of milder winters or the rise of varieties, such as Honeycrisp, that are more susceptible to this disease. However, there really is no explanation as to why more bitter rot is appearing in orchards. Like sooty blotch and fly speck (SBFS), bitter rot has more genetic diversity than previously thought and while not completely immune to resistance, we currently are not very concerned about current pathogen complex treatment programs resulting in fungicide resistance.

Bitter rot exudes an orange, slimy mass that is almost salmon-colored. Black rot and white rot make black fruiting bodies but do not make orange slime. Bitter rot also has a sharper V-shape into the fruit than black and white rot. Bitter rot also causes problems on other fruit crops, weeds, lilac, trees and hedge rows, which suggests it has a wide host range beyond apples. Spores likely enter orchards early in the season (June) through either fire blight infections or some other source. For example, we know that SBFS come off brambles in the woods and hedge rows adjacent to orchards.

Fruit infected with bitter rot are often observed in groupings and clusters on several branches. While bitter rot does not cause big cankers, it can infect quickly. This suggests the source of inoculum is nearby, e.g., overwinter drop, mummied fruit, fire blight canker, rather than a pathogen that has spread via wind or rain storms. The pathogen can overwinter mummified in fallen fruit and in trees. Rotten fruit tend not to decay very well on herbicide strips. Fruitlets on the ground after hand thinning can also become infected and release spores. Dead wood, e.g., infected by fire blight, can become colonized and sporulate by late-July. In strawberry and blue berries, infections can happen in four-to-six hours during wetness, which is relatively fast for a fungus.

Even though the fungus requires vegetation to reproduce, the disease can appear after fruit have been harvested. Heat-stressed fruit also seems to be more susceptible. When humidity is high, evapotranspiration is reduced, slowing fruit cooling. Therefore, growers should ensure trees are well irrigated going into hot weather.

Management options:

  • Applying an SDHI, Strobilurin and Captan are best options for bitter rot.
  • Phosphorous acid fungicides are not effective on bitter rot.
  • Organic options are limited. Results from trials at UW completed by Patty McManus found that Liquid lime sulfur (LLS) had 9% injury, Serenade Optimum 10%, and the control had 7% bitter rot injury. This suggests that none of these fungicides performed better than the control.
  • Cultural controls: Removing and mowing over is likely just fine, the key is getting fruit to decompose, which will destroy the inoculum. A flail mower is likely to destroy the fruit better than a rotary mower.
Location Date of last single-site fungicide application Leaf-wetting hours since last single-site fungicide application Rainfall since last application (in.) Risk
Hasting, MN 7/2/18 78 2.74 Low
7/5/18 47 2.08 Low
7/9/18 40 2.08 Low
Lake City, MN 7/2/18 50 3.18 Low
7/5/18 27 2.79 Low
7/9/18 24 2.79 Low
La Crescent, MN 7/2/18 68 2.93 Low
7/5/18 35 2.34 Low
7/9/18 31 2.34 Low
Eau Claire, WI 7/2/18 130 2.99 Moderate
7/5/18 98 2.38 Moderate
7/9/18 91 2.38 Low
Trempealeau, WI 7/2/18 121 1.92 Moderate
7/5/18 100 1.78 Moderate
7/9/18 86 1.78 Low
Gays Mills, WI 7/2/18 66 2.28 Low
7/5/18 44 1.73 Low
7/9/18 40 1.73 Low
Verona, WI 7/2/18 74 2.81 Low
7/5/18 60 2.81 Low
7/9/18 57 2.36 Low
Racine, WI 7/2/18 107 3.17 Moderate
7/5/18 92 3.17 Low
7/9/18 79 3.17 Low
Mequon, WI 7/2/18 66 3.27 Low
7/5/18 48 2.40 Low
7/9/18 48 2.40 Low
Woodstock, IL 7/2/18 65 1.22 Low
7/5/18 54 1.19 Low
7/9/18 42 1.19 Low
Harvard, IL 7/2/18 116 1.28 Moderate
7/5/18 96 1.28 Low
7/9/18 85 1.28 Low
  Low risk: No action needed.

Moderate risk: Check the 5-day forecast; a cover application should be made if two or more days with precipitation are predicted.

High risk: A cover application for sooty blotch and flyspeck should be made.

Table 1. Summer diseases and leaf-wetting hours update.

Sooty blotch and flyspeck
Growers using leaf-wetness sensors from NEWA stations or Spectrum Technologies stations should have made their first applications at 175 LWH from petal fall. This same accumulation of LWH can be used to determine when we can conclude sprays this fall. From your last SBFS spray, track wetting hours up to harvest, and if only 150 have accumulated at the start of harvest, you are likely fine. However, if accumulations of hours are low, an additional spray prior to harvest may be beneficial. While SBFS is not disfiguring, it can eat away the waxy cuticle, causing fruit to dry out. There are currently no resistance concerns since the diseases are coming from beyond orchard perimeters. If a strobilurin application is planned, be aware that most of these fungicides have a 14- to 30-day PHI. See the PHI chart attached and for additional discussion on SBFS and see recent articles in fruit newsletter and previous AppleTalk notes.

European red mites
Trees are less likely to repair bronzing damage inflicted later in the season. If miticides were applied for bronzing that was detected in late June, trees may not have developed a significant chlorophyll loss. However, significant bronzing and chlorophyll loss beginning in late summer can increase stress going into winter and have a greater impact on fruit finish and quality. Growers who are still seeing steady populations accompanied by females and eggs will experience more important economic losses going forward.

Mite-day counts can be calculated by multiplying the number of mites by the number of days they have been feeding. Sub-threshold populations persisting across many weeks may still cause bronzing and may require treatment. Growers should be maintaining records of mite count data. If predator mites have not taken control of ERM populations in moderate weather conditions, a miticide may be needed on varieties showing bronzing.

San Jose scale
Growers should continue to monitor for second-generation San Jose scale (SJS) crawlers 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. Continue to maintain tapes on branches regardless of management plan. Second-generation adults appear from late-July through early-September, and the live, young crawlers from this generation can be found until the first hard frost in fall. When checking tapes, it is important to note that low trap captures do not reflect overall pressure, i.e., false negative, but rather 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.

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

Calcium (Ca) is important and necessary to maintain fruit quality. The majority of Ca is absorbed into the fruit during the cell expansion phase lasting 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 into the fruit from the soil 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 because leaves have a high transpiration rate and accumulate more Ca material. 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:

  1. 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.
  2. Keep soils adequately hydrated throughout the growing season.
  3. Reduce excessive vegetative growth. Reducing vegetative growth will redirect the transport of Ca from foliage to fruit. Apogee (prohexadione calcium) can be applied to curb vegetative growth. The pre-harvest interval for Apogee is 45 days.
  4. 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.
  5. Calcium sprays can begin at petal fall and continue to end of August; up to six applications may be necessary. Coverage is important – Ca must contact fruit to be effective. The recommended rate is one-to-two pounds of Ca per 100 gallons of water. If visible symptoms of bitter pit are present, it is not too late to apply Ca to prevent further injury.
Trade name Active ingredient PHI* Notes
Insect management
Altacor chlorantraniliprole 5
Delegate spinetoram 7
Exirel cyantraniliprole 3 Exirel is an oil in water emulsion.  Mixing with some fungicides may result in adverse crop response.  See page 5 of product label.
Avaunt indoxacarb 14 Light infestations of codling moth and obliquebanded leafrollers. Not recommended for apple maggot.
Movento spirotetramat 7
Cyd-X, Madex HP, Carpovirusine Cydia pomonella granulosis virus 0
Dipel, Deliver Bacillus thuringiensis 0
Entrust spinosad 7
PyGanic pyrethrins Do not harvest until spray has dried.
Surround WP kaolin clay 0
Imidan phosmet 7
Lorsban chlorpyrifos 28 Trunk application targeting dogwood borer can be applied post-harvest.
Actara thiamethoxam 35 No activity on codling moth.  Label rate for stink bug, apple maggot, Japanese beetle requires 35-day PHI.
Admire Pro, Wrangler imidacloprid 7 Apple maggot, leafhopper, San Jose scale
Assail acetamiprid 7
Envidor spirodiclofen 7
Nealta cyflumetofen 7
Nexter pyridaben 25
Kanemite acequinocyl 14
Portal fenpyroximate 14
Disease management
Captan 80 captan 0 Maximum of 40 pounds of Captan 80 per acre per season.
Flint trifloxystrobin 14
Indar fenbuconazole 14
Inspire Super cyprodinil, difenoconazole 14
Merivon pyraclostrobin, fluxapyroxad 0 Maximum number of application per season: 4
Pristine boscalid, pyraclostrobin 0 Maximum number of application per season: 4
Topsin M thiophanate-methyl 1
NOTE: This table is only a reference, always refer to product label.
*Observe re-entry interval (REI) for zero-day pre-harvest interval (PHI) products.

Table 2. Pre-Harvest Intervals (PHI – Days to harvest after application).