August 18 AppleTalk

AppleTalk Conference Call Summary
Tuesday, August 18, 2020 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM,
Moderator: Peter Werts, IPM Institute of North America; questions or comments, or send to Josie Dillon, .

August 18th Call Stream: CLICK HERE

Regional update

Location Degree Days from January 1st

 (Base 50°F)

Petal fall Date Leaf Wetting Hours (LWH) from Petal Fall First Generation Codling Moth Biofix Date Degree Day Accumulation from First Generation Codling Moth Biofix (Base 50°F)
Eau Claire, WI 2025 May 28 291 June 1 1525
Gays Mills, WI 2010 May 27 150 May 24 1792
Hastings, MN 2074 May 27 174 June 1 1771
Rochester (Ela), WI 1888 May 31 191 May 24 1711
Trempealeau (Ecker’s), WI 2026 May 26 260 May 24 1782
Verona, WI 2001 May 29 197 May 24 1813

Table 1. Degree-day accumulations as of August 18, 2020 using data reported by Cornell NEWA Network.

The forecasted temperatures include highs in the 70’s and 80’s with cooler nights down into the 50’s and even upper 40’s in some locations. These cool evening temperatures will slow down codling moth flights and give us excellent weather for fruit to gain color.

A few locations had a significant second-generation codling moth flight. Three weeks ago, the codling moth flight dropped off significantly and now in the last week, trap captures have increased. If it has been several weeks without a trap capture, and then a significant flight occurs a new biofix can be set and a codling moth larvicide may be applied after 250 degree-days base 50°F post-capture

Nearly all locations have accumulated 175 leaf wetting hours (LWH) from petal fall. There has been very little rain in August and in southern Wisconsin, we have received just over an inch compared to six inches in July. The NEWA stations have not been counting morning dew accurately and the actual LWH is likely higher. Growers should continue to maintain their fungicide programs for summer diseases. The dry weather will require growers maintain irrigation programs as fruit put on significant size in these last few weeks before harvest.

John has seen some woolly apple aphid (WAA) populations begin to increase. Closer (sulfoxaflor) is an option to try because of its short seven-day pre-harvest interval. However, if timing WAA earlier in the season Movento (Spirotetramat) or Beleaf 50 SG (Flonicamid) would be preferred insecticides. The WAA can appear well into September. It is important to apply Closer with a non-ionic surfactant to break through the white tufts that WAA produce for protection.

Even though our minds are shifting away from insect and disease management, it may be a bit soon to put away the sprayer. Growers should remain open to spot spraying varieties that are harvested later in the season, e.g., Honeycrisp, while also keeping in mind pre-harvest intervals.

Disease management
John discussion on summer diseases
John is not expecting the same level of sooty blotch and flyspeck (SBFS) problems this year because we have not had enough recent rains to trigger a lot of SBFS activity. The past three weeks have been very dry compared to other years and while we are at or past 175 LWH and should keep in mind the relative humidity and dew, less rainfall does reduce the risk of infection. If fungicides have been maintained in the orchard, growers may not need to be as concerned about getting a late fungicide applied.

In the July 14 AppleTalk discussion with Dr. Sara Villani, she suggested using Merivon (fluxapyroxad, pyraclostrobin) and reported great results from a few trials she is running. John has had at least two orchards who applied Merivon and was hoping based on Dr. Villani’s report that it would protect fruit that do not have lesions and stop the growth of existing lesions already present on fruit. John has not seen a reduction in the spread of lesions in fruit that are already infected, e.g., reduction in growth of the lesion.

Before growers put the sprayer away, they must assess the bitter rot inoculum in the orchard and try to remove any infected fruit. If fruit cannot be removed, growers must be willing to applying Captan, Merivon or both during the picking season e.g., spot sprays. Another option is a post-harvest dip of captan or other material. Keep in mind this is the worst-case scenario with orchards that have high inoculum.

John has also observed some other secondary rots in several orchards and has not been able to assess what they are yet. Products like Incognito (thiophanate-methyl) or Topsin (thiophanate-methyl) do function well on other rots.

Bitter rot
Bitter rot has been discussed extensively this season, even though incidences of the disease remain limited. This is now the time in the season where orchards with high inoculum are at a greater risk of infection.

The visual symptoms of bitter rot appear as 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 makes a sharper V-shape into the fruit, when cut in half, when compared to black and white rot. This disease can cause 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 rainstorms. The pathogen can overwinter in fallen fruit and in mummified fruit 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 strawberries and blueberries, infections can happen in four-to-six hours during wetting events, which is relatively fast for a fungus. Bitter rot 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.

Insect management
Hail impact on apple maggot
Late-season hail fell over the past week in Eastern Minnesota and Western Wisconsin. This fruit will not recover from this injury and will begin rotting on the tree, which will likely bring in additional fruit flies from outside the orchard. Maintaining good spray coverage for apple maggot will be important to reduce overwintering pest populations. If the damaged fruit is infested with apple maggot and the fruit is left in the orchard, it will increase populations next year. In blocks with hail damage, hang a baited trap to better assess the apple maggot pressure in the orchard. If an insecticide is necessary, Assail (acetamiprid), Exirel (cyantraniliprole) or Imidan (phosmet) should be used to suppress adult populations. Alias (imidacloprid) or Wrangler (imidacloprid) will not have the desired knock-down effect. It is not recommended to apply a pyrethroid or carbaryl because of effects on natural enemies. Even at 15% damage, John would recommend applying an insecticide for AM and hang a baited red sphere.

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. Baited traps do run the risk of drawing apple maggots in from outside the orchard. The Wisconsin Pest Survey Bulletin from DATCP mentions how many AM growers are catching throughout the state.

It is essential to continue monitoring for apple maggot through the end of August. At this juncture in the season we often ask, “How late do we need to monitor? If we catch AM on Labor Day weekend, do we need to spray?” Some literature suggests these late catches do not need to be treated. An occasional catch is okay to ignore, but if you are getting multiple flies on multiple unbaited traps, you may need to apply an insecticide.

Assail (acetamiprid) is often a preferred insecticide for combined management of apple maggot and codling moth, especially late in the season. 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. A final AM application of the season should be a material that has efficacy on the adult fly as well, like Assail (acetamiprid), Imidan (phosmet), or Exirel (cyantraniliprole). If a final product is applied that does not have efficacy on adults, this will result in maggots hatching out when residue efficacy is diminishing and may lead to metabolic resistance.

Note: The fruit essence on baited traps is viable for one week and should be changed accordingly.

Codling moth
Several locations have had late, heavy flights that has led to fruit injury. Some of the injury observed included partial entry into the fruit. This can occur with lower rates of Assail, or if the larvae started entering the fruit, then were exposed to an insecticide. To address pre-harvest intervals, codling moth insecticides may need to be applied before the 250 degree-day interval from trap captures. Depending on the CM trap lure used, it can be difficult to gauge the population density e.g., CMDA lure captures both female and male moths. Do not be lulled by a low capture rate, as percent fruit injury between first and second generation, can increase significantly. If growers had any first-generation codling moth damage, they should stay on top of insecticide sprays. If using mating disruption, this will help reduce the chance of fruit infestation. Growers should consider a product to target both leafrollers and codling moth in August, e.g., Delegate (spinetoram), Altacor (chlorantraniliprole), Exirel (cyantraniliprole). One larvicide application, no matter what product, will not carry you through August and into the first week of September, especially if there is significant rain. If growers are catching 5-15 moths, this is not a massive threat. John considers catching 20+ moths to be more of a threat in terms of urgency to apply an insecticide.

John, Josie, and Peter have observed relatively significant leafroller damage on the surface of the fruit. This injury is observed on mainly early varieties with soft skin, e.g., First Kiss, SweeTango, Zestar and in orchards that have not used larvicides or insect growth regulators and instead primarily used neonicotinoids for apple maggot and second generation codling moth. The second-generation of obliquebanded leafroller (OBLR) will hatch into late-August and can continue into September. This generation typically feeds on ripening fruit rather than on vegetative tissue. The OBLR larvae will only grow to a few millimeters in length before developing a pupa and going into diapause, where the OBLR’s growth and development is suspended until spring. Later larvae will feed under the skin of the fruit, then emerge and will overwinter in the orchard. Growers using MESO combo mating disruption still observed some leafroller injury from mated OBLR flying into orchard from neighboring woodlots and abandoned fruit trees.

The CM larvicides, e.g., Delegate (spinetoram), Altacor (chlorantraniliprole), will control these larvae, whereas the neonicotinoids, e.g., Assail, Admire Pro (imidacloprid), do not. Managing the second generation now, will reduce the overwintering population that may need to be controlled next spring. Three to five percent injury is possible at harvest and scouting needs to be used to determine if a treatment is warranted. A mistake with OBLR may discount an apple from US Fancy grade but is not usually a problem when selling pick-your own fruit since the injury is very small and there is no worm in the apple. Two traps per 20 acres is adequate to determine where treating is necessary.

Please refer to the August 4th, 2020 AppleTalk notes for further information on OBLR management:

Lesser apple worm
Lesser apple worm (LAW) damage resembles codling moth injury, however, has some distinct differences. LAW and oriental fruit moth (OFM) do not burrow into the core/seeds and rather spend their time feeding on the flesh of the fruit. These larvae can be up to an inch long. If an OFM trap is being used, it will also capture LAW. The OFM traps in the region rarely capture OFM and since LAW is in the same genus, these lures may be used to monitor LAW. LAW have a similar degree day model to codling moth and when larvicides are timed for codling moth, they will be managed by these sprays. Therefore, this may be problematic in orchards using mating disruption that are not planning to spray for second generation codling moth. If there are ten or more (threshold is nominal) in a week a larvicide for LAW may be necessary.

Tarnished plant bug
Tarnished plant bug feeding and oviposition injury on fruit has been observed this summer and will likely show up in the pack-out. This injury can be described as a deep, sunken indentation that is conical in shape. The center of the indentation, if cut open, will have a corky appearance that can be observed a few millimeters into the flesh of the apple.

Adult TPB overwinter under debris in the orchard and there are two to three generations per year. Typically feeding injury does not occur after June, and later generations move on to other hosts. Growers can monitor for TPB in the spring from silver tip to petal fall by using a rectangular, white sticky trap. These traps should be stapled to stakes or hung on low branches around the border of the orchard. Traps should have a density of five per block, or one every three to five acres. The action threshold is an average of three per trap, or five or more in a single trap.

There are several cultural control methods that growers can use to reduce the population. This includes eliminating wild apple trees around the orchard border, removing broadleaf weeds, e.g., chickweeds, dandelion, clover, reduce mowing from bloom through petal fall, and preserve natural enemies in the orchard, e.g., true bugs, ladybird beetles, spiders, parasitic wasps. It is important to note that alfalfa and strawberries are alternative hosts. Chemical control should occur early in the season and usually coincides with plum curculio control. For further information, read this fact sheet from Washington State University:

This article offers great representation of stinging insect biology, life cycle, and identifying injury to fruit:

Grower question:
What should we expect for late-season brown marmorated stink bug (BMSB)?

  • Overall, the trap counts in WI remain low. Trap captures continue to be concentrated in Dane and Rock county. These sites had high counts with 10 or more in a week last year in September and October.
  • Low captures will occur until other hosts are harvested, e.g., soybeans. This is when apples become more of a target into September and October.
  • Growers can hang a sticky panel or pyramid trap to monitor populations. Lures can be purchased from Great Lakes IPM:
  • Monitor the perimeter for adult BMSB. If BMSB are observed, a perimeter spray is an option. However, if finding stink bugs throughout the block, the best option is an alternate-row middle spray, as it allows a follow-up application in the remaining un-sprayed rows if necessary.
  • Synthetic pyrethroids are the most effective. A few neonicotinoids are effective, e.g., Scorpion (dinotefuran), but may not be available in Wisconsin. Other pyrethroids include Brigade (bifenthrin), Warrior (lambda-cyhalothrin), Asana (esfenvalerate) and Danitol (fenpropathrin). The most highly rated insecticide is bifenthrin and is the preferred insecticide to use.
  • There is no such thing as fresh stink bug injury. It takes two to three weeks for injury to appear. This can be an issue with stored fruit.
  • Native stink bug research has dropped due to the concern with BMSB.
  • Scaffolds article 8/17:

Determining fruit ripeness and harvest dates
Tracking days from full bloom can be used to plan the harvest of Paula Red and McIntosh. Paula Red harvest typically begins 100 days from full bloom and can last two weeks. Picking for McIntosh starts 115 days from full bloom, with prime picking between 125 and 130 days. The goal is to have all McIntosh fruit harvested within 145 days of bloom.

Background color is primarily used to determine harvest of Zestar. A light greenish background and brown seeds signals a ripe Zestar. There is not currently a good measurable sugar content, i.e., brix, so taste is helpful since it seems Zestar can go from starchy to sweet overnight.

When picking Honeycrisp growers should look for a good yellowish-green background color and red over color. On some sites this color never develops, and the amount of red can depend on the strain of Honeycrisp. Most growers do two to three picks of Honeycrisp. The first pick is usually set aside for storage or late season sales and the following two are sold as soon as possible since over mature Honeycrisp do not store well. In some scenarios the third pick will invariably end up as cider.

When using Extension recommendations for starch-iodine tests, brix, or pressure always consider your orchards unique site-specific parameters and expect some variation between orchards and regions. Use the available tools to gather and generate data and determine what parameters work best for your operation. Harvest maturity equipment can be purchased from Peach Ridge Orchard Supply,!/Maturity/c/12544202/offset=0&sort=normal

Pesticide-residue testing for fruit
Residue testing is expensive and commonly completed by growers who must meet Maximum Residue Limits for export markets. Residue testing is not necessary for fruit sold domestically, but growers interested in this may look for more information through the following labs:

IEH Laboratories & Consulting Group/ Environmental Micro Analysis Inc.
Woodland, CA

Pacific Agricultural Laboratory
Sherwood, OR

Anresco Laboratories
San Francisco, CA

SCS Global Services
East Bay, CA

Leaf and soil samples
From the August 4th AppleTalk Summary:

Leaf and soil samples for nutrient analysis should be collected no later than the week of August 17th from this season’s growing shoots. The purpose of collecting the samples now is to inform nutrient management for next year. Samples may be sent to AgSource Laboratories ( or the UW Soil and Forage Lab in Marshfield Wisconsin ( The UW lab includes soil and tissue samples for $25. Tissue sample pricing from AgSource Laboratories is dependent on your specific location. Contact your nearest lab for pricing options.

Soil analysis through AgSource includes the following soil-sampling packages:

  • Basic Package ($45) – includes: Soil Health Score, CO2Respiration, C:N Ratio.
  • Routine Package ($55) – includes: Soil Health Score, CO2Respiration, C:N Ratio.
  • Complete Package ($65) – includes: Soil Health Score, CO2Respiration, C:N Ratio

When collecting leaves, examine this year’s growing shoots and select several leaves from the middle of the shoot. Leaves should be collected from a representative sample of the block or variety. About 30 leaves are needed to have one cup of dry leaf material that will be ground up for the analysis. Samples should be separated by variety or by health of the tree. Analysis of unhealthy trees should be kept separate. We are unsure if the results in mixed-variety orchards would be skewed by collecting leaves from multiple cultivars and it is recommended to keep samples limited to specific varieties. Once we see nutrient deficiencies this time of year it may be too late to amend this year and results will be focused on soil and tree health next year.

WI Apple Growers calendar
We are now accepting photos for the 2021 Apple A Day IPM Calendar. Please submit your photos by as soon as possible before harvest gets rolling! Photos must be at least 1000 KB (1 MB) to be included in the calendar. This means photos downloaded from your social-media pages will likely be too small. Photos taken on smartphones will likely be large enough. Our goal is to have these calendars out to you in October so they can be sold at farm stores. Please email photos to !