July 16 AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, July 16, 2019, 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 16th Call Stream: CLICK HERE

Regional update

Location Degree Days 7/15/2019 (Base 50°F) Petal Fall Date (NEWA) Total leaf wetting hours, from petal fall Total potential infection event hours, from petal fall Total potential infection events, from petal fall CM Biofix (NEWA) Accumulated DD (Base 50°F) from CM biofix
Eau Claire, WI 985 5/28/2019 185 168 15 6/8/2019 660
Gays Mills, WI 1146 5/30/2019 148 128 14 6/6/2019 764
Hastings, MN 1118 6/1/2019 114 88 12 6/7/2019 754
Harvard (Royal Oak), IL 1099 5/23/2019 250 137 15 6/6/2019 740
Lake City, MN 1119 6/1/2019 146 122 16 6/3/2019 817
Mauston (Northwoods), WI 1077 6/1/2019 122 109 15 6/7/2019 713
Mequon (Barthel), WI 873 6/6/2019 79 63 10 6/15/2019 536
Preston, MN 1075 5/31/2019 140 131 13 6/3/2019 780
Rochester (Ela), WI 991 5/23/2019 194 175 19 5/30/2019 774
Trempealeau (Eckers), WI 1096 5/31/2019 109 97 11 6/6/2019 751
Verona, WI 1136 5/30/2019 120 100 12 6/5/2019 781
White Bear Lake, MN 1071 6/3/2019 119 95 11 6/8/2019 708
Woodstock, IL 1232 5/26/2019 144 125 13 5/28/2019 886

Table 1. Degree-day accumulation and leaf wetness hours to 7/15/2019.  Note: Degree days for codling moth are estimated by NEWA.  Actual dates must be entered by users and are not saved.  This year DD are as much as five days off grower-observed codling moth flights. *All degree days are calculated using a lower-temperature threshold or base temperature of 50°F.  *Leaf wetness events are periods of four or more hours.

High temperatures continue to hover in the mid to upper 80’s and low to mid 90’s.  Many areas have not had significant rain events in at least a week but have been quickly accumulating degree days.  Rain is expected over the weekend in several locations throughout the region with expected accumulations of half-an-inch or more.

Leaf and soil analysis
Leaf and soil samples for nutrient analysis should be collected in mid-July 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 (https://www.agsourcelaboratories.com/) or the UW Soil and Forage Lab in Marshfield Wisconsin (https://uwlab.soils.wisc.edu/).  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 toward soil and tree health next year.

Some growers are also completing fruitlet-nutrition analysis, which is typically done when the fruit weigh between 40 – 50 grams.  There are not clear benchmarks which explain the data from fruit analysis and growers are still learning how to interpret these results.

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/
  4. Haven (wax formulation):  This is a new product we have not worked with and is available from Nutrien Ag Solutions.  Haven doesn’t block stomates or gas exchange on surface of the fruit. The cost is $45 – $90 per 100 gallons of water and is manufactured by Marrone Bio Innovations.  As with most of the sunburn protectants, it needs to be applied a few days before the damaging sunlight.

Additional resources

Sooty blotch and flyspeck (SBFS) and bitter rot
Most orchards are just shy of the 175 leaf-wetting hours needed to trigger a fungicide application for SBFS.  As we begin to have more heavy dew at night and in the morning, dew that lasts longer than four hours, should be triggering wetting events on your NEWA station.  Make note of what time the dew sets in and when it burns off, if it is longer than four hours, these should also be included in the wetting events.  Additionally, high relative humidity above 97% will also trigger infections.

In southern Wisconsin orchards, there are some small pinpoint brown spots beginning to show up.  A hand lens is needed to differentiate between an infected lenticel, sting from apple maggot, codling moth or the beginnings of bitter rot.  They appear as small brown smooth surface circle, about ¼ to ½ mm in diameter.  Scouting should focus on Honeycrisp, as this variety is more susceptible to bitter rot.  If they are bitter rot, they will begin to grow over the next month.  Please see the late-June and early July notes for extensive discussion on bitter rot and SBFS.

Apple maggot: Effective life of maggot sprays
The neonicotinoid class of insecticides has become our primary organophosphate alternative for managing apple maggot.  Unlike pesticides such as Imidan (phosmet) that offer excellent contact mortality against adults, neonicotinoids are absorbed into the skin of the fruit and act as a repellant or a systemic antifeedant and larvicide.  These systemic properties of the neonicotinoids give the insecticide a long lifespan and boosts rainfastness up to two inches (or one inch if the rain event was within 24 hours of application).  Assail and Altacor, for example, can last up to 21 days with very low rainfall. Pesticide rainfastness is much more of a concern for codling moth, but for apple maggot and Japanese beetle, we may achieve adequate control of these pests even as we reach the maximum of two inches of rain.

Apple insecticide precipitation wash-off re-application decision chart. Expected codling moth control in apples, based on each compound’s inherent toxicity to codling moth larvae, maximum residual and wash-off potential from rainfall.
Insecticides Rainfall = 0.5 inch Rainfall = 1 inch Rainfall = 2 inches
*1 day *7 days *1 day *7 days *1 day *7 days
Imidan Sufficient Insufficient Sufficient Insufficient Insufficient Insufficient
Asana Sufficient Insufficient Insufficient Insufficient Insufficient Insufficient
Assail Sufficient Sufficient Insufficient Insufficient Insufficient Insufficient
Proclaim Sufficient Insufficient Sufficient Insufficient Insufficient Insufficient
Rimon Sufficient Sufficient Insufficient Insufficient Insufficient Insufficient
Delegate Sufficient Sufficient Sufficient Sufficient Insufficient Insufficient
Altacor Sufficient Sufficient Sufficient Sufficient Insufficient Insufficient

Apple maggot: Opportunities for spot sprays
Both baited and unbaited, red spheres are effective for attracting AM because the very mobile pests are attracted to fruit both visually and through olfactory senses.  When unbaited spheres are used at three traps per ten acres, the threshold is one fly per trap, while baited spheres have a threshold of up to five flies per trap.  Maggot flies are sometimes only caught in isolated sections of orchards.  If we are using a good density of traps, we can rely on this trap data to determine what part of the orchard needs to be sprayed.  This can help us effectively use spot treatments to manage AM and is particularly useful if codling moth does not need to be treated.  Spot sprays can be an excellent option for AM control, especially in orchards with variable pressure looking to limit insecticide costs or toxicity effects.  Ultimately, it may not be necessary to make an orchard wide application.

Second generation codling moth
As we move towards the end of first-generation codling moth, growers that had washoff events or gaps in spray coverage between 350 and 500 DD should now be able to see injury.  This week Peter observed codling moth larvae at several different instars, between 1st and 4th, suggesting second generation still has some time before the flight will begin.  When looking for injury, inspect the area where fruit clusters touch, as this can sometimes not catch enough pesticide residue, additionally, CM can often be found int the calyx end.  Many growers have used mating disruption this year and if no larvacides were applied to these orchards, growers should consider that injury may be from lesser appleworm (LAW), and to a much lesser extent, oriental fruitmoth (OFM).  This has happened in isolated instances.  If trapping for OFM or LAW and counts have fluctuated between 10-20 in a week, be aware these numbers are high enough to result in fruit damage.

There are approximately 1000-degree days between the biofix for first and second-generation codling moth (CM).  Traditionally we have discussed biofix as a significant biological event where traps catch large amounts of codling moths overnight.  This is easily defined when we have a week with no trap captures between generations.  However, the codling moth flight does not necessarily need to reach zero before we begin to count catches as second-generation moths.  When counts are low and degree-day (DD) accumulations since first generation biofix exceed 1000, we can comfortably assume second generation codling moth have begun to fly.

Most growers experienced lighter flight of moths at the beginning of the season with a couple weeks with higher counts, followed by lower trap counts through the remainder of the flight, but this may not occur the same way for our second generation.  Second-generation population is dependent on the success or failure of management during the first generation.  When fruit are infested early in the season, they generally stop sizing and remain considerably smaller than healthy fruit.  Larvae found in fruit now reflect a management failure from pesticide wash off or a missed spray within the last three weeks, rather than at the beginning of the season.

Good first-generation control should result in low second-generation numbers.  However, wash off during the frequent rain events this season may have allowed fruit to be infested.  With as small as 0.2 percent infestation, orchards will appear clean yet can still generate high trap counts and significant CM pressure.  The second generation is often more difficult to control than the first generation and can easily grow tenfold in population by harvest.

NEWA DD model for codling moth
Several growers have noted the NEWA stations are showing that we are in second-generation codling moth, even though we have not accumulated 1000 degrees.  Most locations are around 750 DD, if there was a biofix between June 3-9.  Orchards that had a biofix at end of May are closer to 900 DD.  However, the NEWA station is telling us that first-generation codling moth is over, when this is clearly not the case.

CMDA + AA lures: A few comments from the Trece’ technical representative Brent Short
Growers using the CMDA + AA lure should not be too concerned if they are not getting trap shutdown in their mating disruption.  Traditionally, the goal with mating disruption is to get trap shutdown using 1x or L2 lures.  This tells us our mating disruption is working but prevents us from tracking the population.  In this scenario a capture of one moth would be threshold and could warrant treatment.  Brent, a Trece representative, described the new lure as being a “hot” lure that pulls in moths more aggressively and captures both male and female moths.  Therefore, catching one or two moths does not necessarily mean we are getting mating and reproduction within the orchard.  Unless there is a strong catch – 4 to 5 moths we don’t need to be terribly concerned.  These CMDA + AA lures have been paired with the Cidetrak Meso mating disruption that disrupts both male and female CM, therefore the idea is the CMDA lure should monitor for trap shutdown within both the male and female population.  However, the AA or acetic acid/pear ester, increases the sensitivity of the traps and is likely the source of the “noise” in the trap data.

Japanese beetle
Japanese beetle (JPB) activity has been delayed this year, compared to much more intense pressure observed earlier in the season, in previous years.  According to WI Fruit News, https://fruit.wisc.edu/wp-content/uploads/sites/343/sites/36/2018/06/Wisconsin-Fruit-News-vol3-issue6FINAL.pdf, JPB females don’t like to lay eggs in grass over three inches long and grass that is kept a bit longer may help prevent some egg laying within the orchard.  Therefore, close mowing of the alleyways should be avoided when Japanese beetles are active in the orchard.  Japanese beetle has a strong preference towards Honeycrisp.  If populations are widely dispersed, it is advised to treat the entire orchard rather than making a targeted spray to the heavily infested blocks.

The JPB use an aggregation pheromone to call in other adults and can result in high populations building up relatively quickly.  If you can slow the process down by using a repellant or antifeedant, this can help avoid more significant injury.  Early signs of visible feeding damage warrant an application of a repellent like neem oil or a full rate application of a neonicotinoid, including Assail (acetamiprid), Belay (clothianidin), and Wrangler/Alias/Montana (imidacloprid).  Most of these neonicotinoids function primarily as a repellant and anti-feedant but Assail generally gives some knockdown of the beetles.  Imidan (phosmet) is one of the only insecticides that will offer quick knockdown, therefore neonicotinoids need to be applied very early during the beginning of the infestation.

Note: Actara (thiamethoxam) is not as effective of a neonicotinoid as these other products.  Where large aggregations are present and require immediate knockdown, options are limited and include BeetleGone (Bt), or Imidan (phosmet).  If large aggregations of JPB are present in orchards, Assail will be the best alternative to organophosphates or synthetic pyrethroids.

Organic and IPM growers also have the option of using neem products (azadirachtin).  There are several different formulated products, in addition to using raw neem oil.  Neemix and Aza-direct are two formulated products.  Most labels don’t talk about the ability to act as a repellant, but even though it will not kill adults, neem oil does repel Japanese beetle from immigrating into the orchard.  Organic growers wanting to use a raw-neem oil with an emulsifier should check with their certifier to ensure the emulsifier is OMRI-approved.  When using a formulated-neem product, the OMRI certificate can be downloaded and generally should be kept with the spray records.  Do not apply neem oil during the heat of the day and apply in the evening or nighttime.

Mites and miticides
European red mite problems have been very minimal in the last half of June and first half of July.  It has been in the last seven days that populations are becoming more visible.  We don’t want mites to blow up in mid-August, so now is an important time to determine where populations exist, and sampling now will set a baseline.

Mite thresholds have increased from 2.5 to 5 mites per leaf and will increase to seven mites in August.  Some growers are just beginning to see mites emerge and in addition to the wide range in performance of miticides, each orchard’s mite populations respond uniquely to a treatment.  Mites don’t travel between orchards and you own your own mites, which means your mites have been exposed to whatever you have applied year after year in your orchard.

Some miticides work only as an ovicide and larvicide, whereas other miticides offer good contact activity on all motile stages.  Where mite populations have exploded, miticides such as Zeal (etoxazole) and Envidor (spirodiclofen) will not offer the level of immediate knockdown of adults that is desired. Miticides with good contact efficacy include Acramite (bifenazate), Kanemite (acequinocyl), Nealta (cyflumetofen) and Portal (fenpyroximate).

If bronzing is still occurring while mite populations are below threshold, action is required to prevent further economic injury to the plant.  This happens when a population of predators have remained active long enough to keep populations below threshold, yet enough mite feeding has occurred to cause leaf bronzing.  Once leaf bronzing occurs, economic injury is happening to the tree and a miticide should be applied.  This scenario is referring to what we call mite days, where the duration of mite activity is just as important as the actual population.  This year may be an interesting one regarding mite days, since we have not had mite populations early on.  If we reach threshold and still cannot see significant damage on any leaves, we may be questioning whether we need to make a miticide application.

Apple rust mites (ARM)
Apple rust mites have often been viewed as food for predatory mites, however, in high-density plantings and non-bearing trees, we are beginning to see more issues with ARM.  The ARM will inhibit shoot growth on young trees and populations that appear while the trees are still pushing growth may need to be managed.  Terminals are set on most trees and most non-bearing trees; however, some locations are still actively growing.  This year we are beginning to see some damage from growing rust mite populations on terminals.  Injured terminals will not recover and may not make it through the winter.  This doesn’t set the young trees up for a healthy fall and winter, if heavily damaged with rust mites or leaf hoppers.  ARM is much less of a concern in mature trees or semi-dwarf orchards.

Envidor works well on rust mites but doesn’t work on two spotted spider mites or European red mites.  If these other mite species are a concern, other options are available that will manage all three.  Make sure to read the labels, some newer products such as Nealta, do not control apple rust mites.

Potato leafhopper
Potato leaf hopper (PLH) adults continue to be problematic in orchards around the region.  Materials including PyGanic, Avaunt and neonicotinoids are effective.  When we look at other crops, as reported in the DATCP pest bulletin, there have been much higher populations of PLH nymphs and adults in other forage crops.  As these forage crops mature and are harvested, e.g., hay cutting, they will continue to invade other suitable crops.  This is a secondary pest, so the risk for losing a crop is very minimal.  However, young trees are responding very rapidly to PLH and hopper burn.  This has been observed across young and mature plantings alike.  Many young trees are still growing and PLH injury will shut this growth down.

Potato leafhopper adults and nymphs will inject a toxic saliva that causes damage to the leaf tissue.  The first sign of leafhopper feeding includes the cupping of leaves.  Further damage appears as a yellowing “hopperburn” of young terminal leaves.  Hopperburn can be described as a triangular yellowing or browning of the leaf tip.  This injury develops more rapidly during hot, dry weather and most of the damage come from nymphs.

Leafhoppers often move in a lateral fashion and will quickly jump to the underside of the leaf if disturbed.  Growers should be most concerned with PLH nymphs, and if needed, an application should wait until nymphs are more commonly observed, instead of targeting the adults.  The main priority is to monitor PLH on leaf terminals in younger trees.  The threshold for PLH is one or more nymph per leaf when hopperburn symptoms is appearing.  In mature trees, much of the leaf cupping and hopperburn has been observed in the upper canopy.  For more detailed information, please visit: http://labs.russell.wisc.edu/vegento/pests/potato-leafhopper/

Wooly apple aphid
WAA populations have been very low this summer and have only been observing occasional colonies.  If you see a white tuft at a shoot and there is only one aphid, it is most likely a single-adult female, even though they look bigger with their “fur coat”.  Do not get too concerned at the first sign of the little-white tufts.  The colonies are forming relatively late and may have a good opportunity for biological control.  Each grower should respond differently to an increasing WAA population based on historic pressure and scouting for biocontrol species, such as, parasitic wasp (Aphelinus mali), syrphid fly larvae and generalist predators that can affect WAA colony growth.

The insecticides Movento (spirotetramat) and/or Beleaf 50 SG (flonicamid), remain the best options to manage WAA, yet need to be applied at petal fall or first cover to offer optimum performance.  If these applications were not made, assessing WAA pressure now is critical.  If areal colonies are observed and still remain small and isolated and you still have growing terminals on trees, an application of Beleaf 50 SG may offer some efficacy or slow down population growth enough to allow beneficial insects to keep populations low later in the summer.  Both Beleaf 50 SG and Movento are sequestered into the tree through young and succulent growth.  Once terminal buds are set and shoots stop growing, it is less likely for these two insecticides to offer their desired level of management.

Closer (sulfoxaflor) may perform better than neonicotinoids since it belongs to a newer subclass of insecticides that have not been widely used.  Do not apply a sticker-type adjuvant, e.g., NuFilm, with insecticides for WAA since the insecticide needs to penetrate the white-waxy coating of the colonies to be effective.  Azadirachtin, e.g. Neem oil are probably the best option for organic producers.

For more information on WAA, visit http://blogs.cornell.edu/jentsch/2018/07/06/mid-season-woolly-apple-aphid-management-july-6th-2018/.