July 2 AppleTalk

AppleTalk Conference Call Summary
Tuesday, July 2, 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 2nd call stream: CLICK HERE

Regional update

Location Degree Days 6/24/2019 (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 824 5/28/2019 175 153 14 6/8/2019 372
Gays Mills, WI 898 5/30/2019 115 128 12 6/6/2019 446
Hastings, MN 890 6/1/2019 78 96 10 6/7/2019 443
Harvard (Royal Oak), IL 887 5/23/2019 166 226 20 6/6/2019 239
Lake City, MN 865 6/1/2019 97 128 15 6/3/2019 507
Mauston (Northwoods), WI 866 6/1/2019 108 103 12 6/7/2019 410
Mequon (Barthel), WI 735 6/6/2019 99 80 9 6/15/2019 263
Preston, MN 865 5/31/2019 115 126 11 6/3/2019 481
Rochester (Ela), WI 846 5/23/2019 156 179 17 5/30/2019 489
Trempealeau (Eckers), WI 899 5/31/2019 111 118 11 6/6/2019 442
Verona, WI 912 5/30/2019 94 98 9 6/5/2019 468
White Bear Lake, MN 858 6/3/2019 81 100 9 6/8/2019 405
Woodstock, IL 1016 5/26/2019 89 114 10 5/28/2019 416

Table 1. Degree-day accumulation and leaf wetness hours to 6/24/2019.  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.

Sooty blotch and flyspeck (SBFS)
Depending on how fungicides for SBFS are timed, there are two distinctly different approaches to managing this disease complex.  Currently, infections have already occurred or are occurring now.  Local NEWA stations have a model for summer diseases and the weather summaries can be used to track leaf wetting hours. We begin monitoring leaf-wetting hours for SBFS beginning at petal fall, which is when the first influx of spores from SBFS are released from adjacent woodlots. At petal fall, many growers are still applying single-site fungicides, which eradicates these early infections that occur between petal fall and first cover. The potential for SBFS to develop resistance to single-site fungicides are minimal because new spores are coming in from outside the orchard and disease is a complex of more than 70 different pathogens.

After 175 to 220 leaf-wetting hours (LWH), a second spore release occurs and fungicides targeting SBFS should be applied. This can happen between three and 11 weeks post-bloom, with an average of seven weeks post-bloom. Captan and Topsin (thiophanate-methyl) are the primary fungicides used to manage SBFS, especially where scab is also present. Where secondary scab is not a concern, the SDHI, strobilurin and DMI fungicides may be used for SBFS. When single-site fungicides are applied following the accumulation of 175 LWH, symptoms are eradicated before they show up. Single-site fungicides are attractive because of their ability to also manage black rot and bitter rot. The reapplication interval following the first application is dependent on rainfall and weathering of the fungicide. Most importantly, the model is reset and we begin counting LWH again until another 175 LWH benchmark is reached, before timing another fungicide.

If SBFS is going to be managed without single site fungicides, then maintaining fungicide coverage is essential.  Under this approach, we are not able to eradicate symptoms and need to protect the fruit from new infections using captan. A 2-3 lb. rate of captan is greatly reduced after two inches of rain or 21 days, higher rates may offer added protection. If apple scab is present, it is essential to avoid exposing these single-site fungicides to secondary scab populations. If soft fungicides are used, they would also be applied as a protectant, since Oxidate, Regalia and Serenade will not eradicate infections that already occurred.

Research completed on SBFS in the upper Midwest found that relative humidity (RH) rather than leaf wetness hours (LWH), is a better predictor of SBFS infections. It was found that 192 hours of RH above 97% was a better predictor than 175 hours of leaf wetness for our region. During the summer, dew usually contributes to more wetting hours than rainfall. Within the tree canopy, RH is more stable. Since we do not have instruments to gather RH at 97%, it is still recommended to use LWH. It is important to place the leaf wetness plates within the canopy to accurately record LWH.

Single-site fungicide options for summer fruit rots
According to research from Dave Rosenberger, professor emeritus at Cornell University, bitter rot, white rot or black rot infections can occur early in the summer and lay latent until the fruit begins to ripen. Considering this, infections that are becoming visible now, and into harvest, may have occurred early in the season when insufficient fungicide residue was present during the infection period.

In our region, Honeycrisp is the most susceptible variety to bitter rot, and captan is often the primary fungicide used to protect against infection. Topsin (thiophanate-methyl) applied for sooty blotch and flyspeck does not control bitter rot. Captan applied alone (5 lb./A) or tank mixed with a strobilurin, e.g. Flint, Sovran, or SDHI fungicide e.g. Aprovia (benzovindiflupyr), Fontelis (penthiopyrad), are the most effective options. If a single-site fungicide is used to manage bitter rot, it is recommended to rotate mode of actions between applications to reduce the risk of the bitter rot pathogen developing resistance to a single mode of action.

Organic fungicides such as sulfur are not very effective and while copper might be effective, it is not safe to use on fruit at this time. Other cultural practices include removing thinned from under the tree, since these can also be infected with bitter rot and spread it to fruit in the canopy.

Characteristics of bitter rot, fruit:

  • Most orchards with bitter rot have their own strain or collection of fungi which make up the complex we manage, which can start to cause resistance problems.
  • Generally, takes several weeks following infection before symptoms develop, may become visible before other rots.
  • Symptoms first appear as small, light-brown, circular spots. Many spots per fruit may be found.
  • Under high temperatures initial lesions may rapidly enlarge and change to dark brown in color.
  • 1/8 to 1/4 inch in diameter lesions are distinctly sunken or saucer shaped.
  • When lesions reach 1/2 inch in diameter, small, black fruiting bodies appear in the sunken lesion. Fruit bodies may be arranged in concentric rings.
  • Fruiting bodies will begin to ooze a gelatinous, salmon-pink mass of spores, which is washed by rains onto other fruit.
  • Beneath the surface of the spot, the flesh is light brown and watery in a cone or V-shaped area, with the small end of the cone toward the fruit center.
  • Cankers can form on vegetative tissue, but are rare.

Characteristics of black rot, fruit:

  • Black rot infections on fruit usually appears at the calyx end and can originate at any wound that penetrates the epidermis, e.g., insect or hail injury.
  • Usually only one spot occurs per fruit, a characteristic that distinguishes black rot from bitter rot.
  • Initial infection becomes brown and stays brown or turns black as it increases in size.
  • A series of concentric rings often forms as the rotten area increases in size. Lesions are usually amorphous. The flesh of the decayed area remains firm and leathery. Fruiting bodies will appear on the surface of the rotted tissue.
  • Fungicides that will offer protection against fruit rots include captan, strobilurins, e.g., Pristine (boscalid, pyraclostrobin) and Flint (trifloxystrobin), and Topsin. Do not apply strobilurins if scab lesions are present. A high rate of captan may provide adequate protection.  Note: to reduce resistance concerns always tank mix single-site fungicides with a protectant.

Bitter rot resources

Root health
Many growers had wet and water-logged soils this spring and some orchards still do.  Look at trees that are four to six years old.  These terminals in the heat of the day should be perky if we have adequate soil moisture and a healthy root system.  If we see droopy terminals on young trees that should have a good root system, this is a red flag that something is not functioning correctly with the root system. Applications of a phosphorous acid fungicide would be an option.

When a tree roots grow, it first has a white appearance.  During this time it is able to uptake nutrients and water and can do this for about two weeks. Once the white root begins to turn brown, a process called suberization begins and turns the root into a woody-structural element for the tree. Once a woody part of the roots system, it no longer functions as a root to pick up water or nutrients or interact with soil microflora.  This is an ongoing and continuous process.  Takes only a few days for free water sitting in soil to produce anoxic conditions, and cause these new roots to die after a few days.  Tree roots do not tolerate conditions without oxygen well.  Applying a phosphorous acid fungicide such as Rampart or Phostrol, etc. is an option to help mitigate invasion of pathogens such as Phytophthora and will not correct roots dying from too much water.

 There is a short series of pod casts produced by the University of California which do an excellent job of explaining irrigation management and root health.  Listen to the series of eight pod casts which are from eight to fifteen minutes long: https://www.growingthevalleypodcast.com/soils-and-irrigation

Apple maggot
Growers in southern Wisconsin have already reported capturing apple maggots on red spheres. High soil moisture and now heat that has been present in the past couple weeks and is likely driving this emergence.  Red spheres should be up in all orchards across the region.  Apple maggot (AM) emergence is often spotty in late June and early July, and reports from growers confirm this with low and isolated trap captures.  We expect trap captures to increase as we move into mid-July and through the month of August.  The last decade many growers have been moving away from Imidan (phosmet) and other organophosphates to manage AM.  Avaunt (indoxacarb) was one product that growers tried five or more years ago and we have found this to not perform very well.  This has left us with neonicotinoids as the primary organophosphate alternative for AM management.  Assail is often a popular choice because it may be used for both AM and second-generation CM.  The downside has been poor management of the summer generations of leafrollers.  Subsequently the use of generic imidacloprid products, e.g., Admire Pro, Wrangler, Montana, in a tax mix with a spinosad or diamide insecticide, has been quite popular.  This tank mix results in a reduced risk, yet broad spectrum spray which can manage AM, CM and summer leafrollers, e.g., obliquebanded and redbanded leafrollers.  Even though we have been successfully managing AM this way, imidacloprid and most of the neonicotinoids do not offer extended-contact knockdown of the female AM fly.  Assail does have more mortality on the adult fly and wears off quickly.  The main control from Assail and imidacloprid is in the egg laying as an ovicide and survivability of the eggs, and as a repellant.  Overall, we have found this strategy to perform well and are yet to hear about AM failures from using the neonicotinoids.  However, this does make it hard to spot spray for AM.  Historically, we used to be able to just apply tanks of insecticide in the sections of the orchards that had captures or employ strategies like alternate-row middle sprays.  Due to how these insecticides perform, complete block or orchard sprays are recommended. When it comes time to apply the final AM spray of the season, an insecticide that is going to kill the adults, e.g., Exirel at high rate or Assail to a lesser degree, are needed, rather than something that impacts egg laying or egg survival.

There is not anything new regarding the timing of AM sprays.  If we are relying on baited or unbaited spheres, the narrative suggests that if you are catching maggot flies on red spheres, they are laying eggs and there is no safe interval to wait to spray.  In practice, the numbers we are catching are fairly low density and if most traps are zero and only catching a few, you are probably okay, however, as numbers increase, the urgency to spray increases.  The threshold developed by Cornell is an average of one fly per sphere, where three unbaited spheres are used per ten acres.  When using a baited trap, this threshold increases to an average of five flies per sphere.

There is no standard rate for how many apple maggot spheres should be used. Where yellow-sticky boards are used, it is important to remember they only last two weeks. When these sticky boards catch apple maggot, no action is needed. When apple maggots first emerge, they are looking for honeydew excreted by aphids.  The yellow board is mimicking the honeydew and aphids.  Growers have time before needing to make the first spray.  The current threshold from Cornell uses three traps per ten acres. If we increase the density, e.g., one trap per two to five acres, it will better improve our ability to identify where they are coming in from outside sources or identify edges that are hot spots. Orchards with lots of woods along their edge would benefit from a higher density. Keeping this high density along wood lines is beneficial because we can’t anticipate changes in wild hosts in the woods.  Even if woods are some distances away, they can fly a pretty good distance. Baited spheres are not going to offer maximum utility until trees have received hail or where we have early varieties, e.g., summer apples, that produce an in-house population that are there year to year.  Monitoring these trees separately from the rest of the orchard is important. Unbaited traps work well for most of the season and as we get closer to harvest, growers can consider using baited spheres.

Codling moth
This week most growers are reaching 400 to 450-degree days from their codling moth biofix.  500DD from biofix 50% of the codling moth population is hatching.  This week it is important for growers to remember to adjust their upper threshold to a maximum of 86°F, if temperatures exceed this.  The NEWA degree-day calculator does have an 86/50 option that should be used when calculating degrees from codling moth biofix.  We can expect the model to start moving faster and within the next week we will be at 500 DD, which is peak-egg hatch and when 50% of the population will begin hatching.

Codling moth trap captures that were significant a few weeks ago are beginning to hatch.  The frequent rains risk significant wash-off and could allow larval survival if protection is not maintained according to the degree-day model. Moths that flew several weeks ago will hatch after 250-degree days.  Codling moths that fly today, will also hatch after 250 DD.  This is in alignment with the model where we target CM between 250 – 350 DD and then again at 500 DD.

Last week John Aue discussed using a penetrating surfactant where neonicotinoids are used. We typically think that Altacor, Exirel, Delegate or Entrust sit on top of the leaf or fruit surface and want to apply a terpene-based sticker.  Research has shown a rate of 8 oz./acre of these terpene stickers does help. After reviewing the new rainfastness article by John Wise, we learned diamide and spinosyn insecticides like Altacor, Entrust and Delegate, do have translaminar activity, where they move from one side of the leaf surface to the other.  This has not been mentioned before in the literature and thought they stayed on the surface of the leaf cuticle. The terpene-based sticker still has utility because some parts of the residue are on the surface.

There is an updated rainfast chart from Michigan State University, which includes the common larvacides used for managing codling moth: https://www.canr.msu.edu/news/rainfast_characteristics_of_insecticides_on_fruit.

Pheromone trap maintenance
The lifespan of our pheromone traps is dependent on three primary factors, the amount of pheromone load, the lure material or medium which regulates the pheromone release and the ambient temperature which can degrade pheromones during extended periods of high heat.  Several extended-life lures exist with varying life spans.  These should all be replaced at the beginning of July, and depending on their life span, they may last the rest of the season or may need to be replaced mid-August.  Any 1x lure used for codling moth, obliquebanded and redbanded leafrollers, oriental fruit moth, lesser appleworm and dogwood borer should expect a lifespan of two to three weeks during periods of extended heat in July and August.

Lure Type Lifespan for 1st Generation Lifespan for 2nd Generation
1x red septum1 3 weeks 2 weeks
10x red septum2 3 weeks 2 weeks
Super Lure2 6-8 weeks 6 weeks
MegaLure (Trece)1 6 – 8weeks 6 – 8 weeks
Biolure CM10x (Suterra brand)2 4 – 6 weeks 4 weeks
CMDA combo lure 8 weeks Probably less than 8 weeks3
Biolure CM1x (Suterra brand)1 6 to 8 weeks Probably closer to 6 weeks3
CM L21 8-12 weeks Probably closer to 8 weeks3

Table 2. Codling moth lure lifespan for first and second generation flights.

1 http://msue.anr.msu.edu/news/using_pheromone_traps_to_monitor_moth_activity_in_orchards1

2 http://entomology.tfrec.wsu.edu/stableipm/WorkshopPDFs/cmmonitoring.pdf

3 No data was available on the lifespan during second generation, but we should presume decreased life of these pheromones based on average temperatures in July and August that have potential to decrease duration of pheromone release.

Potato leafhopper
Potato leaf hopper (PLH) adults have been observed in several orchards throughout the region, with a few nymphs appearing over the past couple days.  Adults are blown in on weather fronts each year, as they overwinter in Gulf Coast states.  Once in our region, PLH populations are high influenced by the surrounding landscape.  Orchards with many adjacent hay or alfalfa fields are appearing to have much higher populations of PLH.  Comparatively, orchards surrounded mostly by woods are showing much lower populations or none at all.

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 the majority of damage come from nymphs.  Leafhoppers often move in a lateral fashion and will quickly go 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 are appearing.  For more detailed information, please visit: http://labs.russell.wisc.edu/vegento/pests/potato-leafhopper/.  For organic producers, Russ Groves, University of Wisconsin Madison – vegetable entomologists, recommends an evening application of PyGanic at the 12 oz./acre rate and a second application at 6 oz./acre.  IPM growers may manage PLH with any of the neonicotinoids, but the imidacloprid products, e.g., Alias, Montana or Wrangler will be the most cost-effective insecticides.

Brown marmorated stink bug (BMSB)
Orchards in Dane county and throughout southern Wisconsin are beginning to catch BMSB.  For now, the first BMSB capture should not be of much concern.  Everyone should have a BMSB trap in their orchard and should not be afraid about the risk of pulling in BMSB from outside the orchard, because if one is caught in the trap, they are already there.  Getting the early warning is critical to manage this pest.  Provisional thresholds have been developed and this will be discussed in greater detail in the up coming calls.  In the meantime, traps for BMSB may be ordered from Ag Bio Inc., http://www.agbio-inc.com/stink-bug-traps.html. The national-clearing house for all information relating to BMSB is on the website,www.stopbmsb.org. Here you can read about all the existing research and different management strategies for different crops.