June 25, 2019 AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, June 25, 2019, 8:00 – 9:00 AM
Guest speaker: Dr. Patricia McManus, University of Wisconsin-Madison, Plant Pathology
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

June 25th Call Stream: CLICK HERE

Regional update


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


5/28/2019 114 109 7 6/8/2019


Gays Mills, WI


5/30/2019 89 76 7 6/6/2019


Hastings, MN


6/1/2019 56 38 6 6/7/2019


Harvard (Royal Oak), IL


5/23/2019 177 171 15 6/6/2019


Lake City, MN


6/1/2019 80 76 11 6/3/2019


Mauston (Northwoods), WI


6/1/2019 67 61 7 6/7/2019


Mequon (Barthel), WI


6/6/2019 57 50 6 6/15/2019


Preston, MN


5/31/2019 93 88 7 6/3/2019


Rochester (Ela), WI


5/23/2019 145 132 15 5/30/2019


Trempealeau (Eckers), WI


5/31/2019 55 45 5 6/6/2019


Verona, WI


5/30/2019 75 63 7 6/5/2019


White Bear Lake, MN


6/3/2019 63 54 6 6/8/2019


Woodstock, IL


5/26/2019 105 92 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.

High temperatures will be in the 80’s and 90’s with scattered rain showers Thursday-Sunday.  Degree days will rapidly accumulate with these hot temperatures through the weekend and most locations will reach 350 DD from CM biofix within the week.  Note: temperatures above 86°F are not counted in the DD model for CM.  If temperatures go above 86°F, use 86°F as the maximum temperature for DD calculations.  Leaf-wetting events of four or more hours will result in potential infections for sooty blotch and flyspeck.  All locations have between five and 15 wetting events since petal fall.

Summer-disease management with Dr. Patty McManus, UW-Plant Pathology
Pruning out winter injury
In the recent article in the UW Fruit News written by Brian Smith, UW River Falls, “Some Cold, Hard Facts About Winter Injury on the First Day of Summer”, he advises to complete pruning of winter injury by the beginning of July, despite potential risks of spreading diseases.  Late pruning may not give enough time for new growth to harden off before winter, however, pruning early could risk spreading several canker diseases, including Botryosphaeria, Colletotrichum and Leucostoma.  These are not aggressive pathogens and need an opening within the tree followed by several days of wet and rainy weather to successfully complete an infection.  Most canker fungi are more active in May, however due to cooler weather, they were likely active in June.

Growers should avoid making pruning cuts before a predicted rain event.  If fungicides are being applied, pruning wounds are likely being protected and the advantages of pruning outweigh the risks of not pruning out winter injury.  By pruning out winter injury, you will be preventing wasted energy going towards the injured branches.  If there is active fire blight in the orchard, this would be an exception.

Read the complete article, “Some Cold, Hard Facts About Winter Injury on the First Day of Summer”, here: https://fruit.wisc.edu/2019/06/20/some-cold-hard-facts-about-winter-injury-on-the-first-day-of-summer/.

Managing silver leaf
Silver leaf is caused by the fungus Chondrostereum purpureum and has only been an occasional disease in orchards for many years.  Beginning in the last six years with the establishment of many more acres of high-density plantings and new varieties, the fungus has been appearing more often.  Silver leaf affects a wide range of deciduous trees, e.g., willow, oak, maple and poplar.  The fungus secretes a toxin that causes the epidermis to lift away from the leaf.  This separation reflects light and causes the silvery appearance in leaves.  Silver leaf is systemic and can appear in either one or two scaffold branches, or the entire tree.

For most of the growing season, the key visual symptom are the silvery leaves.  In the fall, fruiting bodies appear as white brackets or shelf fungi.  There are several other fungi with similar looking fruiting bodies and these too can be difficult to accurately identify.  In theory, this fungus spreads through the fruiting bodies.  The infection can occur over a wide range of temperatures, as low as 38°F and as high as 70°F.  The bracket fungi do overwinter and can spread through pruning wounds.  Early spring is believed to be when the majority of infections take place and when the fungi are most active.

A less diagnostic symptom includes streaking or browning in the vascular tissue.  There are several other diseases that stain the cambium and can be hard to determine if this staining was caused by silver leaf.  If silver leaf penetrates into the trunk or leader, the entire tree can be compromised due to the reduction in photosynthesis that results.  Silver leaf can lead to fruit-quality issues.  Roots can also be stunted and become more susceptible to phytophthora.

If pruning is not occurring until bud break and trees are breaking dormancy, it will take longer for the wound to heal in 45°F temperatures and may increase the risk of infections from silver leaf.  Copper applied at bud break for fire blight might offer some protection, but the efficacy of applying copper to manage silver leaf has not been researched.  Wound sealants are also not recommended.  It has been notoriously difficult to complete research on silver leaf and performing controlled studies are nearly impossible, which is why so much is unknown about silver leaf

Cultural practices such as removing pruning debris from the orchard is recommended to reduce potential inoculum.  Unfortunately, wood lots and hedge rows likely harbor the fungus as well.  Young trees should be fertilized and irrigated to help maintain vigor.  This may help the tree overcome the loss of xylem as a healthy tree can wall off the infected branch.  If the whole tree is affected, then it is likely compromised.  It is recommended to flag trees showing signs of silver leaf to see if symptoms appear the following year.

Silver leaf has always been more prominent at the northern edge of apple production.  In other apple-growing states, e.g., New York, Massachusetts, silver leaf has only been found a few times, if at all.  Honeycrisp, Pazzazz and SweeTango are varieties that are frequently showing signs of silver leaf.

The following factsheet prepared last year by Janet Van Zoeren, UW-Madison Entomology, and Dr. Patricia McManus, UW-Madison Plant Pathology, has additional discussion on the disease, https://pddc.wisc.edu/wp-content/blogs.dir/39/files/Fact_Sheets/LC_PDF/Silver_Leaf.pdf.

Sooty Blotch and flyspeck + summer fruit rots
For decades, sooty blotch and flyspeck (SBFS) has been the primary summer disease of concern.  Over the last decade, summer fruit rots, especially bitter rot has become significantly more important.  This may be attributed to the increase in Honeycrisp plantings, a variety that is particularly susceptible.  What has evolved is a summer-disease complex, which can often be difficult to handle when it comes to timing the first application.

There are a dozen or more different pathogens in the sooty blotch and flyspeck complex, in addition to bitter rot, black rot and white rot.  Sooty blotch and flyspeck fungi feed on the cuticle of the fruit, which leads to fruit quality issues.  In NEWA, a model exists to assess the wetness duration to help growers determine when to apply the first SBFS spray.  For fruit rots, there is no model.  Bitter rot has been a difficult disease to manage in Honeycrisp, both in the field and in storage.  Other rot diseases, e.g., white and black rot, are not as big of a concern as they don’t spread from fruit to fruit.  Fruit with black rot are more obvious early in the season.

Thinned or overwintering fruit are an inoculum source for bitter rot, and it is recommended to remove these fruits from the orchard.  Heat-stressed fruit are particularly susceptible with the infection starting on the exposed portion of the fruit.  Bitter rot infections are occurring in late summer and into October.  There is likely not enough fungicide residue on the fruit, during these late infections and may lead to more bitter rot incidences.  In storage, the fungus does not grow below 40°F, but is also not killed.  Honeycrisp need to be cured at a higher temperature for long-term storage which could be causing some bitter rot to appear.  Storage issues with bitter rot has been an issue in many eastern states as well.

Both strobilurins and SDHI’s work well on bitter rot, but primarily strobilurins work on black rot, white rot and SBFS.  If there is sporulating secondary scab, growers will want to limit their fungicide applications for these diseases.  Dr. McManus recommends staggering a single-site fungicide with captan to include several chemistries for summer-disease management, which will help reduce risk of scab resistance occurring.  Bitter rot may be managed using high rates of captan or single-site fungicides, e.g., Merivon (Pyraclostrobin, Fluxapyroxad), Pristine (Boscalid, Pyraclostrobin) or Flint (trifloxystrobin).

Soft fungicides
In 2015, Dr. McManus gave a talk on using soft fungicides like Regalia (Reynoutria sachalinensis), Serenade (QST 713 strain of Bacillus subtilis) and Oxidate (hydrogen dioxide, peroxyacetic Acid) to manage powdery mildew (PM), apple scab and SBFS.  In the trials, all three fungicides performed better than the control, though none performed as well as captan and Rally (myclobutanil).  If disease pressure is low, using one of these fungicides could be an option.  If there is high disease pressure, using a softer fungicide is not recommended.  However, Dr. McManus does not recommend using any of these products for scab.  A disease like scab has zero tolerance early in the season and hitting it with a stronger fungicide to help control it is essential, otherwise growers will be fighting it all summer long.  Powdery mildew and SBFS are more superficial, which makes them more prone to being disrupted by softer fungicides as they are more surface active.

Syllit (dodine) was once a product labeled for burning out scab, however, that labeled function has now been eliminated.  Several growers have questioned whether using Oxidate as a burnout would be beneficial as a last ditch effort before a rainstorm.  Dr. McManus suggests there is a difference between dodine and Oxidate.  If rain occurs, Oxidate will be washed off and will not offer any further protection where dodine still had efficacy after a rain event.  Captan will offer the same burnout effect if dry, hot weather occurs after the application.  Note: Oxidate may have been discontinued by the manufacturer.

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.  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/

Apple maggot
Since the conference call on Tuesday, at least two growers have confirmed the capture of apple maggots on red spheres in southern, Wisconsin.  Apple maggot spheres should be hung at a density of at least three per ten acres.  The threshold is an average of one per trap across three traps on ten acres, where no bait is used.  If an apple-essence bait is used, the threshold increases to an average of five per trap across three traps per ten acres.  Apple maggot management will be discussed in detail on the July 2nd call.

Codling moth
This week most growers are reaching 350-degree days from their codling moth biofix.  By contrast a year ago we were at 500 to 600-degree days from biofix.  At 350 DD from biofix only 15% 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.

There is an updated rainfast chart from Michigan State University, which includes the common larvicides 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.

Dogwood borer
Traps for dogwood borer (DWB) should be set unless trees are older than ten years.  Traps should be placed 3-4 feet above the ground as opposed to codling moth traps which are set in the upper canopies of trees.  Dogwood borer is a member of over 30 species of clearwing moths in the upper Midwest.  The differences in pheromones produced by these species are so slight that pheromones on the market tend to attract several different species of moths within the Sesiidae family.  Since the pheromones are not species specific and it can be easy to miss identify them.  To properly identify borer pests, we can use the wing length to get a general idea if it is the right species.  Moths with a forewing length larger than one centimeter are probably a different species because DWB adults have a relatively small forewing length of 9mm.  Use a caliper, ruler or tape, to measure the forewing.  Observing damage to graft unions is a great method for monitoring DWB, but by the time injuries become visible it is often too late for treatment to take ef