July 20 AppleTalk

AppleTalk Conference Call Summary
Tuesday, July 20th, 2021, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM,
Moderator: Peter Werts, IPM Institute of North America; questions or comments,

July 20th Call Stream: CLICK HERE


Location Green Tip Date


Mac Petal Fall


Degree Days

(Base 50°F)

Jan 1 – Present

CM May 13 Biofix


CM May 19 Biofix


Eau Claire, WI 4/3 5/16 1369 1258 1195
Galesville, WI 3/21 5/7 1447 1304 1241
Gays Mills, WI 4/3 5/12 1459 1295 1238
Mauston (Northwoods), WI 3/30 5/10 1464 1300 1239
Mequon (Barthel), WI 4/4 5/18 1257 1160 1109
Rochester (Ela), WI 3/30 5/12 1335 1215 1162
Verona, WI 4/3 5/12 1463 1312 1253
Hastings, MN 4/5 5/17 1409 1284 1216
La Crescent, MN 3/23 5/9 1548 1361 1297
Lake City, MN 4/4 5/16 1511 1367 1302
Harvard, IL 3/30 5/11 1433 1272 1214

Table 1. Degree days forecasted for 7/20/21 from Cornell NEWA system. Find your local station today: http://newa.cornell.edu. Note: Leaf wetting hours for sooty blotch and flyspeck use an estimated petal fall date, unless entered by the station operator. NEWA model allows you to add your last systemic fungicide or petal fall date.

Regional roundup
The forecast calls for hot weather, with highs reaching the upper 90s this week and little chances of rain in the forecast.  Under these conditions, diamides and neonicotinoids applied for second generation codling moth or apple maggot could last longer than two weeks if applied at full rates and mixed with a good spreader/sticker/UV protectant, e.g., Attach. Growers are nearing their 250 DD from second generation biofix and apple maggots have been steady for growers with historical pressure. We have accumulated enough RH hours now that all growers should be considering an application of Topsin M to manage summer diseases, even if there has been a lack of rain fall in your area. Blocks with historical pressure from bitter rot could receive a strobilurin application such as Flint (trifloxystrobin), but if bitter rot pressure is low, this can be delayed to August. Organic growers may consider potassium bicarbonate or Regalia for sooty blotch and flyspeck management.

Codling moth
Most growers should have accumulated enough degree days, that moths flying now would be part of the second generation. However, rather than continuing to count degree days from first generation biofix, it is recommended to reset your degree-day counter and tally degree days from zero. Even though there are 1000-degree days between generations, your second generation biofix is not necessarily going to be at 1000-degree days.  Realistically it could occur anytime between 1,000 and 1,250 DD from first generation biofix. For this reason, only use first generation degree days to differentiate first from second generation moths but reset your degree day counting to zero once you have established a second generation biofix.

During the second-generation flight it can be confusing when one trap captures high counts well over threshold and another trap has captures below threshold. Determining the significance of your second-generation flight can be clarified by totaling all the trap numbers by date and add up by week, e.g., combine trap data for a week.

Spray timing for this generation can use the same population model that is used in first generation. The difference between 250 vs. 350 DD can be significant, as at 250 DD there is only 3% egg hatch versus 15% egg hatch at 350 DD. This larvacide application could still be delayed to 350 where trap counts are low, however, if there was a strong flight with captures significantly over threshold, the larvacide would have to go on at 250. A larvacide applied this week will not provide control of the entire generation, but subsequent treatments should be determined based on additional trap counts.

If your goal is to only apply one larvacide during the second generation, consider this should only be done if you got good first-generation control and are not seeing any injury. There is lots of variability in the timing of when second-generation eggs hatch and the longer the larvicide application is delayed from second-generation biofix, the greater number of moths will be targeted by that application. If you are finding injury, e.g., live worms or just the tunneling, expect to have higher numbers in traps during second generation and plan on multiple larvacide applications.

Apple maggot
Despite dry weather for many, this has not held back apple maggot flights.  During last week’s call we discussed apple maggot management in great detail, please see those notes for additional guidance. The following discussion focuses recent efficacy data using feeding attractants and for use of an OMRI approved insecticide which is showing promising results for apple maggot management.

Organic management options for apple maggot are generally limited mostly including frequent sprays of PyGanic, Kaolin-clay or use of apple maggot trap out with red spheres. Newer biopesticides have been in development and two products growers have expressed interest in are Venerate XC and Grandevo.  Both of these are fermented by products bacteria that are naturally occurring and both products are OMRI certified.  Venerate has been found to perform well at repelling brown marmorated stink bug feeding and in apple maggot acts as a stomach poison, e.g., the flies do need to ingest the product. Both Venerate and Grandevo have also been found to perform well against the crawler stage of San Jose scale.

Testing of Venerate was completed season long and while trials were completed for three consecutive years, this data represents 2017 only. Apple maggot sampling was completed using two methods.  On August 24 one bushel of fruit was randomly harvested and inverted on wire racks to allow apple maggot larvae to emerge from fruit at time of pupation and drop into sand.  The number of larvae that emerged from each bushel were counted. Apple maggot tunneling was evaluated on September 11 where 50 fruit were collected and evaluated for tunneling.

The 2ee label for Venerate recommends two quarts per acre, however the trials were completed using one quart per acre and Marrone Bio did confirm that if applied with adequate water and to all rows, e.g., no alternate-row spraying, growers could use the lower one-quart rate. The performance of Venerate is improved when used with a sticker, Nufilm-P was recommended for Organic growers by Marrone and conventional growers could use one of the products included in the trials (Table 2). Venerate is susceptible to washoff, and Marrone cannot attest to its efficacy if spray intervals are extended or if the product is applied more frequently than 14-day intervals. Lastly it should be noted that Venerate XC has not performed well in trials for second generation codling moth.

Marrone Bio has also trialed Grandevo for apple maggot and while there were some instances of it performing well against AM, they feel the data is too inconsistent to support a recommendation for its use against apple maggot.


Product Rate Product/acre Application Timing AM

% tunnels in fruit

# AM larva removed from fruit
Untreated Check 44.3 a 153.0 a
Venerate XC 1 qt /a BCDEFGH 16.8 bcd 53.0 b-e
+ R-56 P 0.13 % v/v BCDEFGH
Venerate XC 1 qt/a BCDEFGH 15.5 bcd 88.5 b
+ Tactic L 30 fl oz/100 gal BCDEFGH
Venerate XC 1 qt/a BCDEFGH 9.8 cde 39.0 cde
+ Indicator 5 90 EC 0.13 % v/v BCDEFGH
Assail 30 SG 5.3 E, F, G 12.5 b-e 32.8 de
+ Mustang max 4 fl. oz/a H


Application Target Application Date
A Pink 26-Apr
B Petal Fall 24-May
C 1C (CM Bio + 250 DD) 8-Jun
D 2C (C +14 days) 22-Jun
E 3C (D + 14 days) 7-Jul
F 4C (E + 14 days) 19-Jul
G 5C (2nd gen. CM Bio + 250 DD) + 14 days 2-Aug
H 6C (F + 14 days) 16-Aug
I 7C (G + 14 days) 30-Aug


Table. 2017 Jon Wise insecticide efficacy trials at Trevor Nichols Research Station.

There have been several studies in recent years demonstrating that any amount of sugar applied to tank mixes can help improve performance of imidacloprid for managing apple maggot. Apple maggots are are nectar feeders and the sugar is replicating the attractiveness of nectar. Since most insecticides need to be ingested by apple maggot in order have efficacy, adding sugar as a feeding stimulant can help increase uptake of the pesticide.  John recommends one quart/100 gallons of molasses or corn syrup.

San Jose scale (SJS)
The hot weather this year, similar to mites, has been a boon to SJS growth and development, so much that we are concerned about the possibility of a third generation this year. In the meantime, expect to see second-generation crawlers in the next three weeks.

SJS has a degree-day development range from 51°F to 90°F, which means DD will accumulate faster than what we calculate for codling moth. The Washington State University model suggests 1% of second-generation crawlers would emerge after 1200 DD from biofix, which is approximately 275 DD from January 1 and 50% second generation crawler emergence would be complete by 1580 DD from biofix. Essentially, to get an estimate on second generation crawler emergence add 275 DD to the table on the WSU site to calculate DD from January 1. So, if 1% second-generation emergence occurs from biofix, this would be approximately 1475 DD from January 1.  Currently, 1371.75 DD base 51F with upper limit of 91F have accumulated since January 1 at the Verona, WI NEWA station. This means some locations in southern WI are only 100 DD from the start of second generation crawlers. http://treefruit.wsu.edu/crop-protection/opm/san-jose-scale/

The recommended management options include Sivanto or Centaur. If neonicotinoids were applied between petal fall and early July, they should not be used to target this second generation of SJS. Even though Beleaf 50 SG has a label for SJS, FMC has indicated it should not be used against SJS. The FMC technical specialists have observed good efficacy of Exirel on SJS crawlers, however, there is no information published to date to support this and SJS is not currently on the label. Additionally, while SJS in organic orchards is uncommon, it is not unheard of, and organic growers with scale populations can target crawlers with either Grandevo or Venerate XC. All of the above options should be applied with a good spreader/sticker and with lots of water, possibly more than 100 Gal/acre where trees are large and canopies are dense. Double sided stick tape or electrical tape with a layer of petroleum jelly should be set on one and two-year old wood where SJS has been observed this year. Once crawlers are caught, they should be targeted immediately.

Mites and miticides
As expected, European red mites have been basking in the hot weather as they delightfully suck the chlorophyl from our apple’s leaves. The abundance of these mites is also countered by very high populations of predatory mites that John and Peter have observed in many orchards. 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.

Mite thresholds have increased from 2.5 to 5 mites per leaf and will increase to seven mites in August.  Some growers have already seen mite captures exceed threshold and growers should be aware that 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 larvacide, 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).

Woolly apple maggot
Woolly apple aphids have been observed with increasing abundance across the region and John and Peter are also observing lots of syrphid fly larva, gall midge maggots and mummification from Aphelinus mali the parasitic wasp that exploits WAA.  This excellent bio control is being observed in orchards where Delegate has been avoided for first generation codling moth. If WAA needs managed, options are limited and include Beleaf (21-day PHI) or Closer (7-day PHI).

Disease management
The drought is playing a major role in affecting tree health this year.  Trees without irrigation are at risk of dropping leaves and defoliating, which is a survival mechanism. Prior to leaf drop you can expect to see chlorosis and other necrotic spots. So, this may be one of the diseases, but could also be from drought stress.

White rot
It is not easy to distinguish black rot from white rot, and the difference is identified by the appearance of the rot going into the core of the fruit. John describes most of these lesions as black rot due to it being observed every year via the frog eyed leaf spot in leaf tissue. However, white rot may be even more widespread. Captan prevents fruit infection but does not help prevent infections of the trunk, though is possible that captan on the bark might offer some protection. The white rot invasions that Peter observed likely happened last spring after the polar vortex, and while it seems the cankers appeared out of nowhere, the fungi have been present for a long time. When trees become stressed, the trees stop producing compounds that can help prevent the spread of these infections.

If trees have bark injury from herbicides, rodents, weed whips, etc., these trees are at risk of being infected by canker fungi when there is warm, wet weather. Many larger infected trees can withstand and fight off many of these infections for years, but the margin of error on a high-density planting is very small. Trees can likely be invaded in year one if they are not cared for properly.

Black rot
Black rot infections on fruit usually appear at the calyx end and can originate at any wound that penetrates the epidermis, e.g., insect or hail injury. Black and white rot can be difficult to distinguish and spore producing lesions are black for both types of rot. 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 and lesions are usually amorphous. The flesh of the decayed area remains firm and leathery, and fruiting bodies will appear on the surface of the rotted tissue.

Fungicides that protect against fruit rots include captan, strobilurins, e.g., Pristine (boscalid, pyraclostrobin) and Flint (trifloxystrobin). 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.

 Leaf damage
In mid to late summer, leaf injury from a variety of causes becomes more visible.  When assessing this injury, it is important to look at the entire shoot and leaf cluster.  Most leaf injury in the form of brown or necrotic spots are present on mature leaves and looks older.  This injury appears as brown spots or burnt necrotic areas of various circular sizes.  Many growers have been reporting small specks and wondering if these symptoms could be a more serious problem.  Many symptoms are the result of black rot infections.  Frogeye leaf spot is a dead-end of the black rot disease life cycle, where alternaria leaf blotch does continue to spread.

Growers need to look at the entirety of the damaged leaf.  If injury is surrounding fruit clusters but all new growth and terminals are not affected, it is unlikely to be from these fungi.  If infections are occurring at the ends of the terminals and on new growth, then this could be related to black rot, frogeye leaf spot or alternaria leaf blotch.  Older leaves could also have damage caused by several chemicals, e.g., oil, Flint (trifloxystrobin) or captan.  Orchard floor hygiene is important when managing overwintering inoculum, including these fungi.

Frogeye leafspot
Symptoms are defined by their purple to red margins around the leaf surface with a brown middle. Lesions appear several weeks after petal fall and will grow to 3-6 mm in diameter. Frogeye leaf spot can be confused with phytotoxicity from pesticide application, use the purple margins as defining characteristics of this disease. Once present on the leaf surface, this disease will not release spores or cause additional infections.

Alternaria leaf blotch
Symptoms appear as brown blotches that are 2-10mm in diameter on leaves and are surrounded by a dark margin. The leaves turn yellow over time and will die prematurely. Fruit appear sunken with small (~2mm) brown spots surrounded by a black border. Alternaria leaf blotch usually affects high value cultivars like Royal Gala, Fuji, Pink Lady and Red Delicious.

Marssonina leaf blotch
Marssonina leaf blotch is a foliar disease with a similar life cycle to apple scab. It overwinters as a fungal spore in leaf litter on the orchard floor. Contrary to apple scab, it is a warm weather disease with infection periods occurring in mid to late summer. A definitive sign is early leaf drop occurring in August and early September. Some cultivars are more susceptible than others.

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 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.

  • Sunburn occurs 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. Cells are not killed, even though the skin loses color.
  • 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. Higher humidity reduces the occurrence of fruit sunburn, while fluctuating temperatures increases the occurrence of fruit sunburn. Sunburn damage can cause fruit to be more susceptible to summer fruit rots, e.g., bitter rot. 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. It may not be necessary to apply a sunburn material if paying attention to fruit rots.

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:

  • Clay based: kaolin clay, e.g., Surround WP.
  • 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.
  • 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/2015/12/raynox-plus-applications-to-prevent.html

Additional resources