July 23 AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, July 23, 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 23rd Call Stream: CLICK HERE

Regional update

Location Degree days 7/22/2019 (Base 50°F) Petal fall (NEWA) Total leaf wetting hours, from petal fall Total potential infection event hours, from petal fall CM Biofix (NEWA) Accumulated DD (Base 50°F) from CM biofix
Eau Claire, WI 1137 5/28/2019 234 213 6/8/2019 820
Gays Mills, WI 1318 5/30/2019 202 173 6/6/2019 948
Hastings, MN 1281 6/1/2019 128 102 6/7/2019 927
Harvard (Royal Oak), IL 1280 5/23/2019 274 156 6/6/2019 930
Lake City, MN 1282 6/1/2019 179 148 6/3/2019 918
Mauston (Northwoods), WI 1255 6/1/2019 146 122 6/7/2019 903
Mequon (Barthel), WI 1052 6/6/2019 109 93 6/15/2019 723
Preston, MN 1241 5/31/2019 188 176 6/3/2019 958
Rochester (Ela), WI 1174 5/23/2019 231 209 5/30/2019 963
Trempealeau (Eckers), WI 1267 5/31/2019 163 155 6/6/2019 936
Verona, WI 1313 5/30/2019 151 127 6/5/2019 969
White Bear Lake, MN 1229 6/3/2019 125 100 6/8/2019 878
Woodstock, IL 1426 5/26/2019 164 140 5/28/2019 1153

Table 1. Degree-day accumulation and leaf wetness hours to 7/22/2019.  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. 

Temperatures will be cooler over the next week with highs in the mid 80’s and lows will drop into the upper 50’s.  Rain is not expected in most of the region until the weekend, with a slight chance on Sunday and Monday.  This will offer excellent spray opportunities with adequate drying time, depending on wind speed and relative humidity.

Codling moth
Most orchards have accumulated 1000 degree days from first generation codling moth biofix.  Trap captures generally drop off and we can see a distinct gap in the flights.  Growers with high pressure may never observe a drop off to zero.  This is when we need to use our degree days to decide when a flight is now part of the second generation.

Unlike in the spring, insecticides targeting second-generation codling moth should not be delayed past 250 degree days (DD), base 50°F, from biofix.  We are able to delay in the spring, because adverse weather conditions and rain during the first flight often reduce the fecundity of female codling moths.  In late summer, we have excellent weather for codling moth mating and can expect a strong flight to require treatment at 250 DD, base 50°F.

The treatment threshold is five moths per trap and after a biofix has been established, blocks that do not go over threshold may not require treatment and may allow for spot treatments only in blocks which caught five moths or more in a weeks’ time.

Until fruit injury from the first generation is assessed, it is not possible to know what kind of risk second-generation CM will pose.  John Aue recently visited an orchard that had not caught many moths during the first-generation flight.  Mating disruption was not being used in this orchard, but larvicides were applied early and John was not overly concerned about CM impact due to the low trap catches.  Last week, John discovered 12 infested fruit within the first ten minutes of scouting.  At that rate, John estimated that one of every 200 fruit were infested which equates to 400 fruit per acre, or 0.5% of the crop.  This low number of infected fruits is not easy to see and may be missed while scouting.  The infested fruit will give rise to second-generation CM where females could lay eggs, leading to damage upwards of 9,000 fruit per acre, or 12% of the crop.  It is important to understand the specific situation in your orchard rather than simply looking at trap counts and the spray interval.

When damaged fruit are found, assessing the timing of when the management failure occurred can help inform future spray decisions.  If there is no frass protruding from the entry point on the fruit, the larva is likely two or three days old.  There is a total of five larvae instars.  The first three instars require each 50-degree days or four or five days to complete each instar.  The fourth and fifth instar require 60 to 65-degree days or five or six days to complete each instar.  In total, about 280 degree days are needed to go from egg to pupae stage.  The only way to tell the exact age of the CM larvae is to measure the width of the head capsule.  The body of each larvae expand during each instar and as they molt, their head size stays the same, but body is smaller.  Therefore, size alone is not enough to get an exact match on their age. Larvae are more commonly found where two apples are touching, or in fruit clusters.  Assess the calyx end for fruit injury or fruit that are prematurely red.  If injury is found, larvacides should be applied as there may likely be more CM hatching, especially if the larvae are still small.


Apple maggot
Apple maggot (AM) catches vary widely throughout the region.  Baited or unbaited red spheres can be utilized to track emergence and population trends of AM.  Monitoring should begin in early varieties and can determine the location and method of insecticide application.  Organic suppression includes Surround WP (kaolin) and PyGanic (pyrethrins).  Conventional control using old insecticides, e.g., Imidan (phosmet), may be achieved with lower insecticide rates and alternate-row-middle applications.  Orchards using newer chemistries, including the neonicotinoids or diamides are advised to use the maximum labeled rate and apply to every row in the block.

In August, Assail (acetamiprid) is often a preferred insecticide for combined management of apple maggot and codling moth.  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.  If Assail was applied with the dual purpose of controlling CM, reference John Wise’s article below to determine when to reapply.  Note: Since neonicotinoids do not perform well against adult flies, trap captures will not be impacted by an application, whereas they would have been if a broad-spectrum material, e.g., Imidan (phosmet), were used.  If pressure is localized spot spraying may offer adequate control.  Note: The fruit essence on baited traps is viable for one week and should be changed accordingly.


The use of ReTain with NAA can extend harvest another seven to ten days. The combinations can continue to promote ripening and also inhibits separation at the abscission zone.  This may be advantageous for growers wishing to extend pick-your own harvest or if fruit are beginning to drop before the anticipated harvest.  ReTain (AVG-HCl) reduces amount of ethylene produced to prevent the abscission layer from forming between the fruit stem and spur.  The general recommendations for use of ReTain on Honeycrisp are to apply a half rate 30 days before harvest.  Other recommendations would allow a ¼ rate to be applied within 14 days of harvest or to include NAA, e.g., Fruitone, at 10 PPM with the ¼ or ½ rates.  Honeycrisp does not produce a lot of ethylene and therefore is more sensitive to ReTain.  This means that a “half rate” is essentially a full rate.

Pre-harvest intervals for late season sprays

Product Pre-harvest interval
Actara (thiamethoxam) 0 – 2.75 oz./acre: 14 Days
2.75 – 5.5 oz./acre: 35 Days
Altacor (chlorantraniliprole) 5 Days
Assail (acetamiprid) 7 Days
Avaunt (indoxacarb) 14 Days
Captan 80WG (captan) 0 Days
Delegate (spinetoram) 7 Days
Esteem (pyriproxyfen) 45 Days
Exirel (cyantraniliprole) 3 Days
Flint (trifloxystrobin) 14 Days
Indar 2F (fenbuconazole) 14 Days
Luna Sensation (fluopyram, trifloxystrobin) 14 Days
Merivon (pyraclostrobin, fluxapyroxad 0 Days
Pristine (boscalid, pyraclostrobin) 0 Days
ReTain (-trans-2-Amino-4-(2-aminoethoxy)-3-butenoic acid hydrochloride 7 Days
Topsin (thiophanate-methyl) 1 Day

Table 2. Pre-harvest intervals of commonly used pesticides.
*Note: This table is only a reference, always refer to the product label.

Secondary pest reminders
Obliquebanded and redbanded leafrollers
The second-generation of obliquebanded leafroller (OBLR) will begin to hatch in August and can continue through Labor Day.  Redbanded leafrollers are flying in moderate to high numbers in several locations but we are generally not seeing many problems from this last hatch.  This generation of OBLR 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.

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 real problem when selling the fruit since the injury is so tiny and there is no worm in the apple. Two traps per 20 acres is adequate to determine where treating is necessary.

Late OBLR from the spring generation may not be managed effectively with an insecticide due to many being tightly rolled up in leaves.  OBLR should not be sprayed if this tight rolling is observed but may indicate that you will have a more substantial late-August flight.

Insecticides for Japanese beetle
Insecticide options for this pest are rather limited.  Neonicotinoids, e.g., Assail (acetamiprid), Actara (thiamethoxam), will offer good repellency if applied before large aggregations of JPB begin to appear.  If populations are large, applying a “knock-down” or contact insecticide, e.g., organophosphate or PyGanic (pyrethrins), may offer good control.  In the past, a combination of 1 – 2 lb. of Imidan (phosmet) tank mixed with a neonicotinoid may give better management of this pest.  Carbamates, e.g., carbaryl, also work, but are much more disruptive to biological controls and other natural enemies that may be active in the orchard.  If you are avoiding organophosphates, carbamates or pyrethroids, then it is very critical to make an application of a neonicotinoid at the first sign of their feeding injury and before the aggregations appear.  If imidacloprid products are applied for AM, e.g., Wrangler, Alias, Montana, these should also offer some repellency and anti-feeding properties for Japanese beetle.

Organic producers have the option of applying neem (azadirachtin) oil products, e.g., Azadirect, Trilogy, or PyGanic.  It is important to be aware that a botanical insecticide such as neem may be phytotoxic if tank mixed with other pesticides.

San Jose scale
This year has been slow for San Jose scale (SJS).  Growers should continue to monitor for second-generation SJS crawlers in blocks with known hotspots.  As harvest begins (or while hand thinning), look for first-generation adults (black cap stage) on fruit and continue to check scale tape on infested limbs for crawlers.  Fruit injury should serve as the indicator for action.  Continue to maintain tapes on branches regardless of management plan.  Second-generation adults appear from late-July through early-September, and the live, young crawlers from this generation can be found until the first hard frost in fall.  When checking tapes, it is important to note that low trap captures do not reflect overall pressure, i.e., false negative, but rather indicate the beginning of the hatch.  Catches of 10-15 crawlers in a couple of days or 10 crawlers on one tape with zero on all other tapes, may warrant application.

A few growers that had SJS infestations in the past and applied Movento (spirotetramat) or Esteem (pyriproxyfen) were able to effectively manage their SJS population.  However, red circles were observed on fruit indicating the presence of SJS.  Further examination found the SJS crawler likely died from the Movento or Esteem application as no crawler was observed at the center of the red circles.

Wooly apple aphid
Continue to monitor for woolly apple aphid (WAA).  If WAA is not changing in population size, this suggests there are predators and parasites keeping the colonies in check.  If a cover spray of carbaryl is applied for apple maggot or Japanese beetle this could reduce the population of the parasitic wasp that helps to manage WAA and could lead to a population explosion at harvest.  If you blow off the fluff, you may find one of three things: 1. A mass of purple aphids that are healthy and vibrant; 2. Black, mummified aphids that have been parasitized or; 3. Minimal fluff and no aphids, which suggests predation by syrphid fly larva or Aphelinus mali, a parasitic wasp, which are not dependent of WAA.

Dogwood borer
There have been differences in trap catches within orchards across the region.  Some growers had high trap catches directly after hanging traps but are now catching very few, while other growers continue to see high catches in the past week, e.g., 30-50 catches in a week.  There is still plenty of time to apply a trunk spray, which can also be applied post-harvest.

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.

Glomerella leaf spot and marssonina leaf blotch may not be an issue this season due to tighter spray schedules to keep up with continuous rain.  Glomerella leaf spot has the same genus as the bitter rot pathogen, Colletotrichum, and in some cases is actually the same fungus.  Glomerella leaf spot is not common in the upper mid-west as it does not survive well in the northern temperate region.

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.  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 

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.