May 14 AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, May 14, 2019, 8:00 – 9:00 AM
Presenter: Dr. Amaya Atucha, UW Madison; John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,

May 14th Call Stream: CLICK HERE

Regional update
Despite warm weather over the weekend, degree days have accumulated and remain variable across the region.  Orchards in northcentral Wisconsin are still at green tip to tight cluster and orchards in northern Illinois at bloom.  Several days of temperatures in the 70s and warm nights in the 50s will push trees through bloom rapidly and allow insect phenology to catch up.  Redbanded leafroller (RBLR) and spotted tentiform leafminer have been reported in the recent WI Department of Agriculture pest bulletin.  These trap captures provide evidence that several of our orchard pests have overwintered relatively well and were not greatly affected by the polar vortex.

Location Degree Days 5/13/2019 (Base 50°F) Degree Days by 5/17/2019 (Base 50°F) Percent Ascospore Maturity 5/13/2019
Eau Claire, WI 56 96 35%
Gays Mills, WI 101 145 69%
Hastings, MN 75 121 45%
Harvard (Royal Oak), IL 87 118 64%
Lake City, MN 83 132 52%
Mauston (Northwoods), WI 67 106 50%
Mequon (Barthel), WI 47 64 34%
Preston, MN 82 129 56%
Rochester (Ela), WI 72 77 61%
Trempealeau (Eckers), WI 76 121 57%
Verona, WI 85 124 65%
White Bear Lake, MN 63 107 37%
Woodstock, IL 111 145 84%

Table 1. Degree days (DD) and ascospore maturity to 5/13/2019 and predicted DD to 5/17/2019.

Insect management
Spring-lepidopteran complex
As orchards exceed accumulation of 100 degree days from January first, expect to find obliquebanded leafroller (OBLR), RBLR, spring canker worm, variegated leafroller and green fruitworm (GFW) larvae feeding on growing terminals and blossom clusters.  Larvae that overwinter as pupae in the groundcover or soil, e.g., RBLR, GFW, are delayed and should progress in this week’s heat.  Second instar OBLR have been observed throughout southern Wisconsin.  When scouting, closely inspect fruitlets for OBLR injury.  Look for small pinholes within leaves or rolled-leaf edges, black frass may be visible on blossoms.

Applications of Bacillus thuringiensis (Bt), i.e., Agree, Deliver or Dipel may be applied to manage these pests when weather is warm and blossoms are open.  If blossoms are still closed, a Bt application will not target larvae that have tunneled into closed blossoms.  Bacillus thuringiensis must be eaten by the insect to be effective and warm temperatures are needed in the 72-hour period following an application for good mortality.  As with most newer insecticides, young larvae are generally more susceptible than older larvae.  Consider waiting to apply an insecticide for these pests until the weather is warm (~60°F) and sunny.  Scout for larvae following the first application of Bt, as an additional application may be needed around early petal fall.  The Bt may only last one to three days before it is washed off by rain or broken down by sunlight.  Sticker substances that promote adherence to leaf surfaces and UV light inhibitors that protect Bt from photo-degradation may enhance efficacy.  For more information on application timing and use of Bt products visit

In addition to Bt, Intrepid (methoxyfenozide) may be applied at pink or bloom.  It is not recommended to apply Esteem (pyriproxyfen) during bloom.  Do not make an application of Bt products, Intrepid or other insecticides until damage or larvae are found.  It is possible to wait until petal fall to manage leafrollers, if they are still actively feeding.  However, orchards that had significant injury last year may not want to wait as populations will be harder to manage when these insects are closer to maturity.

Codling moth mating disruption
The first codling moth flight or Biofix may occur within the next week at orchards that accumulate between 180 and 250 DD from January first.  The codling moth overwinters as full-grown larvae on trees and temperatures below -15⁰F will provide some mortality.  The first CM capture has traditionally been around petal fall and pheromone traps should be hung in the upper third of the tree canopy as soon as possible, if they aren’t up already.  The long-life lures (CM L2) are active for eight to 12 weeks.  If the standard-lure (1x) is used, hang traps at McIntosh bloom and replace lures after three to four weeks.

It is never too late to apply codling moth mating disruption, however, the investment will be much more effective the sooner these technologies are implemented.  Among the three basic mating-disruption tools, the Cidetrak CMDA Combo Meso-A dispenser, manufactured by Trece, is the least labor-intensive, requiring only 18-36 dispensers per acre.  The other labor-saving product is the aerosol emitter, or Puffer, applied at a rate of one per acre.  The third and oldest technology uses 100-400 dispensers per acre and requires substantially more labor than other options (rates vary by product).

If mating disruption is used, hang at least one CM combo lure (CMDA) per block and at least two oriental fruit moth (OFM) traps per orchard.  The CMDA lure will attract female and male CM moths.  Oriental fruit moth and CM injury are very similar.  Oriental fruit moth lures will also attract lesser appleworm (LAW); OFM has three flights per season, first flight can begin as early as pink.  Lesser apple worm has two flights and correspond with CM.  Growers using the Cidetrak CMDA Combo Meso-A mating disruption are advised by the manufacture to use CMDA+AA lures in all traps to get accurate captures since both male and female moths are disrupted by this product.

Disease management
Apple scab
When rain storms occur during the day, ascospore discharge usually begins within 30 minutes after the start of the rain and is largely completed within three to six hours.  When rainfall begins at night, discharge is often delayed until sunrise, although significant night discharge can occur under some conditions.  Sufficient fungicide residue needs to be present during this period to prevent an infection, even if total rainfall exceeds two inches.  Fungicide performance during an infection event is dependent on coverage, application rate, rainfall (rate and intensity) and new leaf tissue since last application.  Growers are suggested to supplement their on-farm weather station data with information from the nearest NEWA weather station,

Ascospore maturity according to NEWA is at 35-84% maturity.  Showers will not result in an infection period if leaves are able to dry quickly.  When several shorter leaf wetting events occur, these may still result in a combined infection.  Specific data can be found in the Mills Table which relates temperature and wetting hours required for infection,  The table identifies the incubation period for scab lesions and can be used as a gauge for when to look for lesions.  Growers may want to consider shortening their protectant spray interval to five to seven days rather than seven to ten days due to rapid leaf growth expected over the next two weeks.

Complete protectant-fungicide wash-off, e.g., EBDCs, captan, occurs after two inches of rain, however, this general rule does not factor differing wash-off rates between rain from a violent rain storm and the same volume of light rain spread out across multiple days.  This does not apply to single-site fungicides which are absorbed into the plant tissue.  Single-site fungicides will still work if there is no rain for six-to-eight days, depending on the amount of leaf expansion.  As leaves expand, the fungicide is thinned out and reapplication is needed.  In blocks with high-scab pressure, it is better to have good coverage and allow the fungicide to wash off immediately following application, rather than making an application post-infection.  Conventional producers have used a variety of fungicides to burn out scab, however, this practice is not advised due the resistance concerns for DMI, SDHI and QoI fungicides.

Liquid-lime sulfur is an option for growers interested in making a fungicide application post-infection.  It has the ability to stop disease activity if applied within 24-72 hours of the infection event.  Liquid-lime sulfur can be used as a bloom thinner – use caution when making an application during this time.  Sulfur can be used during bloom without substantially reducing fruitset.  It is recommended to apply sulfur before a predicted infection, rather than making an application if dry weather is forecasted.

Cedar apple rust
Monitor cedar apple rust (CAR) in red cedars.  Cedar apple rust gals haven’t experienced much growth in the last week but will continue to grow if there are rain showers toward the end of the week.  Extensive discussion on managing CAR is included in the May 7 AppleTalk notes:

Apple blister spot
Apple blister spot, Pseudo-monas syringae pv. papulans, is a bacterial disease that affects fruit and leaves.  This disease overwinters in apple buds, leaf scars and diseased fruit left within the orchard.  Apple blister spot leaves lesions on the apple and affects the cosmetic quality.  In the Cornell Scaffolds Fruit Journal article from May 13th, blister spot was discussed and listed several cultivars that were susceptible to the disease including: Mutsu (‘Crispin’), Fuji, Golden Delicious, Red Delicious, Jonagold, Gala and Cortland.  Scaffolds Fruit Journal May 13th article:

Fire blight
Orchards will be at risk for fire blight infections as trees move into bloom.  Temperatures above 65°F will lead to rapid bacterial growth.  Trees are only susceptible to fire blight infections if blossoms are open and moisture is present.  These basic parameters need to be met for an infection to occur: 1) Inoculum or signs of fire blight in neighborhood last year, 2) open blossoms, 3) moisture, and 4) warm temperatures of greater than 65°F.

Streptomycin applied 24 hours before or after an infection period or rain event will provide control for up to 72 hours of bacterial growth inhibition after the infection.  The fire blight Eepiphytic Infection Potential (EIP), which references bacterial growth, should be tracked starting when blossoms open and restarted when streptomycin is applied after an infection period.  Additionally, the EIP drops to zero when temperatures fall below 40°F.  If blossoms are closed, there is no risk of infection and streptomycin does not need to be applied.  Growers will typically apply streptomycin with 50-60 gallons of water per acre, however, more water will always improve performance of streptomycin.  One hundred gallons of water per acre is recommended by manufacturers.  Tank mixing with other fungicides is generally admissible apart from captan, which should not be applied with streptomycin.

All other bactericides such as copper or Kasumin (kasugamycin) need to be applied before an infection occurs.  If the blossoms are not open, there is no benefit to applying kasugamycin or any other antibiotic.  Copper products like Cueva (copper octanoate) should be applied as the blossoms open.  Copper applications may be beneficial for non-bearing trees or trees where fruit russeting is not a concern.  This is an excellent time to scout for oozing fire blight cankers that could be painted with copper.  Cankers that are not oozing by now most likely are not active fire blight cankers.

For a comprehensive discussion on fire blight and cultivar and rootstock susceptibility read Scaffolds Fruit Journal, May 1st, 2017,

Bitter pit management with Dr. Amaya Atucha, University of Wisconsin Horticulture Department
Return bloom and thinning
Across the region, Honeycrisp blocks are showing 50% good return bloom and 50% light return bloom.  Most of the light return bloom may be attributed to the polar vortex which damaged flower buds.  Bitter pit management is critical for Honeycrisp, regardless of the level of return bloom.  Only 20% of blossoms need to set fruit to have a good crop and growers need to begin thinking about the products to use for thinning.  If return bloom is situated towards the top third of the tree, make sure to adjust the spray height and calibration so more product is applied to where there are blossoms.  Even with a light crop, the goal is to retain the king blossom and thin off the side bloom.

Managing bitter pit under a normal cropload
The standard recommendation to manage bitter pit in Honeycrisp has been to apply five to 15 lb. of actual calcium per acre.  If blocks have a history of bitter pit or will likely have a lower crop load, stick with a higher rate of calcium.  Penn State University has a calcium rate calculator for individual product comparisons (

There are a few different calcium application recommendations depending on the source of the information.  Washington State University recommends six to 12 calcium applications of 1 lb. to 1.5 lb./acre between petal fall and two weeks before harvest.  This equates to about 2 lb. to 4 lb./acre of calcium chloride.  Cornell recommends three to four covers of 1 lb. to 2 lb./acre of calcium chloride (100 gal./acre) starting one week after petal fall and two sprays of 3 lb. to 4 lb./acre of calcium chloride two weeks before harvest.  These applications should be completed on 14-day intervals.  The application window for calcium is quite large, but growers should apply as soon as possible to mitigate the potential for bitter pit issues later on.

Fruit will accumulate calcium beginning at petal fall and will continue to absorb calcium until harvest.  Avoid using products derived from calcium nitrate or applying nitrogen in general as it competes with calcium.  If a nitrogen deficiency is expressed, e.g., yellow leaf coloration, nitrogen can still be applied but should be done in accordance to foliar tests to avoid over applying and to ensure it doesn’t affect calcium uptake.  Calcium travels through the tree via transpiration or within the water stream.  If vigorous shoot growth is occurring, calcium will be deposited into the shoots and leaves rather than the fruit.  This is especially true where there is a light crop; therefore, timing and application volume are crucial as well as minimizing stress within the tree.

Managing bitter pit under a light cropload
Where there is a light cropload, the most important thing to do is to not apply any nitrogen.  There is likely enough nitrogen in the soil to sustain growth for this season.  Reduce or eliminate any potassium, as demands are less with a lighter crop.  The main reason that Honeycrisp is prone to bitter pit is the large gap in the ratio of calcium to nitrogen, magnesium and potassium within the fruit.  A low cropload correlates to low levels of these calcium competitors.

Current research using applications of Apogee (prohexadione calcium) to control shoot growth, reduce vigor and push calcium into fruit, is being completed by Dr. Duane Greene from the University of Massachusetts.  The best time to apply Apogee is around pink because it takes up to two weeks to take effect.  Apply a concentration of 9 oz. to 12 oz. per 100 gallons at pink, and a second application two to two and a half weeks later at 6 oz. per 100 gallons, if trees are still vigorous due to low cropload.  Apogee is especially recommended if you know you have a low cropload and must control shoot growth.  Important: Do not mix Apogee with calcium and make sure the water pH is not too high.  Calcium and high pH can suppress the effects of Apogee.

Researchers at Penn State University are working on a modeling tool to predict the incidence of bitter pit based on the nitrogen and calcium content within the peel compared to the shoot length.  Researchers measured the length of the terminal shoots and collected fruit skin samples three weeks prior to harvest.  Preliminary results are showing a 70% correlation with this method; longer shoots and a higher ratio of nitrogen to calcium lead to a higher chance of bitter pit.  There is a 50-60% greater incidence of bitter pit when the background color is too green at harvest.  Read more on the study here:

Harvest and storage management
Harvest and storage practices also play a role in bitter pit occurrence.  It is recommended to store bitter pit prone apples at a lower temperature for no longer than six weeks.  This means the timing of harvest needs to be kept in mind.  If apples are stored for longer periods of time, they should be harvested early and for apples stored for shorter periods of time, they should be harvested later.  Apples that aren’t prone to bitter pit need to be conditioned to reduce soft scald, which is first seen one to two months into storage.

Soil type and rootstocks
A large portion of calcium within the tree is derived from the soil.  Sandy soils are poor in all nutrients and are more prone to bitter pit problems.  Heavy soils with high concentrations of potassium, magnesium and ammonium, which competes with calcium, will also cause more bitter pit problems.  Quick drying soils have the same issue.  Root growth, especially in the spring, is essential to encourage calcium uptake.  Prior to planting new trees, apply dolomitic lime or calcium lime to assist with calcium uptake.  Only use dolomitic lime with calcium and magnesium, if magnesium is low.  If magnesium is not low, use calcium lime.  Soil pH also must be monitored.  If the pH level is too low, there will be less calcium available to uptake.  Maintain soil pH between six to seven and monitor pH and organic trends over time.  If nitrogen applications are acidifying the soil, the pH will need to be adjusted upwards. Soil tests should be completed every three to four years.

Ongoing research at Cornell University has been investigating how rootstock selection influences the propensity of bitter pit.  Anecdotal results are showing that Bud9 has fewer bitter pit occurrences than Geneva rootstocks because it is much less vigorous.  Within the Geneva rootstocks, G214 and G969 are less susceptible to bitter pit than G41 and G11.

Irrigation is critical and required for low-vigor trees and rootstocks.  Smaller roots need to be kept moist to promote uptake of calcium.  Roots grow every year and new roots are the most efficient at uptaking calcium.  Reduced root growth due to dry or unhealthy soil in the initial growth phase may result in a higher occurrence of bitter pit.

Grower questions
Grower: Some companies try to promote their calcium product saying it is better quality because it is more easily absorbed into the fruit. Is this “luxury” calcium worth the extra expense?

  • Amaya: No, all that matters is the amount of calcium within the product and if it includes nitrogen.  Calcium chloride will work as well.

Grower: We normally use a foliar application of 1 lb. of 20-20-20 to correct nutrient deficiencies. Is that sufficient nitrogen and potassium to effect bitter pit?

  • Amaya: We are looking for a balance between cropload and shoot growth.  If trees are stressed and have a potential for a normal to heavy crop, then nitrogen should be applied.  If the crop is light, nitrogen is going to encourage shoot growth.  Any shoot growth longer than five inches correlates to potential bitter pit issues.  If you have a normal crop, go ahead with regular nutrient management.