May 15, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, May 15, 2018, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,

May 15th Call Stream: CLICK HERE


Regional update
Despite warm weather last Wednesday and Thursday, degree-days are accumulating slowly with relatively high uniformity across the large geographical area, Table 1. Several days of highs in the 70s and 80s combined with warm nights in the forecast this week should run trees through bloom rapidly with insect phenology following suit. Tree phenology will vary largely based on each individual site, but most varieties will have reached full bloom by the end of the week.

Location DD Base 50°F Percent Ascospore Maturity Location DD Base 50°F Percent Ascospore Maturity
Woodstock, IL 189 57% Mequon, WI 116 29%
Harvard, IL 179 40% Merrell, WI 122 26%
Eau Claire, WI 149 41% Richland Center, WI 174 50%
Gays Mills, WI 179 50% Rochester, WI 146 58%
Mauston, WI 166 53% Trempealeau, WI 162 52%
Hastings, MN 171 54% La Crescent, MN 182 50%
Lake City, MN 170 51%

Table 1. Degree days as of May 14, 2018

Insect phenology update
Spring-lepidopteran complex
As temperatures begin to warm, expect to find obliquebanded leafroller (OBLR), redbanded leafroller (RBLR), spring canker worm, variegated leafroller and green fruitworm (GFW) larvae feeding on growing terminals and blossom clusters. Larvae from species that overwinter as pupae in the groundcover or soil, e.g., RBLR, GFW, are likely delayed relative to the tree phenology and should progress in this week’s heat – mean temperatures around 70°F and above could cause rapid alteration in early lepidopteran populations.

Petal fall sprays for plum curculio or applications of Bacillus thuringiensis (Bt) such as 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. Bt 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 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.

It is essential to scout for larvae following the first application of Bt, as an additional application may be needed around early petal fall. Early detection of a pest is critical for good management. The spray deposit 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, other insecticides that are safe for pollinators are very limited. One option includes, Intrepid (methoxyfenozide) an insect-growth regulator that only works on lepidoptera and does not have effect on honeybee larvae. It is not recommended to apply Esteem (pyriproxyfen) during bloom. Do not make application of Bt products, Intrepid or other insecticides until damage or larvae are found.

Plum curculio
The Jentsch Lab in New York reported first egg laying of plum curculio (PC) this week which tends to correspond well to our region. Plum curculio typically emerge around 250 DD, base 50°F, and gradually move into the perimeter of orchards when temperatures exceed 60°F for several days. This model suggests we are still 80 – 100 DD from first PC emergence. Plum curculio are primarily nocturnal, and the entire population does not migrate into the orchard at the same time. Toward the end of the week, Zestar in southern Wisconsin and northern Illinois may have fruitlets approaching five millimeters which is the minimum size for egg-laying susceptibility. Growers who have a consistent history of PC problems should look for crescent-shaped oviposition scars in early sizing varieties like Ida Red, Liberty or Ginger Gold. It is important to avoid making applications until plant damage is observed. We will discuss the PC model in more depth on future calls, and growers are reminded to make note of 95% petal fall of McIntosh.

European red mites
The first hatch of European red mites was observed in orchards located in the Upper Mississippi River Valley. If mites have been problematic, scout historic hotspots for young mites on spur leaves and eggs at the base of fruiting spurs. If mites are detected, the host tree should be flagged for future sampling. Recently hatched mites won’t redistribute through the canopy this early, and a miticide application should be avoided until the sampling thresholds become applicable in early June. If mites haven’t been an issue in the past, no action is recommended at this time.

Codling moth mating disruption
The codling moth (CM) 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 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 weeks. If the standard-lure (1x) is used, wait until McIntosh bloom to hang traps and replace lures after three to four weeks.

It is never too late to put up 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. Many growers may also be familiar with the aerosol emitter, or a 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. Damage caused by OFM is very similar to CM damage. Oriental fruit moth lures will also attract lesser appleworm (LAW); OFM has three flights per season, first flight can begin as early as pink. LAW flights 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.

Rosy apple aphids
First signs of rosy apple aphids are emerging as initial eggs hatch and begin colonies. Trees with historic pressure may begin to show evidence this week. Rosy apple aphids are cultivar specific, and scouting efforts should focus on blocks or cultivars with a history of damage from this pest. Do not treat for RAA if trees are in bloom.

Flower thrips
A grower in Iowa recently reported an infestation of flower thrips. Thrips are almost completely dependent on southerly air flow for transportation into our region, and the recent problems in Iowa due to the insects won’t necessarily translate to outbreaks here. Thrips don’t tend to be a problem in apples, however infested strawberry crops usually experience significant damage once apple bloom is complete. 

Disease management
Apple scab
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. Performance during this scenario 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,

Ascospores are currently at 40-58% maturity, after the significant scab infection period at the end of last week. Upwards of 20% of ascospores were released in some locations while nine or ten percent cumulative discharge was observed elsewhere. No scab infections are forecasted in next five days despite rain expected later in the week. Showers will not result in an infection period if leaves are able to dry off quickly enough. Specific data can be found in the Mills Table which relates temperature and wetting hours required for infection, If you weren’t protected during the rain event, the table identifies the incubation period for scab lesions. This can be used as a gauge for when to look for lesions.

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. The single-site fungicide 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’s better to have good coverage and the fungicide to get washed 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 organic growers interested in making a fungicide application post infection. It has the ability to stop disease activity if applied within 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 period, rather than making an application when many days of dry weather is forecasted.

Cedar apple rust
Cedar apple rust cannot spread from apple to apple or from red cedar to red cedar because the fungus experiences a two-year life cycle, alternating between hosts. The infection period for cedar apple rust (CAR) is between tight cluster and first cover. Spores can be carried long distances (3-5 miles), yet most infections occur when infected eastern red cedars are within a few hundred yards of apple trees. Spores that land on young apple tissue may germinate and infect if a film of water is present for an adequate amount of time, and symptoms will usually appear one to two weeks after infection. If you have access to red cedars, look for galls that resemble dead leaves.

EBDCs applied from tight cluster to first cover should offer adequate control. Susceptibility of cultivar and proximity to infected host will influence disease pressure. Unlike scab, rusts require an alternate host and inoculum is not reflective of how much rust was in your orchard last year. “Heavy” rust infections are produced by long-wetting events with little rain. For more information on temperature and moisture requirements for CAR periods visit:

For fungicide options for managing CAR see: Efficacy of Selected Fungicides Against Apple Diseases, 2018 Midwest Fruit Management Guide, page 33.

Fire blight
When temperatures drop to 40°F or lower the fire blight EIP (epiphytic infection potential; references bacterial growth) drops to zero. If the EIP drops to zero, there should be no infection concern for the next four or five days. Temperatures above 65°F will lead to rapid bacterial growth. Fire blight infections are only a concern 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. Epiphytic infection potential (EIP) should be tracked starting when blossoms opening and restarted when streptomycin is applied after an infection period. Additionally, EIP goes to zero when temperatures drop below 40°F. If blossoms are closed, there is no risk of infection and no need to apply streptomycin. 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 streptomycin, 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 point in the season is an excellent time to scout for oozing fire blight cankers that should be painted with copper. Cankers that are not oozing by now most likely aren’t active fire blight cankers.

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

Powdery mildew
Powdery mildew germination and secondary infections favor temperatures between 50 and 70°F and relative humidity greater than 70%. Powdery mildew is spread by wind but will not spread during rain events because the conidia (asexual spores) cannot germinate in water. New infections can be visible within 48 hours of an infection and can begin sporulating in five days.

It is recommended to apply fungicides for powdery mildew beginning at tight cluster to protect new tissue. Sulfur can be used as an early spray when there is less green tissue to protect and less pressure from the fungus. Do not apply sulfur within 14 days of an oil application. Check product label for verification. Factors that influence infection risk may include: amount of shoot growth, unprotected tissue, fungal activity when it is producing the most spores and warm temperatures.