May 2, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, May 2 2017, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,

May 2nd Call Stream: CLICK HERE

Regional update
Across southern Wisconsin and northern Illinois Zestar and Idared began bloom near April 20th. Most cultivars in this area are currently approaching full bloom. Orchards further north, e.g. Twin Cities to Chippewa Falls, have some bloom on early cultivars and full pink on later ones. Modest crop loads in 2016 and a long, favorable fall and mild winter have resulted in very robust bud appearance. Growth has significantly slowed or stopped in the last six days due weather in the low to mid 40s. The 30-day forecast is predicating below normal precipitation and normal to below normal temperatures, e.g., high in 60s and low in 40s.

Bloom and petal fall thinning
In recent years there has been a growing body of research attesting to the benefits of beginning fruit-thinning programs at bloom and/or petal fall. Generally, thinning at bloom and petal fall is recommended because chemical-thinning agents are far less weather dependent and less likely to have negative impacts on thinning. Making thinning decisions during bloom and petal fall is particularly challenging in 2017 where many orchards across southern Wisconsin are in full bloom and temperatures are not favorable to pollination. Orchards still at pink are in a better position to receive adequate pollination when warmer weather returns later in the week and into the weekend.

Fruit grow very slow from petal fall to 5 mm and initially have low demand for carbohydrates. Therefore, variations in temperature and weather have less impact on the fruit, since it has not begun to grow rapidly, keeping its energy demands low. Applying a growth-regulating thinner, e.g., Amid-Thin (NAD) or NAA, at this time will allow for easier thinning since the chemical will have greater influence on the carbohydrate level compared to weather conditions. Any temperature effect is buffered, however, thinners should only be applied if the temperature is below 85 °F. Applying during cooler temperatures is okay; 6-BA, e.g., MaxCel, Exilis Plus, is not very effective when the temperature is below 68°F. However, our main concern remains: were the apples pollinated or not?

2017: Two paths for early thinning
• Orchards currently in full bloom will likely want to delay any bloom thinning until they can assess the quality of pollination. Applying thinners at petal fall to 5mm may still be very safe, since by petal fall, it should be possible to assess if trees were pollinated and if seeds are beginning to develop. As mentioned above, carbohydrate demands at this time are still low, and growers should be less concerned about the risk of over thinning at petal fall.
• Orchards still at pink are in a better position to experience more ideal bloom conditions over the weekend and into early next week. Should favorable bloom conditions exist, thinning at bloom with NAD or lime sulfur + oil may still be a viable option.

Assessing blossom health during bloom
The following can help assess blossom health and potential impacts from freeze injury:
• Inspect the pistil length when king bloom opens. Flowers with short pistils may be damaged.
• Are any flowers misshapen?
• Are spur leaves twisted, misshapen or damaged? Are they brown or yellow?
• If you are finding damaged pistils and flowers, thinning should be more conservative.
• If the king blossom is lost and a couple of side blossoms look good then applying a petal fall thinner could be ok. In this scenario one of the side blossoms will take over; if no thinning is completed there will likely be too many fruit and thinning will need to be completed at a later time.

Using Amid-Thin bloom and petal fall thinning
• The goal of applying Amid-Thin (NAD) or liquid-lime sulfur + oil is not to get 100% of the thinning completed. Thinning at bloom or petal fall will give us a better idea of what else needs to come off beginning at 7 mm. During petal fall, we know the weather, bloom quality and if the bees had good conditions. Considering this information when thinning at petal fall could make thinning decisions easier once fruit are larger.
• Amid-Thin is not temperature dependent and does not exhibit a dose response, making it a good option for petal fall. If NAA was applied at petal fall, we would still have the concerns about a temperature response to thinning. Trials completed by researchers at the University of Massachusetts used a flat rate of Amid-Thin at 8oz./100 gal. at petal fall. At this rate no over thinning has been observed and heavy clumping of fruit was also reduced. Amid-Thin would only be applied at petal fall, thinning thereafter would still rely on NAA or MaxCel between 7-10 mm.
• Gala and Honeycrisp are good varieties to try petal fall thinning with Amid-Thin. Getting return bloom on Honeycrisp is often a challenge and research suggests the earlier the crop load can be reduced, the better return bloom we can expect. Amid-Thin is not recommended for bloom or petal fall thinning on Fuji, Empire or Red Delicious. NAA would be the preferred option on these varieties for petal-fall thinning.

What is the recommended timing for bloom thinning?
• Liquid-lime sulfur (LLS) + oil is applied at 20% full bloom at a 1% solution of both LLS and oil. The second application is applied at 80% full bloom and the rate is increased to 2% solution of LLS + oil. Both applications are applied at 100 gallons per acre.
• It should be noted the second application appeared to cause the greatest amount of russeting in trials completed at Cornell.

Conservative approach to thinning and key thinning windows
• Bloom/Petal fall: Apply thinners that will be less influenced by weather conditions.
• 6 mm fruit: Begin assessments of fruit growth. Fruit will begin to grow rapidly after this stage.
• 7-9 mm fruit: We should get a good idea of fruitset since we can compare reduction in fruitlet growth.
• 14 mm fruit: Possible thinning window. MaxCel (6-benzyladenine) works well for later thinning.
• 18 mm fruit: This is the cut off for thinning. Ethrel (ethephon) can work as a rescue thinner in some situation.

Tank-mixing considerations
• It is understandable that any opportunity to be efficient with applications of sprays should be taken advantage of, however, we should approach tank mixing with some caution at petal fall. Please consider the following:
• It is common practice for growers to apply additional adjuvants with every spray, LI 700 is a common example. If any adjuvant acts as a penetrant, it will open up the leaf cuticle and increase uptake of any chemicals applied, including thinners. This could result in thinners performing better than anticipated, e.g., you may take off more fruit than expected.
• Thinners are often applied with much more water than your regular fungicide/insecticide tank mix.
• Very little research exists to identify how a thinner + insecticide + fungicide interact when applied as tank mix. A good example of this is the concern regarding mixing Fontelis with other chemicals which contain oil. These tank mixes may or may not result in fruit or plant-tissue damage and it is recommended to apply thinners separately from the fungicide/insecticide petal-fall spray.

Resources for precision thinning
• Precision Crop Load Management, New York Fruit Quarterly
• Part 1:
• Part 2:
• Thinning apples with more confidence, Good Fruit Grower, 2014,
• Cornell apple carbohydrate thinning model

Pollinator pesticide exposure
Pollinators can be exposed to pesticides through direct contact with residues on treated plants or adjacent areas contaminated by drift. Pollinators can also be exposed directly, when they are active in areas, where pesticide applications are being made. In addition, pesticide residues can accumulate in colonies of native and managed bees when pollen and nectar contaminated with pesticides is brought back to the hive.

Pesticides vary greatly in their toxicity to pollinators and in some instances, it could be possible for tank mixtures including a combination of insecticides, fungicides and adjuvants, can be more toxic than the individual pesticides. Exposure to pollinator-toxic pesticides can result in mortality and changes in behavior, navigation, colony weight and/or reproductive rates. While there is still much to learn about pesticide impacts on pollinators and considerable new research is being reported or underway, there are a number practices orchardists can follow now to protect pollinators from pesticide exposure:
• Use the EPA bee-advisory box to identify pesticides toxic to pollinators and look for statements on labels that read, “highly toxic to bees”, “toxic to bees” or “extended residual toxicity.” Avoid using these products when bees are present, and always follow label instructions.
• Do not apply insecticides highly toxic to pollinators until after apple bloom. Historically it was common for apple growers to apply an insecticide at the pink stage of blossom development for tarnished plant bug, spotted tentiform leafminer, aphids and leafrollers. Research suggests that these pests rarely cause economic injury, and delaying the first insecticide application until petal fall can reduce exposure to pollinators. Some fungicides can also be toxic to pollinators. During bloom, apply these when bees are not actively foraging, whenever possible.
• Apply pesticides toxic to pollinators when bees are less active, e.g., evening, nighttime or early morning.
• Manage orchard groundcover to reduce blooming weeds and the likelihood that pollinators will be actively foraging on weeds during pesticide applications or within the period of residual activity for the products applied. This can be accomplished by mowing, planting competitive orchard grasses during orchard establishment and/or through selective herbicide applications.
• Identify and protect nesting and foraging sites from pesticide drift by making sure your sprayer is properly calibrated, and adjust spray schedules and application procedures when wind speed and wind direction could result in pesticide drift to these sites.

Disease and insect updates

Apple scab
Numerous rain storms within the last week (with some regions receiving up to five inches of rain) likely washed off any fungicide that was applied early last week. Note: Complete fungicide wash off occurs after two inches of rain. During the day, ascospore discharge usually begins within 30 minutes after the start of the rain and is largely completed within 3 to 6 hours. Sufficient fungicide residue needs to be present during this period to prevent an infection even if total rainfall during entire rain event is in excess of two inches. Performance during this scenario is dependent on coverage, application rate, rainfall, and new leaf tissue since last application.

Due to cool temperatures, minimal spore maturity has occurred since the infection we had last week (March 29-30) and subsequent infections over the last two days. The severity of these infections depends on inoculum from last year and amount of time from last infection period. Lesions from an infection period won’t become visible for at least 10-14 days.

Liquid-lime sulfur is an option for organic growers interested in burning out visible lesions. 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. Note: Liquid-lime sulfur can induce a thinning response when applied during bloom. Use caution when making an application during this time.

Powdery mildew
The ideal temperatures for powdery mildew germination and secondary infections are when temperatures are between 50 and 70°F and relative humidity is greater than 70%. Powdery mildew is spread by wind and the conidia (asexual spore) cannot germinate in water. This means that powdery mildew will not spread during rain events. 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.

Cedar apple rust
Cedar apple rust cannot spread from apple to apple or from red cedar to red cedar – the fungus must go through the 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 the majority of infections occur when infected eastern red cedars are within a few hundred yards. Spores that land on young apple tissue may germinate and infect if a film of water is present for an adequate amount of time. Symptoms appear one to two weeks after infection. 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 and 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. The cold (<45°F) wet weather we have had the last week is not conducive to infection. 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, 2017 Midwest Fruit Management Guide, page 34.

Fire blight
The risk of a fire blight infection over the last week has been low. 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 temps > 65°F.

Streptomycin applied 24 hours before or after an infection period will provide control. All other bactericides, e.g., copper, Kasumin (kasugamycin), need to be applied before an infection occurs. If the blossoms are not open, there is no benefit to applying an antibiotic, e.g., streptomycin, kasugamycin. Copper products, e.g., Cueva, 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. Note: If the blossoms are closed there is no risk of infection, and no need to apply streptomycin.

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

Early season lepidoptera
Growers can expect to find larvae of obliquebanded leafroller, redbanded leafroller, spring canker worm, variegated leafroller and green fruitworm all feeding on growing terminals and blossom clusters as temperatures begin to warm. These pests can be controlled with petal fall sprays for plum curculio or with applications of Bacillus thuringiensis (Bt), e.g., Agree, Deliver, Dipel, when it 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 (early petal fall). Early detection of a pest is critical for good control. 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

Intrepid (methoxyfenozide) is 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.

Plum curculio
Plum curculio (PC) emerge around 250 DD, base 50°F, and movement into the perimeter of orchards begins when temperatures are above 60°F. This is a gradual process and requires several days of warm weather. Plum curculio are primarily nocturnal and the entire population does not migrate into the orchard at the same time and fruitlets become susceptible to egg-laying when they reach 5 mm. The lack of snow cover and warm temperatures this spring may prompt an early emergence. Yet cool temperatures will slow activity and some individuals that emerged early may expire from starvation or predation.

Codling moth
Codling moth (CM) overwinter as a full grown larva on trees; temperatures below -15⁰F will provide some mortality. The first CM capture has traditionally been around petal fall and pheromone traps should be hung as soon as possible. The long-life lures (CM L2) are active for eight weeks: if traps are deployed May 1 replace lures by July 1. If the standard-lure (1x) is used, wait until McIntosh bloom to hang traps; replace lures after three to four weeks. Hang CM pheromone traps in the upper third of canopy.

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. OFM 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.