April 12, AppleTalk Conference Call

AppleTalk Conference Call Summary
Thursday, April 12 2018, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

April 12th Call Stream: CLICK HERE

Thank you for registering for AppleTalk!  Your participation makes this program possible.  The call recording and agenda will be posted to the blog following the call.  Written summaries will be posted when complete and distributed via email in PDF format.  John Aue, Peter Werts and Thomas Bernard will begin scouting orchards in the coming weeks and are available to answer questions as the season begins.  If you still need to register for AppleTalk visit: https://ipminstitute.org/projects/specialty-crop-grower-services/appletalk/register/.

AppleTalk will begin weekly on Tuesday April 24.

NEWA weather station updates
Network for Environment and Weather Applications (NEWA) weather stations are online and you can now access forecasts and historical weather data for around 20 weather station across WI, in addition to those that have already been available for the last couple of years in MN and IL.  Visit the links below to see if there is a station near you.  The NEWA site offers a friendly interface to monitor insect and disease development and access crop management tools.  Access to the site is free of charge and you don’t need to have a station to use this resource.  This is a resource that we will be using and referencing season long.  If you have any questions with accessing a station please contact Peter, Thomas or John.  Access your local station here:

Regional Extension publications and newsletters
Weekly Extension publications and newsletters distributed by Michigan State University (MSU) and Cornell University are excellent resources.  These resources deliver a broad range of regional topics and we recommend subscribing if you have yet to do so.  See links below.

2018 Fruit insecticide registration update
Visit the following link for insecticide updates to the 2018 MI Fruit Management Guide, http://msue.anr.msu.edu/news/2018_fruit_insecticide_registration_update

Regional comparisons of degree day accumulation, crop phenology and winter injury
Recent articles from MSU (see below) provide a great comparison of regional variations of degree-day accumulation and crop phenology and summarize the potential for winter injury.

Southwest Michigan has accumulated a significantly more degree days compared to sites 30-40 miles away.  To date, degree-day accumulation in SW MI has been less than average, yet more than other areas in the region.  Primary observations suggest there is going to be spotty bud break in areas that are ahead in degree-day accumulation.  In our region we suspecting a clean break and ordered progression into bloom.

The MI winter was warmer than 2014-15, so there should be significantly less winter injury to cold-sensitive crops than during the polar vortex; exceptions might be sweet cherries and some peaches.

Climate change impacts on disease management
Key findings from the 2017 New York orchard climate-change survey were reported on in the March 26 Scaffolds Fruit Journal.  The survey was initiated after the 2017 season, which saw an 80% increase in total precipitation in NY which resulted in water logged soils, increased disease pressure, e.g., apple scab, bitter rot, and plant health concerns.

The study found that a majority of respondents expected effects of climate change, e.g., increased heavy rainfall, short-term summer drought, will become more frequent.  Yet, further on in the survey responses relating to how growers would respond to climate change, thought that it would not impact them and most are not planning for it.  The point is even though they had a year with extreme weather that resulted in fruit loss, still when asked, thought the next year would be “better” or “normal”.  It is really hard to revamp our entire mindset and approach to how we are growing fruit.  See full report here:

Who’s Soggy Now? – Anatomy of a wet year: Insights from New York Farmers (page 6-9), Scaffolds Fruit Journal, March 26 2018, http://www.scaffolds.entomology.cornell.edu/2018/SCAFFOLDS-3-26-18.pdf.

April weather outlook
April temperatures are running 17-24°F below normal for the first 10 days of the month.  Areas with snow on the ground are going to have cooler soils, and soils are going to take longer to warm up.  This impact will be site specific.  If we consider 2012, when we had a very early spring, March temperatures were 14°F above normal.  Normal average high and low are figures we refer to.  If we are within five or six degrees of normal temperatures, we don’t see a noticeable differences in tree or insect growth and development.  For the rest of month temperatures are predicted to remain below normal.  In regard to bud break we are beyond where we should be. Pros and cons of a late spring include:

  • Chance to increase soil moisture before bud break. Some region could get upwards of two inches of rain.
  • Later bud break reduces the chance of frost occurring after bud break. A late bug break will also reduce risk of an extended cold period after green tip when we are still at risk of killing frosts in early or mid-May.
  • We are likely to have temperatures which favor scab development. This is a year to not delay first fungicide sprays, since we are likely to have significant scab maturity prior to tight cluster.
  • Late bud break will equal a short pre-bloom due to the increased photoperiod. Once we have green tissue, even if it stays cools, trees may push faster based on a response to day lengths.
  • Degree-day threshold for plant development is around 42°F, yet threshold for apple scab to develop is 32°F. When you have low temperature below 42°F, we will continue to have scab development.  Apple scab phenology may be ahead of tree (and insect) phenology, compared to previous years.

 Apple scab predictions and management
We will have temps that will conducive to scab development and John does not recommend delaying first scab spray.  If you have had scab last year, it is recommended to start management in high inoculum blocks earlier, rather than later, since there may be significant maturity before tight cluster.

Amount of development in terms of pre-bud break is typically small.  Could release some spores early (pre-bud break), yet will still release bulk of spores during tight cluster to petal fall stage.  John does not recommend using any of the biological fungicide until there is significant leaf surface present.  Snow cover will slow scab development.

A new approach to copper
Many growers choose not to apply copper if fire blight has not been a concern.  Yet with increasing pressure from canker diseases, we may need to rethink this.  When we typically discuss canker diseases in our region we are normally talking about black and white rot, which are warm-weather disease.  Yet we are beginning to see more canker diseases, such as, phomopsis, as time goes on.

The phomopsis pathogen growing in the Northwest is a cool-weather disease that is managed by applying copper at bud break.  We need to begin to consider if applying copper at bud break is a good safety measure to be proactive about increasingly common cool-weather canker diseases.

Preparing for copper and oil at green tip
Copper applications at bud break are used to target fire blight and apple scab.  At this early growth stage and with cool temperatures, bacterial colonies in fire blight cankers are not actively growing.  Enough copper needs to be applied at this time to persist until early pink through bloom to inhibit bacterial growth when the fire blight cankers become active.  The downside of applying too high of a rate of copper, is that if excess copper is present at petal fall it can cause fruit damage and russeting.

Note: Once copper products are dry, they are no longer phytotoxic.  If there is still sufficient copper residue remaining at petal fall, this can be redistributed by rainfall on to the developing fruitlets and cause russeting.  For the standard copper products on the market, it is thought approximately three to four inches of rain between application and fruit-set mitigates this risk.

Tips to mitigate risk of phytotoxicity and russeting

  • Apply when drying conditions are good (low humidity)
  • Do not apply within 24 hours of a freeze event
  • Eliminate the oil from the application
  • Reduce the rate of copper per acre (but not the total gallons of water per acre)

There are many copper-containing products that can be used for fire blight at bud-break.  Formulations may contain copper hydroxide, copper sulfate, copper oxychloride, etc.  All of these formulations function the same way.  They supply copper ions, i.e., metallic copper, and it is these copper ions that inhibit bacterial or fungal growth.  The hydroxyl or sulphate portion of the molecule, does not.  When choosing a copper product for fire blight, it is important to compare the amount of metallic copper contained in the different products.  This is often represented on the package either as a percentage of dry metallic copper by weight or as pounds per liquid volume.

Another important factor in choosing copper is its longevity, which is dependent on the particle size of the copper salts in the formulated products.  The smaller the size, the less likely it is to be dislodged by rain, and theoretically the better the copper will be distributed throughout fire blight cankers.  Getting information on particle size for particular copper products can be difficult, however your distributor would likely be able to assist.  For more information visit:

  • Demystifying Copper for Disease Management, Brian Lehman and Kari Peter, PennState, Click Here.

Copper application rates and adjuvants
At bud break, use 1 – 2 lb. of metallic copper per acre and apply with a high volume of water, e.g., 75 – 125 GPA, depending on tree size.  A 1% concentration of oil can be used to improve the distribution of the copper within bark and cankers.  To reduce risk of bud damage, do not apply oil when temperatures have been, or are forecasted to be, below 32°F within 48 hours of the applications.

Track rainfall from the application date, if three plus inches of rain has accumulated by bloom, it’s likely the copper will be gone and you will need to be more aggressive in controlling bacteria compared to a dryer spring.

New OMRI approved copper formulation: Kocide 3000-O (copper hydroxide), EPA Reg # 91411-11