April 26th AppleTalk Call with Guest Speaker Dr. Amaya Atucha

AppleTalk Conference Call Summary
Tuesday, April 26, 2016, 8:00 – 9:00 AM
Guest speaker: Amaya Atucha, University of Wisconsin, Madison, Horticulture
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments,

April 26th Call download: CLICK HERE

Crop phenology and weather

We may be entering a period of extended bloom due to cooler temperatures forecasted for the next several days.  Across the region nearly all growers have significant amounts of pink buds with Zestar, Cortland and others entering king bloom.

Fire blight
Variable weather across the region, means variable fire blight pressure.  How does this relate to bacterial growth?  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.  The following parameters need to be met: 1) Inoculum or signs of fire blight in neighborhood last year, 2) open blossoms, 3) moisture, and 4) warm temps > 65°F.  The EIP (epiphytic infection potential) references bacterial growth and drops to zero when temperatures are 40°F or lower.  If the EIP drops to zero, i.e., temperatures ≤40°F, there should be no infection concern for the next four or five days.

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 blossom are closed there is no risk of infection, and no need to apply streptomycin.

Scab management
The cool and dry weather forecasted for several days will allow application intervals to be extended.  If fungicides were applied five days ago, the need for reapplication should be determined by how much exposed leaf tissue there is and if there is a forecasted infection period.  During the April 19 AppleTalk call, we discussed good growing conditions can result in unprotected tissue being exposed in three to five days after the last fungicide cover.  Captan and EBDC rates can be reduced in areas with good scab control last year, e.g., low inoculum or varieties less susceptible to scab.  However, it is not recommended to reduce the rate of the single-site fungicide.

The amount of rainfall will also influence timing and need for reapplication.  Studies from Michigan State indicate that after one inch of rain, we lose 50% of our fungicide and insecticide coverage.  If we consider both fungicide loss and unprotected tissue from rapid-leaf growth, reapplication of protectant fungicides will almost always be advised after one inch of rain.

Single-site fungicide, excluding the anilinopyrimidines (AP) fungicides, e.g., Vangard (cyprodinil) and Scala (pyrimethanil), which do not move into new leaf tissue, move translaminarly into new leaf tissue and become diluted as the leaf grows.  Conversely, if a single-site fungicide is applied today, when leaves are large, more fungicide will be absorbed into the leaf, i.e., more fungicide will be absorbed into larger leaves, than smaller leaves.

Powdery mildew management
Growers concerned about powdery mildew should note that infections created last season will begin sporulating at tight cluster.  Temperature below -20°F will kill buds infected by the pathogen.  Since we had a mild winter, we can expect there to be inoculum, where infections occurred in 2015.  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 applying 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.

Insect management
Historically, it was common to apply a pink spray of a synthetic pyrethroid for spring lepidoptera, spotted tentiform leafminer, tarnished plant bugs and aphids.  However, this application comes at a cost by negatively impacting important beneficial insects and being toxic to pollinators.  Growers practicing IPM have found that after eliminating a pink spray, it is rare to see economic damage from these pests.

Growers with high-density plantings and young trees have begun to express more concern about spring lepidoptera stunting terminal growth and causing some fruit injury, most notably green fruitworm.  We will begin to observe these spring lepidoptera as warm temperatures return during bloom.  Necessity to manage these populations need to be confirmed through scouting terminals and blossoms.  If populations are confirmed, applications of Bacillus thuringiensis (Bt) may be applied between tight cluster to bloom.  Bacillus thuringiensis is non-toxic to pollinators.  These products include Agree, Deliver, Dipel, and need to be applied when larvae are small (tight cluster through bloom).  By the time we reach petal fall, these insects have completed much of their feeding and an applications of Bt may not be effective.

It is essential to scout for larvae following the first application of Bt, as an additional application may be needed (early petal fall).  Note: 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.  Early detection of a pest is critical for good control.  The spray deposit may only last one to two 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 http://nysipm.cornell.edu/organic_guide/apples.pdf.


Tree Nutrition and Stress with Dr. Amaya Atucha, UW-Madison Horticulture Department

 Please explain tree stress and carbohydrate production?

  • At this time in the season the trees are slowly transitioning from using nutrients stored in the roots and bark, and are not yet absorbing a lot nutrients and water through the root system.  Last season’s feeder roots (primary function to take up nutrients and water) are converting to support roots which deliver nutrients and water to the tree.  This means the feeder roots are not functioning as we normally assume.  New feeder roots will begin to grow as soil temperature increases.  The exact timing of root growth is variable and can occur once or twice a year in the spring, summer or fall.
  • Heat, water and a heavy crop load are all factors that will limit photosynthesis and will decrease carbohydrate production.  During dormancy carbohydrates are stored with water, in plant tissue and are valuable for cold hardiness and growth in the spring.  A tree with a depleted carbohydrate reserve is more prone to winter injury due to the increased space available for water to freeze in the plant tissue.  A heavy crop load can be one of the greatest stressors, since this depletes carbohydrate reserves at a greater rate.  Maintaining a balanced crop is important for the following season’s yield potential and will also improve cold hardiness and growth during the spring.
  • The amount of sun, temperature (optimum at about 80°F), sunlight captured by leaves, and health of the leaves are the primary weather and tree factors controlling carbohydrate supply.  Temperature, number of shoots and number of fruit are important factors that control the demand for carbohydrates.  Carbohydrate supply and demand will be optimum on cool sunny days with a light initial crop.  The sunny weather will ensure a good supply, while cool temperatures limit excessive demand.  On the other hand, hot cloudy days with a heavy initial set will increase tree stress, as the low sunlight reduces the supply of carbohydrates, but the high temperatures will drive up growth rates and demand.
  • More on understanding the carbohydrate model: http://www.nyshs.org/pdf/fq/2007-Volume-15/Vol-15-No-3/Using-an-Apple-Tree-Carbohydrate-Model-to-Understand-Thinning-Responses-to-Weather-and-Chemical-Thinners.pdf

Can molasses be applied to offset carbohydrate deficit?

  • Molasses applied as a foliar spray can only enter extra-cellular space between the cells of the leaf, but cannot enter the cell and be transported through the vascular tissue of the tree.  Since molasses cannot be converted to a carbohydrate the plant can use, an application of molasses will not result in any plant-health benefits.
  • Conventional foliar nutrients, e.g., zinc, boron, nitrogen, have an elemental charge when they enter the solution in the extra-cellular space between the plant cells.  This charge promotes transmission of the nutrient into the plant cell, and onward to the vascular tissue of the tree.

 How do we respond to tree stress using foliar fertilizers?

  • The application rates of nutrients are dependent on multiple factors, e.g., age of tree, soil organic matter, variety and vigor.  Generally, 5-10% of the total nitrogen applied during the growing season can be applied immediately after harvest.  A foliar application is the recommended method to apply nitrogen post-harvest, all of the nitrogen will be stored in the buds for the following spring.  Nitrogen and dolomite lime can be applied as a ground application to adjust the soil pH.
  • Boron is important for pollen germination and pollen tube growth.  Applying foliar boron and zinc early in the year would help offset any deficiencies identified by foliar-test results from previous season.  The application window for zinc and boron is between green-tip and pink, before blossoms open.  Note: Some zinc products may result in fruit russetting.  Use caution when tank-mixing with multiple products, and if possible experiment tank mixtures on a small amount of trees before applying to the entire orchard.
  • Calcium is important for fruit quality, but does not influence fruit set.  Calcium (Ca) does not easily move from the soil to the fruit, which necessitates foliar applications.  Some growers begin apply Ca at bloom to get an early start on delivering Ca to the fruit.  Waiting to apply Ca until after fruit set will save Ca lost to dropped fruit.
  • Applying nitrogen as foliar spray at this time may increase frost damage and susceptibility to cold injury.  If foliar applications are made, urea applied at 2.5 – 3 lb. per 100 gallons of water is recommended.  Nitrogen should only be applied to soil between bud break and mid-April or late-May and then again right before or after harvest.
  • Growers may be interested in tank mixing foliar fertilizers with fungicide sprays.  However, while it may be appropriate to concentrate a fungicide at 50 or 60 gallons per acre (GPA) of water, fertilizers will be absorbed better by the leaves if applied at 80 to 100 GPA.  Note: Verify the pH of spray solutions when preparing an application.  If the pH of the spray solution is greater than 7, products like Solubor (boron) can precipitate out and are no longer effective.  It is recommended to not to mix fertilizers with pesticides or oils.  Growers concerned about their spray solutions pH are recommended to track and record this information on their fertilizer and pesticide records.

Is there utility in using frost/freeze protection products? 

  • Bacterial or non-ice nucleating products that are advertised to reduce frost/ freeze damage will not likely work in an orchard where there is an abundance of materials, e.g., dust, pollen, that will start, the nucleating or freezing process.  The only thing to reduce frost damage is to make sure the trees are not stressed.  Once ice in tissue and the plant cells rupture there is no way to reduce damage.

Press Release: Introducing the Wisconsin Fruit website and newsletter!

Janet van Zoeren, Christelle Guédot, and Amaya Atucha

University of Wisconsin – Madison, Departments of Entomology and Horticulture


We are very excited to announce that we have just launched our updated Wisconsin Fruit website, which you can find at http://fruit.wisc.edu! This site is divided into sections focusing on berry crops, cranberries, grapes, and tree fruit, and offers a one-stop spot where commercial fruit growers and home gardeners can access links to the most recent management recommendations, pest alerts, and research findings from UW faculties. In this way, it is meant to provide a first step toward finding the answer to any questions you might have about Wisconsin fruit production. In order to make the website more convenient for you to use, we’re working on making it easily accessible through your mobile devices. Over the next couple of months, we will be making the website friendlier to view on smartphones and tablets.

Along with the Wisconsin Fruit website, we are also starting up the Wisconsin Fruit News, a newsletter on fruit production, with the first issue to come out on April 18th. The Wisconsin Fruit News will be issued every other week during the summer, and will contain scouting reports, plant development reports, pest and disease management research updates, and other information pertaining to Wisconsin fruit production. Each issue will be divided into six sections: General Information, Berry Crops, Cranberries, Grapes, Tree Fruits, and an Upcoming Events Calendar.

If you would like a pdf of the newsletter to be delivered directly to your email inbox every other week, you can subscribe on our website! Simply go to http://fruit.wisc.edu and enter your email address on the right hand bar where it says “Sign up for our newsletter!”  In addition, you are now able to link the Wisconsin Fruit updates and newsletters to the IPM Toolkit application, which was created through the University of Wisconsin’s Integrated Pest and Crop Management program (http://ipcm.wisc.edu/apps/ipmtoolkit/). Just download the app, then enter our RSS newsfeed URL (http://fruit.wisc.edu/feed), and you will be able to immediately see our most recent posts and to access the newsletters on your phone.

Additional Resources

Dogwood borer management: http://blogs.cornell.edu/jentsch/2015/04/24/dogwood-borer-and-scale-not-to-be-taken-lightly/

Soil Testing: http://msue.anr.msu.edu/news/more_reasons_for_soil_testing