March 31, AppleTalk Conference Call

AppleTalk Conference Call Summary
Friday, March 31 2017, 8:00 – 9:00 AM
Guest speaker: Amaya Atucha, Horticulture and Fruit Crop Extension Specialist, UW-Madison
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

March 31st 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.

Early season horticulture and new plantings with Dr. Amaya Atucha, Horticulture and Fruit Crop Extension Specialist, UW-Madison
What are the major pre-bloom stressors, e.g., nutrients, water, temperature, carbohydrates of tree fruit?  When are overwintered nutrient reserves available and where in the plant do they come from?

  • Temperature is the only driver of stress in early spring.
  • All development happening before bloom is fueled by readily available nutrient reserves stored in the root system. These reserves are accumulated during the previous fall and will be depleted around bloom.  At this time in the season, the tree is extremely efficient at transporting nutrients from the roots and some sugars are transported through the xylem.  The mild weather last fall, which extended into November, allowed trees to store a lot of carbohydrates after harvest and at this time there is little reason to be concerned about tree nutrition and stress.    For example, during the spring following the polar vortex during the winter of 2013 – 2014, we had root damage and later tree collapse due to injured roots not being able to transport nutrients.

At what developmental-growth stage do trees begin to produce a significant amount of sugar?

  • Fruit trees have two types of leaves with varying functions. Spur leaves are responsible for feeding the fruit, and shoot leaves primarily support shoot development early in the season.  During shoot development, these shoot leaves export all of the carbohydrates they produce to the growing tips.   Later in the season, after the terminals set, some of these carbohydrate are then redirected to the fruit.
  • Spurs that have been formed under shade are far less efficient at producing carbohydrates than spurs that have developed under good sunlight during the growing season. Their leaves are thinner and less productive then leaves on the outside of the canopy.  This is one reason why pruning and training is so incredibly important.  Two to three weeks after bloom 40% of carbohydrates produced by the spur leaves will go to the fruit, after another three weeks, 80% will be exported into fruit.

What is the lower temperature-development threshold for apples?  Temperatures in the range of 33 – 42°F satisfy the chilling requirements for tree fruit.  Does this also reflect the ability for bud development to occur at these temperatures?

Trees that have completed their chilling requirements only remain in ecodormancy (second stage or dormancy, following endodormancy) due to cold or cool weather.  Climate change and milder winters, with a lot of days in January and February above 32°F, cause the trees to go from endodormancy to ecodormancy sooner, and result in bud break in early spring.

  • Temperatures between 45 – 50°F are the minimum to see growth beginning to happen. These values are an estimate and not 100% accurate, due to the limited research into this complicated and dynamic process.  Chilling and growth can happen at the same time and if we accumulate a lot of chilling units, we need less heating units to see growth; if we lack chilling, we need more heating.  Temperatures at 40 – 45°F are complicated!  Are they heating or chilling units?  We don’t know the answer and is one reason why we cannot easily predict degree days to specific growth stages.  There are too many variables which prevent us from accurately modeling tree growth and development.   At this time, evaluating chilling accumulation is the more accurate approach to take.
  • Chilling Accumulation Models: Their Calculation, Explanation, & Comparison, University California–Davis, ucdavis.edu/Weather_Services/chilling_accumulation_models

 When is the best time to apply nutrients if they are low?

  • Complete a soil and foliar analysis before applying micro nutrients to correct an unknown deficiency. Soil pH is one factor that can influence nutrient uptake.  Nutrients applied to soils with a high pH will not be available to the plant.
  • The best time to apply nutrients is from petal fall to first or second cover. Boron and zinc are two micro nutrients that are commonly applied at this time.  To increase boron, Solubor can be applied to the soil or as a foliar application (1 lb. per 100 gal) at petal fall.  Do not tank mix Solubor with oil.  To amend zinc, apply a foliar application of zinc calcite.  Zinc calcite is fairly compatible and if needed can be tank mixed with boron or urea.
  • If magnesium (Mg) levels are low, evaluate the level of calcium and potassium in the soil. Heavy fertilization with potassium can lead to a Mg deficiency.  To correct Mg levels, apply a foliar application of Epsom salt (magnesium sulfate), or a ground application of dolomite lime (calcium carbonate and Mg carbonite).  Most lime applied to fields in Wisconsin is locally mined, agricultural-grade lime, and is not dolomitic.  Check with supplier before purchasing lime to confirm the type.
  • Calcium (Ca) is important for fruit quality, but does not influence fruit set. Calcium does not easily move from the soil to the fruit, which necessitates foliar applications.  Some growers begin to 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 an early season foliar spray can increase susceptibility to cold injury. If foliar applications are made, an application of urea applied at 2.5 – 3 lb. per 100 gallons 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 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.  Add an acidifier if the pH is high.  Digital pH meters are an easy and reliable method to verify your spray water pH.  The following links highlight how water pH effects the stability of pesticides.

Storing bare-root trees

  1. Upon arrival, open boxes of new trees and the plastic liner to prevent fungal development.
  2. Inspect the quality and condition of the trees right away.  Contact the nursery immediately if the trees do not look good.
  3. Roots need to be moist and covered with sawdust, hay or mulch, do not let the roots dry out.
  4. Store the trees at 34°F in a cooler or cold room with good ventilation.  Do not store the trees in a room that is also storing apples or that had apples stored in it immediately before the trees arrived.  Ethylene produced by the ripe apples will stress the trees.  If apples were stored in the room it should be thoroughly aired out, before storing the trees.  The goal is to keep trees from breaking dormancy and at a temperature cooler than 40°F.

Planting bare-root trees

  1. Before establishing a new planting, begin planning and preparing a block at least two years in advance. This will allow you to amend soils, based on soil analysis and complete other site prep, such as managing weeds. .
  2. Purchase quality trees from the nursery. The earlier you order, the higher quality trees you will get.
  3. Plant when the soils are dry enough, and as early in the spring as possible. If possible, plant in the fall so the trees can become established and have a full year to grow the following year.  If planting in fall, weeds need to be under control, weather needs to be good for roots to establish, trees need to be dormant from nursery and protected from feeding by rodents and deer.
  4. Take care of the roots when planting: 1) Trim off broken or damaged roots; don’t reduce the root system more than absolutely necessary; 2) Keep out of the sun and protect trees from drying winds. If roots are exposed for 30 minutes before being planted they’ll be ok.  Serious damage can occur if trees are left out for hours before being planted.  Some growers fill harvesting bins with sawdust, and add water to store and transport the trees into the field.  Use caution if soaking roots for more than two to four hours before planting.  Soaking trees for periods of 24 – 48 hours might not be a good idea, as you are depleting them of oxygen and will deplete carbohydrate reserves.
  5. Plant trees so the graft union is 4 – 6” above the soil line. Pack soil firmly around the tree and irrigate immediately after planting to get rid of air pockets.  Never put fertilizer with the roots in the planting hole.  This will damage the roots.  Salt content of compost, including chicken manure, could be problematic.  Make sure to test any purchased batch of compost for salt and heavy metals.
  6. Irrigate immediately after planting and continue to irrigate with three to five gallons per week. Feathered trees require a lot more water that whips.  It is not recommended to plant a high-density orchards unless an irrigation system is in place.
  7. Apply 0.25 lb. of calcium nitrate two weeks after planting in a donut around the tree.
  8. Weed control is critical to having a successful high-density planting. Options include: applying a pre-emergent before bud break or in fall to control perennial weeds.  A burndown can be mixed with the application.  Do not allow glyphosate to contact green bark.  Wood chips can be used to help control weeds during the first year.

Green tip sprays with John Aue
Using copper at bud break
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, extension.psu.edu/plants/tree-fruit/presentations/2016-winter-tree-fruit-meeting/demystifying-copper-for-disease-management

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.

Tree development is currently seven to 10 days ahead of average.  Consider increasing your normal rate of copper by 25%, even if applying the first week of April.  If the spring is dry more copper will be available later on.  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.

Moderate to high-scab inoculum, highly susceptible cultivars and fire blight is NOT a concern
It is recommended to apply a half rate (3 lb./ acre) of an EBDC, e.g., mancozeb (Koverall, Manzate, Penncozeb, Roper Rainshield) or Polyram (metiram), at green tip to blocks with moderate to high inoculum or susceptible cultivars where copper was not applied.  Do not apply an EBDC if no green tissue is present or immediately imminent.  This season we may have high-scab pressure before tight cluster because of the lack of snow cover and warmer temperatures, may have promoted the development of the fungi.  The effective life of any fungicide applied at this growth stage is no more than a week.  The EBDCs can be tank mixed with oil (1% concentration) to aid distribution and also serve as an insecticide for pests that overwinter on the trees, e.g., San Jose scale, aphids.  If captan is used, rather than an EBDC, do not tank mix with oil.  Apply this early-season spray as a concentrate, at 50 – 60 GPA.

If rapid leaf expansion occurs following this application, reapply in seven to 10 days.  If development really slows down and there is not a lot of new tissue, base re application on rainfall.  Getting initial spray on scab susceptible cultivars is critical.

Organic growers should wait until temperatures warm and there is more leaf surface to apply biologicals, e.g., Serenade (Bacillus subtilis), to colonize new tissue.

Early season insect management
An early application of a dormant oil (1 – 2%) can be used to target pests that over winter on the tree, e.g., San Jose scale, European red mite eggs, rosy apple aphid eggs.  Oil sprays should be applied when temperatures are above 40°F and will remain above freezing for 24 – 48 hours following the application.  Performance of oil sprays will be best when the relative humidity is less than 65% and temperatures are warmer than 60°F.

Efficacy against high populations of San Jose sale can be improved by applying an insect growth regulator, e.g., Esteem (pyriproxyfen) or Centaur (buprofezin), at half-inch green when the increased movement of water and sap triggers the scale to come out of dormancy.  For greatest efficacy, mites and aphids should be targeted with oil at tight cluster to pink.

The GPA application rates of water are also very important.  Adequate coverage in a semi-dwarf orchard is unlikely when oil is applied at a volume less than 100 GPA.  Apply at 100 or more GPA to ensure adequate coverage.  On high-density plantings, a full-dilute application appropriate to tree size, should be applied.

Visit the following links to learn how to maximize your oil sprays:

Early season insect monitoring
Pheromone traps for green fruitworm (GFW) and redbanded leafroller should be hung at green tip.  Growers with young plantings or high-density trees have grown increasingly concerned about GFW injury.  We have also seen GFW injury showing up in our pre-harvest damage assessments.  We can use the pheromone traps to identify the end of the flight and begin scouting for hatched larva 100 degree days (base 50°F) after peak flight, e.g., tight cluster to bloom.  Many of the other pheromone traps are hung at pink.