May 20, AppleTalk Call Summary

AppleTalk Conference Call Summary
Tuesday, May 20th, 2014, 8:00 – 9:00 a.m.
Presenter: John Aue, Threshold IPM.
Moderator: Peter Werts, IPM Institute of North America; questions or comments,
Guest Speaker: Phil Schwallier, Michigan State University

May 20th Call download: Click Here

Phil Schwallier, Michigan State University, will join us to discuss foliar feeding and thinning.

Tree Phenology
Orchards in southern Wisconsin and northern Illinois are at full bloom.  Development too the north ranges from tight cluster to pink with only Zestar nearing bloom.

Insect & Disease Management
Pheromone traps
Codling moth, redbanded leafroller, lesser appleworm, Oriental fruit moth, American plum and lesser peachtree borer traps should be up by this time.  Plum curculio traps can also go out this week.  Plum curculio damage is not a concern at this time, but the warm temperatures will prompt their migration into orchards.

Rosy apple aphid and San Jose scale
If you had any damage last year now is a good time to begin scouting fruit clusters for curled leaves and feeding rosy apple aphids.  Note: If a pre-bloom application of Esteem (pyriproxyfen) was applied for San Jose scale, rosy apple aphid and green fruitworm may have also been treated.

Early lepidoptera
Begin scouting for early lepidoptera, e.g., Green fruitworm and obliquebanded leafroller, during bloom.  Green fruitworm feeding is already present on foliage.  Note: Esteem also impacts lepidoptera.  Early signs of leaf feeding, with no larvae present may prove effectiveness.

Plum curculio
Organic insecticides for plum curculio, e.g., Surround WP (kaolin), need to be applied as a whole orchard spray.  For conventional growers, Avaunt (indoxacarb) maybe used if leafrollers are not found while scouting.  If applying a perimeter spray of Imidan (phosmet) the best timing would be during the first of several warm nights, when plum curculio should be moving in the orchard.  Note: Imidan is extremely toxic to pollinators.  Only apply in the evening, or at night, when target varieties are at petal fall or beyond.

Q&A with guest speaker, Phil Schwallier, Michigan State University
Can you please explain Cornell’s MaluSim Model (carbohydrate model) and review what is involved?
The MaluSim Model is used to predicate the carbohydrate level of an apple tree to indicate tree stress and energy level.  From green tip until mid- July total solar radiation and maximum and minimum temperatures are inputted into the model daily to gain predictions of the carbon balance in the tree.  To determine fruit thinning timing and response, we begin to focus on predictions at bloom and petal fall, when the tree has relatively low stress and until 10mm, when significant stress develops.  Accompanying phenology, weather also has an impact on the model; hot, cloudy days and warm nights calculate stress, while cold sunny days and cool nights will calculate no stress.  The MaluSim Model is used as a guide to predict thinning response by evaluating the grams of carbon available per day.  When thinning the grams/carbon per day is observed for two days prior and four days after the prospective thinning date.

 g/carbon per day Stress level and thinning response
0 to -20 No stress, low thinning response
-30 to -40 Moderate stress, good thinning response
-50 to -60 High stress, excellent thinning response
-70 and above Very high stress, use caution when thinning

Although the MaluSim Model is a helpful tool for thinning, tree health is also necessary to consider.

Trees that broke dormancy later in the spring are showing signs of stress, i.e., Honeycrisp have small, olive drab leaves with slight redness.  Surprised to see small leaves, considering we are in bloom.  Is this an actual indicator of tree stress or just the cultivar?
Yes, it is an indicator of tree stress.

Is nitrogen the primary concern when addressing tree stress?  How much actual nitrogen is useful between pink and the end of bloom to counter act short term carbohydrate stress versus trying to push growth on slow trees?
Nitrogen, zinc and boron are all nutrients to consider when addressing tree stress.  Nitrogen has the greatest influence on tree stress.  Normal or excess levels of nitrogen will result in a healthier fruit set, compared to a tree that is deficient in nitrogen.  Foliar feeding nitrogen and zinc before and after bloom will be beneficial for tree growth and fruit set.  During fruit set also include boron.

Most growers use urea, calcium nitrate and 20-20-20, and fish emulsion for organic production.  Of these first three, the 20-20-20 also has boron.  Is there any more utility in using the 20-20-20 to counter act tree stress versus using calcium nitrate or urea?  Do you have foliar feeding rates you can share with us?
Growers are recommended to follow chemical supplier, and label, recommendations for nitrogen application rates as formulations may differ.  Grand Rapids’ local supplier recommends 5lbs of urea/100 gallons of water.

In terms of supplying zinc, the MSU guide has a window for application to apply through first cover with the zinc EDTA formulation.  Do other zinc formulations have issues with phytotoxicity? 
Growers should use recommendations on rate per acre from suppliers.

Does mancozeb, EBDC, provide an effective amount of zinc when applied in the 3 lb/acre rate?
Fungicides containing mancozeb do not contain enough zinc to supplement nutrients.  A pre-bloom and post-petal fall foliar spray is recommended to correct deficiencies.

Is there utility in foliar feeding to aide winter injury and the impacts of drought stress from 2012?
A ground application of fertilizer is the most effective method in delivering nutrients to the roots, allowing the tree to recover and regrow.  Even though foliar feeding does not provide this function I would not discourage it.

Is carbaryl rate independent?  If this is the case, if we use the 1pt rate of Sevin XLR, can we get the same results if we used the 1 qt rate?  The lower rate will have less of an impact on non-target.
Carbaryl, e.g., Sevin XLR, is not rate dependent.  The same results are achieved if thinning aggressively using two pounds (one quart) of product, or less aggressively using one pound (one pint) of product.

Additional comments on thinning
Phil is encouraging growers to begin at bloom and petal fall.  Trees are not sensitive at bloom, and are most sensitive at 10-12mm and lose sensitivity later.  Waiting to thin until the 10mm stage may present challenging weather conditions, which may force growers to thin later in the season or prevent thinning.  Thinning at bloom to petal fall/ 6mm is a very good time to thin when the risk of over thinning is low.  Fruit size can be increased on varieties such as Empire, Gala and Jonathan by applying MaxCel (benzyladenine) at 100ppm during full bloom and carbaryl at petal fall to 6mm.  On varieties that do not need additional fruit size, e.g., Honeycrisp or Jonagold, NAA (Fruitone) can replace MaxCel at bloom and can be mixed with carbaryl at petal fall to 6mm.  Following this method, once the fruit reaches 10mm, 20-25% thinning has been achieved and crop load can be assessed to determine if additional thinning is needed.  If so, a 10-15% thinning at 10mm provides an appropriate crop load.  For easily thinned varieties, e.g., Cortland, McIntosh and Braeburn, wait until petal fall to 6mm.  If growers are interested in this technique try on a small block first before doing a full orchard application.

What effect does Apogee have on thinning?
Apogee (prohexadione calcium) will stimulate growth on trees and should increase thinning rates by 10-15%.  Use recommended rates.  Do not mix Apogee with nutrient foliar sprays.

When should growers begin thinning young trees?
The first three years of growth are very sensitive to fruiting and years four and five are the transition years from young to bearing trees.  It is recommended to prevent fruiting on these young trees, allowing for vegetative growth, and to begin thinning after the fourth or fifth year.

Additional Articles and Resources
MaluSim Model (carbohydrate model)

  • Network for Environmental and Weather Applications. Zoom out on the map and locate the weather station in Gays Mills, WI.  Under ‘Results’ you can adjust the green tip and bloom date and then calculate results.

  • Codling moth mating disruption

  • Selecting Fungicides to Minimize Resistance Development and Avoid Phytotoxicity and Fruit Finish Problems. Dave Rosenberger. December 17, 2013.