June 4th Apple Talk Summary

Apple Talk Conference Call Summary
Tuesday, June 4th, 8:00 – 9:00
John Aue, Threshold IPM; Phil Schwallier, Michigan State University.
Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org.

June 4th Call download

Registration still open for the June 19th and 21st IPM field days in Eau Claire and Bayfield WI. http://www.ecofruit.wisc.edu/appletalk/wp-content/uploads/sites/343/2013/06/2013-IPM-Field-Day-Brochure-052813.pdf

Thinning Q & A with Phil Schwallier
What changes should we consider when we have less than optimal thinning?

This year Michigan it took 14 days for petal fall thinning, instead of 7 days.  If we applied combinations of MaxCel and NAA we would expect 25% thinning, and it is taking longer this year.  If this was done at 10mm would expect to see more thinning and if we are at 20mm we are at our last chance to do anything.

How much water is appropriate for thinning?
100 GPA for 10 ppm thinning solutions on dwarf and on larger trees rates may increase to 150 GPA, though we still maintain our 10ppm ratio.

Many growers are beyond 10mm and cold weather has been forecasted for the next 7 days, what is the best strategy?
Growers may use an aggressive rate of 100 to 150 ppm of MaxCel with carbaryl.  NAA may be applied at 10-20 ppm with carbaryl.  Fruit will be resistant to thinning in the cold and need to judge fruit and bud health.

With the cold we can still get our desired thinning when the fruit is at 10-15mm.  We are unlikely to get a response at 65F and 10mm fruit.  If it is going to get warmer a few days later, it may be better to thin during the warmer weather, even if you are past 12 mm fruit.

Temperatures in the upper 60s and cloudy and minimum temperatures is in the 50s will not create stress to the tree or fruit because the fruit are not demanding energy and because the trees are not photosynthesizing.

We can determine which fruit will stay or drop by flagging fruit at thinning.  We should see a difference in fruit-diameter growth in four or five days under typical conditions.  This year it is taking closer to seven days to see changes in growth.  Fruit growing half the speed of the king bloom, e.g., anything growing less than half a mm per day will fall off.

If you are at 15mm on June 4th, you only have four or five days left to thinning.  If you are still at 8mm, we can wait for warmer temps that will come a week from today and then thin aggressively at 14mm fruit.

Growers may thin more aggressively by mixing Regulaid or oil and can increase thinning by 10%.  This may not be risky if you need thinning, but if the set is light, the practice could lead to over thinning.  Phil has done this in trials over the last 15 years and has always achieved extra thinning.

Moderate drying conditions are the best for applying thinners.  If we apply during slow drying conditions, we will get additional thinning, e.g., applications made at night that stay wet for 11 to 18 hours and often lead to over thinning.  It is best to thin early in the morning or during the day when we have moderate drying conditions and go with aggressive rates and moderate drying conditions.

What about the use of carbaryl and impacts on bees?
One quart of Sevin XLR (carbaryl) will have some impact on bees, especially when a ground cover has lots of bloom or if there is side bloom remaining.  Phil is telling growers to not use any carbaryl if they are using rented bees.

What are strategies for encouraging return bloom?
Summer NAA or Ethrol may be applied beginning at the fifth week after full bloom, apply first summer NAA at 5ppm, e.g., 4-6 oz per acre of Fruitone or 8 oz per acre on the large trees.  Sprays at five, seven and nine weeks will increase return bloom by 25%, on average.

Apply Ethrol at 1pt per acre, e.g., 300 ppm per acre with 100 gallons of water.  If we apply when we have 90F temperatures, this could cause wilting and leaf drop when growth is lush.  If trees are hardened off, there will not be as much a response from leaves.

Phil is recommending the first spray at King-bloom-petal fall and does not like to wait much beyond ten days.  The later you start applications, the less of an impact you will have on controlling growth.  Phil’s recommendation is to apply two to three sprays two weeks apart.  If the season rate was 24 oz per acre, applications might consist of three 8oz per acre applications.

If fireblight is a concern, then the first spray could be 12 oz per acre then followed by two 6 oz applications.  We don’t have to wait two weeks to reapply.  If we shorten the interval with higher rates on the first application, there will be better early protection for shoot blight.

Phil does not recommend combinations of MaxCel and NAA, but has done it in the last five years of six years of trials.  The concern is an increased risk of developing mummified fruit.  The strategy does work on Gala and Golden Delicious, perhaps generating only 1% mummified fruit.

The sooner you hand thin, the more return bloom you will have.  The first 30 days of handing thinning beginning in July will have an impact, but afterwards you are just thinning for fruit quality and size.

Managing sunscald
Purshade and kaolin clay help to mitigate risk of sunburn and sun scaled.  A June that is hot and clear with minimal cloud cover and the long days around the solstice will begin to damage susceptible varieties, e.g., Honey Crisp, even though they may not show symptoms until later in July.  Phil does not have data re kaolin clay reducing photosynthesis.  However, data shows that kaolin reflects light in the canopy and get more indirect light within the canopy.  Phil does not think it thins any.  Lime sulfur will stress the tree and induce thinning.

Insects and disease
The cool weather has slowed insect activity.  Plum and apple curculio can still be migrating in if not beyond the 308 degree day benchmark from McIntosh petal fall.

Powdery mildew will not be as intense, because we have not had the hot and dry conditions required.

We continue to have perfect conditions for scab.  Most growers are reaching 900 to 1000 degree days, base 32, from McIntosh green tip and moves us out of primary scab season.  Remember lesions take about three weeks to appear after an infection period and may be extended because of the cool weather.  Keeping protectant fungicides applied until several weeks have passed since the last infection period may be a wise decision.

Most growers have had a minimal codling moth flight, however, locations that have had flights have seen significant numbers.  In southeastern Wisconsin a biofix was established in the last few days of May and the La Crosse to Hastings MN region had a biofix around June 1st.

Degree day calculator: http://www.soils.wisc.edu/uwex_agwx/thermal_models/degree_days

Avaunt (indoxacarb) applied as alternate-row-middle applications and split between two sprays is great or used as a perimeter spray is an option.  It is the most rainfast material we have for plum curculio, but as per other products it is all washed off after 2’’ of rain.  What matters is how many warm days the material had to work on PC before rain.

San Jose scale (SJS) crawler activity begins two to three weeks after petal fall and is the first of three generations.  Typical captures on tape range from 40 to 400 in a week.  SJS should be monitored with double-sided-carpet tape on several scaffold branches.  Note: electrical tape does not seem to hold its stickiness.  Crawlers get stuck only on the edge of the tape.  Don’t tape where the bark is rough.  Looking crawlers requires a 10x lens and looking for lemon yellow blobs clustered along the edges and check weekly.  Controls include neonicotinoids, summer oil (but needs good timing) and Esteem.  We do not know how long each generation will be active for, but most insect phenologies have been slightly ahead of trees and tape needs to go up ASAP.

Articles from Phil on 2013 thinning strategies


Plum curculio management guidelines from Michigan State University

Rainfast characteristics of fruit crop insecticides