Has anyone tried Sevin to thin apples? Mine are at about the right stage. I know it will kill bees and can cause a spider mite outbreak. Any other thoughts? How well might it work?
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I use Napthalene Acetic Acid 4-16 Parts per million. NAA is available on Ebay as a raw chemical . use 16 PPM for hard to thin varieties such as golden delicious. use 4 PPM for easy to thin varieties such as Granny Smith. NAA is not toxic to insects.
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lakewoodfarm:
Thank you for that tip!! That’s a much better idea than Sevin. I’ll get some and try it. It’s amazing sometimes what’s on Ebay.
lakewoodfarm:
I’m hoping the NAA will come with mixing instructions. But if not can you tell me how many mg per gallon for 16 ppm? I’ve got 10 grams coming for $8.95.
1 gram in a liter of water is 1/1000. 1 gallon has 128 oz or 256 tablespoons. so you first mix one gram in a liter of water. now you take this 1/1000 “concentrate” . one tablespoon of this concentrate per gallon will give you 4 parts per million. 4 tablespoons of concentrate per gallon will give you 16 PPM.
Thank you, thank you, thank you!!! As you might surmise I’m giddy about this experiment. Besides thinning apples is boring 
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I used it for first time last year. I used 12 PPM. yellow delicious was under thinned. Granny smith was over thinned. Gala was thinned just right
How did this work out? My Gala is way overset and I was thinking of using carbaryl to thin it.
What stage of apple development is best for this?
How do these sprays thin the apples?!!??
I mean, how does the spray know which apples to remove and which apples to leave?
Page 77 of the Apple Management Guide for the SE will get you started, but its more of an art than a science. I under thinned last year but did better this year. Sevin alone is a weak thinner. I added a small amount of NAA this year which helped. The amount of the thinning is determined not only by the chemicals used and the rate, but also the size of the fruit when the chemicals are applied as well as the weather. Warm or cool and sunny or cloudy several days before and several days after the thinning impact the amount of thinning. Also, each variety reacts differently to the thinning chemicals so chemical thinning is never perfect. Its just a best effort attempt to reduce a lot of hand thinning.
Since chemical thinning is not as precise as hand thinning it only makes sense if your have a lot of trees. However, if you spray Sevin at petal fall for insect control its possible to thin and kill the bugs at the same time. Sevin is only moderately effective against the dreaded PC but its very effective on leaf hoppers which have the reputation of spreading fireblight bacteria.
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I think the spray seems to encourage the tree to drop the sort of apples it would eventually drop anyway. The earlier the spray, the greater the thinning effect.
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Interesting. Thanks to you both!
Now what I’m wondering is: how long should it take? When should I see if it’s working?
I’m not sure whether we have any commercial growers on this forum or not. My question is simple though.
I have 23 apple trees and spend hours thinning hundreds of apples from each tree. I can’t see how any commercial orchard with thousands of trees could find the $ and manpower to thin.
Anyone know?
When i first starting getting apples i would use Sevin for pc…i didn’t know at the time it thinned apples. I don’t recall how well it worked…i still had apples. The positive is it should kill pc effectively.
They use multiple applications of different thinning agents combined with detailed logging and analysis of thinning progress. For instance a small developing apple that falls below a certain growth rate is destined to abort. Then at the end they hand thin as a last resort.
Peaches are worse. There are no effective thinners unless they’ve developed something recently.
The worst thing to me to thin is Asian pears. The fruit is hidden in a mass of leaves.
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Fruitnuts explanation was excellent.
I’m learning to chemical thin about 800 dwarf apple trees - roughly 20 varieties. Some varieties thin easy and some like Fuji do not. Weather can greatly impact the results, so the rates of the chemicals need to be adjusted based on last years results as well as the actual weather several days before and predicted weather several days after the thinning spray. Also the size of the fruit at the time of the thinning makes a big difference.
Check out my reply earlier in this thread for a reference to common thinning chemicals in the SouthEast Apple Production Manual. I use the NEWA thinning model from Cornell to help adjust my rates based on weather. Sunny= less thinning. Cool= less thinning.
An article from Penn State explains it well:
http://extension.psu.edu/plants/tree-fruit/commercial-tree-fruit-production/crop-load-management/chemical-thinning-of-apples
I follow up with hand thinning after the chemical thin. With more practice and some luck, I hope to improve the results of my chemical thinning so I can reduce the hand thinning.
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I’ve tried using Florel to eliminate fruit on a crabapple for three years with no luck.
Would NAA work? What concentration should I use and at what point should I spray?