There's an article in current GFG about thinning apples. It says that the young apple fruit is under carbohydrate stress and therefore easier to thin during hot cloudy weather. Hot increases fruit growth rate and cloudy reduces photosynthesis.

I won't think you could blame cool cloudy weather unless it interfered with pollination.

I guess if it's cloudy enough carbo levels could be a factor even in cool weather. I won't think that's the only factor. It's one thing to thin the fruit some and another to end up with a light crop.

The commercial guys in WA state usually apply 2-3 chemical thinners and then might need to hand thin. Are you guys out East really that much worse off that you get a light crop without doing anything? My impression is that yields in New England aren't that much less than WA state. GFG writes about apples out East often and I've been reading that magazine 43 yrs. Those tall spindle apples out there are getting big yields according to Terence Robinson, your apple guru at Cornell.

This post was edited by fruitnut on Sun, May 25, 14 at 12:01

FN read the far right column on page 85. Even in commercial orchards with dawn to dusk sun, cloudy weather sometimes reduces the amount of available carbohydrate to the point that trees may abort fruit during first few weeks after petal fall. The vegetative shoots get preferential treatment.

Here is a link that might be useful: virtual orchard

Maybe the issue is your big vigorous trees are growing wood instead of fruit. Maybe that starts with fruit set. I'd say you've got enough light to require thinning most years if the light is put to proper use.

My big apple trees grow with moderate vigor only. For varieties prone to biennial baring, thinning fruit is not always all that is required- commercial growers here often have to use hormones that induce flowering in addition to thinning materials to insure annual cropping of varieties with a genetic tendency to biennial baring such as Honeycrisp and Fuji.

My problem with apples here may be that much of my crop was frozen out in 2012 which makes them much more difficult to manage in the immediate years following for annual production- even when properly thinned the following year, apparently. Thinning is not always enough according to literature I'm finding now.

My problem with certain plums is not at all about thinning or excessive vigor, but it may be something as simple as leaf hopper damage and subsequent early defoliation which happens to some of my Euro plums.

There is clear research that shows that late season mite damage can drastically reduce return bloom and fruiting of apples. It is a logical leap that anything that reduces the trees ability to store energy can affect crop.

In Texas you can't really evaluate the affects of a much shorter growing season, particularly when talking about a non-commercial orchard that misses several hours of daylight in best conditions because of tall trees.

It is possible that there is a sweet spot where you thin just the right amount of fruit and you get reliable production but in my opinion it is much more likely that other factors are in play.

FN, maybe you will find some of this interesting. Although apple trees may be most affected by cropload in determining the following years floral production, negative factors occurring much later can have influence as the actual blossoms for the following year do not begin to form until much later in the season. What is really interesting here that I did not know is that a lot of development of the flower goes on when trees are dormant- but that is unrelated to this discussion.

The idea that later season issues affect flower formation is not born out here but in a study about the affects of mid and late season mite damage I found elsewhere. I am presuming that other means of reducing carbo storage would have a similar affect, although that may be a bit of a leap.

Here is a link that might be useful: time of flower formation