Mike Basedow, Tree Fruit Extension Specialist, CCE-ENYCHP, Northern NY

I recently evaluated two Honeycrisp blocks in the Champlain Valley for their percentage of flowering buds so the growers could adjust their pruning practices. The first block is a mature planting on M.26 rootstock, trained to a vertical axis system. Bloom was heavy in this block in 2022.    

The second block is a mature planting on M.9 EMLA, trained to a tall spindle system. Bloom was heavy in this block in 2022, despite winter damage to the king buds. Both growers began thinning at bloom in an effort to promote good return bloom in 2023.   

The M.26 block averaged 34% strong floral buds, 45% weak floral buds, and 26% vegetative buds at my assessment last week. The M.9 block averaged 64% strong floral buds, 21% weak floral buds, and 15% vegetative buds.   

Strong floral buds contained a full cluster of kings and laterals. I expect these buds will set fruit provided we have good spring weather and good pollination conditions. Weak floral buds were smaller, and often only had a single king in the cluster. I think these are going to be the smaller, single king flowers we often see on Honeycrisp, and are much less likely to set fruit.  Vegetative buds only had leaf scales in the buds, no floral parts were present.   

 Given the lower quantity of strong floral buds in the M.26, I would advise pruning lightly in this particular block this season, leaving extra insurance buds since we can assume a higher proportion of buds will likely not set fruit this season.  I think the M.9 block can be pruned a bit more heavily, all else being held equal.  (See the above article for how to do the full precision pruning calculations) With the warm temperatures we’ve experienced in February so far, this might be a year to leave even more insurance buds in case we do end up having an early green tip.  

These are of course just two blocks, and only serve as an example. Your Honeycrisp blocks are likely to vary in their percentages of floral buds this year, depending on: 

• your bloom density in 2022, 
• your thinning practices, 
• and your return bloom practices, along with other more difficult to define factors like tree stress during floral bud initiation. 

With all that in mind, I generally expect we’ll have a lighter return bloom in Honeycrisp this year in the Champlain Valley where bloom was strong and trees were set heavily last year, and vice-versa.  To be certain though, knowing your percentage of floral buds can be helpful in determining how hard to prune this winter if you are planning to do some precision pruning. 

 If you are interested in evaluating buds in your own blocks, here are some of my thoughts from the experience: 

• I followed the protocol of two branches (one each from the upper and lower canopy) from 5 representative trees per block. 
•  I looked at 10 spurs per branch, unless the branch had fewer than 10 spurs. If a spur had multiple buds, I chose a single bud from that spur at random. Since Honeycrisp spurs also have a tendency to produce bourse shoots, terminal buds on these were also fair game. 
•  I used a single edged razor blade to cut through the middle of each bud length-wise (figure 1), and looked at the buds under a table top dissecting scope (figure 2). These can be purchased online for around $100. You’re also welcome to come in and use the one at the Clinton County CCE office.   
• In figure 3, you can see what a floral bud (top) vs. a vegetative bud (bottom) looks like under the scope. The vegetative buds are fairly narrow, and will only have leaf primordia at the tip of the bud. Floral buds will appear more rounded, and will have small, light green floral tissues at the tip of the bud. These can be difficult to tell apart at first, so I recommend cutting open a few practice buds until you get your bearings on what is what. I find Honeycrisp particularly challenging to tell apart (it is Honeycrisp, after all). I also looked at buds with a hand lens, but found I couldn’t distinguish the vegetative vs. the floral buds very readily with it. 
•  After getting into the swing of things, each block was taking me about 70 minutes to fully assess. This does not include the time it took to cut the limbs from the orchard. 

So, I recommend giving it a try if you have the time and interest. As stated above though, it can be very difficult to tell them apart, so you might want to prune lightly now, and then make more precise pruning adjustments after green tip when you can tell the buds apart on the tree. Feel free to call Mike Basedow or Dan Donahue with questions.    

Figure 1.   Cutting buds to evaluate under the scope. Try to cut as close to down the center as possible to make the floral tissues easier to see.

Figure 2.     My scope setup. A dissecting scope like this can be purchased online for about $100.

Figure 3. A floral bud (top) vs a vegetative bud (lower). The vegetative bud is narrow, and only shows leaf primordia at the tip of the bud. The floral bud is more rounded, and shows light green floral tissues at the tip of the bud. Photo credits courtesy of Jon Clements and Win Cowgill.