jmcextman: “Half-baked” Research 2021: Part 1 - “Precision” Crop Load Management

Thursday, December 23, 2021

“Half-baked” Research 2021: Part 1 - “Precision” Crop Load Management

2021 was a year of – how shall I say it? – “half-baked” research. With a couple exceptions, too many minor research projects producing variable (aka dubious?) results. But I like to document “stuff.” So I am going to write up some “research” I did during the 2021 growing season for “what it’s worth?” (Hopefully something!) So here is “Half-Baked” Research 2021: Part 1 - “Precision Crop Load Management.”

In April 2021, in a commercial orchard “we” (meaning the grower and I) attempted to initiate a full-fledged research project per a protocol developed by the PACMAN group. PACMAN being “Precision Apple Crop load MANagement,” or as some prefer to call it Precision Crop Load Management (PCLM) of apples. The protocol was developed to address Objective 1. of PACMAN - “Develop and disseminate user-friendly computer-based models and comprehensive crop load management strategies for apple to achieve optimal crop load and maximize crop value.” Real PACMAN researchers in WA, MI, NY, NC, and VA are also following the protocol(s), which basically are as follows:

For Experiment 1 – Pruning treatments: At green tip, reduce the total number of spur floral buds per tree to 50, 100, 150, 200, 250, 300, 350, or 400 with a target of 8 trees at each level. Thinning treatments: 1) Hand thin at full bloom to 2 flower per cluster then thin to single fruitlet (largest) at 10mm fruit size, 2) Chemically thin at bloom with lime sulfur and fish oil guided by the pollen tube growth model, at Petal Fall with NAA+Sevin and 12mm with Maxcel+Sevin if needed. Data collection to include: TCSA, final floral bud number per tree at bloom, final fruit number per tree at harvest, yield, average fruit size, average fruit red color, either actual packout (size and color) or calculated packout from mean fruit size and mean color and using a normal distribution to estimate number of boxes per acre in each size and color category.
For Experiment 2 – At green tip, reduce total number of spur floral buds per tree to 200 on all trees (2 times the target fruit number of 100) The pruning must be done at green tip when floral spur buds can be easily distinguished from vegetative buds. 4 levels of crop load (3, 6, 9, and 12 fruits/cm2 TCSA). At full bloom reduce the number of clusters per tree to the assigned crop load (assuming only 1 fruit per cluster) by removing all flowers of a cluster. Secondly reduce the number of flowers per cluster to 2 (king and L3 lateral flower). Thirdly, at 10mm fruit size reduces the number of fruits/cluster to the desired crop load by hand thinning leaving only 1 fruit per cluster (the largest fruit). No chemical thinning.

All sounded like a good idea. On paper at least. But after thinking about the whole thing longer – and after flagging experimental trees, and starting to follow the protocols – we realized, amongst all the six million other things we had to do during the spring, and all the other projects I had going on (more on all that with upcoming blog posts) we simply could not follow through with all the treatment and data collection protocols. So, what actually happened?

The pruning treatments (Experiment 1) were accomplished on Gala trees. (Despite some grumbling by the grower.) Grower chemically thinned, however, pretty much at will. Farm crew avoided (I believe) hand thinning our flagged treatment trees. In September, we (thanks Jim Krupa) counted the number of apples remaining on the flagged treatment trees across eight replications. Observation of the pruning severity treatment trees was interesting, and we all agreed we liked the look of the Gala apples on the 50 and 100 buds left after green-tip pruning. At the higher bud densities, the Gala apples were “small.” Although the grower said – being a pick-your-own operation – the more apples the better. They agreed, however, they want quality, good-tasting apples for their customers, something they hang their hat on, and aggressively attempt to manage crop load for quality and annual bearing. Want to see the results of the fruit count per tree (across 8 trees per treatment counted) at harvest?

If I were to plot that, because we, as scientists, that’s just what we do, make charts:

Not a bad “fit.” (Red line.) Where is the sweet spot? I think where 100 meets 100, i.e., prune to a bud load of about 100 buds, hope for one apple set per bud, equals 100 apples per tree at harvest. Hope. Maybe best to leave a few more buds to hedge your bets. Picts of the different pruning treatments vs. crop load at harvest follow at the end. You be the judge.

Oh yea, Experiment 2, we did not follow through much at all. Well, the grower did attempt to reduce the 4 levels of crop load – to 3, 6, 9, and 12 fruits/cm2 TCSA – per the protocol, but only on a few reps. These were Honeycrisp trees BTW. Did not see much going on there in the end. We did some fruit counts at harvest. I won’t ever report that because there is nothing there. Half-baked? Yup.

In the Gala experiment, I do think we learned something – that we may be under-pruning if the goal is large Gala’s. We kind of knew that, but this little bit of work bears that out. It will be very interesting to see the results from the real research, but I do know a preliminary analysis of the data suggests that “at a given crop load, larger fruits are produced in some climates than in other climates.” (2021 PCLM Report, T. Robinson et. al.)

Thanks to Tougas Farm for letting this research happen (despite some grumbling) and to Jim Krupa of UMass who so aptly helped me count apples and and held the treatment flagging for the pictures!