Applying Precision Agriculture To Tree Fruit

 

Advertisement

How are pruning and fruit thinning like precision agriculture? In tree fruit, pruning has long been considered an art, requiring the skill of a surgeon and the insights of a poet. Fruit thinning is viewed as an excruciatingly tedious and expensive hand process, and/or a spray program relying on hunches and wishful thinking.

Precision ag is the opposite, relying on accurate measurement, statistics, and modern technological tools. More like a robot with a two-year degree in agronomy who doesn’t care about the weather or time of day.

Precision ag conjures up images of a very large GPS-equipped tractor dispensing a variable rate application of seed, fertilizer, lime in a very large corn field, or perhaps a GIS-based brightly colored aerial map diagramming soil types and drainage patterns, or a photographic image of relative vegetative vigor generated in an aerial flyover or even via satellite.

It would seem that precision ag, in which we seek to measure and manage variation at the field level, has such tremendous potential for tree fruit, since the cost (and potential return) on our input and management investment per unit area are so much higher than extensive crops like corn, wheat, and cotton.

Top Articles
Healthy Soils at Center of New $5 Million Initiative for California Citrus Growers

Additionally, the cost of management inaccuracies or inefficiencies in the early years of orchard establishment are compounded annually, so it would seem even more attractive to understand, characterize, and account for site variability from the get go.

Yet, precision ag remains largely conceptual for tree fruit.

Perhaps part of the problem is that precision ag has tended to highlight the use of tools like satellite imagery, information technology, and geospatial analysis, with a particular emphasis on satellite positioning systems like GPS. These tools are of more obvious and immediate application in field crops. In many orchards, for example, the canopy cover prevents reliable connection with satellites necessary for GPS.

If we shift focus, however, to the approach, rather than the tools, it would seem most tree fruit horticulturists are in fact applying the principles of precision ag every day. They have visceral knowledge of their need to measure and manage intra-field variation. In fact, it would be even better if we could manage at the plant to plant, or even the intra-plant level.

Here is where pruning starts to resemble precision ag. And as we finish up pruning in the Pacific Northwest, blessed with a relatively mild winter, we have already completed the first step in precision management. As pomologists have preached for years, crop load management should start early, with pruning.

This step defines the framework for subsequent management of vegetative and reproductive growth in the tree. As the industry moves unilaterally from low- to high-density plantings, pruning actually becomes more predictable and less poetic, but it is still done by hand. It’s not an easy job even when conditions are mild, and every year there are fewer workers willing to perform it. It is a practice that cries out for optimization.

Thinning For Precision

Mechanical hedging and topping is standard practice in many tree and small fruit crops, as a one-step process or as a setup for subsequent detailed hand pruning. While still mostly in the research arena, efforts are underway to apply mechanical shearing to tree fruit. As amenable genetics and high-density cropping systems evolve to accommodate such mechanical approaches, the tools of precision ag become more applicable.

I believe the same pattern exists in fruit thinning. It is the ideal candidate for precision ag. We certainly need to understand a lot more about the reproductive biology and physiology of pome and stone fruits to claim we are engaged in precision ag, but there is some indication we are getting a lot closer.

Robust apple bloom thinning programs in Washington, when preceded by appropriate pruning and followed by appropriate postbloom spray programs, have dramatically reduced our biennial bearing cycle and created a more reliable supply. As the accompanying graphic illustrates, year-to-year fluctuations in apple crop production have been reduced from 20% to less than 5%.

Bloom and postbloom apple thinning programs are both of great importance in the West (for specific suggested guidelines, go to http://jenny.tfrec.wsu.edu/eb0419/web/Bioregulators), whereas postbloom programs remain the chief means by which Eastern growers manage their crop load. Recently, the mystery and art of these programs has been greatly reduced by the pioneering work of Alan Lakso and Terence Robinson at Cornell University’s Geneva research station. Lakso’s carbohydrate model, still under development but already very useful, is a precision ag tool to optimize this critical step in orchard management.

More research will create the knowledge and tools to bring precision to tree fruit growers. Better sprayers and more accessible training systems will help. In fact, I believe it is inevitable that both pruning and fruit will soon include more mechanization and precision ag tools. Already two exciting research projects in the U.S. are close to making that happen. Learn more at www.abe.psu.edu/scri/picturesvideos.html and www.cascrop.com.

These and other projects are finally bringing the benefits of precision ag to address vexing tree fruit production challenges. Soon enough, digital imaging, information technology, vehicle positioning, and geospatial analysis will help further reduce biennial bearing. In the meantime, it’s time to finish pruning and get aggressive come bloom time.

1