Let there be light
More light means more fruit.
Dr. Todd Einhorn checks the light level inside a shade-covered pear tree.
Ideally, the long-term future will bring a dwarfing rootstock to enable pear growers to switch to more efficient production systems, but a more immediate need is to enhance production on the large trees they already have in the ground.
Dr. Todd Einhorn, horticulturist with Oregon State University in Hood River, is conducting research on how to improve quality and yield in traditional orchards, using modern tools such as a reflective fabric mulch.
Einhorn said there's a direct relationship between the amount of light reaching the tree and the amount of fruit bud regeneration. More light typically means better fruit set, better growth, and more carbohydrates in the tree.
However, in large, old pear trees, very little light reaches the inner third of the canopy, which tends to be composed entirely of structural wood, rather than fruiting wood. There's also a lot of shading in the middle third of the tree, resulting in a lack of fruit buds. The bulk of the crop is grown on the outside third of the tree, where the light is.
Einhorn is experimenting with a reflective fabric to increase the amount of light reaching the inner parts of the canopies. He will study how the increased amount of light reflected into the tree affects fruit buds and the health of the spurs. He will also study fruit growth and the ratio of fruit to leaves. In apples, reflective fabrics have resulted in significantly higher yields.
For the trial, he installed the fabric at full bloom. He will remove some after 65 days, and leave the rest down until harvest, and compare those to treatments with no cloth at all.
He has also enclosed eight trees in a 60 percent shade cloth so the outer part of the canopy has about the same light level as the inner portion of the typical large pear tree. He will study fruit size, and fruit quality and yield over a number of years. By setting the shade at a certain percentage and measuring the proportion of sunlight, he hopes to be able to define a shade threshold for floral bud induction, fruit set, and fruit size and quality.