2018 ASHS Annual Conference

Apple production in Washington State is distributed in five growing regions characterized by a semi-arid climate. However, thanks to the abundance of waters from the Columbia River though the territory this area produces the majority of apples in North America. Crop production in WA is challenged by several environmental factors, such as high light intensity, temperature and wind, that can cause stress to the trees and fruit damage (i.e. sunburn). For those reasons, protective netting is becoming a choice embraced more and more every year by WA growers in order to minimize losses in apple orchards. Originally developed as anti-hail protection, now shading nets can be specifically employed to modify the light spectrum and intensity hitting the orchard canopies by the use of different colors. A commercial orchard of ‘Cameron Select® Honeycrisp’ on Bud-9 orchard was planted in 2013 in Quincy (WA) and trained to V-system (4485 trees/ha). In spring 2015 shade pearl, blue and red nets (approx. 20% shade factor) were installed horizontally over the top of the orchard and deployed after bloom. The goal of our trial was to characterize the light intensity and light quality under three different colored nets and compare the modified light environment to the full sun-no net. Spectra of total light and scattered light (diffuse) were measured monthly by a spectroradiometer outside and underneath the colored nets each summer for two consecutive years (2016-2017). Transmittance of total light (%) for each colored net and scattered light (%) were measured and light intensity parameters (PAR, UV, Blue, Red, Far Red) were calculated. PAR, UV, Blue, Red, Far Red light in total light measures were always significantly lower under the nets compared to the uncovered controls. The scattered light data showed a higher intensity in the PAR range for the Pearl net compared to the other colored nets in both years. The highest PAR/UV ratio in full light measure was reported under Red nets in 2017. These results confirmed the beneficial effect of Pearl and Red nets for improving light quality in orchards and further studies can address the effects of the modified light on the tree physiology.