Field evaluation of leafhopper controls for X-disease management
Author: Tobin Northfield, Louis Nottingham
Published: 2022
Summary: X-disease is currently at epidemic levels in Pacific Northwest stone fruit orchards. A recent survey of 26% of the PNW cherry industry acreage revealed losses of $120 million due to a combination of X-disease and Little cherry virus 2. While the symptoms of these pathogens are indistinguishable, recent test results suggest the vast majority (93%) of diseased trees are infected with X-disease phytoplasma rather than Little cherry virus 2. The leafhoppers that vector X-disease are abundant after harvest, when phytoplasma titers are high, suggesting this is a key time for phytoplasma transmission. Here, we evaluated two postharvest cultural controls, Surround-kaolin clay and Extenday ground cover, that deter leafhoppers from feeding on trees at the block (Extenday) or plant (Surround) level and potentially prevent transmission. Extenday was effective, reducing leafhoppers by 81% in Wenatchee region cherries in 2020 and 88-91% in Wenatchee and Yakima region cherries in 2021, compared to controls. In year two there was a 50-fold difference in peak densities across the control blocks in Wenatchee and Yakima regions, but these effects were consistent. In 2020 and 2021 high-pressure cherry blocks in the Wenatchee and Yakima region, Surround reduced season-wide leafhopper numbers by 47-48%. Furthermore, the Surround reduced the mean height at which leafhoppers were caught compared to the control plots, suggesting they may not be moving into the trees as much. In Yakima region cherries the clay did not significantly reduce leafhopper numbers, but mean counts were very low, peaking at less than 2 leafhoppers per trap (2-week trapping period). Surround also did not reduce leafhopper numbers in nectarine blocks, potentially due to the late harvest date. In summary, we have identified two cultural controls, with one (Extenday) effective at reducing leafhopper numbers in either high pressure or low pressure blocks, and another (Surround) that reduced leafhopper numbers in high pressure blocks, although not to the same effect as Extenday and also appeared to reduce the movement up into trees from the groundcover.
