By Tianna DuPont, Chris Strohm, Cody Molnar, Ricardo Naranjo, WSU Extension; Garret Bishop, GS Long. August 8, 2020
August and early September are good times to remove trees infected with X-disease phytoplasma and Little cherry virus. Quick removal reduces the time infected trees are providing a source of the pathogen for insects to move around. Late summer/ early fall applications of herbicides are likely readily translocated to roots and can identify root grafted adjoining trees.
General recommendations for tree removal include: 1) apply insecticide before tree removal to limit spread; 2) remove infected trees; 3) apply glyphosate to cut stump or frill to identify root grafted trees and kill roots or remove as many roots as possible and test adjoining trees; 4) if more than 20% of block is infected consider whole block removal. Timely removal of infected trees which are the source of spread is most important.
Below are the first three of six case studies on tree removal.
Mattawa case study
Dale Goldy is removing a block of Bing on Mazzard and a Block of Bing on Giesla 6 in the Mattawa area. They have tried herbicide application with the speed sprayer for removal of an entire block and felt it was not effective in killing the whole tree. This year, for 32-42 inch circumference trees (13 inch diameter) they are drilling 4 to 5 holes per tree about 4 ½” deep and 1/2” diameter at a 45 degree angle down and applying a 100% glyphosate concentration to fill holes with a handheld sprayer. They are keeping the block soil moisture at about 60% field capacity to make sure there is enough moisture for trees to move the glyphosate through the plant. Dale feels it is important to remove trees quickly so leafhoppers are not moving the phytoplasma around and he has time this fall to fumigate once the soil cools down. Three weeks after application all trees had significant herbicide injury with about 90% showing symptoms in all leaders. Root suckers also showed herbicide injury a good sign that roots were affected. We will assess root death when trees are removed.
Orondo Case Study
In mid May 2019 we trialed two treatments for tree removal at a block in Orondo of Rainier cherries on Mazzard where trees had tested positive for X-disease phytoplasma last fall. Treatments applied to 35 trees included a 50:50 glyphosate and water concentration – 2”deep holes every 4” with 4ml/hole dilute (3/8”diameter hole) and 100% glyphosate concentration 1”deep holes every 4”with 2 ml/hole concentrate (3/8”diameter hole). Two weeks after herbicide application all trees had 50-80% damage with severe yellowing to browning and death from herbicide treatments. None of the adjoining trees had noticeable herbicide injury. After 4 weeks only 5 adjoining trees showed herbicide injury. Spring may not be a good time of year for herbicide treatments to translocate to roots and adjoining trees.
Yakima Case Study
On July 23, 2019 a trial was conducted in Bing on Gisela 12 with five herbicide treatments for tree removal. Two treatments of interest were a 100% glyphosate concentration applied with a paintbrush to the cut stump at the interface of the bark with the wood/cambium and a notch treatment where 4 notches with 5 ml per notch of 50% glyphosate were applied (See full report.). Four weeks after herbicide application trees in the notching treatment were showing severe herbicide injury (death) in the above-ground portion of the tree (see figure 2). Four weeks after herbicide application only three adjoining trees showed minor herbicide injury to 1 or 2 limbs. At tree removal the spring after herbicides were applied root evaluation found the majority of roots were still living. The notch + glyphosate treatment had significantly larger numbers of injured and dead roots. However, no treatments had near 100% root death. The notch + glyphosate treatment performed best.
Figure 4. Trees in notch + glyphosate injection treatment 4 weeks after herbicide application.
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