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Tree Removal Methods for X-Disease and Little Cherry Disease- Preliminary Trial Report

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Preliminary Trial Report

by Tianna DuPont, WSU Extension Specialist, Assistant Professor, Washington State University Extension, Wenatchee, WA; Cody Molnar, WSU Extension Information Technology Transfer, Yakima, WA; Garett Bishop, GS Long, Yakima, WA; Ricardo Naranjo, WSU Extension Assistant. March 4, 2021

Summary

Immediate removal of trees infected with X-disease phytoplasma and Little cherry virus is essential to limit the spread of these devastating pathogens. Quick removal reduces the time infected trees are providing a source of the pathogen for insects to move around. General recommendations for tree removal include: 1) apply insecticide before tree removal to limit spread; 2) remove infected trees; 3) apply glyphosate via 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 trees are removed because herbicide injury identifies root grafting test adjoining trees 5) if more than 20% of the block is infected consider whole block removal.

In 2019 and 2020 four trials and four grower case studies were conducted to clarify recommendations for tree removal when trees are infected with Little cherry disease or X-disease. This study provides preliminary data showing that glyphosate herbicide applications during tree removal for X-disease and Little cherry disease can create herbicide injury to adjoining trees (helping to identify root-grafted infected trees) and reduce the number of living roots which may transfer pathogens to uninfected trees. Herbicide applications when trees were actively growing had higher efficacy compared to fall applications and water stress appeared to limit effectiveness. Herbicide application with a frill method, drilling or notching into a living tree, was more effective than cut stump application in two of three studies. However, differences were sometimes small, and cut stump applications were also effective in some studies. Herbicide injury to adjoining trees was only apparent in Mazzard rootstocks, indicating that root grafting and the need for herbicide application during tree removal for X-disease and Little cherry disease is likely less in semi-dwarf type rootstocks. Further study is needed to determine best herbicide application rate. Rates of 0.5 to 2.5 fl oz per 30-inch tree were used commonly in these studies.

Introduction

X-disease and Little Cherry Disease are at epidemic levels in Washington and Oregon. X-disease is caused by X-disease phytoplasma and Little cherry virus 1 and 2 cause Little Cherry Disease. Tree removal combined with vector management are essential to slow the spread of these pathogens. No known strategies effectively cure infected trees and as such these trees must be removed to eliminate the source of pathogen spread.

The objective of this project is to clarify recommendations for tree removal when trees are infected with Little Cherry/ X-disease. It is thought that glyphosate herbicide application to infected trees using either a cut stump or frill (drill) application can both kill roots of the infected tree and may help identify adjoining root grafted trees by showing leaf herbicide injury. Managers would like clarification on effective application rates, application timing and methods as well as whether herbicide application is efficacious.

Methods

Four trials were conducted at Wapato, Brays Landing, Zillah and Quincy WA (Table 1). Treatments (Table 3) were applied to single trees designated in a randomized complete block with 5 replications at Wapato, 16 replications at Brays Landing, 5 replications at Zillah, and 8 replications at Quincy with at least two untreated trees between treated trees. Treatments were applied immediately after stumping/frill unless otherwise noted. Trials were evaluated approximately two, four, eight or more weeks after herbicide application (Table 2). Adjoining trees were evaluated for herbicide injury from root grafting on an herbicide percent damage and severity scale where severity of 0 equals green and healthy and 3-4 equals browning and leaf death. The percentage of the adjoining trees with herbicide damage was rated as none (0-4%), slight (5-15%), low (15-39%), medium (40-69%) and high (<70%). Root death of treated and untreated experimental trees was evaluated by examining 10 small roots (< 10 mm diameter) and 5 large roots (10-30 mm diameter) per tree and rating on a 1 to 7 scale where 1 equals living/white and 7 equals dead. Treatment effects were analyzed using an analysis of variance, proc glm with block as a random effect (SAS 9.4). Post hoc pairwise comparisons between treatments were determined using a T test of ls means. All P values were computed using a threshold of 0.05.

image shows a dead tree next to a stump in an orchard with otherwise healthy-looking cherry trees.
Fig. 1. Herbicide application during tree removal for X-disease and Little cherry disease can help identify adjoining trees that are root grafted to infected trees. Trees root grafted to infected trees are likely infected even though symptoms may have not yet developed.

 

side-by-side comparison of brushing glyphosate onto the top of a cut stump versus spraying it on.
Fig. 2. Cut stump herbicide applications were applied either using a paintbrush or hand sprayer to coat the entire cut surface of the stump concentrating on the cambium layer.

 

Multi-panel image showing the steps of applying the herbicide to a notch or drill hole in the tree trunk.
Fig. 3. Frill herbicide applications were done by notching into living trees with a chain saw or drill and applying glyphosate to the notch/frill. Applications to the living trees may help with herbicide uptake and allow orchardists to make additional applications if the tree does not die.

 

Table 1. Study site descriptions.
Study location Variety Rootstock Average Tree Circumference (in) Tree spacing (ft)
Wapato Bing Gisela 12 24 8 x 16
Brays Landing Rainier Mazzard 36 10 x 15
Zillah Santina Gisela 12 11 4.5 x 12
Quincy Skeena Mazzard 32 12 x 12

 

Table 2. Study treatment application and evaluation dates.
Study location Treatment date 2-week evaluation 4-week evaluation 8-week evaluation Root evaluation 1 Root evaluation 2
Wapato July 23, 2019 Aug 8, 2019 Aug 20, 2019 Oct 11, 2019 Apr 24, 2020
Brays Landing May 14, 2020 Jun 4, 2020 —- July 8, 2020 Oct 21, 2020
Zillah Aug 6, 2020 Aug 20, 2020 Sept 3, 2020 Sept 3, 2020 Oct 9, 2020
Quincy Sept 14, 2020 Sept 29, 2020 Oct 13, 2020 Oct 13, 2020 Nov 19, 2020

 

Table 3. Tree removal treatments.
Treatment Herbicide Rate undiluted product
Notes
ml/ 2.5 cm fl oz/ in fl oz/ 30 in
tree circumference
Wapato
Cut stump 100% glyphosate glyphosate 100% ND2 ND ND 100% glyphosate concentration applied with a paintbrush to the cut stump at the interface of the bark with the cambium.1
Cut stump 50% glyphosate glyphosate 50:50 H20 3.6 0.13 3.75 50:50 solution of glyphosate:H20 applied with a liter spray bottle to the cut stump at interface of  bark and cambium. Est 6 oz solution (3 oz AI)/ tree.
Cut stump 50% glyphosate+ ammonium sulfate + surfactant glyphosate 50:50 H20 3.6 0.13 3.75 50:50 solution of glyphosate + 1% NH42SO4 (5.4 oz per liter) + surfactant (0.5% = 5 ml/ liter) applied with a liter spray bottle to the cut stump at the interface of the bark and the cambium. Est 6 oz solution (3 oz AI)/ tree.
Frill-dilute application glyphosate 50:50 H20 0.4 0.01 0.4 4 notches per 24 in circumference tree. 5 ml 50:50 glyphosate:H20 solution per notch.  Trees stumped 4 weeks after application. 20 ml (0.7 oz) solution/ tree or 0.35 oz AI/ tree.
Cut stump, next day 100% glyphosate glyphosate 100% ND ND ND 100% glyphosate applied with a paintbrush the day after stumping (see 100% glyphosate).
Zillah
Cut stump 100% glyphosate glyphosate 100% 2.0 007 2 20 ml of 100% glyphosate concentration applied with a paintbrush to the cut stump across the entire surface making sure to coat the interface of the bark with the wood/cambium within five minutes of cutting.
Frill-dilute application glyphosate 50:50 H20 1.0 0.03 1 4 ml applied per 2” deep hole drilled every 3 in at a 45° angle (3/8” diameter hole). Trees stumped 1-4 weeks after herbicide symptoms are noticeable. Avg 16 ml (0.5 oz) solution/tree or 8 ml (0.25 oz) AI/tree).
Cut stump, No-herbicide control N/A 0 0 0 Stump with no herbicide.
Brays Landing
Frill-dilute application glyphosate 50:50 H20 0.5 0.02 0.5 Frill with drill (3/8 in) 2 in deep holes every 4 in around circumference of tree. 4 ml of 50:50 solution per hole. 36 ml solution (1.3 oz), 18 ml AI (0.6 oz) per 36 in circumference tree.
Frill-concentrate application glyphosate 100% 0.5 0.02 0.5 Frill with drill (3/8 in) 1 in deep holes every 4 in. 2 ml 100% glyphosate per hole. 18 ml AI (0.6 oz)/ 36 in circumference tree.
Quincy
Cut stump 100% glyphosate glyphosate 100% 1 0.04 1 20-30 ml (1 oz) 100% glyphosate applied per tree to the entire cut surface with a paint brush making sure to coat the cambium within several min of cut.
Frill-concentrate application glyphosate 100% 1 0.04 1 4 ml 100% glyphosate per hole drilled every 4 in in at a 45° angle (3/8” diameter hole). 32 ml (approx. 1 oz) per 32 in circumference tree.
Cut stump, No-herbicide control N/A 0 0 0 Stump with no herbicide.
1Treatments applied immediately after stumping trees.
2ND = Not Determined

 

Results

At Wapato only two trees had a very small amount of herbicide leaf injury to trees adjacent to treated trees. One was from the cut stump, next day 100% glyphosate treatment (5-15%, yellowing), and another from the cut stump 50% glyphosate treatment (5-15%, yellowing) (Table 4). This may be due to low rates of herbicide used in this trial, the fact that trees were water stressed due to low irrigation applications after harvest, or to the rootstock Gisela 12. At Wapato herbicide treatments resulted in low root death (Table 5, Figure 5). The frill-dilute application had the greatest root death (29% root death and 56% root injury).

At Brays Landing three trees adjacent to treated trees out of 53 trees had moderate herbicide injury (40-70% of tree) at severity rating 2 (yellowing) (Table 4). All trees with herbicide injury were in the frill dilute versus frill-concentrate application. Trees at this site were stumped four weeks after treatment and stumps left until the fall when trees were evaluated in October. Five months after application 97-100% of roots were dead in both treatments (Figure 6). As trees had been stumped it is possible that root death was natural versus herbicide induced.

At Zillah no adjacent trees showed signs of herbicide injury at four or eight weeks post-treatment. Lack of herbicide injury to adjoining trees may be due to smaller Gisela 12 rootstocks with little root grafting potential. The frill-dilute glyphosate application had 48% root death and the cut stump 100% glyphosate application had 31% root death four weeks after herbicide treatment. Both herbicide treatments had significantly higher root death than the cut stump no-herbicide control. At eight weeks, the frill-dilute application had 48% root death significantly different than cut stump 100% glyphosate application with 23% root death. Both treatments had significantly higher root death than the cut stump no-herbicide control.

At Quincy the cut stump 100% glyphosate treatment had two trees with herbicide injury to adjoining trees where more than 70% of the tree was affected with average severity of 3-5 (brown-dead) and two trees with 40-70% of the tree affected. The frill dilute treatment had one tree with 70% or more of tree affected at severity 5 (dead). The cut stump no-herbicide control had one tree with slight yellowing and one tree with 40-70% of the tree affected. Both of these trees appear to have bacterial canker which would have created symptoms before the trial was initiated but symptoms were not documented. After eight weeks the frill-dilute application had 20% root death compared to 3% in the cut-stump 100% glyphosate and cut stump no-herbicide control (Figure 7).

This illustrates what happens to an adjacent tree where the roots of the herbicide treated tree are grafted together. it results in tree death on the non-target tree.
Fig. 4. Example of herbicide injury to an adjoining tree root grafted to a tree which received glyphosate application at the time of tree removal.

 

Table 4. Percent of adjoining trees with herbicide injury at four weeks.
fl oz glyphosate/ tree** % of tree
40-70%
% of tree
70% +
Severity*
Wapato
Cut stump 100% glyphosate ND 0 0
Cut stump 50% glyphosate 3.75 0 0
50% glyphosate+ ammonium sulfate + surfactant 3.75 0 0
Frill-dilute application 0.42 0 0
Cut stump, next day 100% glyphosate ND 0 0
Zillah
Cut stump 100% glyphosate 2.0 0 0
Frill-dilute application 1.0 0 0
Cut stump, no-herbicide control 0.0 0 0
Brays Landing
Frill-dilute application 0.5 11 0 1-2
Frill-concentrate application 0.5 0 0
Quincy
Cut stump 100% glyphosate 1 7 7 3-5
Frill-concentrate application 1 0 4 5
Cut stump, no-herbicide control 0 4 0 2-5
*0 equals green and healthy and 3-4 equals browning and death

**undiluted product

 

Table 5. Root injury (percentage) rated at stump removal in Wapato, WA the spring after treatment applications.1
AI
fl oz/
tree
Root Death (%)2 Root Injury (%)3
treatments small large total small large total
Cut stump 100% glyphosate ND 6 ± 4 b 0 ± 0 b 4 ± 3 a 26 ± 7 b 32 ± 14 abc 28 ± 4 a
Cut stump 50% glyphosate 3.75 6 ± 2 b 0 ± 0 b 8 ± 3 a 20 ± 4 bc 24 ± 10 bc 22 ± 8 a
50% glyphosate + ammonium sulfate + surfactant 3.75 4 ± 2 b 8 ± 5 ab 5 ± 3 a 14 ± 7 bc 44 ± 15 ab 24 ± 5 a
Frill-dilute application 0.4 34 ± 4 a 20 ± 9 a 29 ± 3 b 52 ± 6 a 64 ± 12 a 56 ± 29 b
Control (next day) ND 2 ± 2 b 0 ± 0 b 1 ± 1 a 8 ± 4 c 12 ± 5 bc 9 ± 1 a
1Treatments followed by different letters after the number are statistically different (p<0.05).
2Roots with a rating of 5 to 7 on a 1 to 7 scale were considered dead.
3Roots with a rating ≥ 3 were considered to have root injury.

 

Table 6. Root injury (percentage) rated four and eight weeks after treatment application at Zillah, WA.1
4 weeks fl oz/
tree
Root Death (%)2 Root Injury (%)3
treatments small large total small large total
Cut stump 100% glyphosate 2 30 ± 13 a 32 ± 16 a 31 ± 15 a 30 ± 13 a 36 ± 18 ab 32 ± 15 a
Frill-dilute application 1 52 ± 4 a 40 ± 13 a 48 ± 5 a 52 ± 4 a 52 ± 8 a 52 ± 4 a
No-herbicide control 0 0 ± 0 b 0 ± 0 a 0 ± 0  b 0 ± 0 b 0 ± 0 b 0 ± 0 b

 

8 weeks fl oz/
tree
Root Death (%)2 Root Injury (%)3
treatments small large total small large total
Cut stump 100% glyphosate 2 22 ± 1 ab 24 ± 12 a 23 ± 7 a 52 ± 11 a 76 ± 15 a 60 ± 12 a
Frill-dilute application 1 38 ± 6 b 68 ± 12 b 48 ± 7 b 64 ± 4 a 88 ± 8 b 72 ± 3 a
No-herbicide control 0 0 ± 0 a 0 ± 0 a 0 ± 0 c 2 ± 2 b 4 ± 4 b 3 ± 2 b
1Treatments followed by different letters after the number are statistically different (p<0.05).
2Roots with a rating of 5 to 7 on a 1 to 7 scale were considered dead.
3Roots with a rating ≥ 3 were considered to have root injury.

 

Table 7. Root injury (percentage) rated at Brays Landing, WA site five months after treatment application date.1
fl oz/
tree
Root Death (%)2 Root Injury (%)3
treatments small large total small large total
Frill-dilute application 0.5 95 ± 3 a 100 ± 0 a 97 ± 2.4 a 95 ± 3 a 100 ± 0 a 97 ± 2 a
Frill-concentrate application 0.5 100 ± 0 a 100 ± 0 a 100 ± 0 a 100 ± 0 a 100 ± 0 a 100 ± 0 a
1Treatments followed by different letters after the number are statistically different (p<0.05).
2Roots with a rating of 5 to 7 on a 1 to 7 scale were considered dead.
3Roots with a rating ≥ 3 were considered to have root injury.

 

Table 8. Root injury (percentage) rated at Quincy, WA site four and eight weeks after treatment application date.1
4 weeks fl oz/
tree
Root Death (%)2 Root Injury (%)3
treatments small large total small large total
Cut stump 100% glyphosate 1 4 ± 3 a 8 ± 4 a 5 ± 3 a 8 ± 3 a 23 ± 10 a 13 ± 4 a
Frill application 1 7 ± 4 a 23 ± 12 a 11 ± 4 a 9 ± 4 a 40 ± 9 a 19 ± 5 a
No-herbicide control 0 7 ± 5 a 21 ± 14 a 7 ± 5  a 7 ± 5 a 14 ± 8 a 10 ± 6 a

 

8 weeks AI
fl oz/
tree
Root Death (%)2 Root Injury (%)3
treatments small large total small large total
Cut stump 100% glyphosate 1 3 ± 2 a 5 ± 3 a 3 ± 2 a 5 ± 3 a 13 ± 5 a 8 ± 3 a
Frill application 1 19 ± 4 b 51 ± 3 b 20 ± 3 b 23 ± 4 b 51 ± 7 b 32 ± 4 b
No-herbicide control 0 7 ± 3 a 6 ± 4 a 3 ± 2 a 7 ± 4 a 49 ± 4 a 7 ± 3 a
1Treatments followed by different letters after the number are statistically different (p<0.05).
2Roots with a rating of 5 to 7 on a 1 to 7 scale were considered dead.
3Roots with a rating ≥ 3 were considered to have root injury.

 

Multi-image comparison of root death preceded by the different treatments.
Fig. 5. Representative Root Death Images from the Wapato site: Cut Stump 100% Glyphosate (A), Cut stump 50% Glyphosate (B), 50% glyphosate+ ammonium sulfate + surfactant (C), Frill Dilute (D), and Control Next Day (E).
side-by-side comparison of root death from dilute and concentrated treatments.
Fig. 6. Representative Root Death Images from the Bray’s Landing Site: Frill Dilute (A) and Frill Concentrate (B).
Side-by-side-images illustrating the difference in severity of the treatments compared to the control.
Fig. 7. Representative Root Death Images from the Quincy Site: 100% Glyphosate (A), Frill Application (B), and No-Herbicide control (C).
Table 9. Treatment details, root death, and herbicide injury to adjoining trees in non-replicated grower case studies.
Glyphosate application Glyphosate application rate Root
death
Herbicide
injury to
adjoining trees
Case
study
Rootstock Timing Type ml/cm ml/ 2.5 cm fl oz/ in fl oz/ 30 in
5 Mazzard late July cut stump 1.00 2.5 0.10 2.57 80% none
6 Krymsk® 6 early Aug cut stump 0.80 2.0 0.07 2.03 38% none1
7 Gisella 6/ Mazzard mid July Frill (notch) 0.70 1.8 0.06 1.78 98% none
1 Mazzard mid July Frill (drilled) 0.81 2.0 0.07 2.10 88% NR2
1Grower has seen injury to adjoining trees on Mazzard using this method.
2All of the trees in this orchard were treated and so adjoining trees could not be rated.
*Note case studies 2-4 in case study articles correspond with replicated trials above.

 

Discussion

Tree removal combined with vector management are essential to slow the spread of X-disease phytoplasma and Little cherry virus 2. Infected trees are a source of the pathogen in the orchard. For effective tree removal managers should scout their orchards for symptoms beginning a week before harvest when symptomatic fruit start to become easily distinguished from unripe fruit. Scouts should mark symptomatic trees. If X-disease or Little cherry disease is confirmed in the block, clearly symptomatic trees should be removed as soon as possible. If X-disease or Little Cherry Virus have not been confirmed in the block or symptoms are not obvious managers should sample trees and send for laboratory analysis. When removing trees treat insect vectors before removal to limit the movement of infected insects to adjoining trees. Herbicide applications when removing infected trees can both kill roots of the infected tree and may help identify adjoining root grafted trees by showing leaf herbicide injury. Remove trees adjacent to infected-removed trees which show herbicide injury. Then test trees adjacent to trees with herbicide injury that are removed. General recommendations for tree removal include: 1) apply insecticide before tree removal to limit spread; 2) remove infected trees; 3) apply glyphosate via 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 trees are removed because herbicide injury identifies root grafting, test adjoining trees 5) if more than 20% of block is infected consider whole block removal.

This study provides preliminary data demonstrating that both cut stump and frill applications of glyphosate can create herbicide injury to adjoining trees (helping to identify root-grafted infected trees) and reduce the number of living roots which may transfer pathogens to uninfected trees. The frill glyphosate application provided significantly greater root death compared to cut stump glyphosate applications in two of three trials. However, root death in glyphosate treated trees was still quite low in many cases. In grower case studies where 1.75 to 2.1 oz per tree (30-inch circumference) was applied as a frill application in mid-July to actively growing trees 88% and 98% of roots were rated as dead (Table 9). Frill applications may help growers increase the effectiveness of herbicide applications.

Herbicide injury to adjoining trees was only detected in trees on Mazzard rootstock in replicated trials. No herbicide injury to adjoining trees was detected on Gisela rootstock. Grower case studies agreed with these findings where growers reported only observing herbicide injury to adjoining trees in Mazzard rootstocks. Root grafting and the need for herbicide applications may be less important for trees grafted to smaller rootstocks.

Application timing of herbicides during active tree growth appears to be important for root death and translocation to adjoining trees. Both April and August application timings resulted in root death in this study. September applications did not result in root death at the time of fall observation and may be too late for good herbicide movement into roots. In non-replicated case studies (Table 9) July application timings resulted in a high percentage of root death. Water applications also appear to be important. In one site (Wapato) water to trees was limited after harvest when herbicide applications were applied and may have limited herbicide transfer to roots. In contrast in case study 1 the grower kept soil moisture at 60% of field capacity and 98% of roots died.

Further study is needed to determine best herbicide application rate. Initial trials included in this study had rates as low as 0.5 fl oz of glyphosate per 30-inch circumference tree. A rate of 0.5 fl oz per 30-inch tree as a frill application resulted in 100% root death in study Brays Landing but only 30% in study Wapato. In contrast in grower case studies where high root death was achieved, approximately 2 fl oz per 30-inch tree was more commonly used.

This study provides preliminary data showing that glyphosate herbicide applications during tree removal for X-disease and Little cherry disease can create herbicide injury to adjoining trees (helping to identify root-grafted infected trees) and reduce the number of living roots which may transfer pathogens to uninfected trees. Herbicide applications when trees were actively growing had higher efficacy compared to fall applications and water stress appeared to limit effectiveness. Application with a frill method, drilling or notching into a living tree, was more effective than cut stump application in two of three studies. However, differences were sometimes small, and cut stump applications were also effective in some studies. Herbicide injury to adjoining trees was only apparent in Mazzard rootstocks, indicating that root grafting and the need for herbicide application during tree removal for X-disease and Little cherry disease is likely less in semi-dwarf type rootstocks. Further study is needed to determine best herbicide application rate. Rates of 0.5 to 2.5 fl oz per 30-inch tree were used commonly in these studies.

ADDITIONAL INFORMATION

BMPs for tree removal for X disease and Little Cherry Virus infected trees http://treefruit.wsu.edu/article/bmps-for-tree-removal-for-x-disease-and-little-cherry-virus-infected-trees/

http://treefruit.wsu.edu/crop-protection/disease-management/western-x/

Tree Removal Case Studies for X-disease and Little cherry disease

http://treefruit.wsu.edu/article/tree-removal-case-studies/

http://treefruit.wsu.edu/article/tree-removal-case-studies-2/


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NOTE: Some of the pesticides discussed in this presentation were tested under an experimental use permit granted by WSDA. Application of a pesticide to a crop or site that is not on the label is a violation of pesticide law and may subject the applicator to civil penalties up to $7,500. In addition, such an application may also result in illegal residues that could subject the crop to seizure or embargo action by WSDA and/or the U.S. Food and Drug Administration. It is your responsibility to check the label before using the product to ensure lawful use and obtain all necessary permits in advance.


Contact

Img1380Tianna DuPont, WSU Tree Fruit Extension Specialist

Tree Fruit Research & Extension Center, Wenatchee, WA

tianna.dupont@wsu.edu, (509) 663-8181


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