Progress report for GS23-288
Project Information
Ambrosia beetles (Xylosandrus spp.), wood-boring insects, and Phytophthora cinnamomi, a soilborne pathogen, are economically important and destructive issues in nursery trees. Like biotic stresses, abiotic stress also contributes to the declining health of nursery crops. Plants stressed with abiotic stress factors such as flooding, drought, and freezing have a decreased host defense mechanism and experience increased susceptibility to different diseases and pests. Flooding has become a problem in Tennessee and increasing flooding events are contributing to the increased attacks by the ambrosia beetles and Phytophthora cinnamomi. Flooded trees are susceptible to both ambrosia beetles and P. cinnamomi. Ethanol is a primary ambrosia beetle attractant; thus, stressed trees releasing it are more prone to attack and colonization by ambrosia beetles. Current chemical control measures are mostly inconsistent and variable and have negative consequences on the environment. Moreover, flood stress can affect insecticide efficacy since insecticide was ineffective at preventing ambrosia beetle attacks when container substrate moisture levels exceeded 50%. This necessitated the need for alternative sustainable management strategies. The specific objective is to explore the role of flooding and P. cinnamomi in predisposing trees to ambrosia beetle attacks and to test the effectiveness of plant defense elicitors Acibenzolar-S-methyl (ASM) (Actigard), and ASM + chlorothalonil (Daconil Action) for the control of P. cinnamomi and ambrosia beetles in container-grown flowering dogwoods exposed to flood stress conditions.
Objective 1. To understand the role of abiotic and biotic stressors in predisposing trees to ambrosia beetle attacks
The purpose of this objective is to assess the role of simulated flood and Phytophthora root rot caused by P. cinnamomi in predisposing flowering dogwood trees to ambrosia beetle attacks. This information will be helpful to growers to prepare for taking necessary management tactics.
Objective 2. To evaluate plant defense elicitors (i) acibenzolar-S-methyl (Actigard), and (ii) acibenzolar-S-methyl + chlorothalonil (Daconil Action) for controlling Phytophthora root rot and ambrosia beetles
The purpose of this objective is to find effective plant defense elicitors for the control of ambrosia beetles and P. cinnamomi in flowering dogwoods under simulated flood stress conditions.
Research
Objective 1. To understand the role of abiotic and biotic stressors in predisposing trees to ambrosia beetle attacks
Objective 1.1. To understand the role of flood stress in predisposing flowering dogwood to ambrosia beetle attacks
Two trials will be conducted from September through October (trial 1) in 2023 and in the summer of 2024 (trial 2) to understand how flood stress predisposes flowering dogwood trees to ambrosia beetle attacks. Two-year-old container-grown flowering dogwoods (average diameter of 1.7 to 2 cm) will be assigned to flooding and sufficient water. The experiments will be arranged in a randomized complete block design with ten single plant replications adjacent to the woodlot in McMinnville, TN. The flooding conditions will be maintained for 28 days. Flooding conditions will be imposed using a pot-in-pot system whereby the potted trees growing in a 19 L or equivalent pot will be placed into an outer, larger diameter pot (e.g., 26 L) lined with a plastic bag of 0.076 mm thickness (Ranger et al. 2013). Potting mix inside the container will be maintained fully submerged up to the tree crown. Trees assigned to sufficient water will receive water sufficient to keep the potting mix moist. Ambrosia beetle attacks will be recorded every other day after the initiation of water stress. On the 28th day, ambrosia beetle attacked plants will be returned to the laboratories and stored in the cooler (~11°C) until they were dissected. The number of attacks with gallery formation, gallery depth, galleries with fungal colonization, galleries with egg, larvae and adult will be recorded by dissecting the plants. Plant tissue samples will be collected in 7 and 14 days post-water stress and ethanol production will be quantified using solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS).
Objective 1.2. To understand the role of Phytophthora cinnamomi in predisposing flowering dogwood to ambrosia beetle attacks
Two trials will be carried out from September to October 2023 (trial 1) and in the summer of 2024 (trial 2) to observe the influence of Phytophthora cinnamomi infections on ambrosia beetle attacks. Flowering dogwood plants of average 1.8 cm diameter size will be inoculated with the P. cinnamomi, and non-inoculated plants represent control. After 6 days of inoculation, plants will be moved to the experimental site adjacent to woodlots. The plants will be arranged in a randomized complete block design with ten single plant replications. Plants will be monitored every other day to record ambrosia beetle attacks for 28 days. The number of attacks with gallery formation, gallery depth, galleries with fungal colonization, galleries with egg, larvae and adult will be recorded by dissecting the plants. Plant tissue samples will be collected in 7 and 14 d post-water stress and ethanol production will be quantified using solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS).
Objective 2. To evaluate plant defense elicitors (i) acibenzolar-S-methyl, and (ii) acibenzolar-S-methyl + chlorothalonil for controlling Phytophthora root rot and ambrosia beetles
Two trials will be conducted near the edge of a deciduous forest in the summer of 2025 at the Otis L. Floyd Nursery Research Center, Tennessee State University, McMinnville, TN. Dogwood trees will be preventatively treated with acibenzolar-S-methyl (ASM) (Actigard 50WG, Syngenta) and acibenzolar-S-methyl + chlorothalonil (Daconil Action, Syngenta) three days before initiating flood stress. The commercial product actigard contains 50% acibenzolar-S-methyl, while daconil action contains 53.94% chlorothalonil and 0.11% acibenzolar-S-methyl. They will be applied as drench and foliage to see which method is more effective. Drench application will be performed by applying 500 ml diluted ASM solution in the potting mix surrounding the base of the tree. The foliar application will be done by thoroughly spraying diluted solution to foliage and stem until runoff using a backpack CO2-pressurized sprayer with TeeJet XR8002VS nozzle at 30 psi (R&D Sprayers, Opelousas, LA, USA). Trees will be inoculated with pathogens one week prior to flooding. Treated trees will be moved to the experimental site and simulated flooding will be imposed. Treatment details are listed in Table 1. Treatments will be arranged in a randomized complete block design with six single plant replications. Trees within each block will be 3 m apart and replicated blocks will be separated by 6 m. Flooding will continue for 28 days. Monitoring ambrosia beetles and ethanol content will be as described in objective 1.1. In 28 days, tree roots will be evaluated for root rot severity.
Table 1. List of treatments for this study
|
Treatment |
Simulated flooding |
P. cinnamomi Pathogen inoculation |
Defense elicitor |
|
T1 |
Yes |
Yes |
ASM drench |
|
T2 |
Yes |
Yes |
ASM foliar |
|
T3 |
Yes |
Yes |
ASM + chlorothalonil drench |
|
T4 |
Yes |
Yes |
ASM + chlorothalonil foliar |
|
T5 |
Yes |
Yes |
no defense inducer |
|
T6 |
Yes |
No |
ASM drench |
|
T7 |
Yes |
No |
ASM foliar |
|
T8 |
Yes |
No |
ASM + chlorothalonil drench |
|
T9 |
Yes |
No |
ASM + chlorothalonil foliar |
|
T10 |
Yes |
No |
no defense inducer |
|
T11 |
No |
Yes |
ASM drench |
|
T12 |
No |
Yes |
ASM foliar |
|
T13 |
No |
Yes |
ASM + chlorothalonil drench |
|
T14 |
No |
Yes |
ASM + chlorothalonil foliar |
|
T15 |
No |
Yes |
no defense inducer |
|
T16 |
No |
No |
ASM drench |
|
T17 |
No |
No |
ASM foliar |
|
T18 |
No |
No |
ASM + chlorothalonil drench |
|
T19 |
No |
No |
ASM + chlorothalonil foliar |
|
T20 |
No |
No |
no defense inducer |
Statistical analysis
The number of ambrosia beetle attacks and ethanol content will be analyzed using PROC GENMOD fitted to a negative binomial distribution (SAS 9.4, SAS Institute, Inc., Cary, NC, USA). The depth of the gallery (% of diameter), % of attacks with successful gallery formation, and fungal colonization (% of galleries) will be analyzed using General Linear Mixed Model fitted to beta distribution with logit link (PROC GLIMMIX, SAS 9.4, SAS Institute, Inc., Cary, NC, USA). The presence of eggs, larvae, and adults in each gallery will be analyzed using PROC GENMOD with gamma distribution (SAS 9.4, SAS Institute, Inc., Cary, NC, USA).
Flood stress predisposes nursery tree crops to ambrosia beetle attacks, but the impacts of drought stress and Phytophthora root rot caused by Phytophthora cinnamomi have not been studied sufficiently. The objective of this study was to explore the role of biotic (Phytophthora cinnamomic) and abiotic (flood, drought and sufficient) stressors in predisposing flowering dogwood to ambrosia beetle attacks. A trial was conducted from 18 August to 15 September 2023. Flood and drought stress was imposed on trees for 28 days, and control plants received water as needed (sufficient). Ambrosia beetle attacks were counted every other day for 28 days. Plant tissue samples were collected at 7 and 14 days after flooding to determine ethanol content using solid-phase microextraction–gas chromatography–mass spectrometry (SPME-GC-MS). Results showed that ambrosia beetle attacks were found only in flooded dogwood trees. Dogwood trees assigned to drought and sufficient water were not attacked. Likewise, Phytophthora cinnamomi inoculated and non-inoculated dogwood trees had no ambrosia beetle attacks.
Educational & Outreach Activities
Participation Summary:
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Project Outcomes
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