The purpose of this project is to investigate the use of cover crops to prevent flatheaded appletree borer (FAB), Chrysobothris femorata (Olivier) (Coleoptera: Buprestidae) attacks on maple trees and suppress competitive weeds in tree rows and middles. Flatheaded appletree borer has long been identified as a significant economic pest in orchards, nurseries and urban landscapes. Larval tunneling by FAB can girdle small trees, causing rapid decline of economically important hosts, with some nurseries reporting infestation rates of 30% or more on susceptible tree species. These infested trees can be killed outright by trunk girdling or rendered unmarketable due to borer damage. In production nurseries, red maples are one of the most problematic trees for FAB attacks in Tennessee. Frequency of FAB attacks in nurseries varies for a number of reasons, including timing of protective sprays, size of trees at planting, site conditions, and localized borer populations. Transplant stress alone does not explain attack frequency because FAB damage continues to be added to nursery blocks over time. Since any FAB damage ruins the marketability of a nursery tree, the economic threshold for damage is essentially zero. Therefore, treatments or cultural practices that prevent FAB damage are very important to nursery growers to prevent economic losses.
Our preliminary research suggests that the presence of a winter cover crop may be a favorable option for nursery growers, acting as (1) a barrier to FAB oviposition in the spring and early summer, (2) an aid to preventing leaching of imidacloprid from the root zone of the trees and (3) as a natural suppression system for opportunistic weed species. We therefore propose a systems approach to in-field nursery tree production by incorporating a winter cover crop system combined with optimized pesticide use in order to simultaneously maximize FAB control and plant growth while minimize crop damage, weed competition and insecticide runoff.
For the performance period described here, objectives were to:
- Establish 2015 winter cover crop
- Take initial maple tree measurements
- Transplant trees into the field
- Stake and fertilize trees
- Train masters student(s) in imidacloprid ELISA techniques
- Begin spring plot evaluations
- Treat insecticide plots
4) Materials and Methods
Field Plots. Containerized (1/4 in) caliper susceptible red maple trees ‘Franks’s Red’ were transplanted in the fall of 2015 into four field blocks at Moore Nursery in Warren County, TN. Trees were planted in five rows with row spacing of 2.1 m (7 ft) apart with 1.8 m (6 ft) in-row spacing between trees. A single tree space was skipped after the 5th and 10th trees in each row as a buffer zone between treatment plots. Trees were fertilized based on soil test recommendations. Soil was tested for phosphorous and potassium levels and supplemented asnecessary. For all treatments, a total of 100 trees will be planted as previously recommended for statistical robustness.
Test of Cover Crop Plant for Combined FAB and Weed Management. In the fall of 2015, each field was divided into 4 treatment plot areas of 25 trees and assigned randomly to one of 4 treatments prior to planting: (1) no cover crop, insecticide & herbicide (current recommended practice), (2) cover crop, no insecticide (3) cover crop, insecticide (4) no cover crop, herbicide (positive control) (4 plots per treatment = 100 trees total per treatment).
Current Practice Plots. Plots in this treatment had grass and broadleaf pre-emergent herbicides applied to tree rows following transplant in October 2015. Discus at the half-rate of 10 ml/ 2.5 cm of trunk diameter was applied in April of 2016. Pre-emergent herbicide was applied each spring (2016, 2017) and fall (2016, 2017) according to recommended timing (mid-April in the spring, and late-October in the fall).
Cover Crop Plots with Insecticide. The field plots assigned to this cover crop treatment were sown with winter wheat and crimson clover in mid-October prior to tree transplant at half the high rate and disked in to a depth of 1 inch. In April 2016, trees in insecticide treated cover crop plots were treated with Discus at the half-rate of 10 ml/ 2.5 cm of trunk diameter. In year 2, crimson clover and annual ryegrass was sown by broadcasting seed across the plots. The cover crop was allowed to senesce naturally in order to develop a baseline for tree growth under unmanaged cover crop conditions.
Cover Crop Plots without Insecticide. The ‘cover crop only’ treatment allow us to assess the effect of oviposition site apparency alone on FAB control. The production methods were the same as the Cover Crop with Insecticide treatment, except no insecticide will be applied.
Tree growth measurements were taken at transplant and recorded again in October of the following two years for all treatments. Trunk diameter was measured at 6 cm above ground level and canopy size index will be recorded for all treatments. Canopy size index will be calculated by the following formula (canopy width at widest point + width perpendicular to widest point + canopy height )/3.
Flatheaded appletree borer damage was rated annually in mid-April and the height location of attacks relative to the soil surface measured. Maximal vegetation height in cover crop treatments was measured. A semi-quantitative analysis of tree leaf tissue imidacloprid content was performed for insecticide treatments with and without the cover crop using an ELISA analysis (EnviroLogix QuantiPlate Kit) in September of each year following methods previously developed in the Addesso lab. In addition to primary pests, secondary arthropod pests were evaluated (maple tip borer, maple tip moth, ambrosia beetles, spider mites, broad mite, potato leafhopper), summer weeds, soil-borne pathogens.
5) Results and Discussion/Milestones
Flatheaded Appletree Borer Assessment
The primary objective of this study was to evaluate flatheaded appletree borer (FHAB) control in plots with and without cover crops. Four treatments were evaluated: (1) herbicide + imidacloprid soil drench (current recommended practice), (2) herbicide only, (3) cover crop + imidacloprid and (4) cover crop only. Following trunk evaluations one year post transplant (October 2016), a total of 22 trees had been attacked by FHAB. One of those trees was in the cover crop treatment (cover: χ2(1) = 24.61, P < 0.0001). The remaining 21 trees were in the herbicide only plots. No attacks were observed in plots treated with imidacloprid (herbicide or cover cropped; insecticide: χ2(1) = 32.97, P < 0.0001). There was also no difference in initial trunk caliper in the attacked and non-attacked trees within the herbicided plots, so initial size did not appear to be a factor in tree selection (hit = 1.17 ± 0.03, not hit = 1.12 ± 0.2; t = -1.64, P = 0.1067). The presence of cover crop reduced attacks by 95% compared to 100% in imidacloprid treated plots. An important measure of cover crop density for our treatment trees was trunk temperature at 20 cm – the FHAB preferred oviposition site. Trunk temperature was measured for every tree on the southwest side from March-June, 2016. On average, trunk temperatures at this height were 2⁰C lower in the cover crop treatments than the herbicided treatments. In addition to the cover crop acting as a barrier to the FHAB, the beetle’s preference for depositing eggs on the southwest (sunny) side of the tree trunk indicates a preference for higher trunk temperature. The cooler temperatures in the cover crop plots could make these trees less preferable oviposition sites.
Tree Growth Assessment
Tree height and trunk diameter (at 6″ height) were measured in October, 2016 and compared to data taken at transplant the previous year. Treatments with herbicide had greater growth both in height and diameter than cover cropped plots. Percent increase in height was 41.9, 26.5, 6.7 and 5.4 for treatments 1-4, respectively. Percent increase in diameter was 128.2, 103.6, 27.4 and 36.3. The canopy size index in October 2016 was greatest for the herbicide + imidacloprid trees (113.3) followed by the herbicide only (90.4) and cover crop with and without insecticide (54.3 and 52.3). The number of new tips counted in May was also lower in trees in cover cropped plots (Cover: χ2(1) = 80.79, P < 0.0001 ). The impact of cover crops grown unmanaged in tree rows was considerable in the first year following transplant, which was not unexpected. The decision was made to allow cover crops to senesce naturally in order to provide a baseline for lost growth due to competition from row covers. The size differential between the herbicide treated and cover cropped plots is visually similar to previous studies where weed-free tree rows were compared to weedy plots. Nurseries wishing to grow large trees quickly will need to manage winter cover crops so that they do not directly compete with trees during the early/middle of summer. Options include selecting alternate cover crops, seeding at lower densities, or killing the cover crop in late spring. More research is needed to identify proper management techniques for cover cropping against FHAB. In this, our second year cover cropping, we will determine whether established trees in cover cropped plots continue to lag behind in growth.
Other Arthropod Pests of Maple
A major concern for this study was that the presence of cover crops might inadvertently cause an increase in secondary insect pests of red maple. We surveyed for the following pests in 2016: ambrosia beetles, maple twig borer, maple leaf tier, spider mites, broad mites, and potato leafhopper. No ambrosia beetle, spider mite or broad mite damage was observed in any of the treatment plots. For the maple twig borer, the presence of cover crop had no effect on the number of twigs damaged per tree but did have a slight effect on percent damage (cover: 10.3 ± 1.5 %, herbicide: 5.7 ± 0.9 %; χ2(1) = 14.53, P = 0.0001) because there was more new growth on the herbicide treated plots. The same pattern was observed with maple leaf tier damage later in the summer with cover cropped trees having slightly higher percent damage (cover: 11.5 ± 2.0 %, herbicide: 8.3 ± 0.8 %; Cover: χ2(1) = 4.08, P = 0.0434). The presence or absence of cover crop did not affect moth movement into or out of plots, at least at this scale. Potato leafhopper damage was minimal in 2016, but was consistently lower in plots treated with imidacloprid, and higher in the herbicide plots, which had more new growth for the leafhoppers to feed on. Overall, the presence of cover crop did not cause any unusual secondary pest pressure on maple trees.
Imidacloprid content in maple leaves was higher in year 1 in the cover crop plots than in the herbicide plots (F = 47.55, df = 1,6, P = 0.0005), likely due to a concentration effect related to lack of tree growth in the cover cropped trees. No imidacloprid was detectable in cover crop tissue tested adjacent to treated trees. The imidacloprid was applied close to the base of each tree in a small volume of water when cover crops were still relatively small. The deliberate application method minimizes the potential for runoff or subsequent uptake by other competing plants. While some imidacloprid may find its way into cover crop material at the base of the trees, levels were below the limit of detection with the semi-quantitative method used here (0.2 ppb) and were unlikely to affect most of the cover in the field.
The pre-emergent herbicide treatments kept the herbicide rows clean from October 2015 – March 2017. The winter cover crop was able to suppress most winter weeds. The weed problem arose in late spring when summer weeds began to germinate as the cover crop senesced. These weeds overtook the tree rows by late summer and were a source of competition for the trees in the cover crop plots. When biomass data was collected in late July 2016, cover crop dry weight averaged 31.5 g per sq ft but an additional 26.7 g of live weed material was present at that time. Due to the inability of the winter cover to suppress these summer weeds, it is possible some of the difference in cover crop treatment effect can be attributed to summer weeds and not the winter cover crop. Future research for FHAB management should include either spring seeding of a summer cover crop or the application of pre-emergent or post emergent herbicides to prevent summer weed growth in tree rows.
Soil Borne Disease Pressure
Post Emergence Damping Off. Red maple seeds were germinated in soil sampled from field plots to determine incidence of soilborne pathogens in treatments. Soil was sampled in May and again in September following cover crop incorporation. Seedlings germinated in cover cropped soil had lower root disease scores than seedlings in herbicided plots (F = 8.47, df = 1,17, P = 0.0097). Soil incorporation of the cover crop also decreased root disease scores compared to the before incorporation treatments in soil (F = 3.41, df = 2,17, P = 0.0568).
6) Impacts and Results/Outcomes
To date, we have determined:
- tested cover crops can protect susceptible trees from flatheaded appletree borer attack as well as imidacloprid drenches in the season following transplant
- tested cover crops do not change the secondary arthropod pest pressure
- cover cropping may reduce soilborne disease inoculum
- winter cover crops will require early summer kill/additional management to prevent loss of tree crop growth
What demonstrable impacts do you expect the project to have in the future?
The results of this study lead the way for an alternative management practice for flatheaded appletree borer management in newly transplanted trees. Current practices include a soil drench of imidacloprid to protect trees from borer damage up to 4 years. Imidacloprid is a product of concern for its effects on pollinators and customer choice. This production method would allow growers to provide wholesalers with ‘bee friendly’ trees.
7) Economic Analysis
An economic analysis was not conducted during this project. Once optimal methods are determined it should be straight forward to perform a cost analysis of the conventional and cover crop methods.
Dawadi, Sujan. A Systems Approach for Red Maple Pest Management by Cover Crop Incorporation. MS Thesis. Tennessee State University, (in prep, July 2017).
Dawadi, Sujan, Jason B. Oliver, Anthony Witcher and Karla M. Addesso. (in prep). Cover cropping as an alternative to systemic imidacloprid treatments for preventing flatheaded appletree borer in field grown nursery production.
Dawadi, Sujan, Jason B. Oliver and Karla M. Addesso. (in prep). Impact of cover cropping on secondary arthropod pests of maple trees in nursery production.
Dawadi, Sujan. Karla M. Addesso and Fulya Baysal-Gurel.(in prep) Soil-borne pathogen pressure in cover cropped and conventional nursery production fields.
Karla Addesso and Jason Oliver. Cover cropping: An alternative to imidacloprid drenches for flatheaded appletree borer management in susceptible trees. Tennessee Greentimes (submission for winter 2017)
Karla Addesso and Jason Oliver. Use of cover crops to protect trees from flatheaded appletree borer damage in nursery production. Tennessee State University Extension (submission for winter 2017)
Dawadi, Sujan (student), Karla M. Addesso, Jason B. Oliver and Paul O’Neal. Relationship between field environmental conditions, tree growth, and incidence of flatheaded appletree borer attack. Southeastern Branch of the Entomological Society of America, Memphis, TN, March 12th-15th, 2017.
Karla Addesso. Ornamental and Landscape Pest Management. Rutherford County Master Gardeners. Feb 28th, 2017.
Karla Addesso and J.B. Oliver. Insect Control in Ornamentals March 2nd, 2017. Dean’s Seminar Series. Tennessee State University, Nashville, TN.
Dawadi, S.(student), K.M. Addesso and J.B. Oliver. 2017. Evaluation of conventional and cover cropped maple production systems on tree growth and incidence of flatheaded appletree borer attack. TSU 39th Annual University-Wide Research Symposium, 17-21 Apr. 2017. Nashville, TN.
Sujan Dawadi (student), Karla M. Addesso, Jason B. Oliver and Paul A. O’Neal. Impacts of Cover Crops Presence on Red Maple Tree Insect Pests. Tennessee Entomological Society, Knoxville, TN, Oct 6th-7th, 2016.
Sujan Dawadi (student), Karla Addesso, Jason B. Oliver and Manoj Pandey (student). Incidence of red maple tree insect pests in cover crop and non-cover crop production plots. International Congress of Entomology/Entomological Society of America Meeting, Orlando, FL, September 24th-30th.
Addesso, Karla, Sujan Dawadi, Jason Oliver and Paul O’Neal. Management of flatheaded appletree borer in nursery production with cover crops. November, 2017. Entomological Society of America. Denver, CO.
Addesso, Karla, Jason Oliver and Anthony Witcher. Managing flatheaded appletree borer with cover crops. Tennessee Green Industry Expo. Fall 2017. McMinnville, TN.
Addesso, Karla, Jason Oliver and Anthony Witcher. Managing flatheaded appletree borer with cover crops. Southern Nursery Association Annual Meeting. January 8-9th, 2018. Mid-Atlantic Nursery Trade Show, Baltimore, MD.
9) Farmer Adoption
Report here the extent to which farmers have adopted new technologies, production methods and systems addressed in the project. List the number of farmers reached by your project so far through publications, field days and workshops or other training/outreach activities. What specific recommendations would you make to farmers in terms of day-to day operations? What should a farmer do or stop doing? Attach any testimonials or letters from farmers in a mailed appendix.
Once we have completed the two-year study, we will have enough information to share this management method with other growers. The main concern with the cover crop system as a viable alternative to imidacloprid drenches is the reduction in growth by the trees in the cover crop treatments compared to herbicided plots. The grower who participated in this on-farm trial is familiar with the benefits of pre-emergent herbicides and recognizes that his clean rows encourage growth, while weedy or cover cropped fields reduce growth. If trees in cover cropped plots require an extra year of growth to sell or need to be sold at smaller diameter then they would need to be sold at a premium to make the method worthwhile. If, however, a management plan for the cover crop can be developed to minimize loss in growth the cover crop would be a viable option.
10) Areas Needing Additional Study
Second Year Cover Crop Application
Due to the need to seed in tree rows and middles, cover crops were selected that could germinate with minimal disturbance to soil. Annual ryegrass and crimson clover were seeded in September for winter of 2017. The annual ryegrass was included in order to once again have a grass that would grow to the appropriate height to cover the base of the tree (winter wheat and crimson clover were used in 2016). Winter wheat was originally chosen for the first year cover but we are unlikely to recommend use of this crop due to its high water competition and late senescence. Work done simultaneously with this study suggests winter rye may be a better transplant year cover crop for this purpose in the southeast. Second year and beyond is the greater challenge since it is not possible to disturb the soil in the tree rows. Cover crop seed selections must be able to germinate on contact with soil and maintain a stand of dead plant material through the flatheaded appletree borer oviposition period of May-June. Previous research has shown that additional FHAB attacks occur each year of production. Whether the annual ryegrass/crimson clover combination is effective in year two will be seen this coming fall.
We are currently monitoring these field plots for a second year to end in October 2017 to give us two years of data on the use of cover crops in FHAB management. When the two-year trial is completed we will use the accumulated data to plan our next set of management trials to optimize this management technique to maximize tree growth while retaining the benefits of protection from FHAB. Future focus will be on alternative cover crop selection and early termination.
Educational & Outreach Activities
Talks were given at TSU Nursery Research Center Field Days (2016 and 2017) as well as at TNLA/MTNA grower educational meetings. Preliminary results were presented at the International Congress of Entomology/Entomological Society of America Meeting 2016, the Southeastern Branch Entomological Society Meeting (2017) and will be presented at the Southern Nursery Association meeting in 2017. Three scientific publications are being prepared based on these studies: one on flatheaded appletree borer management, one on secondary arthropod pests in cover cropped trees and a third on soil-borne pathogens in cover cropped and non-cover cropped systems (to be submitted winter 2017 ). One extension flyer will be prepared upon completion of the study (Fall 2017 to by submitted to Tennessee Greentimes) to describe the use of cover crops as an alternative to systemic imidacloprid treatments.
During the performance period, we established that: (1) planting trees into a winter cover crop is unlikely to protect them from FHAB due to poor recovery of wheat/clover from soil disruption by the transplanter and (2) transplanting trees into fall seeded cover crops can be a successful method for establishing row middle covers.
Maple field plot establishment, Fall 2015
In October of 2015, a mix of wheat and crimson clover were established in a half acre field plot. Trees were measured (height, caliper at 6 in) and transplanted dormant in November into the field plots using a tractor with transplanter attachment. Plot rows were overseeded after transplanting of trees since disturbed soil caused severe disruption of cover crop. In early spring, the cover crop plots were evaluated and it was determined that the fall cover crop failed to recover at adequate densities in the tree rows (tree middles had good establishment of wheat and clover). In addition to field work, students participating in the project were trained on how to collect maple leaves and process them for imidacloprid analysis by ELISA.
Since the primary goal of the project is to block FHAB oviposition at the base of the trees, the tree rows required an additional application of a spring cover crop. Annual ryegrass was chosen based on its quick establishment, spring growth and maximal height in late spring/early summer (2-3 ft) required to block preferred oviposition sites and was applied on March 9th. Annual ryegrass will also senesce naturally in summer heat. The results of this initial fall cover seeding indicate that standard methods of winter cover cropping and fall nursery transplant timing are not compatible if the goal is to have cover established in the tree rows. While it is possible that earlier plantings of cover crop may prove more resilient, the amount of soil disruption caused by the trasplanter is a serious obstacle. Planting into fall seeded winter wheat/clover for the purpose of maintaining cover in tree middles is compatible with current transplanting methods. It is more likely that in Year 1 of field production, a combination of winter cover for middles and early spring cover for tree rows will be required if the goal is protection from FHAB.
Trees were staked and fertilized on March 8th. Pre and post-emergent herbicides were applied on March 25th to the tree rows in control treatments. Row middles were mowed on March 29th in all plots and will be maintained bi-weekly. Annual ryegrass has begun to establish. As of April 1st, measurements of soil moisture and temperature in rows and middles in all plot treatments have begun. In addition, tree trunk temperatures are also being recorded at the preferred site of FHAB oviposition (SW side of each tree at 20 cm). These measurements will be repeated bi-weekly through June. On March 28th, bee bowls were deployed and will be set out monthly at the center of each plot to evaluate pollinator presence in each treatment and correlated with the presence of flowering weeds, trees and cover crops. Beginning in April, cover crop density/coverage and weed penetration will be evaluated bi-monthly in all plots in tree rows and middles. Imidacloprid drench application to insecticide treated plots is also scheduled for the week of April 10th.