Incorporating a Cover Crop into Field Grown Nursery Production to Manage Flatheaded Appletree Borer with the Simultaneous Benefit of Improved and Sustainable Weed Management

View the project final report

• 2016 annual report

Commodities

• Agronomic: annual ryegrass, clovers
• Additional Plants: ornamentals, trees

Practices

• Crop Production: cover crops, nurseries
• Education and Training: on-farm/ranch research
• Pest Management: cultural control, integrated pest management
• Production Systems: agroecosystems

The flatheaded appletree borer (FAB), Chrysobothris femorata (Olivier) (Coleoptera: Buprestidae), is a species native to the continental United States, Canada and northern Mexico. The borer has an unusually wide host range compared to many buprestids, attacking popular deciduous shade (Acer, Cornus, Cercis, Quercus, Ulmus), nut (Carya, Juglans) and fruit trees (Malus, Prusus) (Nelson 2008). Oviposition occurances are concentrated within the first 20 cm of the trunk and subsequent larval tunneling can girdle small trees, causing rapid decline of economically important hosts. In production nurseries, red maples are one of the most problematic trees for FAB attacks in Tennessee with infestation rates of non-protected trees as high as 40% of the crop by three years post planting (Oliver et al. 2010). Unpublished surveys (2002-2005) performed in field-grown nurseries where growers routinely apply preventative sprays of contact insecticides like chlorpyrifos or bifenthrin revealed damage ranging from up to 26% of maple and dogwood crops. 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 (Oliver et al. 2010). Since 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 lessen economic losses. Three years of unpublished research evaluating imidacloprid and herbicide interactions showed that the presence of weeds in fields improved FAB control. The mechanism of this interaction is still unknown, but we hypothesize that a decrease in oviposition site apparency (i.e., camouflage) or direct blocking of preferred oviposition sites are the major causes of decreased FAB attacks.

Our preliminary research suggests that the presence of a winter cover crop may be a favorable option for nursery growers seeking to control flatheaded appletree borer, 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.

Field Plots. Susceptible red maple trees > 1.9 cm (1/2 in) caliper such as 'Franks's Red' will be transplanted in the fall of 2015 into four field blocks at Flower City Nursery in Warren County, TN. Trees will be 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 will be skipped after the 5th and 10th trees in each row as a buffer zone between treatment plots. Trees will be fertilized based on soil test recommendations. Soil will be tested for phosphorous and potassium levels and will be supplemented if necessary. 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 will be divided into three treatment plot areas of 25 trees and assigned randomly to one of three treatments prior to planting: (1) no cover crop, insecticide & herbicide (current recommended practice), (2) cover crop, no insecticide (3) cover crop, insecticide (4 plots per treatment = 100 trees total per treatment).

Current Practice Plots. Plots in this treatment will have grass and broadleaf pre-emergent herbicides applied prior to tree transplant in October 2015. Discus at the half-rate of 10 ml/ 2.5 cm of trunk diameter will be applied in April of 2016. Pre-emergent herbicide will again be 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 will be sown with winter wheat in mid-October prior to tree transplant at a broadcast rate of 100 lb/acre and disked in to a depth of 1 inch. In April 2016, trees in insecticide treated cover crop plots will be treated with Discus at the half-rate of 10 ml/ 2.5 cm of trunk diameter. Winter wheat will be sown in year 2 by broadcasting wheat seed at 150 lb/acre and disking in the row middles. The cover crop will be killed with a grass specific herbicide (Envoy Plus, Fusilade, Segment, etc.) in early April each year as trees break dormancy to prevent competition from impeding tree growth.

Cover Crop Plots without Insecticide. The 'cover crop only' treatment will allow us to assess the effect of oviposition site apparency alone on FAB control. The production methods will be the same as the Cover Crop with Insecticide treatment, except no insecticide will be applied.

Tree growth measurements will be taken at transplant and recorded again in September of the following two years for all treatments. Trunk diameter will be 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 will be rated annually in mid-April and the height location of attacks relative to the soil surface measured. Maximal vegetation height in cover crop treatments will be measured on a monthly basis. A semi-quantitative analysis of tree leaf tissue imidacloprid content will be 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.

Data Analysis. Count data for insect attacks does not often conform to the assumptions of a normal distribution or homogeneity of variance. All FAB hit data will be compared among treatments using a generalized linear interactive model (GLIM) (PROC GENMOD) with a log link, and assuming a negative binomial distribution with means separated by least squares means (Agresti 2002, SAS Institute 2003). For treatments with no borers recovered, a value of 0.5 will be arbitrarily used in one replicate because GLIM with negative binomial distribution do not perform well with zero values. Tree health parameters (caliper, height and canopy size) and imidacloprid values are most often normally distributed and will be analyzed by generalized linear model (PROC GLM) with means separated by LSD.