Cover Crops in Woody Ornamental Production: Impact on Plant Growth, Arthropod Pests, Soil-Borne Pathogens and Weeds

Progress report for LS18-287

Project Type: Research and Education
Funds awarded in 2018: $284,869.00
Projected End Date: 09/30/2021
Grant Recipient: Tennessee State University
Region: Southern
State: Tennessee
Principal Investigator:
Dr. Karla Addesso
Tennessee State University
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Project Information

Abstract:

The purpose of this project is to move nursery production towards more sustainable management practices. To accomplish this task, evidence-based recommendations are needed to improve wood ornamental cropping while minimizing weed, pest arthropod and disease concerns. Our project will evaluate the impacts of cover crop use in field-grown woody ornamental production.

While the impact of cover crops have been studied extensively in row crop and vegetable production, less is known about how cover crops may positively or negatively affect perennial woody ornamental production. Woody ornamental production systems are complicated to manage due to the many plant species grown on a single nursery. To effectively serve this industry, management solutions must be applicable to a wide range of tree and shrub crops. Of particular interest to growers is the amount of competition endured by trees in fields with cover crops growing within tree rows as compared to rows with weeds or those kept clean with pre-emergent herbicides. The presence of cover crops may alter arthropod pest and beneficial communities as well. An additional gap in our knowledge base is the efficacy of biofumigant cover crops for management of soil-borne diseases in multi-year cropping systems such as those of woody perennials.

Project Objectives:

The objectives include an investigation of the use of cover crops in woody ornamental production systems through:

  1. The evaluation of winter cover crop stand recovery and tree seedling development after fall or spring transplant of tree liners;
  2. The evaluation of summer and winter cover crop rotations in established tree production areas;
  3. Optimization of winter cover crops methods for management of key woody ornamental tree pest, the flatheaded appletree borer, and;
  4. The incorporation of biofumigant cover crops for treatment of soils prior to liner transplant.

The impact of these practices on soil-borne pathogens, soil quality, pest and beneficial arthropod populations, weed pressure, and plant growth will be evaluated.

Cooperators

Click linked name(s) to expand

Research

Materials and methods:

Obj 1. Studies will be conducted at the Otis L. Floyd Nursery Research Center in McMinnville, TN (TSUNRC) and at field sites in the five-county nursery production area of middle Tennessee with grower cooperators. We will use a popular cultivar of red maple as our model woody ornamental tree (‘Brandywine’).

Maple Field Plots and Containerized Trees. Rooted cuttings of red maple will be grown to approximately ¼ in diameter in #3 nursery pots. Containers will be fertilized with a complete slow release fertilizer with micronutrients for transplant into field blocks. Trees will be planted in a common nursery industry pattern of five rows with row spacing of 7 ft apart with 6 ft in-row spacing between trees. Soil will be tested for phosphorous and potassium levels and will be supplemented if necessary. Trees will be fertilized with a granular slow release fertilizer at 50 lb N/acre (15-15-15 [NPK]; 0.4 oz/tree) in February and thereafter in subsequent years during February at the same rate.

Cover Crop Plot Establishment. The purpose of this experiment is to identify cover crops that are compatible with standard woody ornamental field transplant practices. Winter cover crops (e.g. winter wheat, crimson clover) will be planted in September – October (optimal timing for each cover crop species) in 32 ´ 32 ft field plots with four replicates per cover crop. Plots will be prepared by disk harrow and cover crop seeds broadcast, followed by a cultipacker to incorporate seed into the soil. Field preparation and seeding will be timed prior to a rain event, if possible, to maximize cover crop establishment. Plots with no cover crop will be used as controls. In early November (fall transplant) or early March (spring transplant), tree rows will be planted into the cover crop plots with a transplanter (25 trees per plot, 100 trees total per cover crop treatment). The disturbed soil will be re-packed following the pass by the transplanter. A pre-emergent herbicide (e.g., Sureguard, Marengo rotation) will be applied post-transplant within tree rows to prevent weed/cover crop competition at the base of the trees.

Soil Evaluation. Soil temperature and soil moisture (volumetric water content) will be evaluated. Each plot will be sampled randomly at 4 locations each within rows and within middles. Readings will be taken monthly using a Decagon GS3 Soil Moisture Sensor with Decagon ProCheck handheld reader. Soil mineral content and organic matter analysis will be assessed at project termination by pooling three samples per plot and analyzed by the UT Soil, Plant and Pest Center for analysis.

Cover Crop Plot Evaluation. Cover crop density will be evaluated in the plots before tree planting.  Following tree planting, density of cover crop and weed pressure will be evaluated monthly in tree rows and middles in four locations within rows and middles for each plot.  Cover crops will be allowed to senesce naturally and then mowed in early August. Percent coverage will be assessed every two months using 12 in. sampling squares at four random locations each within rows and within middles for each plot. Biomass will be evaluated at project termination using 12 in. sampling squares at four random locations each within rows and within middles for each plot.

Weed Assessment. Percent coverage will be collected every two months using 12-inch sampling squares at four random locations each within rows and within middles for each plot. Species frequency data will be collected to assess differences in weed species distribution between treatments.

Tree Growth. Tree height and trunk diameter (6 in. above the soil line) of all test trees will be recorded at transplant and during subsequent years in September to determine growth effects of different cover crops for the initial growing season. Trees will be marked at the initial trunk diameter measurement with a paint marker to ensure all future measurements are taken at the same location on the tree trunk.

Soil Sampling and Greenhouse Bioassay for Soil-borne Pathogen Analysis. Soil sampling to evaluate soil pathogens will be conducted at cover crop senescence each year for the first and second year bioassays, respectively. Four soil samples (from 12 × 12 in. and 8 in. deep) will be taken randomly from the plots, mixed in situ with a spade, and placed in a plastic bucket (for each treatment: 4 replications each; 8 samples total). The soil will be stored for 1 week, at ambient temperature in a greenhouse before use.

A greenhouse experiment will be conducted to determine whether cover crop soil can suppresses two common maple tree pathogens (R. solani and P. nicotianae). A 13 lb soil sample from each treatment/plot will be taken and divided into a 1 lb soil capacity container pot for each of the two-soil pathogen and one-control treatments. Control treatments will consist of non-cover cropped soils from the same production fields to assess background pathogen pressure. Rooted cuttings of red maple will be transplanted into the field soil and disease symptoms will be assessed 2 months later. For each bioassay, the experimental design will be a randomized complete block design (RCBD) with four replicates.

Pest and Beneficial Insect Assessments. Maple tree plots will be evaluated for major arthropod pests of maple trees including FAB and other insects and mites (Table 2). FAB evaluations will be done in October and April each year of the study.  Evaluations of most pests will be made throughout the growing season to determine whether cover crops alter pest pressure. Monthly surveys for arthropod predators (ladybugs, lacewings, spiders, predatory bugs and mites etc.) will be conducted from May – September by beat sampling a sub-sample of trees at the center of each cover crop plot. 

Obj 2. The purpose of this objective is to identify cover crop species and methods compatible with established nursery fields. Field tree plots (32 ´ 32 ft) previously established by the research team or grower collaborators will be used for these trials. Winter and summer cover crop seed (e.g. winter rye, crimson clover, cowpea, pearl millet) will be applied in September – October (winter cover crop) and March – April (summer cover crop) to established field plots in 32 × 32 ft blocks in a RCBD with four replicates per cover crop. Seed will be applied to plots by three methods (1) with a broadcast spreader and disked lightly into row middles and (2) with seed drill. Plots with no cover crop will be used as controls. A pre-emergent herbicide (e.g. Sureguard, Marengo) will be applied to the tree rows to prevent weed/cover crop competition at the base of the trees. Evaluations will follow the methods of Obj 1.

Obj 3 (a) Method development to maximize tree growth in cover-cropped plots. Previous research has demonstrated that winter cover crop stands grown within tree rows can prevent FAB attacks on tree trunks. However, the presence of cover crops at the base of the trees resulted in significant reductions in growth during the first and second years of planting compared to trees in rows that were kept clean with pre-emergent herbicides. Three methods of cover crop management will be evaluated to maximize growth of trees while minimizing the threat of FAB attacks. 1) Trees will be transplanted and grown with tree ring mulch mats extending in a 1 ft radius around the base of the tree; 2) a selective post-emergent herbicide will be used to kill the cover crop within the tree rows when it reaches 60 cm in height to reduce competition; and 3) a pre-emergent herbicide will be used to maintain a clean 1 ft radius around the tree trunks. Control trees will be grown under the current recommended practice, maintaining clean tree rows with pre-emergent herbicide applications. Tree growth and FAB attacks will be evaluated for 2 years post- transplant. While not specifically an objective of this experiment, the use of mulch mats to prevent weeds at tree bases will address the current debate among researchers over whether or not pre-emergent herbicide treatments cause more FAB attacks.     

(b) Evaluation of tree growth recovery. (2017-2019). Based on previous studies, we know that most FAB attacks occur during the first and second years post-planting. Once trees are better established, a cover crop maintained at the base of trees might not be necessary for protection against FAB. Red maple tree plots from a previous FAB cover crop study (SSARE #OS14-084) will be used to assess the growth of trees in years 3 and 4 post-planting with all trees are grown with clean rows. Four pre-treatments (from years 1 and 2) will be evaluated: (1) cover cropped plots (2) cover cropped and insecticide treated plots (3) herbicide treated plots and (4) herbicide and insecticide treated plots. For all tree plots, middles will be sown with a cover crop while tree rows will be kept clean with pre-emergent herbicide applications. Tree growth will be measured in years 3 and 4 to determine whether trees grown with cover crops in tree rows during establishment years 1 and 2 can catch up to larger trees during the following two years of production. Attacks by FAB in years 3 and 4, while rarer, will also be monitored. 

Obj 4. Field Evaluation Trial. White mustard, purple top forage turnips, astro arugula, mighty mustard, dwarf essex rape, amara mustard and oriental mustard biofumigant cover crops will be evaluated in field trials at the TSUNRC (Table 3) based on the preliminary data from greenhouse studies showing efficacy of these plants as biofumigants (Liyanapathiranage 2017). The experiments will be established as a RCBD with four replications. At the TSUNRC, field beds will be artificially inoculated with Phytophthora nicotinanae and Rhizoctonia solani using established protocols developed by Dr. Baysal-Gurel. Biofumigants will be direct seeded into 26 ´ 8 ft beds at the recommended seed rate. Flowering biofumigant plants will be dug from randomly chosen 1-ft2 areas in each plot to determine plant biomass volumes. Biofumigants will be disked 6 in. deep into the soil in late July. After incorporation, plots will be covered with a polythene sheet for 15 days. Temperature and soil moisture in the plots will be monitored using WatchDog mini stations. Two additional treatments without biofumigant cover crops or polythene sheets will be used as controls, including: (1) inoculated and (2) non-inoculated plots. Soil tests will be performed to determine levels of macro and micro- nutrients, soil pH and organic matter.

Soil Pathogen Evaluation. Before and after incorporation of biofumigant cover crops, population density of R. solani, P. nicotinanae and fluorescent pseudononads bacteria will be determined using selective or semi-selective media. Soil samples will be taken to a depth of 6 in. from each plot and stored at 40°F for 1 day. Isolated colonies will be confirmed by pathogen morphology. Maple tree liners will be planted after biofumigation the following fall. Plots will be irrigated as needed. Disease occurrence and incidence will be evaluated the following spring. Area Under the Disease Progress Curves will be calculated using the formula AUDPC = Σ[(Xi+1 + Xi)/2](ti+1–ti) (Simko and Piepho 2012). Plants will be evaluated for root development and disease severity on roots at the end of the trial using a 1-5 ordinal scale where 1 = healthy, 2 = 25% or less roots necrotic, 3 = 26 – 50% roots necrotic, 4 = more than 50% roots necrotic, and 5= plant dead. Fresh weight and plant height will be recorded at the end of the trial in addition to a plant phytotoxicity rating for trees in each biofumigant treatment.

Soil Macro- and Micro-invertebrate Evaluation. Four soil core samples will be taken with a golf cup cutter (6 in. depth × 4.5 in. width)from the center region of each cover crop and control plots immediately following solarization and at 3 and 6 months post treatment. Macro- and micro-invertebrates will be extracted from soil with a Tullgren funnel and identified to order (at minimum) on a per gram soil basis.

Tree Growth Measures: Tree height and trunk diameter will be measured as previously described to assess biofumigant cover crop effects on plant growth.  Trees also will be rated in early summer for any visual phytotoxicity symptoms resulting from the metabolic byproducts of the biofumigant cover crops. Although it is unlikely biofumigant cover crops will impact FAB, trees will still be rated as previously described in case metabolic byproducts of biofumigants reduce FAB activity.

On-Farm Evaluation Trial. On-farm trials will be set up at two locations in middle Tennessee, each varying in soil type and prevalent naturally-occurring soil-borne pathogen pressure (see letters of collaboration). Methods for this trial will be the same as 1C.1 except that soils will not be artificially inoculated with pathogens and only the most effective biofumigant plant from 1C.1 will be evaluated. Soil samples will be collected and the effects on naturally occurring soil-borne pathogens assessed as previously described. Fresh weight and plant height will be recorded at the end of the trial.

Research results and discussion:

Obj 1. Cover crops were established in October 2018 and maple trees were transplanted into the field in fall and spring. Baseline levels of soil moisture have been recorded since cover crop was established and the initial height and diameter of the trees has been measured. Cover crop densities were evaluated in March 2019 and will be repeated again in April 2019. 

Cover crop and weedy middles. 

Data from insect populations, tree growth and soil health were collected from April-July 2019. Insect samples were collected using yellow sticky cards held just above the cover crop and pitfall traps arranged at the center of each plot. Samples will be processed to the lowest classification possible. Soil samples were collected and bioassayed for pathogenicity. Preliminary results suggest that cover crop and weedy plots have different insect communities and resistance to soilborne pathogens. Also, spring transplanted trees grew more than fall transplanted trees in the first year. We hypothesize that this is due to earlier bud break of spring transplanted trees due to the deeper dormancy of fall planted trees compared to trees which were held under plastic over winter.  

In fall 2019, a second trial of the same experiment was initiated. Fall trees were transplanted in November and spring trees will be planted in March. In 2020, soil microinvertebrates and weeds will be assessed. 

Obj 2. Cover crops were established in October 2018 in established tree fields. Baseline levels of soil moisture have been recorded since cover crops were established. Cover crop densities were evaluated in March 2019 and will be repeated again in April 2019. 

Field seeded in October. Flower City, McMinnville, TN.   

Data from insect populations, tree growth and soil health were collected from April-July 2019. Insect samples were collected using yellow sticky cards held just above the cover crop and pitfall traps arranged at the center of each plot. Samples will be processed to the lowest classification possible. Soil samples were collected and bioassayed for pathogenicity. Preliminary results suggest that cover crop and weedy plots have different insect communities and resistance to soilborne pathogens. Also, planting by drill was essential for establishment of grain cover crops (triticale), but also useful for crimson clover. 

This trial will be written up and published in 2020. 

A summer cover crop trial was established in spring 2019. While the cover crop did germinate, all plants died due to extended drought and did not recover. Winter cover crops senesced over the early summer and provided some mulch/weed suppression. While we may investigate summer cover crops in the future, the high likelihood of drought at this time of year suggests that such crops would not be ideal for nursery fields lacking irrigation. 

A second winter cover crop experiment was established in fall 2019. In this trial, crimson clover and triticale were seeded with a drill at low and high rates alone and in combination. Cover crop establishment, weed penetration and soil health will be assessed.   

Obj 3. (a) Cover crop was established in October and red maple trees (‘Sun Valley’) were transplanted in December. Initial height and diameter of trees as well as soil moisture and temperature readings have been recorded. Germination of cover crop was evaluated in March and will be repeated in April. Treatments will be applied in early to mid April.

Field plot establishment. Moore Farm, Irving College, TN.

Tree growth was measured in fall 2019 and flatheaded borer damage assessed. Preliminary results suggest that early killed cover crop did not provide the same level of protection from borers as the live cover crop. Also, trees protected from weeds using mulch mats had similar amounts of damage as herbicided trees, suggesting that herbicide is not the cause of attacks, but rather open access to the tree trunk is the primary cause of attacks. 

(b) Height, diameter and canopy size was recorded for trees in Fall 2018. Tree rows were maintained bare with pre-emergent herbicides. The final year of growth/borer attacks (year 4) was assessed for this previous study plot. We found that by the final year of production, trees in the cover crop plots remained smaller than herbicided trees, however, the trees had grown more in the previous year than the herbicided trees, suggesting they would recover lost growth in time. Trees will be graded for quality prior to termination of the experiment. 

This trial will be written up and published in 2020. 

Obj 4.

In summer, Phytophthora experimental plots were inoculated with P. nicotianae infested rice grains. Four rice grains were placed 5 cm below the surface soil every 30 cm. Rhizoctonia experimental plots were drench-inoculated with slurry of R. solani (7-day old cultures on PDA were homogenized) at a rate of 100 ml/ 0.1 m2. Non-treated, non-inoculated and inoculated plots served as controls. Selected cover crop seeds (Table 1) were seeded into the plots with 1.76 oz of coarse sand for even distribution. At the flowering stage cover crops plant were chopped and incorporated properly into 15 cm deep using ploughs.

Table 1. Selected cover crops seed and organic input rates for the TSUNRC field experiment.

Treatment

Scientific Name

Company

Rate

Amara mustard

Brassica carinata

Johnny’s Selected seeds

2.3 x 106seeds/A

Astro arugula

Eruca vesicaria spp. sativa

Johnny’s Selected seeds

8.3 x 105seeds/A

Mighty mustard® pacific gold

B. juncea

Johnny’s Selected seeds

5.6 x 105seeds/A

Oilseed radish

Raphanus sativus

Johnny’s Selected seeds

9.8 x 105seeds/A

Purple top forage turnips

B. rapa

Johnny’s Selected seeds

1.8 x 106seeds/A

Compost cow manure

 

Farm Fuel Inc. Freedom, GA

50 tons/A

Mustard meal

 

Farmers Organic. Newton, GA

968 lb/A

Then the dedicated plots were covered for two and four weeks with 3.0-mil transparent polythene (clear poly polyethylene sheeting, Wrap Bros, Chicago, IL) with no opening at the edges. After two and four weeks polythene covers were removed from specific field plots and mixed it properly. Solarization alone- plots were covered with polythene on 3 July for six weeks and irrigated properly to increase moisture for trapping more temperature (Fig. 1). Non-treated plots served as control. Average temperature of solarized beds, cover crop incorporated solarized beds and non-treated beds were 31.03℃, 29.48℃ and 27.06℃, respectively.

Phytophthora root rot disease severity in boxwood was high experiment with non-treated, inoculated control plants showing 58.94% disease severity. All the tested cover crops- amara mustard, astro arugula mighty mustard, radish and turnips in combination with solarization (2-weeks or 4-weeks), solarization alone (6-weeks) and organic inputs (compost and mustard meal) significantly reduced root rot severity on boxwood roots compared to the non-treated control plants (Table 2). There were no significant differences among tested cover crops in combination with solarization (2-weeks or 4-weeks) compared to the other treatments in reducing Phytophthora root rot disease. There were no significant differences among treatments in plant fresh weight, plant height, and plant width (Table 2).

Table 2. Effect of solarization and organic inputs for the control of Phytophthora root rot disease of boxwood in field conditions

Treatment

Phytophthora root rot severity (%)x

Plant fresh weight

(g)

Plant height

(cm)

Plant width    (cm)

Amara mustard + Solarization (2 weeks)

40.25 by

22.00 a

22.63 a

10.63 a

Amara mustard + Solarization (4 weeks)

28.75 bc

26.00 a

23.44 a

9.88 a

Astro arugula + Solarization (2 weeks)

32.88 b

31.06 a

21.19 a

9.81 a

Astro arugula + Solarization (4 weeks)

27.50 bc

28.44 a

22.31 a

10.63 a

Mighty mustard® pacific gold + Solarization (2 weeks)

37.75 b

22.56 a

22.63 a

9.69 a

Mighty mustard® pacific gold + Solarization (4 weeks)

34.63 b

25.00 a

23.44 a

9.94 a

Radish + Solarization (2 weeks)

29.88 b

29.31 a

22.81 a

10.88 a

Radish + Solarization (4 weeks)

29.75 b

30.50 a

22.69 a

11.59 a

Turnips + Solarization (2 weeks)

36.13 b

25.19 a

22.00 a

9.84 a

Turnips + Solarization (4 weeks)

32.63 b

21.19 a

22.69 a

9.81 a

Solarization alone (6 weeks)

28.69 bc

26.53 a

22.05 a

10.00 a

Compost

36.06 b

25.22 a

20.94 a

10.00 a

Mustard meal

31.63 b

34.44 a

24.81 a

11.38 a

Non-treated, inoculated control

58.75 a

28.22 a

21.81 a

10.28 a

Non-treated, non- inoculated control

13.63 c

28.72 a

24.09 a

9.98 a

P-value

<.0001

0.1039

0.1878

0.2042

xDisease severity was based on percentage of roots affected. yValues are the means of four replicates; treatments followed by the same letter within a column are not significantly different at P£0.05.

Rhizoctonia root rot disease severity in viburnum was high with non-treated, inoculated control plants showing 68.94% disease severity. All the tested cover crops except astro arugula and radish in combination with solarization (2-weeks or 4-weeks), solarization alone (6-weeks) and compost organic input significantly reduced Rhizoctonia root rot severity on viburnum roots compared to the non-treated, inoculated control plants (Table 3). There were no significant differences among all the tested cover crops in combination with solarization (2-weeks or 4-weeks) and other treatments except astro arugula in combination with 2 weeks solarization in disease severity. There were no significant differences in plant fresh weight, root weight, plant height and plant width among treatments (Table 3).

Table 3. Effect of solarization and organic inputs for the control of Rhizoctonia root rot disease of viburnum plants in field conditions

Treatment

Phytophthora root rot severity (%)x

Plant fresh weight

(g)

Root weight (g)

Plant height (cm)

Plant width    (cm)

Amara mustard + Solarization (2 weeks)

40.38 bcy

28.06 a

15.19 a

36.63 a

10.81 a

Amara mustard + Solarization (4 weeks)

46.88 bc

17.38 a

9.13 a

27.50 a

13.50 a

Astro arugula + Solarization (2 weeks)

59.75 ab

14.19 a

7.13 a

28.88 a

11.81 a

Astro arugula + Solarization (4 weeks)

52.50 abc

14.88 a

7.00 a

30.25 a

10.69 a

Mighty mustard + Solarization (2 weeks)

35.75 c

24.56 a

11.56 a

39.25 a

10.38 a

Mighty mustard + Solarization (4 weeks)

43.50 bc

14.00 a

6.00 a

31.50 a

11.13 a

Radish + Solarization (2 weeks)

56.00 abc

15.25 a

7.44 a

29.00 a

9.19 a

Radish + Solarization (4 weeks)

46.38 bc

24.31 a

12.94 a

27.25 a

14.75 a

Turnips + Solarization (2 weeks)

46.50 bc

21.88 a

13.06 a

28.75 a

11.50 a

Turnips + Solarization (4 weeks)

46.50 bc

22.56 a

11.31 a

34.13 a

12.94 a

Solarization alone (6 weeks)

42.75 bc

25.97 a

14.22 a

35.75 a

10.84 a

Compost

44.13 bc

17.88 a

7.94 a

30.25 a

10.56 a

Mustard meal

53.63 abc

23.69 a

13.31 a

30.38 a

9.94 a

Non-treated, inoculated control

68.94 a

18.09 a

10.34 a

34.06 a

12.16 a

Non-treated, non- inoculated control

14.56 d

20.94 a

11.38 a

33.56 a

12.69 a

P-value

<0.0001

0.1407

0.1287

0.2341

0.7237

yDisease severity was based on percentage of roots affected. xValues are the means of four replicates; treatments followed by the same letter within a column are not significantly different at P£0.05.

Root pieces taken from boxwood and viburnum plants were placed on Rhizoctonia and Phytophthora (PARPH-V8) selective media. According to the analysis, highest Phytophthora root rot plant pathogen recovery was observed in compost treated plants and non-treated, inoculated control plants (more than 30%); and there were no differences among treatments in Rhizoctonia root rot pathogen recovery (Table 4).

Table 4. Pathogen recovery percentages from the roots at the end of the field experiment

Treatment

Pathogen recovery from roots (%)x

P. nicotianae

R. solani

Amara mustard + Solarization (2 weeks)

21.25 bcdy

65.00 a

Amara mustard + Solarization (4 weeks)

20.00 bcd

76.25 a

Astro arugula + Solarization (2 weeks)

13.75 bcd

77.50 a

Astro arugula + Solarization (4 weeks)

10.00 bcd

75.00 a

Mighty mustard® pacific gold + Solarization (2 weeks)

27.50 abcd

73.75 a

Mighty mustard® pacific gold + Solarization (4 weeks)

13.75 bcd

62.50 a

Radish + Solarization (2 weeks)

16.25 bcd

63.75 a

Radish + Solarization (4 weeks)

20.00 bcd

67.50 a

Turnips + Solarization (2 weeks)

13.75 bcd

67.50 a

Turnips + Solarization (4 weeks)

18.75 bcd

60.00 a

Solarization alone (6 weeks)

8.75 cd

58.75 a

Compost

33.75 ab

85.00 a

Mustard meal

28.75 abc

85.00 a

Non-treated, inoculated control

47.50 a

95.00 a

Non-treated, non- inoculated control

3.75 d

6.25 b

P-value

<.0001

<.0001

xPathogen recovery was based on percentage of roots cultured.  yValues are the means of three replicates; treatments followed by the same letter within a column are not significantly different at P£0.05.

In this study we have evaluated five selected cover crops (Amara mustard, astro arugula, turnips, mighty mustard ® pacific gold, and radish) in combination with solarization (Liyanapathiranage 2017), solarization alone and two organic amendments (compost and mustard meal) against soilborne diseases such as Phytophthora and Rhizoctonia root rot diseases. The results of these studies showed that solarization with or without cover crops can significantly reduce root rot diseases.

An integrated management approach should be used to control soilborne pathogens (Rhizoctonia and Phytophthora). Results of both on-farm and field experiments indicate that cover crops (Amara mustard, astro arugula, turnips, mighty mustard ® pacific gold, and radish) can be used in combination with solarization to control soilborne pathogens in nursery productions. Nursery producers could benefit from using solarization alone or in a combination with cover crop to control soilborne diseases.

Each Phytophthora experimental plot consisted of 4 boxwood rooted cuttings spaced 60 cm apart with 2 m between rows. Each hizoctonia experimental plot consisted of 5 viburnum rooted cuttings spaced 60 cm apart with 2 m between rows. Boxwood rooted cuttings and viburnum rooted cuttings were planted. Plants were fertilized with 10 g of 18-6-8 Nutricote controlled-release fertilizer. Plants were watered as needed using drip irrigation system. The herbicide (Finale 31.3 ml/L) was applied as spot treatment into the test field.

Manuscripts for these trials were written and published in 2019. 

 

Participation Summary
3 Farmers participating in research

Educational & Outreach Activities

10 Consultations
3 Curricula, factsheets or educational tools
4 Journal articles
1 On-farm demonstrations
1 Tours
7 Webinars / talks / presentations
2 Workshop field days

Participation Summary

400 Farmers
400 Ag professionals participated
Education/outreach description:

Consultations. On farm consultations of soil solarization and biofumigation were conducted on 4 occasions in the summer of 2018 and 6 occasions in 2019.  

Fact Sheets. Three fact sheets were developed on beneficial insects found naturally in cover crops or aided by natural habitats. 

Journal Articles. Four journal articles related to cover crops were published in 2019. 

Talks. Seven presentations at scientific conferences were given (3-Gonzalez, 2 – Panth, 2 – Neupane). 

Eight extension talks were given by faculty to growers, landscapers and other stakeholders (1- Addesso, 3- Baysal-Gurel, 4 – Witcher).

Addesso, K. 2020. Flatheaded borer identification. Lawn and Landscape 101. Rutherford County Extension. February 13, 2020. Murfreesboro, TN. 

Baysal-Gurel, F. 2019. Phytophthora Disease Management. TSU Nursery Field Day. July 25, 2019. McMinnville, TN.

Baysal-Gurel, F. 2019. Ornamental Disease Management Research Updates. Advanced Pest &Disease Workshop, WinterGreen Trade show & Conference. January 24, 2019. Duluth, GA.

Baysal-Gurel, F. 2018. Biofumigation: opportunities and challenges for control of soilborne diseases in nursery production. University of Georgia, Athens, GA. Aug 27, 2018.

Witcher, A. Cover Crops in the Nursery; Franklin County Extension Program, Morgan Franklin. 8/22/2019.

Witcher, A. Cover Crops in the Nursery; Grundy County Extension Program, Creig Kimbro. 8/29/2019.

Witcher, A. Synthetic vs Organic. Middle TN Landscape Management Short Course. Murfreesboro, TN. 1/14/2020.

Witcher, A. Weed Management Practices and IPM. South Carolina Green Conference and Trade Show, Columbia, SC. 1/21/2020

Tours. One tour of the facility during the Southern International Plant Propagators Society was conducted on Oct 21st 2018. The tour group consisted of over two hundred participants including growers, extension agents, researchers and other stakeholders. One tour of the nursery research center was held on July 25th, 2019. Fifty growers toured the labs and cover crop field plots. 

Project Outcomes

1 Grant received that built upon this project
1 New working collaboration
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.