Soilborne Disease Research Grant Progress Report –January 2006

Project Title: Effective Rotation Crops for Control of Powdery Scab and Other Soilborne Diseases

Principal Investigator: Robert Larkin¹, Plant Pathologist

Co-investigators: Dave Lambert², Plant Pathologist,

Tim Griffin¹, Agronomist, and

John Halloran¹, Agricultural Economist.

Address/Affiliation: ¹USDA, ARS, New England Plant, Soil, and Water Lab, University of Maine, Orono, ME 04469. ²Dept. Plant, Soil, and Environmental Sciences, University of Maine.

Project Objective: To evaluate the effects of selected rotation crops on multiple soilborne diseases, tuber yield and quality, and economic viability.

Executive Summary: Numerous soilborne diseases are persistent, recurrent problems in potato production, resulting in reduced plant growth and vigor, lower tuber quality, and reduced marketable yield. These diseases include Rhizoctonia, common scab, white mold, pink rot, Pythium leak, silver scurf, and powdery scab. Powdery scab, in particular, has emerged as a difficult and increasing problem, with virtually no effective control options available. The objective of this project is to evaluate the effects of selected rotation crops on multiple soilborne diseases, tuber yield and quality, and economic viability, with special emphasis placed on the efficacy of Brassica crops (canola, rape, and assorted mustard varieties) in managing serious soilborne disease problems. The project focuses on the establishment and assessment of various rotation crop treatments in on-farm trials at multiple locations with a history of soilborne disease problems. It also assesses different management options to determine how to best utilize Brassica crops in potato production. In 2005, field trials were established at two on-farm locations (in central and northern Aroostook county), and at the ARS Research Farm in Newport, Maine. At each location, multiple two-year rotations were established with up to six different Brassica rotation crops (canola, winter rapeseed, condiment mustard, oriental mustard, oilseed radish and a high-glucosinolate mustard blend), as well as a standard rotation crop control (barley, oats, or buckwheat, depending on the particular farm). Green manure rotation crops were incorporated into the soil in early fall 2005. At some locations, plots were also split to include an additional fall cover crop of rapeseed planted after the summer rotation crop on half of each plot, to assess the potential benefits of a fall-planted Brassica crop. All plots will be planted to potato in 2006 and assessed for disease and yield effects. An additional rotation study (with barley, canola, and mustard rotations), began in 2004, at UM Aroostook Farm in Presque Isle on plots with a history of pink rot, was continued. In 2005, plots were planted to Russet Norkotah and evaluated for pink rot, Rhizoctonia, and common scab diseases. Greenhouse experiments assessing the capabilities of different Brassica crops and mustard varieties for reducing inoculum and disease from soilborne pathogens also have been continuing, to determine the best varieties for use in field assays. More than 15 different Brassica species and varieties have or are being tested. This was the first full year of a proposed 3-year project. Brassica crops continue to look promising for managing multiple soilborne disease problems, and over the next 2 years, this research will provide detailed information on their efficacy and implementation in potato production.

Field experiments. Field trials were established in June 2005 at two on-farm locations in northern Maine and at the USDA-ARS research site in central Maine. At each location, multiple two-year rotations were established. Soil samples taken from each location in the spring and fall are currently being analyzed in the laboratory for characterization of and changes within soil microbial populations. The techniques include fatty acid extractions, soil dilution plating, and Biolog analyses. Research also continued at plots established in 2004 at Aroostook farm.

Site 1: Northern Aroostook

This site has a history of powdery scab, Rhizoctonia disease, and common scab. Four blocks with seven rotation treatments were established in June 2005. Each plot is 30 feet x 150 feet. The seven rotations are as follows: condiment mustard (‘Ace Yellow’), high-glucosinolate mustard blend (‘Caliente-119’), canola (‘Hyola 401’), rapeseed (’Dwarf Essex’), oriental mustard, oilseed radish, and buckwheat (as rotation standard), all planted at approximately 8 lbs/acre. The high-glucosinolate mustard, rapeseed, oriental mustard and oilseed radish were mowed and tilled on August 4. The other plots were mowed and raked at this time. All plots were planted again two weeks later with a winter rapeseed (‘Dwarf Essex’). This cover crop will be mechanically incorporated in spring 2006 prior to potato establishment.

Site 2: Central Aroostook

This site has a history of common scab , powdery scab, and Rhizoctonia disease. Four blocks with five rotation treatments were established in June 2005. Each plot is 10 feet x 60 feet. The rotations are as follows: condiment mustard (‘Ace Yellow’), high-glucosinolate mustard blend (‘Caliente-119’), canola (‘Hyola 401’), rapeseed (‘Dwarf Essex’), and ryegrass (‘Lemtal’) (as the standard rotation crop). The mustard blend and rapeseed were mowed and mechanically incorporated on August 11 (the condiment mustard was also mowed and combined). The canola took a very long time to mature and the grower mechanically incorporated the plots on September 8 while the plants were still quite green (not dried-down). One-half of each plot was planted to winter rapeseed on September 14, but growth was quite poor.

Site 3: USDA Research Farm, Newport

Research was conducted on previous research plots established in 2001 (with a history of Rhizoctonia and common scab) as part of a separate crop rotation study. Four replicate blocks with three rotation treatments were established in June 2005. Each rotation plot is 12 x 60 ft. The rotation treatments are: a high-glucosinolate mustard blend (‘Caliente-119’) representing the Brassica crops, barley underseeded with ryegrass, representing a standard rotation crop, and continuous potato as a nonrotation control. Mustard was planted on June 9 at approximately 6 lbs/acre, barley/ryegrass was planted at 25 lbs/acre. Plots were to be split, with half of each plot to receive a fall cover crop of rapeseed (‘Dwarf Essex’) in September, for comparisons of each rotation with and without a Brassica cover crop. However, due to record amounts of rainfall received in September, the fall cover crop was not able to be planted in 2005. We will attempt an early spring short-season (April-May) planting of rapeseed in 2006, prior to planting all plots to potato (June 2006).

Site 4: UM Aroostook Farm, Presque Isle

Dave Lambert (UMaine) established research plots in 2004 at Aroostook Farm in a location with a history of pink rot (soil infested in previous years) and other soilborne diseases. The experiment was established with four replicate plots (12 x 36 ft) of three different rotations (canola, mustard and barley). In 2005, all plots were planted to Russet Norkotah potatoes and evaluated for pink rot, Rhizoctonia, and yield. 2005 results are still being tabulated, evaluated, and analyzed, and will be available soon, but were not yet ready at the time of this report.

Plans for 2006:

At all locations (except Aroostook Farm, which was in potato in 2005), potato will be planted following each of the rotation crops and/or fall cover crops. After planting, sprout emergence, plant stands, and disease problems will be monitored throughout the season, including sampling of underground plant parts for assessment of powdery scab galls, Rhizoctonia cankers, etc. At harvest, tuber yield and quality will be measured, and tubers assessed for symptoms of powdery scab, common scab, black scurf, etc. (whatever soilborne diseases are present) for all plots and subplots. In addition, adjacent field areas to those established in 2005, will be planted in 2006 to the same rotation crops as in 2005, and evaluated for disease and yield effects in 2007. Thus, two full two-year rotation cycles (rotation crop-potato) may be accomplished within a three-year period (2005-2007). Economic analyses of the rotation sequences will also be conducted to determine the effects on profitability and risk. Potential economic benefits include lower disease control costs (including product loss) and higher marketable yields within the potato crop.

Greenhouse experiments. Greenhouse tests were continued evaluating different Brassica crops for efficacy in reducing soilborne pathogen inoculum and diseases. In one test, four different Brassica crops (rapeseed, oriental mustard, turnip, and oilseed radish were compared with non-Brassica crops ryegrass, clover, and potato, for their effects on Rhizoctonia (Table 1). Tests were conducted in seedling trays (6 x 12 x 4 in.), with 4 replicate trays per rotation crop. Crop plants were grown in infested soil trays for 4-6 weeks, harvested, then crops replanted and grown another 4-6 weeks. Plant material was then incorporated into the soil as much as possible, and allowed to decompose and equilibrate for 2-3 weeks. Soil samples were taken after the first and second crop growth periods and evaluated for effects on pathogen inoculum levels. Three seedpieces of ‘Shepody’ potato were planted in each tray and allowed to grow for ~ 4 weeks and disease assessed on the seedlings. After the first crop planting, Rhizoctonia inoculum had been reduced by 39-50% across all rotations, with rapeseed, turnip, oilseed radish and oriental mustard significantly reducing inoculum concentration relative to the control (Table 1). Although inoculum levels increased slightly in some treatments after the second planting and there were no significant differences among crops, Rhizoctonia levels were still reduced 39-42% relative to initial inoculum levels. In subsequent disease assessments, only rapeseed significantly reduced stem canker relative to the control, but rapeseed, turnip, and clover all significantly reduced the development of black scurf on the seed tubers (Table 1).

Table 1. Effect of different rotation crops on reduction of inoculum of Rhizoctonia solani (relative to initial levels) and Rhizoctonia diseases (stem canker and black scurf).

	Inoculum reduction (%) reduction^A		Disease Rating (0-5)
Rotation	1^st planting	2^nd planting	Canker	Scurf
Control (no crop) TBarenburg’o[p	39.1	38.9	1.50	1.75
Ryegrass-‘Lemtal’	42.9	41.5	0.82	0.91
Clover	43.6	38.5	0.36	0.36*
Rapeseed-‘Dwarf Essex’	45.6*	38.6	0.09*	0.18*
Turnip ‘Purple Top’	47.0*	40.6	0.73	0.45*
Oilseed radish	49.4*	38.6	1.50	1.55
Chinese mustard	50.4*	41.1	1.27	1.00
LSD (P=0.05)	5.5	4.6	1.36	0.84

In other experiments, a collection of different mustard species and varieties were evaluated for their growth characteristics and effects on pathogen inoculum and disease development in the greenhouse to further assess varieties with potential for field evaluations. In these tests, four different white mustards, five different oriental mustards, a mustard blend, and an arrugula, were compared with ryegrass as rotation crops. The experiment was conducted once in May 2005 with inconclusive results, and is currently being conducted again. Although no significant differences among crops were observed in ratings of Rhizoctonia inoculum levels (Table 2), most crops reduced inoculum relative to initial levels. One mustard, Pacificgold, had higher Rhizoctonia ratings than most other crops. Problems and inconsistencies with the potato seed assay prevented disease assessments in this test. All varieties grew well and produced abundant biomass.

Table 2. Mustard varieties and other crops tested for effects on inoculum of Rhizoctonia solani in a greenhouse test after incorporation of crops as a green manure.

Crop type Variety Average soil colony rating (1-5 scale)

White mustard (Sinapis alba) Idagold 0.83

“ Martigena 0.92

“ Tilney 1.02

Oriental mustard (Brassica juncea) Pacificgold 1.40

“ ISCI-61 1.12

“ ISCI-20 0.97

“ ISCI-99 0.96

Mustard Blend (S.alba/B.juncea) Caliente-119 0.95

Arugala (Eruca sativa) Nemat 1.08

Ryegrass (Lolium Lemtal 0.75

Conclusions:

Because the work outlined in this report only represents the first year of a proposed 3-yr project, there is little that can be concluded at this point. Most of the work done over the past year consisted of establishing the test rotations at on-farm and other field sites. Over the next 2 field seasons, disease and yield assessments will determine which crops and management approaches are most effective. Greenhouse studies continue to give indications of which varieties may be most useful for field testing.