|
|
Impact |
© 2007 Plant Management Network. Effect of a Mustard Green Manure on Potato Yield and Disease Incidence in a Rainfed Environment Peter Sexton, Andrew Plant, and Steven B. Johnson, PO Box 727, University of Maine Cooperative Extension, Presque Isle 04769; and John Jemison, Jr., 495 College Avenue, University of Maine Cooperative Extension, Orono 04469 Corresponding author: Peter Sexton. psexton@umext.maine.edu Sexton, P., Plant, A., Johnson, S. B., and Jemison, J., Jr. 2007. Effect of a mustard green manure on potato yield and disease incidence in a rainfed environment. Online. Crop Management doi:10.1094/CM-2007-0122-02-RS. Abstract The goal of this work was to evaluate the short-term effects of a mustard green manure on potato yield and disease incidence for potatoes grown in a rainfed cropping system. Diseases of interest were black scurf (Rhizoctonia solani), powdery scab (Spongospora subterranea), and white mold (Sclerotinia sclerotiorum). On-farm trials with large (60-ft wide) replicated plots were established at three sites in 2003 and 2004, in Maine. Mustard (Sinapis alba and Brassica juncea blend) was sown at a seed rate of 10 lb/acre, mowed at late flowering, and then disked into the soil. In the following season, tuber yield was measured at each site and compared to that of potatoes grown in barley (Hordeum vulgare) check plots. Incidence of white mold on leaves and stems, and Rhizoctonia incidence on tubers, were evaluated at one site over two years. On average across all the sites, total tuber yield was 8% greater following mustard green manure versus barley. Mustard green manure was associated with decreased incidence of Rhizoctonia on tubers, and increased incidence of white mold on leaves and stems, in the following potato crop. No effect was observed on incidence of powdery scab. Introduction The goal of this work was to evaluate the short-term effects of a mustard green manure on tuber yield and disease incidence of potatoes in a rainfed cropping system. In the Columbia Basin of Washington and Oregon, where potatoes are grown under irrigation with very high yield potential, green manure mustard has provided similar tuber yields as compared to fumigation with metam sodium (2,7). The putative mode of action for suppression of some soil pathogens following a Brassica sp. green manure is the release of compounds from glucosinolates which occurs when tissue is macerated (10). In response to wounding, glucosinolates are hydrolyzed by the enzyme myrosinase releasing a range of breakdown products. The nature of the breakdown products depends on the type of side chain the parent molecule possessed. Volatiles released from breakdown of glucosinolates have shown a range of activity against various species of nematodes, insects, weeds, bacteria, and fungi (e.g., 1,3,8,9,11). However, other studies have failed to show a strong response in the levels of soil pests to use of Brassica soil amendments or cover crops (2,13). It should be noted that there is large genotypic variation among Brassica species and cultivars in the amount and kinds of glucosinolates present (up to five fold range in glucosinolate concentration) (6). Also pathogens differ in their susceptibility to glucosinolate breakdown products (11,12). In the northeastern US, potatoes are predominantly grown under rainfed conditions with moderate yield potential. In this region, Rhizoctonia, white mold, and powdery scab are several diseases of concern to potato growers. Previous work suggests that Brassica cover crops may have some efficacy against Rhizoctonia on tubers (4). On the other hand, Brassicas are a host to white mold, and white mold sclerotia have shown some resistance to glucosinolate breakdown products (12). White mold sclerotia can persist up to 5 years (5), and this disease is common to potatoes and mustard (i.e., the same species will infect both crops). Therefore this is a point of concern for potato farmers. The objective of this work was to evaluate the effect of a mustard green manure crop on potato yield, and on incidence of the diseases cited above, in a rainfed environment. The conventional rotation for potatoes in northern Maine is barley or oats followed by potatoes (1:1 rotation). On-farm trials were conducted over two cropping cycles with potato growers in the state of Maine comparing a mustard green manure to the conventional practice of growing barley. The study has two aspects: one broader effort across several sites that primarily considered effects on yield, and a second more focused effort at one site that also considered effects on disease incidence. Field Experimentation Mustard green manure plots were established in replicated trials on three farms over two seasons (2003 and 2004). In 2003 trials were established at Presque Isle, Crouseville, and Exeter, ME. In 2004 trials were established at Presque Isle, Crouseville, and Easton, ME. The trials were set up in a randomized complete-block design at each site with four replications, except for the Easton site which had only two replications. ‘Caliente 119’ (High Performance Seeds, Moses Lake, WA) was chosen as a mustard cultivar because it has a history of commercial use as a biofumigant for potatoes grown in the Pacific Northwest. ‘Caliente 119’ is a blend of materials predominantly made up of ‘ISCI 20,’ an Italian variety of Brassica juncea selected for putative biofumigant properties. It also contains other lines of both Brassica juncea and Sinapis alba. At five of the six sites, mustard and barley plots were established in mid-May to early June. At the remaining site, mustard was planted in early August after harvest of small-grain silage in late July. In all cases, barley (sown at the same time as the mustard) was included as a control treatment. Mustard was sown at a rate of 10 lb/acre at each site. Plots were 60 ft wide and varied in length based on the shape of the field. Mustard biomass samples (three 0.3 m˛ subsamples per plot) were taken within one week of mowing. Mustard plots were mowed with a rotary mower at late bloom and disked into the ground. Barley plots were managed along with the rest of the field and when mature were combined for grain. Each field was uniformly managed during the potato cycle of the rotation. Potato varieties grown were as follows: at Presque Isle, Russet Burbank in 2004 and Shepody in 2005; at Crouseville, proprietary round white chip stock in both seasons; at Exeter, FL 1533 in 2004; at Easton, Russet Burbank in 2005. Potato yield samples were hand-dug from each plot after vine killing. Three subsamples (area of 4.5 m˛) per plot were taken at the Presque Isle site, and two subsamples per plot were taken at the other farms. Tubers were graded and weighed. Data from subsamples within a given plot were averaged to give one value for each plot. To analyze yield data across sites and years, values were averaged for each treatment in a given trial, and then each farm and season was treated as one replication in a randomized complete block design. In this way, differences in management between farms would be accounted for as block effects and not be confounded with treatment effects. The yield data across sites was then analyzed as a randomized complete block design using the PROC GLM routine in SAS statistical software (SAS Institute Inc., Cary, NC). Mustard Growth and Potato Yield Across test sites, the amount of above-ground mustard biomass produced ranged from 2760 to 4370 lb/acre, on a dry matter basis (Table 1). The amount of biomass produced at the Exeter site was less than at other sites because it was sown later in the season (after a barley silage crop), so it had a shorter growing season available to it. Table 1. Total above-ground biomass produced by mustard grown as a
On average across all the sites, the mustard green manure was associated with an 8% increase in total tuber yield (320 vs. 298 cwt/acre for mustard and barley, respectively) and a 7% increase in yield of tubers greater than 4 oz in size (273 vs. 254 cwt/acre for mustard and barley, respectively). These differences were both statistically significant (P < 0.01). To give an idea of variation in response between sites, yields from each site are plotted in Figure 1. Average total tuber yield across all the sites and treatments for the two seasons was 308 cwt per acre (range of 229 to 362 cwt/acre).
Rhizoctonia, White Mold, and Powdery Scab The Presque Isle location (Roope Farm) was the primary test site for this study and had more intensive data collection than did the other sites. This was the only site where white mold was monitored. Also canola was included in the trial at this site in order to get a measure of how it affected white mold incidence. White mold incidence and severity was estimated by rating 20 plants within the middle rows of each plot using the following scale: 0 = no stem/leaf symptoms; 1 = < 10% stem/leaf symptoms; 2 = 10% to 30% stem/leaf symptoms, stem lesion at base; 3 = 30% to 60% stem/leaf symptoms, slight girdling, external sclerotia; 4 = >60% stem/leaf symptoms, girdling and death of 25% to 50% primary stems; and 5 = death of > 50% of primary stems, stem/leaf symptoms on remaining plant tissue, and presence of internal sclerotia. Integration of rating values over sampling dates was performed using relative area under the curve analysis and the data was subjected to analysis of variance. Incidence of white mold in potatoes was greater following mustard than barley in both 2004 and 2005 at the Roope Farm (Tables 2 and 3). White mold incidence also tended to be higher in plots where canola was grown the previous year. On the rating scale used, the magnitude of the increase in disease incidence was on the order of 10 to 20% in plots where mustard or canola had been grown versus barley. Nevertheless, yields were greater following green manure mustard than following barley. Apparently, the advantage gained from the mustard was greater than the cost of the small increase in white mold incidence. On the other hand, white mold sclerotia can survive in the soil up to 5 years, so a small problem could accrue over time and become a larger problem. In rainfed environments, moisture cannot be managed and excess moisture is sometimes a problem. Whether the white mold problem observed in this study would be an issue in drier climates or not is an open question. Table 2. Tuber yield, white mold incidence on stems, and Rhizoctonia
* RAUDPC stands for "Relative area under the disease progress curve." Table 3. Tuber yield, white mold incidence on stems, Rhizoctonia and powdery scab incidence on tubers, for ‘Shepody’ potatoes grown in 2005 after mustard green manure, annual ryegrass green manure, canola, and barley grown the previous year. The canola and barley were grown and harvested as seed crops. This trial was conducted at the Roope Farm in Presque Isle, ME.
* RAUDPC stands for "Relative area under the disease progress curve." Tubers were visually rated for incidence of Rhizoctonia and powdery scab when they were graded at Presque Isle in both seasons. Use of ‘Caliente 119’ mustard green manure was consistently associated with decreased levels of Rhizoctonia on tubers at these sites. Compared to the barley check at the Roope Farm, growing mustard or canola decreased tuber incidence of Rhizoctonia on Russet Burbanks in 2004 (Table 2). There was a strong trend (P < 0.10) for less Rhizoctonia after mustard on Shepody in 2005 (Table 3). Rhizoctonia and powdery scab were observed at the Crouseville site in 2004, so those plots were rated as well and showed a significant decrease in Rhizoctonia associated with use of a mustard green manure (4% incidence following barley versus < 1% following mustard, P < 0.01). There was no evidence of the mustard green manure decreasing incidence of powdery scab at the two sites where it occurred in our trials. At the Roope Farm in 2005, powdery scab incidence on Shepody was substantial across all of the treatments (Table 3). At the Crouseville site in 2004, powdery scab incidence averaged 7% across treatments, with no significant differences between treatments observed. At all the other sites, powdery scab incidence was never greater than 2% and so was not evaluated. Mustard green manure was associated with increased tuber yield and decreased incidence of Rhizoctonia. Where Rhizoctonia is a problem and is difficult to control (e.g., organic systems), mustard green manure could be a valuable tool for growers. On the other hand, mustard green manures were also associated with small but significant increases in white mold incidence. Given that white mold sclerotia survive up to five years in the soil, this disease can be expected to build up over time if it is not properly managed. Mustard green manures should probably be avoided in fields that have a history of white mold problems, and on varieties of potatoes that are susceptible to white mold (e.g., ‘Superior’). To avoid building up levels of white mold sclerotia in the soil, mustard green manures should not be included in close rotation with itself or with other rotation crops that are susceptible to white mold. Another factor to consider in planning rotations is that mustard may share diseases (such as clubroot) that affect other Brassica crops (e.g., broccoli, cauliflower, cabbages). From an economic perspective, the value of the potato crop is approximately 20 times greater than the value of the barley grain crop. In Maine, a potato crop grown for processing would typically have a value of about $1700/acre (300 cwt/acre at $5.75/cwt). The value of a barley crop sold at harvest, which is the conventional practice for potato growers in this area, would typically be about $80 per acre (60 bu/acre at $1.40/bu). Thus a small improvement in the yield of the potato crop can justify replacing the barley crop in favor of a green manure. Based on discussions with the growers involved in these trials, the cost of growing the mustard green manure, mowing it, and tilling it into the ground, is practically the same as growing barley for grain ($115 vs. $125 per acre, for mustard versus barley, respectively). The data from this study indicates a yield benefit of approximately 7% for potatoes following ‘Caliente’ mustard green manure; this translates into an economic return on the order of $120/acre. This is about $40/acre greater than the gross value of the barley crop, not considering the greater cost of growing barley. Thus mustard grown as a green manure appears to have potential as an alternative rotation crop for potatoes grown under rainfed conditions in the northeastern US. Conclusions Across six on-farm trials in rainfed potato production systems, total tuber yield averaged 8% greater following a mustard green manure (variety ‘Caliente 119’) than following barley. The mustard green manure was associated with decreased incidence of Rhizoctonia on tubers, and with increased incidence of white mold on stems and leaves. While inclusion of a mustard green manure appears to be a profitable practice (relative to growing barley), it should be avoided on potato fields where there is a history of white mold problems, and on varieties that are highly susceptible to white mold. It also seems advisable to avoid short rotations with other crops that are susceptible to white mold, as well as to avoid short rotations with other members of the Brassica family. Acknowledgments The authors wish to acknowledge the cooperating growers without whom this trial would not have been possible: Brandon and Bruce Roope, Bruce and Jerry Flewelling, Fred Flewelling, and John Dorman. We also acknowledge the assistance of Erik Ireland and Jeff Dorman in conducting field work. This work was partially funded by a grant from the USDA-SARE program. Literature Cited 1. Brown, P. D., and Morra, M. J. 1995. Glucosinolate-containing plant tissues as bioherbicides. J. Agric. Food Chem. 43:3070-3074. 2. Collins, H. P., Alva, A., Boydston, R. A., Cochran, R. L., Hamm, P. B., McGuire, A., and Riga, E. 2006. Soil microbial, fungal, and nematode responses to soil fumigation and cover crops under potato production. Biol. Fertil. Soils 42:247-257. 3. Delaquis, P. J., and Sholberg, P. L. 1997. Antimicrobial activity of gaseous allyl isothiocyanate. J. Food Protect. 60:943-947. 4. Dhingra, O. D., Costa, M. L. N., Silva, G. J., Jr., and Mizubuti, E. S. G. 2004. Essential oil of mustard to control Rhizoctonia solani causing seedling damping off and seedling blight in nursery. Fitopatol. Bras. 29:683-686. 5. Huang, H. C., and Kozub, G. C. 1994. Longevity of normal and abnormal sclerotia of Sclerotinia sclerotiorum. Plant Disease 78:1164-1166. 6. Kirkegaard, J. A., and Sarwar, M. 1998. Biofumigation potential of brassicas I. Variation in glucosinolate profiles of diverse field-grown brassicas. Plant Soil 201:71-89. 8. Peterson, C. J., Tsao, R., and Coats, J. R. 1998. Glucosinolate aglucones and analogues: Insecticidal properties and a QSAR. Pest. Sci. 54:35-42. 9. Potter, M. J., Davies, K., and Rathjen, A. J. 1998. Suppressive impact of glucosinolates in Brassica vegetative tissues on root lesion nematode Pratylenchus neglectus. J. Chem. Ecol. 24:67-80. 10. Rosa, E. A. S., Heaney, R. K., Fenwick, G. R., and Portas, C. A. M. 1997. Glucosinolates in crop plants. Pages 99-215 in: Horticultural Reviews, Vol 19. J. Janick, ed. John Wiley & Sons, New York. 11. Sarwar, M., Kirkegaard, J. A., Wong, P. T. W., and Desmarchelier, J. M. 1998. Biofumigation potential of brassicas. III. In vitro toxicity of isothiocyanates to soil-borne fungal pathogens. Plant Soil 201:103-112. 12. Smolinska, U., and Horbowicz, M. 1999. Fungicidal activity of volatiles from selected cruciferous plants against resting propagules of soil-borne fungal pathogens. J. Phytopathol. 147:119-124. |
