Organic Methods for Control of Root Rot in Pea and Spinach in Northeastern U. S




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16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/12572

Organic Methods for Control of Root Rot in Pea and Spinach in Northeastern U.S.

Schrum, H.1, Kotcon, J.2, Verlinden, S.3

Keywords: root rot, organic disease control

Abstract

The root rot disease complex is a limiting factor in organic production of cool season crops. This study aimed to increase seedling stands of peas and spinach by altering the seed environment such that the growing conditions of the seeds were favored over those of the pathogens. We compared treatments of raised (ridged) seed beds, dairy and vermicompost troughs, transplanting, and a biocontrol soil drench. Of the methods tested, transplanting provided the most reliable and best crop stands for both seasons (p=0.05) Since this method relies on the biological resistance the plants develop naturally with age, this method could prove applicable across many climates and other crops which are threatened by root rot.

Introduction

Root rot, seed rot, and damping off collectively represent a detrimental disease complex (hence referred to as root rot) which affects many vegetable crops. Root rot is marked by poor seedling emergence; infected seeds are soft, mushy and quickly deteriorate. In this study the pathogens identified were Pythium spp, Fusarium spp. and Rhizoctonia solani. The host crops in this study are spinach (Spinacia oleracea) and pea (Pisum sativum).

Conventional management of root rot relies on fungicidal seed treatments or, in severe infestations, methyl bromide fumigation. However, these treatments are not permitted in certified organic crops. Organic growers have few options for overcoming the detrimental effects of a root rot infestation. For many growers in the northeast U.S. obtaining a marketable crop of either peas or spinach can be nearly impossible due to the poor stands caused by root rot.

Peas and spinach share similar environmental growth conditions as root rot pathogens. Creating a seed bed which favors growth of the seed over that of the pathogen can be accomplished by exploiting the slight differences in the optimum growing conditions of the plants over that of the pathogens. Two important environmental factors which impact soil fungi are soil temperature and moisture, with the latter having greater potential influence on the severity of the disease. Kumar et al. (1999) have shown that the pathogens are more destructive at lower temperatures and higher moisture. Cultural management and techniques should therefore be geared towards creating higher temperatures and lower moisture environments than found in normal field conditions. Our objective was to compare ridge and furrow planting; compost amendments; a commercially available, certified organic soil drench; and transplanting as methods to establish these favorable environmental conditions, thus improving crop stands.

Ridge planting (Hodges, 2003) refers to planting seeds in a raised seedbed created during tillage. Another manipulation of the seed bed is to plant seeds in a furrow or trough of compost. By forming a physical barrier around the seed exudates, the compost environment may allow seedlings to develop beyond susceptibility of the pathogen (Mandelbaum Hadar, 1990). Additionally, the increase of antagonistic bacteria from the compost may suppress pathogen growth (Sullivan, 2004). It is well documented that mature composts contain a wealth of microbial populations (Boehm et al., 1993), although variation between types and batches of compost creates inconsistencies (Sullivan, 2004). We evaluated a locally-made dairy manure compost and commercially-produced vermicompost (from earthworm castings). The next treatment was the use of transplants. Seedlings are grown in flats of sterile media (usually 10-14 days, or until seedling shows 3-4 sets of true leaves) to mature beyond the most vulnerable stage of susceptibility to the seed rot pathogens. The seedlings are then transplanted into the field. We were able to compare the change in time and labour necessary for this by using records and data from a previous study (Childers, 2005). Finally, we evaluated a commercially available soil drench of Trichoderma harzianum as an antagonist to root rot pathogens. This product is registered for suppression of root rots in organic agriculture.

Materials and methods

All research was conducted at the West Virginia University Organic Research Farm located in Morgantown, WV, USA. The farm has been certified organic since 2003; all research complies with USDA organic standards. Spinach (Spinacia oleracea 'Whale F1') and garden pea (Pisum sativum 'Oregon Giant') seeds were used in all experiments. A 15.2-by- 7.6m plot, prone to root rot disease, was tilled and prepared for planting in fall 2006, spring 2007, and fall 2007. Eight treatments with three replicates each were established in a completely randomized design.

Treatments 1-4) Compost troughs (dairy manure compost and vermicompost, each at 2 rates): The planting rows were excavated of field soil and the trough was filled with either dairy manure compost (from WVU dairy research farms) or vermicompost (UNCO Industries, Racine, WI) at two rates: 1,967 cm3 compost m-1 or 3,387 cm3 m-1, referred to as Low and High respectively. The seeds were planted into the compost troughs such seeds were encased within the compost and had no contact with the field soil. 5-6) Ridge planting: In a prepared bed, the field soil was mounded to create a convex-shaped seed bed. Two different heights of the ridge bed (7.5 cm and 15 cm) were compared. 7) Transplanting: Seeds were sown in flats using organic growing media (made with WVU dairy compost, peat, and perlite) and allowed to develop for 10-14 days before being placed in the field (at the same time as seeds in the other treatments were sown). Both pea and spinach were transplanted as clumped groups containing 5-7 seedlings in each clump. 8) Control: Seeds were sown using traditional planting methods placing seeds directly into level rows.

Each treatment row (containing peas) was 1.2 m in length. Peas were planted 5 cm deep, 5 cm apart. Rows containing spinach were 60 cm long with seeds sown 3 mm deep, 5 cm apart. Seedling emergence/survival was recorded at 10, 15 and 21 days after planting. Soil moisture and temperature measurements were recorded continuously from the time of planting until the final field observation (21 days) with WatchDog data loggers (model 400, Spectrum Technology, East-Plainfield, IL). In fall 2007 we compared a commercially available organic soil drench, Root Guardian Biofungicide (Trichoderma harzianum, Gardens Alive, Lawrenceburg, IN), transplanting, and a control for their effect on seed emergence. Seeds were sown into the field and Root Guardian was applied as a soil drench at the recommended rate of 12 ml/L immediately after planting. The transplanting and control treatments were as described above.



Tab. 1: Mean emergence (%) of spinach and peas after 21 days in fall 2006 and spring 2007




Fall-Spinach

Spring-Spinach

Fall-Peas

Spring-Peas

Transplant

95 a

90 a

99.1 a

93 a

Control

0 c

4.3 b

11.4 d

10.3 bc

Vermicompost-High

43.3 b

2.6 b

27.7 bc

8.6 c

Ridge-15cm

2.5 c

6 b

15.9 cd

16.6 bc

Dairy-High

3.3 c

1.6 b

19.6 bcd

31.3 b

Vermicompost-Low

29.1

5.3 b

39.2 b

8 c

Ridge-7.5cm

1.6 c

7.6 b

16.4 bcd

20.3 bc

Dairy-Low

6.6 c

8.6 b

15.9 bcd

21 bc

* Means separated by Tukey-Kramers HSD. P<0.05

Results

Transplanting of both pea and spinach resulted in survival rates nearing 100% for both years (Fig.1-4). Spinach emergence was greater (P = 0.05) in plots with high vermicompost than controls in 2006, but not in 2007. None of the other treatments differed significantly from the control in either year (Fig. 1 and 2). Pea emergence in plots with the high dairy compost treatment was greater (P = 0.05) than in controls or the high ridge treatment in 2006, but these differences were not significant in 2007 (Fig. 3 and 4). Pea emergence in the low vermicompost treatment was greater (P=0.05) than in controls in 2006, but the high vermicompost treatment did not differ from controls in 2006, and both vermicompost treatments resulted in the lowest pea emergence in 2007. In the fall 2007 experiment with Root Guardian, the transplanting treatment resulted in the highest plant (pea and spinach) survival (data not shown). No significant differences were observed between the Root Guardian treatment and the control. Temperature and moisture sensors were placed in only one replicate of each treatment, so statistical comparisons are not possible (data not shown); however no consistent correlations occurred between treatments or seasons and stand emergence for either crop.



Conclusions

Despite anecdotal evidence suggesting that improving drainage by planting seeds on a ridge will help in controlling root rot,

we concluded that the differences in soil moisture or temperature between ridge plantings and the control did not significantly impact crop stands in our silt loam soil. Interestingly, the volume of compost made no difference in the results associated with the treatments, which we think illustrates the tenacity of the pathogens to migrate considerable distances in the rhizosphere to reach sprouting seeds. The pathogen population may be too overwhelming for an effective antagonistic suppression to take place. The inconsistent results between the two seasons demonstrated that these methods are unpredictable in resulting in an improved seed stand. This may be due to a significant interaction between climate and treatment that needs to be explored in more detail. We found the soil drench, Root Guardian, to be an ineffective treatment, as it was not statistically different from the control. We recognize the possibility of a seasonal interaction, and thus we will repeat the experiment with Root Guardian in spring 2008.

Finally, due to the overwhelming success of the transplanting method, small scale growers whose fields show poor stands of peas and spinach due to root rot are recommended to follow this technique. Though this method increased our planting time/labor by 25% we felt that this could be reduced by the efficiency of a larger scale farm operation. Moreover the additional time and labor was justified by the insurance of not losing crops to root rot. The minimal cost inputs created by the flats and media could be distributed over many seasons.



References

Boehm, M.J., L.V. Madden, & H. Hoitink. (1993). Effect of organic matter decomposition level on bacterial species diversity and composition in relationship to pythium damping-off severity. Applied and Environmental Microbiology 59(12): 4171-4179

Childers, Todd Bradley (2005). The Effect of Low and High Fertility Treatments on Soil Quality, Yields, Pest Incidence and Labor Requirements of a Post-transitional Organic Market Garden System, Master's Thesis, West Virginia University, [On-line Abstract].

Hodges, L. (2003). Damping off of seedling and transplants. University of Nebraska-Lincoln Extension publication G1522

Kumar, S., K. Sivasithamparam, J.S. Gill, & M.W. Sweetingham. (1999). Temperature and water potential effects on growth and pathonogencity of Rhizoctonia solani AG-11 to lupin. Canadian Journal of Microbiology 45: 389-395.

Mandelbaum, R. & Y. Hadar. (1990). Effects of available carbon source on microbial activity and suppression of Pythium aphanidermatum in compost and peat container media. Phytopathology 80(9): 800-804.




1 West Virginia University, Morgantown, WV, USA. Email: hannahwitten@yahoo.com

2 As above.

3 As above



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