Effect of Alternative Fungicides on Alternaria solani Control and Productivity of Organic Tomatoes

Project Overview

GNC02-007
Project Type: Graduate Student
Funds awarded in 2002: $7,500.00
Projected End Date: 12/31/2005
Grant Recipient: Iowa State University
Region: North Central
State: Iowa
Graduate Student:
Faculty Advisor:
Faculty Advisor:
Kathleen Delate
Iowa State University

Annual Reports

Commodities

  • Vegetables: tomatoes

Practices

  • Pest Management: biological control, compost extracts

    Abstract:

    The efficacy of organic fungicides and compost teas to control Septoria leaf spot (Septoria lycopersici Speg.) on tomatoes was evaluated. Tomato plants (‘Mountain Spring’) were transplanted into black plastic mulch in May of 2003 and 2004, inoculated with 7.5 x 108 conidia×ha-1 and treated with: (i) control (no foliar spray), (ii) alternated applications of chlorothalonil plus copper hydroxide and mancozeb plus copper hydroxide ( iii) Copper hydroxide only, (iv) Bacillus subtilis only, (v) WCCM tea, (vi) VCCM tea, and (vii) SporanTM. The only treatments effective in reducing disease severity were copper hydroxide and copper hydroxide plus chlorothalonil or mancozeb. Treatments that received B. subtilis, SporanTM , or compost extracts were not effective at controlling S. lycopersici.

    Introduction:

    Managing diseases of tomatoes organically poses challenges for producers in humid climates. Septoria lycopersici is a common fungal disease of tomatoes. Resistant or tolerant cultivars are not available; therefore growers must rely on cultural and chemical control practices, including the use of copper (Cu) fungicides for disease control (Jones et al., 1991). There are currently five Cu based fungicides allowed in certified organic production. Concerns regarding the use of Cu fungicides have been expressed due to their potential to reduce crop yield (Rhoads et al., 1989) and to cause toxicity to earthworms, nematodes (Burrows and Edwards, 2002), and entomopathogenic fungi (Ropek and Para, 2002). Furthermore, the potential for Cu accumulation in the soil surface (Kabata-Pendias and Pendias, 1992) and concerns about pathogen resistance also have led producers to seek alternatives.

    An alternative disease-management technique available to organic producers is the use of biological control agents that are commercially available or producer created. Bacillus subtilisâ (Bacillus subtilis Cohn; AgraQuest, Davis, CA) is a commercially available, broad-spectrum biofungicide registered for use on tomatoes to control foliar diseases caused by bacterial and fungal pathogens. However, independent research regarding its efficacy in controlling S. lycopersici has not been repeated.

    Compost tea, a liquid extract with microorganisms (Diver, 1998), is a producer-created biofungicide. There are two main ways in which teas can be made; one includes aeration whereas the other does not. Research on non-aerated compost teas has found that control of plant pathogens in the phyllosphere from beneficial organisms is acquired through induced resistance, inhibition of spore germination, antagonism, or competition. Such studies have not been performed on aerated compost tea (Scheuerell and Mahaffee, 2002). Bacteria and fungi are the agents in compost tea that control foliar diseases, specifically those belonging to the genera Bacillus Cohn, Pseudomonas van Hall, Serratia Sm., Penicillium Link, and Trichoderma Pers. (Brinton et al., 1996). There are many factors that affect the efficacy of compost tea including compost source, dilution ratio, and organism extraction and application methods (Scheuerell and Mahaffee, 2002).
    The efficacy of these new commercial organic products and techniques available to farmers has not been evaluated. Scientific evaluation of the efficacy of pesticide products registered for use in organic agriculture is vital for growers’ success.

    Literature Cited

    Brinton, W.F., A. Tranker, and M. Droffner.
    1996. Investigations into liquid compost
    extracts (“teas”) for the control of plant
    pathogenic fungi. Biocycle 37:68-70.

    Burrows, L.A. and C.A. Edwards. 2002. The use
    of integrated soil microorganisms to effects
    of pesticides on soil ecosystems.
    Eur. J. Soil Biol. 38:245-249.

    Diver, S. 1998. Compost teas for plant disease
    control; a pest management technical note.
    National Sustainable Agriculture Information
    Service, Fayetteville, AR.

    Jones, J.B., J.P. Jones, R.E. Stall, and T.A.
    Zitter, eds. 1991. Compendium of tomato
    diseases. American Phytopathological
    Society, St. Paul, MN.

    Kabata-Pendias, A. and H. Pendias. 1992. Trace
    elements in soils and plants. 2nd Edition.
    CRC Press, Boca Raton, FL.

    Rhoads, F.M., S.M. Olson, and A. Manning. 1989.
    Copper toxicity in tomato plants. J. Environ.
    Qual. 18:195-197.

    Ropek, D. and A. Para. 2002. The effect of
    heavy metal ions and their complexions
    upon the growth, sporulation and
    pathogenicity of the entomopathogenic fungus
    Verticillium lecanii. J. Invertabr. Pathol.
    79:123-125.

    Scheuerell, S. and W. Mahaffee. 2002. Compost
    tea: principles and prospects for plant
    disease control. Compost Sci. Util. 10:313-
    338.

    Project objectives:

    Our objectives were to evaluate the efficacy of organic fungicides and compost tea from either windrow-composted cattle manure (WCCM) or vermicomposted cattle manure (VCCM). We also compared the efficacy of organic and conventional fungicides.

    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.