Efficacy of compost tea on Septoria leaf spot in field and greenhouse studies

View the project final report

• 2007 annual report

Commodities

• Vegetables: tomatoes

Practices

• Pest Management: compost extracts

Field and greenhouse trials were conducted to evaluate the efficacy of compost tea on Septoria lycopersici, causal agent of Septoria leaf spot on tomato, in Kansas, in 2006 and 2007. Compost tea with several additives sprayed weekly on tomato plants prior to and after disease onset in the field led to no significant difference in control of the pathogen compared to untreated controls. In the greenhouse, inclusion of specific additives did not reduce disease compared to unamended compost tea. However, inclusion of hydrolyzed fish fertilizer increased disease severity compared to other treatments.

Introduction:

Compost tea has been cited as an option for conventional and organic growers to suppress plant pathogens (Diver, 2002; Ingham, 2005a; Kannangara, 2006; Tsror 1999). Compost tea is an aqueous solution that results from the extraction of microorganisms, fine particulate organic matter, and soluble chemical components of compost, that is intended to maintain or increase the beneficial microorganism population of the source compost (NOSB, 2006). Beneficial microorganisms in compost tea are thought to suppress plant diseases by occupying spatial niches on the phylloplane, competing with pathogens for leaf/seed exudates, or directly antagonizing pathogens (Diver, 2002; Ingham, 2005a). Compost teas are also thought to enhance crop fertility by introducing microorganisms that might aid in soil nutrient retention and extraction, and by adding soluble nutrients, further adding to their potential value as a part of an integrated crop management plan (Diver, 2002; Ingham, 2005a; Kannangara, 2006; Merrill and McKeon, 2001).

There are several methods for producing compost tea, and variables can include aeration (injecting air into the brew tank or recirculating the contents), compost source (ex: cow manure, yard waste, bark, etc), additives (ex: molasses, fish hydrolysate, humic acid, kelp), brewing/production time, and compost-to-water ratio (Ingham, 2005b; Diver, 2002; Al-Dahmani et al, 2003; Elad and Shtienberg, 1994, Welke, 2004; Scheuerell and Mahaffee 2004).

Al-Dahmani, et al. (2003) investigated the effects of compost source (cow manure, pine bark, yard waste, and organic farm compost), compost maturity (5, 10, 16 months), aeration, compost-to-water ratio (1:1,1:3, and 1:5), and filtration on compost efficacy against the bacterial pathogen Xanthomonas vesicatoria on young tomato plants in the greenhouse. In their trials all formulations provided significant disease suppression (Al-Dahmani, et al. 2003). Elad and Shtienberg (1994) investigated the effects of various production intervals (4 hours, 1 week, and 2 weeks), the addition of a proprietary nutrient broth, pasteurization, and dilution on efficacy of a non-aerated compost tea against Botrytis cinerea on tomato leaves, pepper leaves, and grape berries in growth chamber and greenhouse studies. They found that brewing for ten to fourteen days was more effective, but addition of nutrients did not increase the suppressiveness. Pasteurization to eliminate the microflora of the compost tea had no effect on disease suppression, but dilution reduced its effectiveness (Elad and Shtienberg, 1996). Welke (2004) investigated the effects of aeration and water-to-compost ratio on the efficacy of CT against Botrytis cinerea on strawberry fruit. While both aerated and non-aerated compost tea suppressed disease, only aerated compost tea resulted in greater yields. Interestingly, 8:1 concentrations of water-to-compost resulted in significant differences in disease while 4:1 concentrations did not (Welke, 2004).

Scheuerell and Mahaffee (2004) investigated the effects of aeration, additives, and compost source on compost tea efficacy against cucumber seedling damping off caused by Pythium ultimum. Their investigations reported that ACT and NCT significantly reduced the occurance of damping off, but only ACT reduced its occurance consistently. Their results indicated that NCT without additives resulted in no significant reduction of damping-off while NCT produced with either fungal (seaweed powder, humic acids, and rock dust) or bacteria (a proprietary bacterial nutrient solution) promoting additives significantly, but inconsistently, reduced damping-off. Aerated CT produced without additives or with the putative bacteria promoting additive resulted in inconsistent reduction of damping-off, while aerated CT produced with the putative fungal additives consistently gave significant control of the pathogen (Scheuerell and Mahaffee, 2004). Septoria lycopersici Speg., the causal agent of Septoria leaf spot on tomato (Lycopersicon esculentum Mill.), is an important fungal disease of tomato (Parker, et al. 1997). Symptoms are circular lesions up to 1/8 inch in diameter that begin as yellow areas that then turn brown, sometimes with a light or dark border (Sherf and Macnab, 1986/ compendium). After several days, lesions may begin to produce black pycnidia, which distinguish this disease from others (Sherf and Macnab, 1986). Septoria leaf spot occurs in most U.S. states where tomato is grown and can cause severe defoliation and yield loss (Sherf and Macnab, 1986). All released tomato cultivars are susceptible to this disease (Parker, et al. 1995; Sugha and Kumar, 1998). Control of this pathogen has been achieved through cultural controls and fungicide applications (Blum, 2000; Elmer and Fernandino, 1995; Parker, et al. 1995; Tu, et al. 1998). In the Midwest/Great Plains, a number of fungicides are labeled for preventative use for foliar diseases of tomato (Egel, et al. 2007). For organic growers, fungicide options are limited. Copper fungicides (Bordeaux mixes, copper hydroxide, copper oxide, copper oxychloride, and copper sulfate) are currently labeled for control of S. lycopersici in organic production, but their use is controversial because they are toxic to many microorganisms at recommended rates (Diver, et al. 1999). Because these fungicides have provided adequate control, historically there has been little work done to develop resistant cultivars (Tu and Poysa, 1990), though breeding programs have recently begun to target this disease (Tu, et al. 1998). In the meantime, CT may provide a means of controlling Septoria leaf spot in tomato production.

Blum (2000) demonstrated that it is possible to reduce the incidence of this disease through the introduction of bacteria and yeast isolates onto the phylloplane. Kashyap (1978) inhibited leaf necrosis due to Septoria lycopersici through the introduction of antagonists Trichoderma viride strain 3, Acremonium charticola, and Cladosporium sphaerospermum strain 3. Silva, et al (2004) reported that when used alone, Bacillus cereus moderately lowered area under the disease progress curve (AUDPC) values of Septoria leaf spot as well as early and late blight on tomato. Gangaiah (2005) studied the efficacy of CT against Septoria leaf spot and early blight on tomato. He reported greater control and marketable yields with CT and mancozeb than untreated plots, though the treated plots had high (>80%) disease severity.

The objectives of this research were to re-evaluate the efficacy of the general compost tea formulation investigated by Gangaiah (2005) in the field, and to investigate the role of different additives in the greenhouse.