Cover crops such as rye, hairy vetch, and subterranean clover (Trifolium subterraneum) have been used in no tillage and reduced tillage vegetable and agronomic crop production systems to reduce soil erosion, improve organic matter content, increase crop yield, supply nitrogen to subsequent crops, increase soil water-holding capacity, control weeds, and reduce competition and damage caused by pests (Abdul-Baki and Teasdale, 1993; Blevins et al., 1990; Creamer et al., 1996a, 1996b; Mills et al., 2002; Mitchell and Teel, 1977; Price and Baughan, 1987; Vaughan and Evanylo, 1998).
Soil splashing can help disseminate important fungal pathogens of tomato such as anthracnose fruit rot, early blight (Alternaria solani), and septoria leaf spot (Septoria lycopersici). Cover crop mulches left on the soil surface may help break disease cycles and suppress the dissemination of soil-borne plant pathogens (Creamer et al., 1996a), and provide a more cohesive soil in which soil particles are less likely to be dislodged and splashed onto crop foliage (Mills et al., 2002). Soil splashed onto foliage as a direct result of rainfall or overhead irrigation may disseminate pathogen inoculum that acts to initiate primary infections early in the growing season. An intact cover crop mulch on the soil surface may intercept splashed soil and thus reduce the amount of soil that reaches the plant canopy. Coverage of tomato leaflets with soil was reduced in plots with polyethylene or hairy vetch mulches versus bare soil or compost in 2 years of assessment (Mills et al., 2002). Surface topography of groundcover and plant canopy were major factors controlling splash dispersal of anthracnose (Colletotrichum acutatum) of strawberry (Fragaria ×ananassa) through effects on splash droplet trajectories and loss of inoculum (Yang et al., 1990). Straw mulch alone provided 95% to 99% control of leather rot (Phytophthora cactorum), and straw mulch between the rows was equally or more effective than fungicides for controlling leather rot of strawberry (Ellis et al., 1998).
In contrast, another study showed that soil diseases affecting tomato were not controlled by mulches. Soil populations of verticillium wilt (Verticillium dahlia) and Fusarium wilt (Fusarium spp.) in processing tomato production were unaffected by overwintered mustard (Brassica hirta) cover crops, and there was no evidence of soil-borne disease suppression on subsequent tomato crops (Hartz et al., 2005).
Fruit quality is especially important in processing tomato production because of stringent requirements imposed by the U.S. Food and Drug Administration and processors (i.e., local) regarding acceptable mold counts and fruit rot incidence (Byrne et al., 1997). To help reduce mold and fruit rots, fungicides are applied to nearly 100% of the processing tomato crop grown in the midwestern region of the United States, with applications occurring every 7 to 10 d starting from a few weeks after transplanting and continuing until harvest (Precheur et al., 1992). Even with a good fungicide program, fruit rot caused by anthracnose can be as high as 15% (Dillard et al., 1997; Sherf and MacNab, 1986).
The disease forecasting system, Tom-Cast, was developed to help tomato grower's time fungicide applications for the control of early blight, anthracnose fruit rot, and septoria leaf spot (Pitblado, 1992). Tom-Cast predicts fungal disease development by recording field data on leaf wetness and temperature, which is then used to create disease severity values (DSV) that correspond to the severity of disease pressure affecting the tomato crop. Fungicide applications are then recommended based on the accumulation of those DSV. In several years of field trials, the Tom-Cast disease-forecasting system reduced fungicide applications by 34% and was widely adopted by processing tomato growers in the midwestern United States (Gleason et al., 1995). In other studies, Tom-Cast consistently reduced the amount of fungicide applied to tomato crops by 50% compared with 7-d spray programs (Kienath et al., 1996; Sikora et al., 1994). Tom-Cast has been evaluated and modified for managing diseases in tomato crops in North America and Australia (Cowgill et al., 2005; Fulling et al., 1995; Minchinton et al., 2006; Patterson et al., 2001; Pitblado et al., 2006), and has been tested for use in other crops such as carrot (Daucus carota), celery (Apium graveolens), and potato (Solanum tuberosum) (Bounds and Hausbeck, 2007; Bounds et al., 2006, 2007; Grunwald et al., 2000; Rogers and Stevenson, 2006). In general, when fungicide applications to crops are reduced as a result of using Tom-Cast, grower costs are also reduced (Bounds et al., 2006, 2007; Sikora et al., 2002).
Combining cover crop mulches with disease-forecasting systems may help reduce the amount of fungicide needed during the growing season. A study evaluating the use of a zone-tilled cover crop mulch system combined with Tom-Cast had no effect on marketable yield or percentage of total molded fruit, and no consistent effect on defoliation caused by early blight (Louws et al., 1996). However, in this study, Tom-Cast–timed spray schedules required 45% to 80% fewer fungicide applications to limit fruit mold incidence caused by early blight, anthracnose fruit rot, and soil rot (Rhizoctonia solani) (Louws et al., 1996).
The objectives of this study were to determine the effects of a fall sown winter rye + hairy vetch cover crop mulch with the tomato disease-forecasting system, Tom-Cast, on the development of anthracnose- and ground rot-infected fruit in processing tomato production.
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