Evaluation Of Three Control Measures For Verticillium
Wilt In Processing Tomatoes: Sudangrass Cover Crop, Field Corn, And Metham
Gene Miyao and Mike Davis
Objectives
Our objective was to evaluate the reported success of a Sudangrass cover
crop in controlling Verticillium wilt, a widespread pathogen of statewide
importance to processing tomato growers. Our interest is in reducing vine
collapse and yield reductions caused by strain 2. Our 1993 data indicates
tomato yields, in one of 2 trials, increased about 20% following a Sudangrass
summer-grown crop. We could not detect a reduction in Verticillium incidence.
Procedures
Sudangrass was grown during the summer of 1994 in preparation for a
1995 tomato crop. We compared the summer-grown cover crop of Sudangrass
to an untreated control and to a chemical treatment of 12 in.-deep shanked,
banded metham. Field corn as a previous year's crop was also grown as a
comparison to Sudangrass. Plant infection was evaluated by cutting stems
at ground level and examining degree of vascular discoloration. The field
plots were about 50 feet long with border rows on both sides of a central
bed. Treatments were replicated 8 times. Only the central 20' by 5' portion
of the center bed was harvested for yield. We changed our 'susceptible'
variety to La Rossa on the basis of lab tests conducted by UC Berkeley
pathologist Tom Gordon.
Results
Our Sudangrass trial in 1995 was not successful in reducing Verticillium wilt in tomatoes. Canopy cover of tomatoes was less with the Sudangrass planting as compared to the untreated (44% vs. 31%), which resulted in more sunburned fruit at harvest. Vine deterioration was least following metham. Sudangrass had no measurable effect on infection level of plants as measured by vascular discoloration. Though the reason is unclear, yields were lower in the Sudangrass and corn treatments as compared to the untreated control (about 36 vs 46 tons/A).
Over the 3 years of tests on the UC Davis campus, no convincing evidence
was found to support the hypothesis that a summer-grown crop of Sudan grass
prior to growing tomatoes would reduce the impact of Verticillium
in processing tomatoes.
|
Table 1. Influence of Sudangrass, metham, and field corn on incidence of Verticillium wilt, and yield of processing tomatoes La Rossa, UC Davis, 1995. |
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|
Micro- Sclerotia/ (g) soil |
Stem Infection Level* |
Stand (seedlings per foot) |
% Canopy Loss |
Marketable Yield Tons/A |
% Fruit Biomass |
Sunburn Fruit |
|
|
1. Untreated |
12.3 |
1.5 |
4.3 |
31 |
45.8 |
51.0 |
9 |
|
2. Sudangrass |
10.0 |
1.5 |
2.8 |
44 |
36.1 |
42.2 |
13 |
|
3. Metham |
9.4 |
1.4 |
2.7 |
22 |
46.7 |
51.6 |
8 |
|
4. Field Corn |
12.2 |
1.4 |
3.6 |
37 |
36.6 |
42.2 |
12 |
|
5. LSD 5% |
NS |
NS |
NS |
6.7 |
2.5 |
2.6 |
1.2 |
|
*stem infection level: 0=none, 3=severe with dark internal discoloration |
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