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Empire State Fruit and Vegetable Expo Report: Bacterial Pathogens and Early and Late Blight Control Options Discussed

The Tomato Magazine
April 2007

While copper-based pesticides remain the standard for control of various bacterial pathogens of tomatoes, Cornell University researchers are looking at other alternative strategies, including the use of plant activators and bacteriaphage.

So reported Christine Smart, speaking Feb. 14 during the 2007 Empire State Fruit & Vegetable Expo tomato and pepper session held in Syracuse, N.Y. She was one of three speakers addressing tomato-related topics. Others were: Tom Zitter, a Cornell University plant pathologist, and Dale Mutch, an extension specialist with Michigan State University.

Activators were tested in the fi eld against bacterial speck, while bacteriaphage were tested in the greenhouse against bacterial canker, Smart said.

“Compounds that can activate plant defense responses are known as plant activators, plant defense activators or systemic acquired resistance (SAR) inducers and are frequently termed biopesticides,” the speaker explained. “Additionally, many of these compounds are said to increase plant health and yield, and are expected to be environmentally friendly, having no direct effect upon the pathogen.”

Two Types of Activators
There are two types of plant activators, she added. The first consists of living microbes that colonize plant roots and activate a resistance mechanism known as induced systemic resistance (ISR). These products are frequently plant growth-promoting rhizobacteria (PGPR) or yield-enhancement biologicals which claim to increase yield while reducing pathogen problems.

The second type of activator induces a specifi c plant defense pathway known as systemic acquired resistance (SAR), she explained. The SAR activator included in the study reported was Actigard (acibenzolar-S-methyl, produced by Syngenta) which is applied to the foliage. This SAR-inducing compound is commonly used in New Jersey and other states to control bacterial diseases of tomato, but has not been widely used in New York.

“Unlike ISR, there have been several reports of a decrease in yield following application of a SAR-inducing compound,” Smart told the group.

“While both ISR and SAR induce the plant’s natural defense mechanisms, they are not the same, and it is unknown which mechanism will have greater efficacy against pathogens of tomato in New York. Additionally, it is completely unknown if the two products used together could act synergistically to enhance both yield and disease control.”

High winds and a damaging hail story complicated the researcher’s 2006 field study. Wind and hail damage to the pants was extreme. Bacterial speck symptoms were severe across all treatments due to the large number of wounds caused by the hail storm.

“Although disease levels were high in all plots, the number of lesions in all treated plots on July 28 was significantly less than the untreated control,” Smart reported. “The Actigard treatments reduced the number of leaf lesions and the early Actigard treatment (starting one week after transplanting) had the fewest infected fruit and the highest yield. Yield for both BioYield and the control treatments were reduced compared to the other treatments, but this difference was not signifi cant.”

In addition to bacterial speck, bacterial canker moved into the fi eld plots in late July. Based on the timing and pattern of symptom development, she speculated that several fl ats of transplants were contaminated with the pathogen in the greenhouse prior to planting in the field.

“Bacterial canker was most severe in lower areas of the field where standing water occurred after the hail storm,” Smart told the group. “By the time of harvest (Aug. 22), many of the plants were nearly dead due to a combination of fl ood damage, wind and hail damage, bacterial speck and bacterial canker. While no treatment was extremely effective against canker, the Actigard early treatment appeared a bit healthier than other treatments (although not
statistically signifi cant).

Actigard Results Encouraging
“ The Actigard results are encouraging for fresh-market tomato production in New York,” the researcher continued. “In contrast to previous studies, we did not fi nd any decrease in yield relative to the untreated control.”

Actigard treatments provided the best control of bacterial speck, although not statistically different form the copper treatments,” Smart said, noting that there is suffi cient evidence that Actigard can be a weapon used to compliment a copper spray program.

The PGPR product, however, did not provide protection from bacterial speck or canker of tomato nor did it provide any growth enhancing effects, she said.
Reporting on greenhouse testing of bacteriaphage (also known as phage), the researcher saw no statistical differences between treated and untreated plants, even though “there does appear to be a reduction in the number of bacteria on plants,” Smart said.

The Search for Blight Resistance
In the second presentation, Tom Zitter substituted for Martha Mutschler, who was unable to make the session on time. He and Mutschler have been looking at tomato lines for the Northeast, particularly those with resistance to early and late blight. In the Northeast, both early and late blight are major problems for tomato production, Zitter said. Hence, both diseases have been given high priority in Cornell’s breeding program.

The research team has completed two out of a three-year study testing late and early blight resistant lines and then hybrids possessing both resistances for utility and acceptability in the region. The results of the 2005 Cornell trial confi rmed that most of the Cornell lines were fi xed for early blight resistance, Zitter noted. The results of this trial also demonstrated differences in the degree of disease control the resistance provides on stems versus foliage. The 2006 season trials focused on further testing of the subset of late and early blight lines, the researcher said. Trials were expanded in New York and Pennsylvania. One of the wettest summers on record caused havoc with growing plants.

The first late blight-resistant processing tomato hybrids for the Northeast were marketed in the spring of 2006, Zitter said. High quality early blight-resistant varieties have been harder to come up with, as all tested to date require additional fungicide applications to afford adequate protection.

Based upon the fi rst two years of results, several lines have been selected for production of experimental hybrids that will be homozygous for late and early blight resistance, the speaker said. Seed is being generated for these hybrids for trialing in 2007 under traditional and organic production methods.

Cover Crop Benefits
Dale Mutch reported on experiments conducted at the Southwest Michigan Research and Extension Center in Benton Harbor, Mich., evaluating cover crops for conventional and organic tomato production.

In the study, conventional tomatoes were grown comparing fumigation versus no fumigation, low fertility versus high fertility and cover crops versus no cover crops. Organic tomatoes were grown comparing compost versus no compost and cover crops versus no cover crops.

Why should tomato growers consider the extra expense of growing a cover crop? Mutch gave a number of reasons, including improved soil health and productivity; better nitrogen management; improved erosion control; improved weed control; decreased nitrogen leaching; and increased numbers of benefi cial insects and other organisms. Growing a cover crop is “not a one year-solution,” the speaker emphasized. The practice should be part of an ongoing farm
management program.

© 2007 Columbia Publishing

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