Empire State Fruit and Vegetable Expo Report:
Bacterial Pathogens and Early and Late Blight
Control Options Discussed
The Tomato Magazine
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,
“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
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
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
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
group. “By the time of harvest (Aug. 22), many of the plants
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
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
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
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.
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
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
© 2007 Columbia
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