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Grape Replant DisorderAn Integrated Management
Approach
S. Schneider, USDA-ARS,
Postharvest Quality and Genetics Research Unit, Fresno, CA 93727, H. Ajwa
and T. Trout, USDA-ARS, Water
Management Research Lab, Fresno, CA 93727, and J. Sims, Dept. of Plant
Pathology, University of California, Riverside,
CA 92521
Pre-plant soil fumigation with methyl bromide has commonly been used to
prevent or lessen replant disorder when replanting grapes into
vineyards infested with soilborne pests. Methyl bromide is effective against a
wide range of soil pests including insects, nematodes, weeds, and pathogens.
Accurate diagnosis of the specific problem in a given vineyard has not been
necessary, since methyl bromide is effective against such a wide spectrum of
pests. Methyl bromide can be used effectively against soil pests over a range
of soil types, temperatures, and moistures resulting in greater flexibility of
use and less risk of crop loss than is possible with many other soil
treatments. Another strength of methyl bromide is its ability to kill old grape
roots deep in the soil. If these are not killed, they serve as a reservoir of
inoculum for soilborne pests.
Growers who need to replant vineyards that have existing soil pest problems
will need alternatives to methyl bromide because of the scheduled ban on import
and manufacture in 2005. Unless a silver bullet that is effective
against a wide range of pests and over a range of soil conditions can be found
and made available, the first challenge will be to accurately diagnose the
problem(s) in a specific field. Once the problem is identified, a management
strategy must be generated that is: 1) effective against the identified pest;
2) effective under the soil conditions found in that vineyard or field; 3)
economically feasible; and 4) environmentally acceptable. This strategy might
be a single action or, more likely, an integrated approach using multiple
biological, chemical, and cultural tools and approaches.
Because of the brief time before the ban on methyl bromide is implemented,
adapting the use of existing commercially available compounds as components of
integrated systems is being tested as a transitional solution during the more
time-consuming development of culturally and biologically based management
systems. An additional level of complexity results from the spatial variability
of pest populations and soil physical, chemical, and biological factors which
will impact the fruit yield and quality. Some management strategies have been
hindered by inconsistent performancesometimes they work, sometimes they
dont. This could be due to the spatial variability of soil factors that
affect the efficacy of the management option. Understanding the biological,
chemical, and physical interactions will allow growers to select options best
suited to their conditions. Management strategies will have to be tailored to
the specific pest problems and soil conditions in order to maximize the
probability of successful replanting.
Our approach to research on the replant problem in vineyards is to identify
and characterize factors contributing to the problem and then mount a
two-pronged attack: first, eliminate or minimize factors that negatively impact
growth and yield and, second, introduce or enhance factors that positively
impact growth and yield. Novel delivery systems such as drip irrigation systems
and introduction of beneficial organisms/materials into nursery materials will
be evaluated.
In the fall of 1997, a field trial was initiated in a 15-year-old
Thompson Seedless vineyard at the ARS research location in Parlier,
CA. The nine treatments were:
1) a six-month fallow (the untreated control);
2) a combination application of Telone II EC (35 gal/acre) in 60 mm of water
through a buried drip tape plus Vapam (26 gal/acre of 42% metam sodium) applied
through surface microsprinklers;
3) same as #2 except the Telone was applied in 100 mm of water;
4) a shanked application of methyl iodide (400 lbs/acre), tarped;
5) a shanked application of methyl bromide (400 lbs/acre), tarped (the
treated control);
6) 18-month fallow;
7) same as #2 following an 18-month fallow;
8) same as #3 following an 18-month fallow; and
9) 18-month fallow plus a sorghum-sudangrass hybrid cover crop.
Each treatment was replicated 5 times. The telone/vapam treatments were
applied in early January, 1998. The methyl bromide and methyl iodide treatments
were applied in late April, 1998.
The telone/vapam combinations are novel applications which reduce worker
exposure to currently available chemicals. Methyl iodide is not currently
registered, but has been shown to be effective in tests on replant disorder in
other crops. Fallow treatments remove the existing above ground portions of the
vines and the roots that can be easily pulled out, but does not remove all of
the roots, especially those deeper in the soil. An 18-month fallow results in a
loss of use of the vineyard for an additional year, but also removes the
actively growing vine and upper roots as biological factors in the ecosystem
for that year.
In July of 1998, each plot was planted with three grape variety/rootstock
combinations; own-rooted Thompson Seedless, Merlot on Harmony rootstock, and
Merlot on Teleki 5C rootstock. The rootstocks vary in levels of resistance to
nematodes, which are thought to play a role in replant disorder. Data on plant
growth and nematode populations will be collected for at least five years in
order to determine the impact of the treatments not only on vegetative plant
growth, but also on fruit yield and quality. Susceptible St. George rootstocks
were interplanted between the primary vines to be used as bioassay plants to
determine if the nematodes present in the soil are still infective.
Soil samples were collected from each plot at planting to a depth of 5 feet
and assayed for plant parasitic nematodes. There was no significant difference
between the numbers of rootknot nematode (Meloidogyne spp.) in the
untreated control, 18-month fallow (18F), and 18-month fallow plus cover crop
(18F+CC). Rootknot numbers were not significantly different between the methyl
bromide (MB), methyl iodide (MI), and all four telone/vapam (T/V) combinations,
and were significantly less than the untreated control. All nematodes in the
MB, MI, and T/V treatments were dead and coiled, whereas the nematodes
extracted from the fallow treatments were active. Numbers of dagger nematode
(Xiphinema spp.) were slightly higher in the untreated control and 18
month fallow treatments than in the other treatments, but not significantly so.
Total dagger nematode populations were relatively low across all treatments.
Ring nematode (Criconemella spp.) was significantly higher in the 18F
and 18F+CC plots than in all other treatments. Pin nematode (Paratylenchus
spp.) numbers were higher in the untreated control, 18F, and 18F+CC
treatments than all other treatments.
A qualitative rating of weed abundance was made approximately three weeks
after vines were planted (7 months after the T/V treatments and 3.5 months
after the MB and MI treatments). The untreated control, 18F, and 18F+CC plots
contained a dense cover of weeds. The T/V plots had a few weeds. The MB and MI
plots were essentially weed-free.
In February, 1999, the dormant vines were pruned back to 2 nodes above the
graft union. Pruning weight per plant for Thompson Seedless vines was highest
for MI plots, intermediate for the MB and T/V plots, and lowest in the
untreated control, 18F, and 18F+CC plots. There were no differences in Merlot
pruning weights for the Harmony and Teleki 5C rootstocks across treatments.
Soil samples were collected to a depth of 24 inches in late May 1999,
approximately one year after planting, 18 months after the telone/vapam
applications, and 13 months after the methyl bromide and methyl iodide
applications. There were no detectable plant parasitic nematodes in any of the
plots treated with methyl bromide, methyl iodide, or the telone/vapam
combinations. There was no significant difference in citrus nematode
populations in the untreated control, 18F, or 18F+CC treatments on each of the
rootstocks and all were significantly higher than the chemical treatments for
their respective rootstocks.
In the Thompson Seedless plots, rootknot nematode populations were
significantly higher in the untreated control than in the 18F and the 18F+CC
treatments. There was no significant difference between the ring, dagger, and
pin nematode populations on Thompson Seedless in the untreated control, 18F,
and 18F+CC plots.
On the Teleki 5C rootstock, rootknot nematode populations were significantly
higher in the untreated control plots than in the 18F+CC, and intermediate in
the 18F treatments. Ring nematode populations were significantly higher in the
18F+CC plots than in the untreated control, and intermediate in the 18F
treatments. Pin nematode populations were significantly higher on Teleki 5C in
the 18F+CC treatments than in the untreated control or the 18F. Dagger nematode
populations on Teleki 5C were significantly higher in the 18F than in the
untreated control or 18F+CC treatments.
On the Harmony rootstock, rootknot and dagger nematode populations in the
untreated control and 18F+CC treatments were significantly higher than the 18F
treatment. Ring and pin nematode populations on Harmony were significantly
higher in the untreated control than in the 18F+CC treatments and were
intermediate in the 18F treatments. Soil samples will be collected again in the
fall.
Bioassay samples will be collected this summer to determine the populations
of rootknot nematode in the roots. For each succeeding year of the test, soil
samples will be collected in spring and fall to determine the population levels
of the plant parasitic nematodes and plant growth measurements will be made.
Evaluation of the soil samples for other biotic and abiotic factors will be
conducted as resources allow. When the vines begin bearing fruit, fruit yield
and quality will also be evaluated. The entire experiment is being repeated in
1999.
Additional lab and greenhouse tests are being conducted to evaluate various
biological, chemical, and cultural management strategies for their negative
impacts on pests and positive impacts on plant growth. Agri-50, a colloidal
compound, prevented hatch of rootknot nematode eggs at high concentrations and
killed infective juveniles at lower concentrations. Greenhouse and field tests
are being conducted to evaluate this product in a soil ecosystem. Ceres and
Liqui-comp, both microbial products, appear to enhance plant growth in
preliminary tests in non-fumigated field replant soils, but did not kill
rootknot juveniles or eggs in the lab.
In the short term, novel applications of currently available chemicals
appear to be the most likely alternatives to methyl bromide. These will serve
as stepping stones during the transition to an integrated systems management
approach based on an understanding of the interactions and spatial variability
of biological, chemical, and physical factors in the agro-ecosystem. Such a
system will include management strategies to reduce or eliminate pests, enhance
beneficial organisms, promote good plant growth, kill old roots deep in the
soil that serve as pest reservoirs, and protect the environment.
New Editor
Sharon Durham joins the ARS
Information Staff as the new editor of the USDA Methyl Bromide
Alternatives Newsletter. She can be reached at 5601 Sunnyside Ave.,
Beltsville, MD 207055129; phone (301) 5041611, fax (301)
5041641.
[October 1999 Table of Contents]
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Last Updated: October 1, 1999
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