Methyl bromide alternatives

10 Pages·2001·2.7 MB·English

Historic, Archive Document
Do not assume content reflects current
scientific knowledge, policies, or practices.

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USDA
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Bromide
Vol. 7, No. 1
January 2001
ANIA MATOS
From the Agricultural Research .
service Administrator
Inside This Issue The loss of methyl bromide for most current uses is now only 4
years away. With the latest Montreal Protocol-mandated reduction
that occurred January 1, 2001, the availability of methyl bromide is
reduced to 50 percent of what it was in 1998. Availability will be
further reduced to 30 percent of the 1998 baseline in 2003. Methyl
bromide shortages and increased costs for the available methyl
bromide will present daunting challenges to many growers and other
users as they try to adapt to this changing environment. Although
research isn’t the sole answer to finding methyl bromide replace-
ments, it is a vital part of that activity. ARS intends to continue
working as hard as we can with growers and other methyl bromide
users, public and private scientists, and regulatory officials to make
the widest array of methyl bromide alternatives available for the
greatest number of uses possible.
Even though much work remains to be done, progress has been
made. For some major crops, adequate alternatives have been found
that will continue profitable operation by growers. In some cases,
technically effective alternatives cannot be fully utilized because of
regulatory constraints. USDA is working closely with the U.S.
Environmental Protection Agency and state regulatory agencies to
find safer ways to use these pesticides so that restrictions can be
relaxed.
Small-acreage crops continue to be at highest risk of not having
methyl bromide alternatives. With limited resources, ARS and other
research organizations have been forced to focus their efforts on the
crops that use the most methyl bromide. To add to this problem,
pesticide companies have been reluctant to register pesticides for
small-acreage, high-value crops. Many floriculture crops fall in this
category. In recognition of this situation, Congress appropriated in
its FY 2001 budget enough new funds to allow ARS to hire two new
scientists to work on methyl bromide alternatives for floriculture
crops. One scientist will be located in Florida and the other in
California; recruitment for both is under way.
i U.S. Department of Agriculture
Vol. 7, No. 1 Methyl bromide alternatives, January 2001
Finally, I would like to announce that Dr. Roy Gingery has returned to active research and has accepted
a research leader position at our Wooster, Ohio, laboratory. For the last 7 years, he has been ARS Na-
tional Program Leader for Plant Health and an important part of our ARS methyl bromide alternatives
research management team. I hope that those of you who have worked with him over the years will join
me in thanking him for a job well done.
Best wishes,
Wat
Floyd Horn
Administrator
Methyl Bromide The path to approval can prove long
tives research efforts to identify
and laborious. EPA establishes review
Alternatives: Winding efficacious alternatives. EPA’s role is
priorities and schedules for new active
to identify data that needs to be
Their Way Through
ingredients and other submissions for
generated and review it to make
EPA registration decisions in a timely each fiscal year. Because of the
manner. extraordinary circumstances surround-
ing the methyl bromide phaseout,
Since the announcement that methyl
applications for alternatives are
The Review Process
bromide would be phased out due to
expedited—given top priority for
its role as an ozone-depleter, the focus
To that end, EPA decided an expedited review in the scheduling process and
has been on finding new alternatives
are reviewed before other scheduled
review of methyl bromide alternatives
and getting them to market for use by
was warranted. The normal time submissions.
industry. Throughout that time, the
required to review an application for a
Environmental Protection Agency
new ingredient chemical, from receipt Under the current process, new
(EPA), the lead Federal regulatory
chemical registrations first undergo
to decision, is approximately 31 to 36
entity, has been responsive to the
months. An expedited review process front-end processing, for about a
needs of commercial growers by
is completed in about 18 to 22 months. month, which includes screening by
working with methyl bromide re-
staff for adherence to format and by
searchers, who are identifying viable
scientists for scientific viability. Next,
The long time frame, however,
alternatives, and the companies that
intrudes on the patent-protection in-depth science reviews, lasting 14 to
are developing the data to support
period. Since many companies apply 22 months, are conducted for health
registration of these alternatives.
for patents before the formal applica- effects, residues on crops, lab valida-
tion of analytical methods for detect-
tion review process, it is imperative to
The need of the Nation’s growers to ing residues, worker and residential
proceed as quickly as possible.
have an effective replacement, or
exposure, ecological and environmen-
Generally, patents are in force for 7
combination of replacements, for
tal effects, and potential drinking
years, and the amount of time taken
methyl bromide, remains the focus of
for review and approval reduces that water exposures. Following this, peer
the USDA-EPA Methyl Bromide
review and risk assessments are
patent-protection time. Also, since the
Alternatives Working Group. USDA’s
product is not on the market during executed, during which safety factors,
Cooperative State Research, Educa-
part of the patent-protected period, hazards, and risks are examined; this
tion, and Extension Service (CSREES)
there is unrecoverable lost revenue takes about 5-1/2 to 8 months to
and ARS sponsored research programs
complete. The process then continues
during that time.
with IR-4s methyl bromide alterna-
with risk management and a regula-
U.S. Department of Agriculture
Vol. 7, No. 1 Methyl bromide alternatives, January 2001
tory decision—trisk assessors review Jersey, is a specialty chemical manu- still slow, according to many chemical
risk-mitigation measures and work out facturer with about $1 billion a year in companies. “While the agency has
solutions with the registrants. This sales and a successfully registered been very responsive and communica-
step takes from 1 to 3 months. If phosphine gas fumigant called tive, industry feels the process could
approved, the Federal Register notice Eco2Fume. still be faster,’ says Deskin.
is prepared, programwide concurrence
is obtained, management signatures Caulkins also believes information Houtman says, “The industry recog-
are affixed, and the notice is published provided to registrants can be empow- nizes that the limiting factor is EPA
for public review. ering. For instance, the average resources.” To that end, a fee-for-
rejection rate for data submitted by service program, like one in place at
As cumbersome as this may seem, it is registrants was 33 percent in 1988. the Food and Drug Administration, is
speedy by normal standards, but those “EPA provided each registrant with being discussed by industry execu-
in industry would like to see an even their company-specific rejection rate, tives. Fee-for-service would involve
swifter pace. Bruce Houtman is the as well as the rejection rates of their registrants paying EPA to hire addi-
global regulatory leader for Dow competitors, which provided a tional staff and contractors to review
AgroSciences’ methyl bromide tremendous incentive for them to the applications. However, industry
alternatives products, including Telone improve,” he explains. representatives would have to appeal
(1,3-dichloropropene) and Vikane/ to their congressional representatives
Profume (sulfury] fluoride). Houtman “A huge amount of time and resources to get such a system and the necessary
says, “It is important to understand were being wasted in rework,” says funds, with accountability, in place.
what an expedited review is and what Caulkins. “Studies often had to be
it isn’t. An expedited review shortens returned to be upgraded and resubmit- Even with the long registration
the period that the registration package ted, or studies needed to be repeated.” process, registrants are encouraged.
waits for review, but it doesn’t shorten EPA identified the rejection factors “This is a good deal for the agricul-
any aspect of the review itself. An that most frequently occurred for each tural community because registering
expedited review is as thorough, study required, and they, along with methyl bromide alternatives is a high
complete, and comprehensive as all company scientists, worked together priority for EPA, as well as for
other EPA reviews. In the case of all to find solutions. registrants,” says Houtman.
regulatory reviews, the process could
be made more efficient and provide This was the first time many of the Methyl Bromide
new agricultural tools to the grower company scientists were involved with
Phaseout and Florida
community more quickly by applying EPA to address specific rejection
additional resources.” factors. The cooperation allowed EPA Floriculture
and commercial scientists to identify
EPA Steps To Improve Process and solve prevalent rejection factors. Florida is the second largest floricul-
The sharing of this information also ture producer in the country, with over
EPA has made considerable efforts to allowed companies to benefit from $650 million in sales in 1998. More
become service-oriented. “EPA has each others’ experiences in a noncom-
than 1,500 growers commit 14,500
approached perceived inadequacies by petitive fashion. By 1998, the acres to floriculture, including cut
knowing and working with our industry-wide average rejection rate flowers, potted flowering plants, and
customers—the registrants,” says had been reduced from 33 percent to bedding/garden plants.
Peter Caulkins, associate director of 3.6 percent. Through a combination
EPA’s Registration Division. Preregis- of such information and services, While floriculture is a vital part of
tration conferences have proven quite registrants have shown an enhanced Florida’s agricultural economy, it
useful to EPA and registrants. ability to be successful with their data pales in comparison to other crops in
submissions the first time around. the amount of methyl bromide used.
“The chance to sit down face-to-face The U.S. utilizes about 38 percent of
with agency representatives resulted in What’s Next? all methyl bromide applied worldwide
better results and an overall positive each year. About 79 percent of the
experience,” according to Dr. Randy EPA will continue working with methyl bromide produced in the U.S.
Deskin, director of regulatory affairs registrants to approve those chemicals is used for soil fumigation before
and toxicology for Cytec Industries, which are acceptable to their stan- planting crops, about 9 percent is used
Inc. Cytec Industries, based in New dards. But the pace of approvals is to fumigate harvested commodities
U.S. Department of Agriculture
Vol. 7, No. 1 Methy! bromide alternatives, January 2001
during storage and export, and about 5 combinations for soilborne pest control of weeds, but control of
percent is used for structural fumiga- control in caladium in 1998. Treat- soilborne disease pests, such as
tions, such as for food processing ments consisted of methyl bromide + Fusarium, was not statistically
plants, warehouses, museums, chloropicrin (90 percent/10 percent), different from the untreated control.
antiques, and transport vehicles. The 1,3-dichloropropene + chloropicrin
remaining 7 percent is used in the (83 percent/17 percent), and metham + 1,3-D + chloropicrin, along with a
production of other chemicals. chloropicrin (75 gal/acre + 200 Ib/ surface application of metolachlor and
acre. A nontreated control was oryzalin, displayed excellent early
Florida accounts for about 38 percent included in the study. Plots treated control of weeds. This method also
of preplant methyl bromide use in the with 1,3-dichloropropene or metham performed equivalently to all other
U.S. Fresh-market tomatoes and were given soil-surface sprays of treatments in disease pest control. In
peppers grown in Florida account for metalochlor during planting and this treatment, more jumbo tubers
about 33 percent of the Nation’s oryzalin about 7 weeks later. Plots were produced than in other treatment
preplant methyl bromide use and treated with methyl bromide received plots.
about 88 percent of the State’s only oryzalin; nontreated controls
preplant methyl bromide use. Straw- received no herbicide and were hand Research results suggest that 1,3-D +
berries account for an additional 8 weeded. chloropicrin (83 percent/17 percent) at
percent of preplant use there. To- 35 gal/acre may be a viable replace-
gether, strawberries, tomatoes, and Early (25 days after application in ment for methyl bromide, when
peppers constitute 96 percent of midsummer) weed control was good combined with metolachlor herbicide
preplant methyl bromide used in with treatments that included at planting, followed by a midsummer
Florida, providing a strong impetus to metolachor, but methyl bromide plots application of oryzalin. This research
find methyl bromide alternatives for displayed early infestations of is being continued to determine the
these crops. crabgrass and pigweed, indicating that long-term effects of these fumigant
they, too, may have benefitted from and herbicide combinations on pest
The remaining crops, including metolachlor at planting. This may control and tuber production.
floriculture crops, use about 4 percent also suggest methyl bromide evacu-
of preplant methyl bromide. Unfortu- ated from the top 2 inches of soil too Steam Sterilization in
nately, because this sector of agricul- quickly for good weed control. Chrysanthemums
ture uses such a small amount of Oryzalin was still providing good
methyl bromide, the stimulus to fund weed control 75 days after application, The lack of research in floriculture has
research has been very low. However, and the chemical reduced the total forced some growers to find their own
some potential alternatives for number of all weed plants, compared solutions. Yoder Brothers in Alva,
caladiums and chrysanthemums have to areas where no herbicide was Florida, looked at steam sterilization
been identified. applied. Oryzalin was still providing to control soilborne pests, as com-
good control of pigweed, purslane, pared to methyl bromide. “Methyl
Caladiums and Linnaria canadensis (a winter bromide is the backbone of our IPM
annual), a late emerging weed, 119 strategy,” says Patrick Crump, director
More than 95 percent of the world’s days after application and 54 days of production for Yoder Brothers. “It
production of caladium tubers comes after the final weeding. is used after every crop rotation to
from a small geographical region close prepare the soil for planting, and it is
to Lake Placid, Florida. Most of the The methyl bromide + chloropicrin used to meet quarantine restrictions.”
production is on muck or high- plot exhibited early infestations of
organic-matter soils. Soilborne pest crabgrass and pigweed, but control of Yoder Brothers installed two station-
control is a major problem for soilborne pests, such as Fusarium, was ary boilers (250 horsepower) with
producers. These pests include weeds, equivalent to all other treatments. overhead pipes leading to the beds at a
root-knot nematodes, and soilborne Tuber production was equivalent to cost of $500,000 to treat one-third of
diseases, such as Fusarium. the metham + chloropicrin plot. their 1.3 million square feet of beds.
Nematodes were not present in any The method seems to work, but is very
James Gilreath, Robert McSorley, and soil samples of any plots. expensive. “If we were to use this
Robert McGovern, at the University of method exclusively, costs would
Florida, Gulf Coast Research and Metham + chloropicrin, with a surface increase by $800,000 per year,”
Education Center, in Bradenton, application of metolachlor and explains Crump. This amount would
studied soil fumigant and herbicide oryzalin, displayed excellent early fluctuate depending upon labor and
4
U.S. Department of Agriculture
Vol. 7, No. 1 Methyl bromide alternatives, January 2001
diesel fuel costs. “Methyl bromide is package solution. Some cut flowers Corn Belt. Seipel says, “Our equip-
easier from a management stand- are in good shape for herbicide ment, historically, is used for conser-
point,” he says. options, but many are not.” ARS’ vation tillage and fertilizer placement,
additional funding and resources may but grower needs are changing.
There are some problems facing steam provide some relief in the long-term, Telone injection is a new avenue we
sterilization. Because growers are but choices are limited in the short- are pursuing due to the methyl
working in an open area, the steam term. bromide phaseout. The market is
dissipates, which means applying it
changing so changes in technology
for longer periods of time. The Application and application are needed.”
amount of soil moisture and tempera-
Technology for
ture also affects the amount of steam The new 2986 coulter 30-inch
used and the duration of treatment. Injecting Telone Avenger, took several months of
development by Mirusso, the Yetter
Yoder Brothers met the first 25 Current reductions of methyl bromide company, and Jerry Nance, Dow
percent reduction in methyl bromide AgroSciences’ Telone specialist. “It
and the eventual loss of the gas
availability without too much diffi- fumigant in 2005 have prompted a lot features, as indicated in its name, a 30-
culty. “We achieved a 6 to 7 percent of research in a relatively short period inch coulter that allows for fumigant
reduction by calibrating our equip- of time. Researchers have conducted application up to 12 inches, as
ment and reducing waste,” says numerous studies to find a chemical or compared to 6 inches with a standard
Crump. chemical combination to replace Yetter coulter,’ says weed scientist
methyl bromide. In the meantime, James Gilreath of the University of
With steam sterilization, Crump found Florida’s Gulf Coast Research and
some researchers are exploring new
yield to be the same or slightly better ways to use existing chemical fumi- Education Center, Bradenton.
than with methyl bromide. “But the gants.
yield doesn’t warrant the increased “We looked at a lot of equipment
costs associated with steam steriliza- before settling on the 2986 coulter 30-
Telone is an effective fumigant against
tion,” Crump warns. nematodes and soilborne disease and, inch Avenger,” says Nance. “The
when combined with an herbicide, it emissions are very low, so using the
Now that the 50-percent methyl rig makes fumigating the field a one-
can approximate the control of methyl
bromide reduction is in effect, Yoder person job. This significantly affects
bromide. However, regulations that
Brothers will have to add another govern personal protection equipment growers, who must use personal
phase of steam, resulting in $1.5 and buffer zones make its use prohibi- protection equipment when fumigat-
million in boiler expenses, to cover tive for some. ing. ”°
1.3 million bed square feet. As of
October 1, 2000, Yoder Brothers’ cost John Mirusso, fumigation consultant Sealing devices were added to the
to steam sterilize the soil was $1,550 to Dow AgroSciences, developed a knives that follow the coulter. The
per 10,000 square feet, compared to piece of farm equipment that injects knife has a tube in the back side that
$685 for methyl bromide treatment. Telone into the soil and slows its delivers the fumigant to the bottom of
“Unless someone comes up with escape. Mirusso contacted Yetter the groove. The beaver tail is angled
something else, we will have to use Farm Equipment of Illinois 2 years so it compacts or presses a bit of soil
steam sterilization,” says Crump. ago to discuss modifications to a about 3 inches from the bottom of the
coulter assembly to accommodate soil chisel groove. “This keeps the
ARS recognizes the dearth of research injections of Telone. “John told us he fumigant from moving rapidly up the
in floriculture and is addressing the needed a piece of equipment that groove and dissipating into the
gap. As noted in ARS Administrator could handle field residues from atmosphere,” explains Gilreath.
Floyd Horn’s letter on the cover of this previous crops and inject a fumigant
issue, Congress appropriated funds in to a depth of 12 inches, with minimal Following each coulter assembly is a
the FY 2001 budget to hire two new soil disturbance,” recounts Mark set of press wheels that presses the soil
scientists to research methyl bromide Seipel, regional sales manager for surface to seal the knife and coulter
alternatives in floriculture crops. Yetter. groove at the surface. The amount of
force applied to them is adjustable.
According to James Gilreath, ““Telone Yetter, a 71-year-old business, focuses “One can use chisels without the
products will be part of everyone’s mostly on equipment for use in the coulter,’ Gilreath says. But he
U.S. Department of Agriculture
Vol. 7, No. 1 Methyl bromide alternatives, January 2001
cautions, “If there is tying string or Historically one of the primary reasons root systems of these plants also are
plastic mulch residue in the soil, it for soil fumigation was to reduce the less well developed and have necrotic
gets hung up on the chisels and can be incidence of Verticillium wilt, the most lesions. This translates into a smaller,
dragged around. This results in chisel important lethal disease of strawberry. less thrifty plant in the early spring
grooves substantially larger than the However, a number of other nonlethal that is not able to support the fruiting
chisel itself, and this allows rapid soilborne fungal pathogens also can level that is expected for plants in an
outgassing of fumigant.” contribute to significant losses when economically viable production field.
strawberry is grown in nonfumigated Attempts to control these pathogens
According to Nance, this is definitely fields. In one field plot that did not are being approached from several
not what a grower wants. “You want have Verticillium wilt a 46 percent directions:
the chemical in the ground to do its reduction in marketable yield was
job and then degrade. What escapes is observed in 1998 when the strawberry Host Tolerance
unused and useless product.” cultivar Selva was grown in
nonfumigated soil; based on root One approach for mitigating the loss
It also contributes to air emissions that isolations this yield decline was of methyl bromide soil fumigation for
can affect the size of buffer zones. attributed to root rot caused by disease control would be to plant
“Air emissions are measured to help Pythium, binucleate Rhizoctonia, and strawberry cultivars that are tolerant
determine buffer zones. If the Cylindrocarpon spp. Collectively to specific root pathogens. Screening
fumigant does not escape into the air, these general, nonspecific pathogens programs are currently underway in
then neighbors are not exposed to the cause a root disease commonly other laboratories in California
fumigant,” says Peter Caulkins, referred to as black root rot, a name evaluating tolerance to Verticillium
associate director of EPA’s Registra- that is descriptive of the appearance of wilt and Phytophthora root and crown
tion Division. the roots (reviewed in Wing et al., rot. These are two important diseases
Advances in Strawberry Research of strawberry that can cause signifi-
So far, the amount of outgassing is 13:13-19). Depending on the produc- cant crop losses by reducing yield as
low, according to Mirusso. “The tion location, the lesion nematode well as killing the plant. The efforts
numbers look great and the Telone is Pratylenchus penetrans has also been of this research program have focused
expanding out at the depth of injec- associated with this disease complex on determining the contribution of the
tion, which increases effectiveness.” (LaMonda, J. A. and Martin, S. B. individual pathogens associated with
1989. Plant Dis. 73:107-110). Sample black root rot on the severity of the
These types of innovative collabora- assays of test plots in Watsonville and disease complex in the field as well as
tions will have to continue to adjust to Salinas did not reveal significant evaluating host germplasm for
life without methyl bromide. “Agri- nematode levels in our research plots, pathogen tolerance in the greenhouse
culture is going through tremendous so the research effort has focused on and field. The most common Pythium
changes now and modifications are the fungal pathogens. Greenhouse spp. encountered in the central coastal
necessary. The best products are trials have confirmed the involvement California production area is Pythium
made with input from our consum- of the isolated fungal pathogens in the ultimum, a broad host range species.
ers—the farmers,” says Seipel. disease complex and their ability to The Rhizoctonia spp. most commonly
stunt plant growth (described in more encountered are binucleate species in
Technical Report detail below; Martin, FN. 2000. anastomosis group (AG) A, G, and I.
Phytopathology 90:345-353). In fact,
in view of the high level of recovery of Greenhouse Trials
Approaches For Management
these pathogens from the roots the first
of Root Diseases of Strawberry
4-5 months after transplanting it is Greenhouse evaluations for tolerance
suspected that they contribute to the to Pythium ultimum and different AGs
Frank N. Martin, USDA-ARS,
significant reductions in plant growth of binucleate Rhizoctonia (a mixture
1636 East Alisal St., Salinas, CA
observed when strawberry is grown in of isolates in AG-A, —G, and -I)
93905
nonfumigated soil. At both the revealed different levels of tolerance
Watsonville and Salinas test plot to these pathogens among the various
Essentially all of the approximately
locations reductions in shoot growth cultivars. In evaluations with P.
25,000 acres planted to strawberry in
by 10-15 percent are often observed ultimum at 200 p/g soil, Aromas,
the state of California are fumigated
within 8 weeks of transplanting for Selva, Seascape and Carlsbad exhib-
with methyl bromide + chloropicrin to
control root diseases and weeds. plants grown in nonfumigated soil; the ited greater tolerance to the pathogen
U.S. Department of Agriculture
Vol. 7, No. 1 Methyl bromide alternatives, January 2001
than did Camarosa, Chandler, Torrey cultivars evaluated had reductions tions of soilborne pathogens. Field
and Pajaro, which were susceptible. ranging from 10-20 percent. trials evaluating the influence of
The presence of the binucleate
rotation with broccoli, Brussels
Rhizoctonia isolates caused significant A wide range in yield also was sprouts, or lettuce on the population
reductions in shoot growth for all observed among cultivars. For dynamics of Pythium spp. and
cultivars examined, with the cultivars example, there was no difference in Verticillium dahliae are in progress at
Capitola, Diamante, Laguna, Selva, total yield for Capitola grown in the Watsonville test site (done in
and Seascape exhibiting the greatest nonfumigated compared to the collaboration with Dr. Krishna
level of tolerance. fumigated control; in contrast Oso Subbarao, UC Davis and Steve Koike,
Grande, Camarosa, and Diamante Monterey County Cooperative
Field Evaluations exhibited approximately a 70 percent, Extension). The field was cropped in
45 percent and 52 percent reduction in vegetable rotation in the 1997 season,
Field trials to evaluate cultivar yield, respectively, when grown in strawberry (Selva) in the 1998 season,
performance in nonfumigated soil nonfumigated compared to fumigated vegetable rotation in 1999 and was in
have been conducted in test plots in soil. While the yield in nonfumigated strawberry in 2000. After harvesting
Salinas. The location has not been soil was proportional to the yield in the vegetable crops, the stubble was
previously fumigated and is naturally fumigated soil for some cultivars, this mowed with a flail mower, allowed to
infested with the pathogens associated was not observed for all comparisons. dry on the soil surface for several days
with black root rot. Importantly, For example, total yield in fumigated and then incorporated into the soil.
Verticillium wilt and Phytophthora soil for Gaviota, Irvine, Laguna, and Two cropping cycles were planted for
root and crown rot have not been a Oso Grande were similar (data not broccoli and lettuce and one for
problem at this test location, so trials shown), however, in nonfumigated Brussels sprouts. While cropping
evaluating the contribution of the soil Oso Grande has dramatically practices had no consistent influence
general root pathogens associated with lower yields than the other cultivars. of population densities of total
black root rot on plant growth and Pythium spp., broccoli and Brussels
yield can be conducted independent of Based on the greenhouse evaluations it sprouts reduced V. dahliae inoculum
these lethal pathogens. In an effort to appears that there is a differential densities by 80-90 percent (to a final
build up black root rot pathogens in sensitivity of cultivars to some of the inoculum density of 1-2
the plots, strawberry was cropped in general root-rotting pathogens. microsclerotia/g soil). Although the
the test plots for 2 years prior to Likewise, field evaluations confirm market yield for all rotation treatments
initiating these trials. that there is a range in cultivar was below the MB + Pic fumigated
performance when grown in controls in 1998, strawberry grown in
There were dramatic differences in nonfumigated soil naturally infested the broccoli rotation plots had only a
growth and yield performance among with pathogens responsible for 23 percent reduction in yield com-
the cultivars. Analysis of variance causing black root rot. Unfortunately, pared to the fumigated control while
reveals that these differences are some of the more tolerant and best Brussels sprouts and lettuce had yield
significant (P < 0.001 between performing cultivars tested are no reductions of 31 percent and 39
fumigation treatments; P < 0.001 longer used commercially due to percent, respectively. Strawberry
between cultivars; P = 0.0032 for undesirable horticultural traits. yield data for the 2000 season is
fumigation x cultivar interaction). However, knowing that there are currently being analyzed. These trials
With the exception of Laguna, all cultivars more tolerant of these have been expanded at the Watsonville
cultivars exhibited significant reduc- pathogens may assist future efforts at test site to include larger test areas as
tions in plant diameter measurements developing new cultivars with reduced well as the addition of a test plot in an
for 5 !/2-month-old plants when grown susceptibility to disease. organic production field. Similar
in nonfumigated soil compared to the experiments (rotation with broccoli,
MB + Pic fumigated control. The Crop rotation cauliflower, or lettuce) also are under
greatest reduction in growth was way at the Salinas plots as well to
observed for Oso Grande, which had A number of strawberry root patho- evaluate the effect of rotation treat-
approximately a 50 percent reduction gens have a broad host range and are ment on black root rot pathogen
in plant diameter. Camarosa and capable of infecting other crops, so in population dynamics and disease
Diamante exhibited growth reductions the absence of effective soil fumiga- severity.
of 30 percent while the remaining tion crop rotation can have a signifi-
cant influence on maintaining popula-
U.S. Department of Agriculture
Methyl! bromide alternatives, January 2001
Vol. 7, No. 1
The influence of root colonizers of ever, trials in the 1999 season did not nylon mesh bags and buried at two
root health, plant growth, and yield reveal significant differences among depths 8 cm from the center of the
the treatments. One possible reason strawberry beds. The bags were
Preliminary investigations on the for this could be that there was much recovered 6.5 weeks after fumigation
population structure and seasonal less rainfall in 1999 compared to 1998 and the pathogen populations deter-
fluctuations of fungal, bacterial, and (31 vs 74 cm, respectively). Since soil mined by plating on a selective
actinomycete root colonizers have moisture can have a significant effect medium. All fumigation treatments
been done for plants grown in fumi- on the ability of introduced microbial completely eliminated P. ultimum with
gated and nonfumigated soils. A inoculants to colonize roots, the drier the exception of the Telone C-35
number of the recovered isolates have conditions in 1999 could have lead to treatments at the 40 cm depth (20
been evaluated for their effect on lower root colonization levels which percent and 10 percent survival for the
shoot and root growth in greenhouse/ in turn would lead to a reduced effect drip and shank treatment, respec-
growth chamber trials. While most on strawberry yield. To alleviate tively). One possible reason for this
isolates had no effect on plant growth, potential problems with insufficient could be spacing of the drip tape or
some were identified that increased root colonization, trials are in progress bed fumigation shanks in relation to
either shoot growth (up to a 40 percent with several of these isolates where where the inoculum bag was placed.
increase), root growth (up to a 138 additional treatments with the micro- Assays also were conducted in
percent increase), or a general bial inoculants are applied via the drip naturally infested field soil with the
stimulatory effect on both shoot and system. Trials evaluating the efficacy fumigants applied through the drip
root growth. Several isolates also of several commercial biological lines; Iodomethane + Chloropicrin
were identified that had inhibitory control agents are under way as well. (1:1) at 200 Ibs/acre and propargyl
effects on root growth (up to a 26 bromide at 180 Ibs of 80 percent AI/
percent reduction). Trials in the 1998 Fumigation trials acre controlled P. ultimum in the
season at the USDA test site in Salinas planting line of the bed to a depth of
in nonfumigated soil identified several Fumigation trials have been done in 25 cm. Additional trials evaluating
beneficial isolates that significantly collaboration with Husein Ajwa fumigation efficacy in strawberry
increased yield over the untreated (USDA-ARS, Fresno, CA) to evaluate nursery and fruit production fields is
control plants when plants were the efficacy of alternative fumigants currently in progress with collabora-
treated at the time of transplanting and methods for application for their tors from Industry, the California
(one isolate gave a 35.5 percent ability to control Pythium ultimum. Strawberry Commission, USDA-ARS,
increase in marketable yield). How- Naturally infested soil was placed into and the University of California.
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