Historic, Archive Document Do not assume content reflects current scientific knowledge, policies, or practices. ae e USDA ae 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. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. This publication reports research involving pesticides. It does not contain recommendations for their use nor does it imply that uses discussed here have been registered. All uses of pesticides must be registered by appropriate State and/or Federal agencies before they can be recommended. The United States Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to all programs.) 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