Papers by Steven Fennimore
Hortscience, Mar 1, 2017
One challenge of conducting research regarding agricultural production systems is that field tria... more One challenge of conducting research regarding agricultural production systems is that field trials are time consuming and expensive, limiting their scale and scope. Thus, policymakers and producers benefit from researchers extracting as much information as possible from each trial. We used the Monte Carlo techniques and the sensitivity analyses to enhance our analysis of the competitiveness of steam as an alternative to fumigation for preplant soil disinfestation in California strawberry production. Chloropicrin + 1,3-dichloropropene 59.6:39 (CP + 1,3-D) resulted in higher mean net returns than did steam. However, the Monte Carlo analysis showed that in one field trial there was a high probability that steam would be more profitable, whereas in the other it was quite unlikely. We also assessed the change in economic performance of steam when it was applied combined with soil amendments of mustard seed meal (MSM). Switching from steam to steam + MSM would have reduced mean net returns. The Monte Carlo results showed that steam + MSM performed at least as well as steam alone around half the time. We evaluated factors that were likely to affect the net returns, defined as total returns minus treatment, weeding, and harvest labor costs, of using steam in the near future. Reductions in application time increased net returns. A decrease in the price of propane increased net returns.
Retention of broadcast-applied fumigants with impermeable film in strawberry
ABSTRACT Field studies were conducted to evaluate the potential for virtually impermeable films (... more ABSTRACT Field studies were conducted to evaluate the potential for virtually impermeable films (VIF) to increase fumigant retention, improve weed control and improve strawberry yields in broadcast fumigation. Broadcast-applied treatments made by a commercial applicator were methyl bromide/chloropicrin (MBPic) at 350 lbs/A and Telone II (1,3-D) at 15 GPA co-injected with chloropicrin at 200 lbs/A. Both fumigant treatments were tarped with VIF and standard film. Assessments made were weed control, fruit yield and fumigant concentration under the film. No differences were observed between the films in terms of weed control, fruit yield or MBPic retention. However, VIF does appear to increase retention of 1,3-D compared to standard film. Introduction. We have found that the use of VIF in drip fumigation systems, normally improves weed control compared to standard film and that strawberry yields are sometimes higher than with the use of standard film. We set out to conduct research to determine if similar benefits could be achieved with VIF using available commercial broadcast fumigation technology. Materials and methods. Eight field studies were conducted on commercial farms in the 2004-05 and 2005-06 seasons (Table 1). California locations were Oxnard, Pajaro (Watsonville), Santa Maria, and Spence (Salinas) USDA Farm. Applications made by a commercial applicator were: MBPic 67:33 at 350 lb ai/A and Telone II (1,3-D) at 15 gallons/A co-injected with chloropicrin at 200 lbs/A. The two fumigant treatments were applied under both standard and VIF tarps. VIF was glued by inserting a narrow strip of plastic between the two VIF layers which allowed the glue to dry in 2004-05 and by direct gluing in 2005-06. Treatments were replicated twice and arranged in a randomized complete block. Fumigant concentrations under the film were monitored for about one week after application. Fumigant gas concentration samples from charcoal tubes were analyzed in the lab with a gas chromatograph mass spectrograph. Weed biomass and hand weeding times were monitored as were fruit yields. Weed and yield data were subjected to analysis of variance. Factors considered in the analysis were fumigant concentration under the film, fumigant treatment, and the interaction term. Fumigant concentration data were fitted to a first order degradation function in Sigma plot.
Hortscience, Jun 1, 2022
Soil disinfestation with steam has been evaluated in strawberry fruiting fields as a nonchemical ... more Soil disinfestation with steam has been evaluated in strawberry fruiting fields as a nonchemical method of soil disinfestation; however, little is known about the use of steam for field production of strawberry daughter plants. The objective of this study was to compare daughter plant production in soils previously treated with steam compared to those treated with standard methyl bromide (MB) and chloropicrin (Pic) treatments. A prototype field steam applicator and a self-propelled dieselfueled steam generator and applicator were tested at two high-elevation nurseries near Macdoel, CA, in Sept. 2018 and Aug. 2020, respectively. The steam application heated the soil above 60 C for %60 minutes to a depth of 25 cm at both nurseries. The pest control efficacy of the steam applications against weeds, Verticillium spp., Tylenchulus semipenetrans, and Pythium ultimum were similar to that of MB:Pic. The stolons and daughter plants densities in fields with steam treatment were similar to those in fields with MB:Pic treatment. Therefore, we suggest that soil disinfestation with steam may be a viable method of producing healthy strawberry plants. However, more research is needed to verify plant sanitation and quality.
Hortscience, Apr 1, 2021
Soil disinfestation with steam has potential to partially replace fumigants such as methyl bromid... more Soil disinfestation with steam has potential to partially replace fumigants such as methyl bromide, chloropicrin, and 1,3-dichloropropene because it is effective, safer to apply, and has less negative impact on the environment. Here, we compared the efficacy of steam and steam + mustard seed meal (MSM) to chloropicrin on soil disinfection, plant growth, and fruit yield in a strawberry (Fragaria 3ananassa) fruiting field. The MSM was applied at 3368 kg • ha L1 before the steam application. Steam was injected into a 3-mwide reverse tiller that was set to till 30 to 40 cm deep. Soil temperatures at depths of 10, 20, 25, and 35 cm were monitored. Steam and steam + MSM treatments reduced the viability of purslane seeds and nutsedge tubers, microsclerotia density of Verticillium dahliae, propagule density of Pythium ultimum, cumulative weed densities, and biomass compared with the nontreated control. Moreover, the steam application was as efficacious as chloropicrin on these pests. The growth and fruit yield of strawberries grown on soils previously treated with the steam and steam + MSM treatments were similar to those in the chloropicrin treatment and were higher than those in the nontreated control. Our study indicated that steam, steam + MSM, and chloropicrin are equally effective at suppressing weeds and soilborne pathogens. These results suggest that the steam and steam + MSM treatment can be a practical alternative for soil disinfestation in conventional and organic strawberry fields.
Hortscience, Jul 1, 2001
Field studies were conducted to determine the potential economic impact of the loss of pronamide ... more Field studies were conducted to determine the potential economic impact of the loss of pronamide herbicide to artichoke (Cynara scolymus L.) growers, and to evaluate pendimethalin as an alternative herbicide during establishment of artichoke. Two rates of pronamide and one rate of pendimethalin were applied to perennial and annual artichokes. With the exception of wild oat (Avena fatua L.), pendimethalin controlled weeds as well as or better than pronamide. Financial analysis of treatment effects was based on weed management expenses and value of yield. The financial effect of using pronamide in perennial artichoke ranged from a loss of $247 to a gain of $326 per ha, whereas its use in annual artichoke increased revenue $542 to $5499 per ha. The effects on revenue of using pendimethalin varied with weed species composition and density. For three sites, revenue increased from $267 to $5056 per ha, while a loss of $1034 per ha occurred at a site with a heavy infestation of wild oat. We conclude that pendimethalin has potential as a pronamide replacement, or as a complement to pronamide. Chemical names used: 3,5dichloro (N-1,1-dimethyl-2-propynyl)benzamide (pronamide); N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin).
Hortscience, Nov 1, 2022
Steam injected into the soil, raising soil temperatures to >70 C for 15 to 20 minutes, will contr... more Steam injected into the soil, raising soil temperatures to >70 C for 15 to 20 minutes, will control weed seed and soilborne pathogens. The effect of this reduction in the weed seedbank viability results in weed control in the treated zone that can persist for several weeks or months. The effect of steam pasteurization of soil on weed seeds produces results similar to a preemergence herbicide. In our study, steam was applied to the soil to control weed seed and propagules of Sclerotinia minor and Pythium spp. Replicated field trials in carrot, lettuce, and spinach were conducted using two types of band steam applicators in 2020 and 2021. Data collected were soil temperatures after steam application, weed control, hand weeding times, diseased plant counts, pathogen populations in the soil, and crop yields. Poststeam soil temperature intervals >70 C in the top 10 cm of the soil ranged from 67 to 176 minutes. Steam reduced weed densities by 64% to 100% and lowered hand weeding times by 23% to 91%. The reduction of S. minor sclerotia propagules after steaming was 69% to 95% compared with the no steam control. The percentage of lettuce plants infected with lettuce drop was reduced by 60% to 70% and the reduction of Pythium spp. propagules in the soil was reduced by 50% to 100% compared with the no steam control, respectively. Lettuce head diameters in steamed soils were 10% to 24% larger compared with the no steam control. Carrots grown in the steam-treated soil had a 10% greater root diameter than the no steam control. Steam increased lettuce yields in two of three trials 22% to 28% compared with the no steam control. Gross revenues for the steamtreated lettuce were $3231/ha higher than in the no steam control. The data suggest that band steam is a viable soil pest control treatment for vegetable crops.
International Journal of Fruit Science, Jul 20, 2016
Increasingly stricter fumigant regulations will limit their use and require effective non-fumigan... more Increasingly stricter fumigant regulations will limit their use and require effective non-fumigant treatments if large-scale strawberry production is to continue in California. Steam has long been used for soil disinfestation in greenhouse soils where it controls most soil pests. The challenge of field-scale soil disinfestation with steam in place of fumigants is availability of machinery capable of treating a large acreage in a timely manner while making the most efficient use of fuel and water. Steam can be a component within an integrated set of fumigant and nonfumigant practices. Steam used together with other practices may permit technically and economically sustainable strawberry production into the future by allowing growers to adapt to more stringent fumigant use restrictions. It may be possible to overcome some of the limitations of steam because steam generator technology has advanced in recent years as well as recent developments in co-applications with steam, including exothermic compounds co-applied with steam and mustard seed meal coapplied with steam. Regarding steam generator technology, direct-fire steam generators are more energy efficient than traditional steam boilers and avoid the hazards of steam pressure vessels. Steam is arguably the most effective non-fumigant method of soil disinfestation and it likely has a role in a future California strawberry production system that is forced to use much less fumigant than it does at present.
California Agriculture, Apr 1, 2008
California strawberry runner plants are propagated in high-elevation nurseries such as this one n... more California strawberry runner plants are propagated in high-elevation nurseries such as this one near Macdoel, north of Mt. Shasta. The harvested runner plants are transported to fruiting fields in California or exported to other states or countries.
California Agriculture, Apr 1, 2008
California strawberry runner plants are propagated in high-elevation nurseries such as this one n... more California strawberry runner plants are propagated in high-elevation nurseries such as this one near Macdoel, north of Mt. Shasta. The harvested runner plants are transported to fruiting fields in California or exported to other states or countries.
Horttechnology, Apr 1, 2020
Hortscience, Oct 1, 2005
For years, strawberry (Fragaria ×ananassa L.) runner plant nurseries have relied on methyl bromid... more For years, strawberry (Fragaria ×ananassa L.) runner plant nurseries have relied on methyl bromide (MB) fumigation of soil to produce healthy transplants. Methyl bromide, however, has been phased out due to its environmental risks. The potential for alternative fumigants to replace MB was evaluated at low and high elevation strawberry nurseries in California. The alternative fumigant iodomethane plus chloropicrin (IMPic) and a nonfumigated control (NF) were compared to methyl bromide plus chloropicrin (MBPic) at a low elevation nursery (LEN) and at a high elevation nursery (HEN) near Susanville, Calif. At a HEN near Macdoel, Calif., MBPic was compared to alternative fumigants IMPic, 1,3dichloropropene plus chloropicrin mixture (Telone C35) followed by dazomet, chloropicrin (Pic) followed by dazomet and NF. Plants produced at the LEN were transplanted at the Macdoel HEN to measure the effects of soil fumigant history on plant health and runner plant production. Plants produced at both high elevation nurseries were evaluated for fruit yield and quality at two commercial fruit production sites in soils previously fumigated with MBPic or Pic. Runner plant production at the nurseries was similar in plots fumigated with either MBPic or alternative fumigants. All fumigation treatments had higher runner plant production than plants produced for two production cycles on NF soils. Generally, fruit yields from nursery plants produced on soils fumigated with IMPic, Pic followed by dazomet, or Telone C35 followed by dazomet, were similar to fruit yields from plants produced on MBPic fumigated soils. Overall, our results indicate that preplant soil treatments with IMPic, Pic followed by dazomet, and Telone C35 followed by dazomet, are potential alternatives to MBPic fumigation for strawberry runner plant nurseries. Fruit yields by plants in MBPic and Pic fumigated soils were comparable; however, they were more variable in Pic fumigated soils. Chemical names used: 1,3-dichloropropene (1,3-D), methyl bromide, methyl iodide (iodomethane), trichloronitromethane (chloropicrin), tetrahydro-3, 5-dimethyl-2 H-1,3,5-thiadiazine-2-thione (dazomet).
California Agriculture, Oct 1, 2011
About 80% of California strawberry fields, such as these in Santa Maria, are treated with soil fu... more About 80% of California strawberry fields, such as these in Santa Maria, are treated with soil fumigants prior to planting. Plastic tarps are applied to prevent leakage of the fumigants.
Applied Economic Perspectives and Policy, Jun 1, 2005
Methyl bromide has been applied to California strawberries for forty years. However, it will be b... more Methyl bromide has been applied to California strawberries for forty years. However, it will be banned in the United States and other developed countries in 2005. Critical use exemptions provide a mechanism that allows its continued use after this date for industries that do not have technically and economically feasible alternatives, and are consequently subject to significant market disruption. Integrating scientific and economic results from a multidisciplinary research project, we evaluate whether California strawberries are eligible for a critical use exemption. M ethyl bromide (MBr) is an efficacious soil fumigant that controls a wide range of pests, including weeds, nematodes, and other pathogens. Mixed with chloropicrin, it is widely used for pre-plant fumigation in vegetable and fruit crops. Because it is an ozone-depleting chemical, MBr is being phased-out in the United States under the Montreal Protocol. In the United States and other developed countries, MBr use was reduced to 75% of 1991 baseline levels in 1999. In 2001, the use dropped to 50% of the 1991 level,
Hortscience, Feb 1, 2003
The loss of methyl bromide (MB) as a soil fumigant has created the need for new weed management s... more The loss of methyl bromide (MB) as a soil fumigant has created the need for new weed management systems for crops such as strawberry (Fragaria ×ananassa Duchesne). Potential alternative chemicals to replace methyl bromide fu mi ga tion include 1,3-D, chloropicrin (CP), and metam sodium. Application of emulsifi ed formulations of these fumigants through the drip irrigation system is being tested as an alternative to the standard shank injection method of fumigant application in strawberry pro duc tion. The goal of this research was to evaluate the weed control effi cacy of al ter na tive fumigants applied through the drip irrigation system and by shank injection. The fumigant 1,3-D in a mixture with CP was drip-applied as InLine (60% 1
Soil Science Society of America Journal, Nov 1, 2005
fungal pathogens, but is not as effective against nematodes as MeBr . Therefore, Methyl bromide (... more fungal pathogens, but is not as effective against nematodes as MeBr . Therefore, Methyl bromide (MeBr; CH 3 Br) use for soil fumigation will be a mixture of MeBr and CP is usually applied to control banned in 2005 due to its ozone depleting properties. Potential alternasoil-borne fungal pathogens such as Verticillium wilt tive chemicals to replace MeBr include chloropicrin (CP; CCl 3 NO 2 ), (Verticillium dahliae Kleb.) and weeds (Wilhelm et al., 1,3-dichloropropene (1,3-D; C 3 H 4 Cl 2 ), iodomethane (IM; CH 3 I), and propargyl bromide (PrBr; C 3 H 3 Br). The goal of this research was to 1961). Recent research found that an emulsifiable conassess changes in soil fungal populations, microbial biomass C (MB C ) centrate (EC) formulation of CP applied through drip and respiration, nitrification potential, and enzyme activities after irrigation systems at rates Ͼ 200 kg ha Ϫ1 provided consisfumigation with MeBr and alternative fumigants. Four formulations tent cost-effective pest and weed control in strawberry of alternative fumigants (CP, InLine [61% 1,3-D plus 33% CP], Midas production (Ajwa et al. 2002a, 2002b; [50% IM plus 50% CP], and PrBr) were applied at commercial rates
Pic-Clor 60 retention under totally impermeable film in strawberry
Totally impermeable film (TIF) was compared to standard film (STD) for retention of 39% 1,3-dichl... more Totally impermeable film (TIF) was compared to standard film (STD) for retention of 39% 1,3-dichloropropene, 59% chloropicrin v/v mixture (Pic-Clor 60) at 0, 50, 100, 200, 300 and 400 lb/A applied by chemigation through the drip irrigation system. Weed control was monitored, weed seed bioassays were conducted and strawberry fruit yield was monitored. TIF increased retention of Pic-Clor60 compared to standard film, weed control was improved with TIF and strawberry fruit yields were also higher.
Soil/Media Disinfestation for Management of Florists’ Crops Diseases
Handbook of plant disease management, 2016
My view
Weed Science, 2000
Hortscience, Jun 1, 2020
Steam has long been used to disinfest greenhouse soils. However, there is increasing interest in ... more Steam has long been used to disinfest greenhouse soils. However, there is increasing interest in expanding the use of steam for in-field soil disinfestation as an alternative to chemical fumigants. Previous studies demonstrated that allyl-isothiocyanate (AITC) reduced viability of weed seeds and plant pathogen propagules, but AITC has a low vapor pressure and is relatively immobile in soil. Heat has been used in the past to enhance the mobility of soil fumigants such as methyl bromide (i.e., ''hot gassing''). The effect of steam heat on the mobility of AITC is unknown. The objective of this study was to investigate the potential synergistic effect of steam plus ATIC against weed seeds and a plant pathogen. AITC alone did not reduce the viability of the four weed species and the number of Verticillium dahliae microsclerotia. The steam + AITC treatment reduced the viability of V. dahliae at 12.5 and 18 cm distances by 82% and 88%, respectively, and knotweed and nettle seeds at 70 cm from injection point by 75% and 86%, respectively, from the center of microplots compared with steam alone. The results suggest that AITC and steam have a complementary effect on soilborne pests because steam increases the mobility of AITC.
PLOS ONE
Soil disinfestation with steam was evaluated as an alternative to fumigation. Following soil disi... more Soil disinfestation with steam was evaluated as an alternative to fumigation. Following soil disinfestation, plant health has traditionally been measured using plant size and yield. Plant health can be measured in a timely manner more efficiently, more easily and non-destructively using image analysis. We hypothesized that plant health could be quantified and treatments can be differentiated using an RGB (Red, Green, Blue) image analysis program, particularly by observing the greenness of plant leaves. However, plant size or the proportion of green area could be unreliable due to plant loss and camera’s position and angle. To this end, we decided to evaluate plant health by analyzing the RGB codes associated with the green color only, which detects the chlorophyll reflectance and nutrient status, noting that the degree of greenness within the green-leaf-area was not affected by the plant size. We identified five RGB codes that are commonly observed in the plant leaves and ordered th...
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Papers by Steven Fennimore