ABSTRACT
We evaluated the effectiveness of alternative fumigants on weed control and plant productivity in two nurseries located at high elevation and low latitude (Ciudad Guzman, Jalisco), during 2013 and 2014 at Driscoll’s and Lassen Canyon South nurseries. Treatments were: MB:chloropicrin (MB:CP); 1,3-dichloropropene:CP; CP alone; metam sodium (MS) alone; dimethyl disulphide (DMDS):CP; and sequentially applied CP and MS. A rotary spading machine was used for MS and CP followed by MS. All treatments produced similar pest suppression and runner-plant yields during 2013 and 2014. However, CP alone showed very poor control of the most abundant weed (barnyardgrass, Echinochloa crus-galli). Two years of work on MB alternatives were not sufficient to provide reliable recommendations on this critical need, therefore, the Methyl Bromide Technical Options Committee recommended critical use nomination for MB in 2015.
Introduction
The Mexican Government, through the Secretary of Environment and Natural Resources (SEMARNAT), in cooperation with the United Nations Industrial Development Organization (UNIDO), has developed a Pilot Project for the demonstrations of alternatives to the methyl bromide (MB) for strawberry and raspberry fruit and plant production. This Project has allowed field-scale activities since 2007–08 at San Quintín (Baja, California), and since 2010–11 at Zamora/Jacona and Tangancícuaro (Michoacán) and Jocotepec (Jalisco) in cooperation with Berrymex, Driscoll’s, and other berry companies. For nursery plant production we have conducted field scale experiments and demonstrations in 2013 and 2014 in cooperation with Driscoll’s and Lassen Canyon South.
For years, strawberry (Fragaria × ananassa L.) runner plant nurseries have relied on MB or mixtures of MB and chloropicrin (CP) as soil fumigants to produce healthy transplants (Kabir et al., Citation2005). However, MB has been classified as an ozone depleting substance and it has been banned in all countries of Montreal Protocol (MP). In the specific case of Article 5 countries of MP (such as Mexico), the MB phase-out deadline is expected in 2015, with the exception of possible critical use exemptions (CUE).
The majority of MB used in Mexico until 2014 has been for pre-plant fumigation in strawberry fruit and nursery production. In 2013, there were more than 600 ha of strawberry nurseries (260 ha in Jalisco and 349 ha in Michoacán) (SAGARPA-Servicio de Información Agroalimentaria y Pesquera-SIAP) and nursery production is rapidly expanding. The nurseries are located in several locations in Jalisco (Ciudad Guzman, Tapalpa, and others) and Michoacán (Tangancicuaro, Mazamitla, and others) with additional locations at Puebla State. Central Mexico (Michoacán and Jalisco) uses an “off-season,” low latitude system (19/20° N parallel) and nurseries in high-elevation areas (1600–2000 m above sea level) to produce the plants (López-Aranda et al., Citation2011). The mother plants are transplanted in the nurseries during January and February and daughter runner plants are harvested during mid-July to mid-August. Rotations with cereals (sorghum and corn) are common.
Soilborne pathogens (such as Phythophthora cactorum, Verticillium spp., Rhizoctonia spp., Pythium spp., and Fusarium spp.) and weeds are common pests of Mexican strawberry nurseries. Our work here focused on weeds control and yield. Alternative fumigants must control weeds in strawberry nurseries because strawberry runner plant yields are sensitive to weed competition and because weeds can be hosts of several pathogens (García-Méndez et al., Citation2008). The majority of weeds that infest Mexican strawberry nurseries are annuals, although perennial weeds, such as yellow nutsedge (Cyperus esculentus L.), bermudagrass (Cynodon dactilon L.), tree tobacco (Nicotiana glauca Graham), and others, are found. Generally, MB:CP preplant fumigation controls most of these weeds, with the exception of cheeseweed or little mallow (Malva parviflora L.) (Dávalos et al., Citation2011). Another challenge is that a replacement fumigant must maintain runner plant yields and quality at the level of MB. Porter et al. (Citation2004), suggested that chemical and non-chemical alternatives to MB have not been developed for strawberry runner plant production to the extent that they have been for strawberry fruit production. Dávalos et al. (Citation2011) and Rodríguez-Bautista et al. (Citation2012) have presented updated information about some aspects of Mexican strawberry nursery technology. So far, no specific research has been conducted on weed control and yield for strawberry nurseries in Mexico, the fourth largest industry in the world.
In Mexico, commercially-available alternatives to MB are: CP alone, metam sodium (MS), metam potassium (MK), dazomet, 1,3 dichloropropene (1,3-D), 1,3-D:CP mixture, and, recently, dimethyl disulphide (DMDS), alone and/or in combination with CP (cofepris.gob.mx). Applications of 1,3-D:CP, CP, and MS are the most widespread chemical solutions for strawberry fruit and nursery production in conventional areas of production in the world (López-Aranda, Citation2014). DMDS alone or in combination with CP, MS, and/or dazomet have been evaluated for strawberry nurseries in Spain only, since 2002 (De Cal et al., Citation2004, Citation2005; García-Méndez et al., Citation2008; García-Sinovas et al., Citation2014).
CP has always been applied mainly in combination with MB as a soil fumigant and limited information is available for the weed control efficacy of CP alone in strawberry runner plant nurseries (García-Méndez et al., Citation2008). In previous work it has been reported that MS was less effective than MB:CP and 1,3-D:CP for runner plant production (López-Aranda et al., Citation2002). However, new systems of MS injection like Spading machines can improve distribution and efficacy (Runia and Molendijk, Citation2007). Although CP has considerable utility as a stand-alone soil fumigant, it is more likely to be used in sequential applications with MS to enhance weed control (Duniway, Citation2002; Fennimore et al., Citation2001; López-Medina et al., Citation2007). Other authors pointed out that sequential combination of MS + CP provided better weed control than 1,3D:CP mixture (61:35) (Donohoe et al., Citation2001). Sequential application of CP (300 lb/ac) or 1,3D:CP (392 lb/ac) for pathogen control, followed by dazomet (250 lb/ac) for weed control in the nurseries resulted in runner-plant production equivalent to the standard MB:CP treatment (Kabir et al., Citation2005). Nevertheless, sequential application of each one of these chemicals requires significantly more time than using MB alone since growers must wait longer after fumigation to put the strawberry root stock in the ground (MB USA Strawberry Nursery CUN 2006).
Appropriate viable alternatives to MB are necessary for strawberry nurseries in Mexico for the short- and long-term. Our objectives were: (a) to identify alternative soil disinfestations treatments that control weeds and produce strawberry runner plant yields similar to MB, and (b) to carry forward the most promising treatments to commercial-scale evaluations.
Materials and methods
Fumigation trials were conducted in 2014–15 at high-elevation nurseries located in Ciudad Guzmán (Jalisco, Mexico) (1560 m above sea level and latitude 19° 41′ N). Trials were conducted in both replicated experiments and large commercial-scale demonstration fields.
Mother plants of ‘Osceola’ were planted in each trial of Driscoll’s nursery (Rancho La Autopista) and of ‘San Andreas’ and ‘Sweet Ann’ of Lassen Canyon South nursery, at Rancho Bertha Toledo (BT), in 2013 and 2014, respectively. Standard cultural practices of each company for runner plant production were followed. Replicated plot experiments (Rancho La Autopista) and demonstration fields (Rancho La Autopista and Rancho BT) were carried out. Soils at both sites were sandy loams with a pH of 5.4–6.3 and 1.9–2.4% organic matter. The cropping history was a rotation of corn with sorghum at Rancho La Autopista and pasture land with corn at Rancho BT.
Fumigation treatments, rates, methods of application, and dates of main operations (application, planting, and harvest) used at each site are listed in and . Treatments (five in 2013 and seven in 2014) for replicated plot experiments at Rancho La Autopista (Driscoll’s) were arranged in a randomized complete block design with four replicates per treatment in 2013 and seven replicates per treatment in 2014. Individual plots were 162.5 m2 in 2013 and 650 m2 in 2014. In both years at both locations the same treatments for demonstration fields were arranged with no replications in 1.00 and 0.45 ha blocks per treatment at Rancho La Autopista and 0.5 ha per treatment in Rancho BT (Lassen Canyon South). Each season, plants were planted 0.30 m apart in 1.80-m-wide rows (Rancho La Autopista) and 0.50 m apart in 0.90-m-wide rows (Rancho BT) at plant densities of 18,000 and 22,000 plants/ha at the two locations. Plants were irrigated as needed by sprinkler with 10 × 10 m spacing between heads.
Table 1. Treatments 2013–14.
Table 2. Main operating dates.
To monitor weed populations at each location, areas of sample quadrats were monitored in each plot throughout the duration of each season of cultivation. The size of sampling quadrats was 5.6 m2/replicate in experiments (La Autopista) and 2 × 15 m2/treatment in demonstration fields (La Autopista and BT) during 2013 and 15 m2/treatment in experiments (La Autopista) and 2 × 15 m2/treatment in demonstration fields (La Autopista and BT) during 2014. Weeds in the sample quadrats were collected on four (2013) or six dates (2014) from the end of February until the end of July. At each sampling date, weed species present were identified, counted to determine weed densities by species, and removed with roots to determine total fresh weights in each treatment.
Strawberry runner plants were harvested by hand from three randomly selected 1 m2 areas in the central part of each plot in experiments and demonstration fields in mid-August 2013 and 2014 at La Autopista and on first August (2013) and end-July (2014) at BT. Daughter plants harvested inside these three areas were classified as either marketable (i.e., >8 mm diameter crown, more than six roots, healthy crown), or unmarketable (i.e., <8 mm diameter crown, damaged crown) and counts of each plant category were recorded. Also, strawberry runner plants were machine-harvested from the whole replicated experiments and large commercial-scale demonstration fields and trained crews sorted and counted the total number of marketable plants after standard trimming of roots and petioles in the trim shed.
Weed densities, fresh weed weights, and yields were subjected to analysis of variance using the STATISTIX 8.0 program (Analytical Software, Ltd., La Jolla, CA, USA). Effects of treatments and locations and their interaction on the study variables were assessed by a two-way analysis of variance (ANOVA). When significant differences were found, a multiple comparison test was used for mean separation. All data were tested for normality and transformed as needed, and back-transformed when necessary for data presentation. Significant mean differences among fumigant treatments in weed density, weed fresh weight, and number of runner plants harvested were separated using LSD test (P < 0.05).
Results and discussion
Weed community composition was not very different across the two locations and years. Altogether, 22 weed species were observed in the study of which 12 were present in all locations (). The species common to all sites and years included: hairy fleabane (rama negra) (Conyza bonariensis), barnyardgrass (zacate de agua) (Echinochloa crus-galli), bermudagrass (grama) (Cynodon dactylon), Canadian horseweed (cola de caballo) (Conyza canadensis), crabgrasses (zacate fresadillo) (Digitaria spp.), little mallow (malva) (Malva parviflora), common sowthistle (borraja) (Sonchus oleraceus), pepperweed (lentejilla) (Lepidium sp.), Mexican pricklypoppy (chicalote) (Argemone mexicana), burcucumber (chayotillo) (Sicyos angulata), tree tobacco (gigante cimarrón) (Nicotiana glauca), and yellow nutsedge (coquillo) (Cyperus esculentus). Weed life cycles (annual and/or perennial), types (graminoid and forbs), families, and their presence/absence at all sites and years are presented in .
Table 3. Weeds species, life cycles and types, families, and presence/absence at experimental sites.
On each date of sampling, weeds were classified in two main categories following USDA Plant Database (Citationn.d.) criteria (graminoids and forbs). Graminoids included 6 species: Cynodon dactylon, Cyperus esculentus, Digitaria spp., Echinochloa crus-galli, Eragrostis pectinacea, and corn (maíz) Zea mays, and the 16 forb species were: Conyza bonariensis, Conyza canadensis, Malva parviflora, Sonchus oleraceus, cutleaf groundcherry (tomatillo) (Physalis angulata), Lepidium sp., lambsquarters (quelite cenizo) (Chenopodium album), common purslane (verdolaga) (Portulaca oleracea), Argemone mexicana, Sicyos angulata, roundleaf geranium (cilantrillo) (Geranium rotundifolium), smooth pigweed (quelite bledo) (Amaranthus hybridus), tall morningglory (campanilla) (Ipomoea purpurea), tree marigold (tacote) (Tithonia tubaeiformis), including the shrub tree type of tree tobacco (gigante cimarrón) (Nicotiana glauca) and beebrush (oreganillo) (Aloysia lycioides).
Total weed densities and fresh weights are presented in (demonstration fields in 2013), (demonstration fields in 2014), and (replicated plot experiments at Rancho La Autopista in 2013 and 2014). Weed densities in 2014 were greater than in 2013 at all locations. Also, weed populations of graminoid species were two to three times greater than forbs/shrub tree species and accounted for 74% and 75% (fresh weight and number) at Rancho La Autopista, and 73.7% and 68.8% at Rancho BT in the demonstration fields during 2013. In 2014, demonstration fields weed populations, graminoid species accounted for 82.1% and 78.4% (fresh weight and number) at La Autopista, and 83.6% and 85.4% at BT. In replicated plot experiments at La Autopista graminoid weeds accounted for 86.2% and 90.0% (fresh weight and number) in 2013 and 66.2% and 68.1% in 2014.
Table 4. Total weed densities and fresh weights in demonstration fields in 2013.
Table 5. Total weed densities and fresh weights in demonstration fields in 2014.
Table 6. Total weed densities and fresh weights in replicated plot experiments at Rancho La Autopista.
Significant differences (P < 0.05) were more frequent for graminoid densities and weights than for forbs/shrub tree species. In general, T1 (MB:CP) (50/50 w/w) treatments showed greater control, but without significant differences (P < 0.05) from other fumigant treatments, except the shank applied T3 (CP) alone. All of the fumigation treatments resulted in similar fresh weights and weed densities, except for T3 (CP) alone. Similar to the studies by Shrestha et al. (2008, 2009), the 2014 weed density in this project was generally reduced by all of the fumigation treatments compared to the non-fumigated control T0, with the exception of shank-applied T3 (CP) alone. In fact, the consistent effect among treatments was the poorest weed control (evidenced by both weed densities and fresh weights) in CP treatment, especially for graminoid species, at all sites and in all years (–).
Weed control for each species was also evaluated. The most abundant weed in all locations and years was the graminoid barnyardgrass (zacate de agua) (Echinochloa crus-galli), due to the very poor control of it inT3 (CP) alone (), even less than the untreated control in 2014.
Table 7. Total weed densities and fresh weights of Barnyardgrass (Zacate de agua) (Echinochloa crus-galli).
The estimation of commercial runner plants per m2 just before harvest is presented in . All treatments produced similar runner-plant yields during 2013 and 2014. Few significant differences (P < 0.05) were detected among treatments, with optimum results for T2 (1,3D:CP) and T3 (CP) in 2013 and T1 (MB:CP) in 2014. Due to the large size of experimental and demonstration plots, it was possible to count the total number of marketable plants after machine harvesting and trim-shed manipulation, just before shipping the plants to the customers. The results without statistical analysis for large-scale demonstration fields are presented in . Also, small practical differences were observed among the most important fumigant treatments in 2013, with optimal results for T2 (1,3D:CP) and T1 (MB:CP) treatments in BT and La Autopista demonstration fields. For the 2014 season, practical differences were greater among treatments, with optimum yields for T2 (1,3D:CP) at Rancho BT demonstrations and T1 (MB:CP) at La Autopista. For replicated plot experiments at La Autopista nursery, no significant differences were carried out in 2013 and in 2014 among chemical fumigant treatments. However, in accordance with Meszka and Malusà (Citation2014), the number of daughter plants produced from plants grown on plots treated with all chemical fumigants at La Autopista location was higher than in the non-fumigated control T0 in 2014, except for T6 (DMDS:CP) demonstration field ( and ).
Table 8. Estimation of commercial daughter-plant yield.
Table 9. Total number of commercial plants harvested per hectare after trim shed sorting.
Finally, 2 years of work on MB alternatives were not sufficient at all to provide reliable recommendations on this critical need, therefore the Methyl Bromide Technical Options Committee (MBTOC) (TEAP, Citation2014) recommended MB as critical uses nomination (CUN) for the Mexican Strawberry Nursery industry in 2015. In a similar manner than other international strawberry nursery industries (García-Méndez et al., Citation2008), it is necessary to continue evaluation of alternative fumigants for strawberry nurseries in Mexico, to focus on improved methods of application, to evaluate new alternatives treatments, to estimate the potential economic viability of these alternatives treatments, and to evaluate the most promising alternative fumigant treatments in commercial field-scale demonstrations.
Acknowledgments
We wish to thank Driscoll’s and Lassen Canyon South’s technical staff and workers in Ciudad Guzmán nurseries.
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