Simulated Leaching of Foliar Applied Copper Bactericides on the Soil Microbiome Utilizing Various Beta Diversity Resemblance Measurements.

Copper bactericides are routinely used to control Xanthomonas perforans (XP), causal agent of bacterial spot of tomato. Given the widespread tolerance to copper in XP strains in FL, USA, nanotechnology-based elemental composites have gained interest for their potential applications in agriculture in part due to their enhanced antimicrobial properties and toxicity to copper-tolerant strains. However, little is known about the potential impact of conventional copper bactericides as well as nano-based elemental composites on soil microbial communities, as determined by high-throughput sequencing of the 16S rDNA. We compared the effects of 2 and 200 µg/mL of core-shell (CS), a metallic copper composite, and a conventional copper bactericide + mancozeb (Cu+Man) on the soil microbiome. These treatments were compared to three controls, the microbial profile of the soil prior to application of copper products, a water application, and spiking the soil with a soilborne phytobacterium, Ralstonia solanacearum (RS). The RS treatment was included to determine if downstream analysis could detect the artificial inoculation. Utilizing multiple ß diversity measurements, each emphasizing various tenets of ecology, provided a greater perspective of the effects the treatments had on the microbiome. Analysis of HTS data revealed that the two treatments containing field applied rates of metallic copper, CS 200 and Cu+Man, had the largest impact on the soil microbiome at seven-days posttreatment compared to water. However, we simulated field applied rates of CS 200 entering the soil by treating soil with CS 2 and determined this concentration had a negligible effect on the soil microbiome. IMPORTANCE Nanotechnology-based elemental composites have gained popularity for their potential applications in plant disease management due to their enhanced antimicrobial properties. However, little is known about their potential impact on the environment. Foliar applications of nano metallic composites upon leaching into the soil have the potential to impact soil microbial populations that in turn influence soil health. Utilizing multiple ß diversity measurements, high-throughput sequencing analysis revealed that field applied rates of metallic copper (200 µg/mL) from an advanced copper composite (core-shell [CS]) and a conventional copper bactericide in combination with mancozeb had the largest impact on the soil microbiome compared to water and nontreated control. To simulate leaching from the leaf surface, a lower concentration (2 µg/mL) of CS was also applied to the soil and had a negligible effect on the soil microbiome. Thus, field applied rates of CS may have a minimal effect on soil microbial communities.

First Report of Colletotrichum lupini on Lupinus hartwegii and L. mutabilis.

During the 2013 winter cut flower production season, a severe anthracnose epidemic was observed on Lupinus mutabilis (syn L. cruckshanksii) on a commercial flower farm in Martin County, FL. Approximately 50% of the crop was lost to the disease. Symptoms included dark brown, irregularly shaped leaf spots, but more typically, there was a single severe twist in the stem, forming a distinctive necrotic crook. Margins of necrotic lesions were excised and surface sterilized by immersion in 1% sodium hypochlorite for 90 s, rinsed in sterile deionized water, and plated onto potato dextrose agar (PDA). Plates were incubated at approximately 27°C with cycles of 12 h light/12 h darkness. Infected tissue consistently produced colonies that were typical of the genus Colletotrichum. Conidia were primarily oval, with one rounded end and one pointed end, and were highly variable in size, ranging from 10 to 15 µm in length and 3.5 to 5.5 µm in width. Cultures were gray with orange spots, and no setae were observed. These morphological characteristics are consistent with those of Colletotrichum lupini (2). Identification of this species was confirmed by performing a BLASTn search with ITS sequence data (primers ITS4 and ITS5), which shared 99% identity with GenBank submission AJ301968, C. lupini var. setosum strain BBA 71310, isolated from L. luteus in Poland. Inoculum was produced by flooding PDA cultures with sterile deionized water, scraping with a rubber policeman, and passing the suspension through four layers of sterile cheesecloth. This preparation was used to inoculate 10 L. mutabilis and 10 L. hartwegii plants by injecting 10 µl of a suspension of 105 conidia/ml into the stem using a hypodermic needle (1). Ten additional plants were injected with sterile deionized water and maintained with the inoculated plants in the greenhouse for 4 weeks. All of the inoculated plants developed the previously-observed necrotic crook in the stem, whereas control plants developed no symptoms. The same organism was isolated from all inoculated plants. The ITS region was again sequenced, and the Polish strain was the closest match. The Floridian isolate sequence was deposited in GenBank (KF207599). Epidemics of anthracnose on ornamental lupins are common in most areas in which they are grown. In 1939, research plots of L. angustifolius were found with symptoms of anthracnose caused by Glomerella cingulata (3). Although it is not possible to determine if this isolate would be redefined as C. lupini, it does not seem likely since pathogenicity was confirmed on L. angustifolius and L. albus, but it did not cause infection on L. luteus (3) as has been reported for C. lupini (2). The finding of a lupin anthracnose in southeastern Florida is important to both the cut flower producers as well as vegetable producers who might consider some species of Lupinus as potential green manure crops. To the best of our knowledge, this is the first report of C. lupini or any Colletotrichum species on L. hartwegii and L. mutabilis in Florida. References: (1) W. H. Elmer et al. Plant Dis 85:216, 2001. (2) H. I. Nirenger et al. Mycologia 94:307, 2002. (3) J. L. Weimer. Phytopathology 43:249, 1943.

First Report of the Root-Knot Nematode Meloidogyne arenaria on Cheeseweed Mallow (Malva parviflora) in the United States.

During a 2010 field trial for examining alternatives to methyl bromide soil fumigation for the production of field-grown cut flowers, weeds were collected for identification and evaluated for their potential as hosts for plant pathogenic nematodes. In one cut flower field located in Martin County, FL, six cheeseweed mallow (Malva parviflora L.) plants were collected that had root-galling typical of infection by a root-knot nematode (Meloidogyne spp.). Field collected plants were used for species identification of the weed and maintained in the greenhouse for seed production. Several gravid female nematodes were extracted from field collected mallow roots and individually identified as Meloidogyne arenaria based on their esterase phenotype (PhastSystem, GE Healthcare) (1). A single egg mass was then extracted from the field collected mallow roots and inoculated onto a tomato plant (Solanum lycopersicum, 'Rutgers') grown in steamed builders sand in the greenhouse. The single egg mass culture was increased for 8 weeks, until galling was sufficient to produce adequate nematode inoculum to complete Koch's postulates on the original mallow host. Ten mallow plants were inoculated with single egg masses originally isolated from mallow and increased on tomato. Ten additional plants were maintained in the greenhouse as uninoculated controls. Inoculated and control mallow plants were grown in the greenhouse for 8 weeks, after which the roots were evaluated for galling, and root-knot nematode J2 were extracted from roots and soil and counted. All inoculated plants produced galled roots and control plants did not. Gravid females were extracted from mallow roots and identified as M. arenaria based on esterase phenotype as previously described. Ten gravid females for each DNA extraction were collected from mallow roots and DNA was isolated with the PowerSoil DNA Isolation Kit (MO BIO Laboratories, Inc., Carlsbad, CA). Identification of M. arenaria was confirmed by using species-specific primers F5'-TCGAGGGCATCTAATAAAGG-3' and R5'-GGGCTGAATAATCAAAGGAA-3' (2) and F5'-TCGGCGATAGAGGTAAATGAC-3' and R5'-TCGGCGATAGACACTACAACT-3' (4), which produced single amplicon bands of the expected size of 420 and 950 bp, respectively. This weed species has been reported as a host for M. javanica in Algeria and as an experimental host in Egypt (3), but this report, to our knowledge, constitutes the first documentation of Malva parviflora as a natural host of M. arenaria. The importance of weeds as hosts for plant parasitic nematodes cannot be over emphasized. As growers, particularly in Florida and California, continue to lose tools for broad-spectrum pest control, the ability of nematodes to reproduce on uncontrolled weeds will become increasingly important. References: (1) J. A. Brito et al. Nematology 10:757, 2008. (2) K. Dong et al. Nematropica 31:273, 2001. (3) M. Quader et al. Australas. Plant Pathol. 30:357, 2001. (4) C. Zijlstra et al. Nematology 2:847, 2000.

Cucurbit yellow stunting disorder virus Detected in Pigweed in Florida.

Pigweeds (genus Amaranthus) are problematic weeds in crop production throughout the world and are responsible for significant yield losses in many crops (2). Members of this genus can produce hundreds of thousands of seeds per plant and are also capable of supporting populations of important crop pathogens including viruses, nematodes, fungi, and oomycetes. Thirty-one pigweed samples (tentatively identified as Amaranthus lividus L. based on leaf notch and growth habit) were collected in November and December of 2009 from a watermelon field near Immokalee, FL, previously found to contain watermelon plants infected with three whitefly-transmitted viruses: Cucurbit yellow stunting disorder virus (CYSDV), Cucurbit leaf crumple virus (CuLCrV), and Squash vein yellowing virus (SqVYV). Although no obvious virus symptoms were observed on any of the pigweed plants, whiteflies (Bemisia tabaci), a known vector of CYSDV, CuLCrV, and SqVYV, were observed on leaves. Consequently, replica tissue blots were made from all pigweed samples and tested independently by tissue blot nucleic acid hybridization assay for CYSDV, CuLCrV, or SqVYV (3). Tissue blots indicated CYSDV infection in six pigweed samples. Neither CuLCrV nor SqVYV was detected. Three of the tissue blot-positive pigweed samples were further tested by reverse transcription (RT)-PCR amplification from total RNA (extracted from leaf tissue with TRIzol Reagent [Invitrogen, Carlsbad, CA]) with HSP70 and coat protein (CP) gene primers (1). HSP70 and CP gene RT-PCR products of the expected sizes (175 and 707 nt, respectively) were amplified, sequenced, and found to be 100% identical for all three pigweed samples. The partial HSP70 gene sequence from pigweed shared 98.3 to 100% nucleotide identity with CYSDV isolates from Arizona, California, and Spain (GenBank Accession Nos. FJ492808, EU596530, and NC_004810, respectively). The partial CP gene sequence from pigweed shared 88.8 to 100% nucleotide identity with CYSDV isolates from Arizona, Saudi Arabia, Texas, and Spain (GenBank Accession Nos. EF210558, AF312811, AF312806, and AF312808, respectively). To our knowledge, this is the first report of CYSDV infection of pigweed in Florida. Infection of redroot pigweed (A. retroflexus) was recently reported in California (4). These results collectively indicate that control of noncucurbit weeds may be important for effective management of CYSDV in cucurbit crops. References: (1) S. Adkins et al. Online publication. doi:10.1094/PHP-2009-1118-01-BR. Plant Health Progress, 2009. (2) L. Holm et al. World's Weeds: Natural Histories and Distributions. John Wiley and Sons, Inc. New York, NY, 1997. (3) W. W. Turechek et al. Phytopathology 100:1194, 2010. (4) W. M. Wintermantel et al. Plant Dis. 93:685, 2009.

Bidens mottle virus and Apium virus Y Identified in Ammi majus in Florida.

Ammi majus (bishop's weed), a member of the Apiaceae, is grown from seed for cut flowers in South Florida. In March 2005, plants were found to be showing virus-like symptoms including mosaic, vein clearing, and leaf rugosity (3) that rendered their flowers unmarketable. Inclusion morphology in epidermal strips from these infected plants indicated the presence of one or more potyviruses. This was confirmed by ELISA with commercially available antiserum for potyvirus identification (Agdia, Elkhart, IN). Clover yellow vein virus (ClYVV) was identified by sequencing and confirmed with specific antiserum (4). However, ClYVV was not identified in all potyvirus-infected samples from 2005, indicating the presence of one or more additional potyviruses. Bidens mottle virus (BiMoV) was subsequently identified in one of three potyvirus-infected samples by immunodiffusion tests using specific antiserum for BiMoV (Department of Plant Pathology, University of Florida), cylindrical inclusion morphology in epidermal strips, host range data, and sequencing of cloned reverse transcription (RT)-PCR products from degenerate potyvirus primers (2). Nucleotide and deduced amino acid sequences of a partial polyprotein gene sequence (GenBank Accession No. EU255631) were 95 and 98% identical, respectively, to a Florida isolate of BiMoV recently reported from tropical soda apple (1). Similar virus-like symptoms were again observed in A. majus in January 2007 and persisted through March. ELISA testing again indicated the presence of a potyvirus. However, neither ClYVV nor BiMoV were identified in the initial 2007 samples. Instead, sequence analysis of the cloned RT-PCR products amplified with degenerate potyvirus primers (2) from seven potyvirus-infected samples collected on two dates in January and one each in February and March revealed the presence of Apium virus Y (ApVY). The 3' terminal portion of the genome (GenBank Accession No. EU255632) was found to be 90 to 91% identical to ApVY sequences in GenBank at the nucleotide level. Deduced amino acid sequences of the NIb and CP regions of these RT-PCR products were 96 and 95% identical, respectively, to ApVY sequences in GenBank. One of these seven ApVY-infected samples (collected in March 2007) was determined to be coinfected with BiMoV by sequence analysis of the cloned RT-PCR products. Six clones were sequenced. Three were determined to be ApVY as indicated above. Nucleotide and deduced amino acid sequences of a partial polyprotein gene sequence from the other three clones were 95 and 97% identical, respectively, to the 2005 A. majus BiMoV isolate. Although ClYVV and BiMoV have previously been reported in other hosts in Florida, to the best of our knowledge, this is the first report of BiMoV and ApVY in A. majus anywhere and the first report of ApVY in North America. References: (1.) C. A. Baker et al. Plant Dis. 91:905, 2007. (2.) A. Gibbs and A. J. Mackenzie. J. Virol. Methods 63:9, 1997. (3.) M. S. Irey et al. (Abstr.) Phytopathology (suppl.)95:S46, 2005. (4.) M. S. Irey et al. Plant Dis. 90:380, 2006.

Tropical soda apple mosaic virus Identified in Solanum capsicoides in Florida.

Red soda apple (Solanum capsicoides All.), a member of the Solanaceae, is a weed originally from Brazil (3). It is a perennial in southern Florida and is characterized by abundant prickles on stems, petioles, and leaves. Prickles on stems are more dense than those on its larger, noxious weed relative, tropical soda apple (Solanum viarum Dunal), and the mature red soda apple fruits are bright red in contrast to the yellow fruits of tropical soda apple (2). Virus-like foliar symptoms of light and dark green mosaic were observed on the leaves of a red soda apple in a Lee County cow pasture during a tropical soda apple survey during the fall of 2004. The appearance of necrotic local lesions following inoculation of Nicotiana tabacum cv. Xanthi nc with sap from the symptomatic red soda apple leaves suggested the presence of a tobamovirus. Tropical soda apple mosaic virus (TSAMV), a recently described tobamovirus isolated from tropical soda apple in Florida, was specifically identified by a double-antibody sandwich-ELISA (1). An additional six similarly symptomatic red soda apple plants were later collected in the Devils Garden area of Hendry County. Inoculation of N. tabacum cv. Xanthi nc with sap from each of these symptomatic plants also resulted in necrotic local lesions. Sequence analysis of the TSAMV coat protein (CP) gene amplified from total RNA by reverse transcription (RT)-PCR with a mixture of upstream (SolA5'CPv = 5'-GAACTTWCAGAAGMAGTYGTTGATGAGTT-3'; SolB5'CPv = 5'-GAACTCACTGARRMRGTTGTTGAKGAGTT-3') and downstream (SolA3'CPvc = 5'-CCCTTCGATTTAAGTGGAGGGAAAAAC-3'; SolB3'CPvc = 5'-CGTTTMKATTYAAGTGGASGRAHAAMCACT-3') degenerate primers flanking the CP gene of Solanaceae-infecting tobamoviruses confirmed the presence of TSAMV in all plants from both locations. Nucleotide and deduced amino acid sequences of the 483-bp CP gene were both 98 to 99% identical to the original TSAMV CP gene sequences in GenBank (Accession No. AY956381). TSAMV was previously identified in tropical soda apple in these two locations in Lee and Hendry counties and three other areas in Florida (1). Sequence analysis of the RT-PCR products also revealed the presence of Tomato mosaic virus in the plant from Lee County. To our knowledge, this represents the first report of natural TSAMV infection of any host other than tropical soda apple and suggests that TSAMV may be more widely distributed in solanaceous weeds than initially reported. References: (1) S. Adkins et al. Plant Dis. 91:287, 2007. (2) N. Coile. Fla. Dep. Agric. Consum. Serv. Div. Plant Ind. Bot. Circ. 27, 1993. (3) U.S. Dep. Agric., NRCS. The PLANTS Database. National Plant Data Center. Baton Rouge, LA. Published online, 2006.

Effect of Fertilization and Biopesticides on the Infection of Catharanthus roseus by Phytophthora nicotianae.

Experiments were carried out in a greenhouse to determine the effect of fertilizer concentration (0, 0.5, 1.0, and 2.0× Hoagland solutions) and various commercial biopesticides on the severity of Phytophthora nicotianae infection of Madagascar periwinkle. Application of biopesticides and fertilizer concentration significantly influenced the severity of infection, but there was no significant effect from the interaction of these two factors. Overall, disease severity showed a tendency to increase with the concentration of applied fertilizer. Compared with the control plants, disease was significantly less severe in plants that were treated with the biopesticides, except for plants treated with metabolites of Myrothecium verrucaria (DiTera). However, only the products containing potassium phosphonates and potassium phosphates (FNX-100 and FNX-2500) provided a satisfactory level of control when compared with either the control plants or those that received any of the other products tested. Additional experiments were carried out in growth chambers to test the effects of increasing fertilizer concentrations in plants that were inoculated with different P. nicotianae inoculum levels. In these trials, there was no consistent indication that disease is most severe in plants that received the highest fertilizer concentration even at the highest inoculum level.

Influence of Epidemiological Factors on the Bioherbicidal Efficacy of Phomopsis amaranthicola on Amaranthus hybridus.

Greenhouse experiments were performed to determine the effect of dew period temperature and duration, plant growth stage, conidial concentration, and the addition of adjuvants on the bioherbicidal efficacy of Phomopsis amaranthicola on Amaranthus spp., using Amaranthus hybridus as test plant. P. amaranthicola infected A. hybridus at 20, 25, 30, and 35°C but the disease level achieved at 20°C may not be sufficient to cause high plant mortality. Plant mortality was also significantly lower in plants that were exposed to 4 h of dew. Plants at less than two- to two- to four-leaf stage were more easily killed than older plants, and increasing conidial concentration from 105 to 106 or 107 conidia ml-1 did not result in higher mortality levels. Among the adjuvants tested, polyalkyleneoxide-modified heptamethyltrisiloxane, algal polysaccharide, hyrdroxyethyl cellulose, and octylphenoxy polyethoxyethanol reduced conidial germination. Conidia applied with invert emulsion caused the highest plant mortality (74%) but invert emulsion alone caused 33% plant death due to phytotoxicity. Results indicate that P. amaranthicola can infect and kill Amaranthus spp. under a range of temperature, dew period, and inoculum levels and, therefore, has good potential as a bioherbicide agent.

First Report of Pythium Root Rot of Rau Ram (Polygonum odoratum).

Polygonum odoratum (= Persicaria odorata), known as rau ram or sang hum, is native to southeastern Asia and is a common herb in Vietnamese cuisine (1). It has been studied most extensively for its aromatic compound content (2). In Florida, rau ram commonly is grown hydroponically in greenhouses using large, cement beds with recirculated water. The plants form dense mats from which new growth is trimmed for market. During January of 2002, a severe dieback was observed in one production house in Saint Lucie County, FL. Plants with less severe symptoms were yellowed and stunted. Roots of symptomatic plants were largely decayed with root symptoms beginning as a tip necrosis. The cortex of severely affected roots slipped off easily, leaving a stringy vascular system. Plating of symptomatic tissue from 20 randomly selected plant samples was performed with multiple general and selective media including potato dextrose agar, corn meal agar with pimaricin, ampicillin, rifampicin, and pentachloronitrobenzene (PARP) (3). All colonies produced were identified as Pythium helicoides Drechsler on the basis of sporangial, oogonial, and antheridial characteristics (4). Isolates had proliferous, obovoid, papillate sporangia, and were homothallic with smooth-walled oogonia and thick-walled, aplerotic oospores. Multiple antheridial attachments per oogonium were common with the antheridium attached along its entire length. Pathogenicity tests were conducted using P. odoratum plants grown from commercial transplants. Two tests were performed. Each test was conducted using eight inoculated and eight control plants. In the first test, plants were maintained in 10-cm pots immersed in sterilized pond water for the duration of the test. Plants were inoculated with five 7- × 70-mm sections of freshly growing mycelial culture per plant using 10-day-old cultures of Pythium helicoides grown on water agar. Chlorosis was observed at approximately 2 months after inoculation. Root necrosis was observed in inoculated plants approximately 5 months after inoculation. This test was performed in the greenhouse with temperatures ranging from 20 to 30°C. The second test was performed in growth chambers at 35 to 40°C. Plants were maintained in 10-cm pots immersed in Hoagland's solution and were inoculated with four 6-mm plugs per plant. Symptoms were observed on inoculated plants at this temperature within 1 week of inoculation. No chlorosis or root decay was observed in noninoculated, immersed plants. The pathogen was reisolated from inoculated, symptomatic tissue. To our knowledge, this is the first report of root rot of P. odoratum caused by Pythium helicoides. References: (1) R. E. Bond. Herbarist 55:34, 1989. (2) N. X. Dung et al. J. Essent. Oil Res. 7:339, 1995. (3) M. E. Kannwischer and D. J. Mitchell. Phytopathology 68:1760, 1978. (4) A. J. van der Plaats-Niterink. Monograph of the Genus Pythium. Vol. 21, Studies in Mycology. Centraalbureau voor Schimmelcutltures, Baarn, The Netherlands, 1981.

First Report of the Root-Knot Nematode Meloidogyne arenaria on Tropical Soda Apple (Solanum viarum) in Florida.

Tropical soda apple (TSA), Solanum viarum Dunal, is an invasive, noxious, perennial weed that has invaded large areas of the southeastern United States. TSA is found growing in pasture lands and is spread by cattle, wildlife, and in the movement of sod and hay. Pasture land is commonly rotated into vegetable production. In November 2003, numerous TSA plants were collected from a vegetable farm growing cucumbers and tomatoes. This land in Martin County, Florida was previously used for pasture for grazing cattle. Root galling caused by root-knot nematode (Meloidogyne sp.) was observed. Female Meloidogyne sp. were randomly extracted from the roots and placed in extraction buffer (10% wt/vol sucrose, 2% vol/vol Triton X-100, 0.01% wt/vol bromophenol blue). The females were crushed, loaded on a polyacrylamide gel, and separated by electrophoresis using the PhastSystem (Amersham Biosciences, Piscataway, NJ) (1). The activities of malate dehydrogenase and esterase enzymes were detected using standard techniques (2). Isozyme phenotype and perineal patterns consistent with Meloidogyne arenaria (Neal) Chitwood were observed. Root galling consisted of round, bead-like galls that coalesced as the infection level increased. This is consistent with galling of tomato roots by M. arenaria. Thus, TSA is a potential reservoir for M. arenaria in Florida and throughout the southern United States. The large host range of root-knot nematodes implies that multiple crops may be affected if TSA is not managed in prior land uses. To our knowledge, this is the first report of M. arenaria occurring on tropical soda apple, S. viarum. References: (1) P. R. Esbenshade and A. C. Triantaphyllou. J. Nematol. 22:10, 1990. (2) H. Harris and D. A. Hopkinson. Handbook of Enzyme Electrophoresis in Human Genetics. North-Holland Publishing, New York, 1976.

Pythium spp. Associated with Bell Pepper Production in Florida.

Ten species of Pythium and a group of isolates that produced filamentous sporangia but did not form sexual structures (Pythium 'group F') were recovered from the root systems of fresh market bell pepper plants grown on polyethylene-mulched production systems in Florida. Pathogenicity tests using pasteurized field soil inoculated with infested wheat seed demonstrated that P. aphanidermatum, P. myriotylum, P. helicoides, and P. splendens can cause significant root rot and reductions in root growth of pepper. P. aphanidermatum and P. myriotylum caused the most severe root rot, the greatest reductions in plant weight, and 42 and 62% plant mortality, respectively. In pathogenicity tests with tomato plants, these four species produced similar plant weight losses and disease ratings to those observed in pepper, but little or no plant mortality. Low incidences of root tip necrosis in pepper plants were observed with P. arrhenomanes, P. catenulatum, P. graminicola, and P. irregulare, but none of these species caused losses in root weight and only P. irregulare reduced shoot weight. P. periplocum, P. spinosum, and Pythium sp. F colonized root tissue of pepper but caused no significant root rot and did not adversely affect growth. Similar trends were observed with tomato, except that P. arrhenomanes caused limited root tip necrosis without affecting plant growth and P. catenulatum, P. graminicola, P. irregulare, P. spinosum, and Pythium sp. F colonized at least some of the plants but did not cause root disease. A significant interaction between temperature and P. aphanidermatum or P. myriotylum was observed on pepper transplants. The greatest reductions in growth occurred at 28°C, whereas plant mortality only occurred at 34°C.

Field Evaluation of Phomopsis amaranthicola, A Biological Control Agent of Amaranthus spp.

There are approximately 60 species in the genus Amaranthus, of which seven are used as grains, leafy vegetables, or ornamentals. The majority of the remaining species are considered important weeds. A new fungal species, Phomopsis amaranthicola, isolated from stem and leaf lesions on an Amaranthus sp. plant, was found to be pathogenic to 22 species of Amaranthus tested. The efficacy of this fungus was tested in field trials using one or two postemergent applications of the fungus consisting of two concentrations of conidia or mycelial suspensions. Species tested for susceptibility in the field included Amaranthus hybridus, A. lividus, A. viridus, A. spinosus, and a triazine-resistant A. hybridus. The cumulative disease incidence data for each treatment within each species were plotted versus time using regression for lifetime data. Plant mortality was recorded 2, 4, and 6 weeks after inoculation. There were significant differences between the treatment effects in the control plots versus the plots treated with P. amaranthicola. The highest level of control was obtained in the first trial when the fungus was applied at 6 × 107 conidia per ml. Final mortality of all species, except A. hybridus, reached 100% in inoculated plots 25 days earlier than in noninoculated control plots. Conidial suspensions were more effective in controlling the species in the second trial than were mycelial suspensions. Spread of the pathogen to noninoculated control plots was faster in the second year than in other years. High levels of plant mortality were achieved in plots of A. spinosus, A. lividus, and A. viridis. A. hybridus and the triazine-resistant A. hybridus were not effectively controlled in the second year due to the advanced stage of plant growth (8 to 10 true leaves) at the time of pathogen application. Results confirmed that P. amaranthicola is an effective biocontrol agent of some of the Amaranthus spp. tested.