Panicum Texanum Research Articles

Non-targeted Colonization by the Endomycorrhizal Fungus, Serendipita vermifera, in Three Weeds Typically Co-occurring with Switchgrass.

Serendipita vermifera (=Sebacina vermifera; isolate MAFF305830) is a mycorrhizal fungus originally isolated from the roots of an Australian orchid that we have previously shown to be beneficial in enhancing biomass yield and drought tolerance in switchgrass, an important bioenergy crop for cellulosic ethanol production in the United States. However, almost nothing is known about how this root-associated fungus proliferates and grows through the soil matrix. Such information is critical to evaluate the possibility of non-target effects, such as unintended spread to weedy plants growing near a colonized switchgrass plant in a field environment. A microcosm experiment was conducted to study movement of vegetative mycelia of S. vermifera between intentionally inoculated switchgrass (Panicum virgatum L.) and nearby weeds. We constructed size-exclusion microcosms to test three different common weeds, large crabgrass (Digitaria sanguinalis L.), Texas panicum (Panicum texanum L.), and Broadleaf signalgrass (Brachiaria platyphylla L.), all species that typically co-occur in Southern Oklahoma and potentially compete with switchgrass. We report that such colonization of non-target plants by S. vermifera can indeed occur, seemingly via co-mingled root systems. As a consequence of colonization, significant enhancement of growth was noted in signalgrass, while a mild increase (albeit not significant) was evident in crabgrass. Migration of the fungus seems unlikely in root-free bulk soil, as we failed to see transmission when the roots were kept separate. This research is the first documentation of non-targeted colonization of this unique root symbiotic fungus and highlights the need for such assessments prior to deployment of biological organisms in the field.

Co-regulation of dark and light reactions in three biochemical subtypes of C4 species

Regulation of light harvesting in response to changes in light intensity, CO(2) and O(2) concentration was studied in C(4) species representing three different metabolic subtypes: Sorghum bicolor (NADP-malic enzyme), Amaranthus edulis (NAD-malic enzyme), and Panicum texanum (PEP-carboxykinase). Several photosynthetic parameters were measured on the intact leaf level including CO(2) assimilation rates, O(2) evolution, photosystem II activities, thylakoid proton circuit and dissipation of excitation energy. Gross rates of O(2) evolution (J(O)₂'), measured by analysis of chlorophyll fluorescence), net rates of O(2) evolution and CO(2) assimilation responded in parallel to changes in light and CO(2) levels. The C(4) subtypes had similar energy requirements for photosynthesis since there were no significant differences in maximal quantum efficiencies for gross rates of O(2) evolution (average value = 0.072 O(2)/quanta absorbed, approximately 14 quanta per O(2) evolved). At saturating actinic light intensities, when photosynthesis was suppressed by decreasing CO(2), ATP synthase proton conductivity (g (H) (+)) responded strongly to changes in electron flow, decreasing linearly with J(O)₂', which was previously observed in C(3) plants. It is proposed that g (H) (+) is controlled at the substrate level by inorganic phosphate availability. The results suggest development of nonphotochemical quenching in C(4) plants is controlled by a decrease in g (H) (+), which causes an increase in proton motive force by restricting proton efflux from the lumen, rather than by cyclic or pseudocyclic electron flow.

Effect of glyphosate and fungicide combinations on weed control in soybeans

Field studies were conducted in 2005 and 2006 along the upper Texas Gulf Coast near Yoakum, Texas and in 2005 near Tifton, Georgia to determine weed control and soybean response to glyphosate plus fungicide tank-mixes. In Texas, glyphosate at 0.77 kg a.e./ha in combination with azoxystrobin, tebuconazole, pyraclostrobin, and tetraconazole applied at the V3 or R1 soybean growth stage controlled Amaranthus palmeri and Panicum texanum at least 97% control while glyphosate alone controlled both weeds 100%. In Georgia, glyphosate applied alone to a mixed stand of annual grasses [ P. texanum L., Digitaria ciliaris (Retz.) Koel., and Dactyloctenium aegyptium (L.) Willd.] at the V3 stage of soybean development provided only 68% control and at the R1 stage provided 94% control. When rated approximately four weeks after treatment application, increased control of the mixed stand of annual grasses was obtained with glyphosate plus azoxystrobin or pyraclostrobin applied at the R1 stage rather than the V3 growth stage. No yield results were obtained at the Georgia location; however, at the Texas location, soybean yields were higher when glyphosate plus azoxystrobin or tetraconazole was applied at V3 compared with the R1 stage. In conclusion, tank mixing of glyphosate with a fungicide is a good option and can be used to reduce production costs. If glyphosate applications are delayed too long, yield reductions can occur due to early season weed competition.

Weed Control and Bermudagrass Tolerance to Imazapic Plus 2,4-D

Field studies were conducted during the 2000 and 2001 growing seasons to evaluate imazapic plus 2,4-D for weed control and bermudagrass tolerance. Imazapic at 140 g ai/ha plus 2,4-D at 280 g ai/ha or greater controlled dallisgrass at least 82% and provided at least 90% control of field sandbur, johnsongrass, and field mint. A mixed stand of Texas panicum and large crabgrass was controlled less than 75% and bahiagrass less than 25% with all rates of imazapic plus 2,4-D. Coastal bermudagrass injury was greater than 24% at three of four locations and Tifton 85 injury was greater than 50% at 3 wk after treatment with rates of imazapic plus 2,4-D as low as 70 plus 140 g/ha. Coastal bermudagrass yield was reduced at the first cutting with imazapic plus 2,4-D at 140 plus 210 g/ha and 240 plus 420 g/ha. Imazapic plus 2,4-D at 200 plus 350 g/ha reduced Tifton 85 forage production at the first two cuttings.Nomenclature: Imazapic, 2,4-D, dallisgrass, Paspalum dilatatum Poir. PASDI, field mint, Perilla frutescens (L.) Britt. PRJFR, field sandbur, Cenchrus incertus M. A. Curtis CCHIN, johnsongrass, Sorghum halepense (L.) Pers. SORHA, Texas panicum, Panicum texanum Buckl. PANTE, large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA, bahiagrass, Paspalum notatum Fluegge PASNO, bermudagrass, Cynodon dactylon (L.) Pers. CYNDA, ‘Coastal’, ‘Tifton 85’

Weed control and peanut ( Arachis hypogaea) response to sulfentrazone

Field experiments were conducted at several Texas peanut growing regions during the 1999 and 2000 growing seasons to study weed control and peanut response to sulfentrazone. Sulfentrazone applied preplant incorporated (PPI) or preemergence (PRE) caused up to 80% peanut stunt when rated 4–5 weeks after planting (WAP). The severity of stunting increased as sulfentrazone dose increased. Panicum texanum control was less than 40% regardless of dose. Cyperus esculentus control with sulfentrazone was better in south Texas than west Texas. In south Texas, C. esculentus was controlled at least 93% with sulfentrazone at 0.11 kg/ha or higher applied PPI or PRE when rated 4 and 12 WAP. Sulfentrazone at 0.06 kg/ha applied PPI controlled C. esculentus 93% 4 WAP but only 78% 14 WAP. The same dose of sulfentrazone applied PRE controlled yellow nutsedge 75% 4 WAP and 89% 14 WAP. In west Texas, C. esculentus control never exceeded 65% during the growing season regardless of dose or application timing. Ipomoea lacunosa control with sulfentrazone at 0.17 or 0.22 kg/ha was at least 90% season-long at both locations regardless of dose or application timing. The use of sulfentrazone in peanut in Texas is not recommended as it causes unacceptable crop stunting at the doses necessary for adequate control of various weeds.

Efficacy of KIH-485 on Texas Panicum (Panicum texanum) and Selected Broadleaf Weeds in Corn1

KIH-485 is an experimental herbicide being evaluated for preemergence weed control in corn. Field experiments were conducted in Burleson County, Texas, in 2003 and 2004 to compare weed control, corn tolerance, and corn yield with various rates of KIH-485 or S-metolachlor. Each herbicide was applied in single preemergence applications at four rates, or in combination with atrazine. KIH-485 at 500 g ai/ha provided better Texas panicum control than S-metolachlor by 9 WAT. KIH-485 or S-metolachlor treatments controlled Palmer amaranth at least 91% at all evaluation dates. In 2003, no other treatment controlled velvetleaf better than 500 g/ha KIH-485. The following year, all KIH-485 rates above 125 g/ha controlled velvetleaf better than any rate of S-metolachlor alone. Moreover, KIH-485 controlled all weed species as good as or better than S-metolachlor plus atrazine, regardless of KIH-485 rate. There was no significant corn injury observed, and grain yield reflected the effects of weed control. Nomenclature: ...

Flufenacet and Isoxaflutole Combinations for Weed Control and Corn (Zea mays) Tolerance1

Field studies were conducted in 1999 and 2000 at seven locations in south Texas to evaluate flufenacet plus isoxaflutole for weed control and corn tolerance. Palmer amaranth control with flufenacent plus isoxaflutole was variable, with no greater than 60% control at one location and greater than 95% control at another. The poor control at the one location was probably due to lack of rainfall for 3 to 4 wk after corn was planted. Flufenacet plus isoxaflutole at 0.56 or 0.7 kg/ha controlled Texas panicum at least 80%, whereas flufenacet plus isoxaflutole rates lower than 0.56 kg/ha provided variable control (55 to 99%). Flufenacet plus isoxaflutole at 0.35 and 0.49 kg/ha controlled pitted morningglory at least 83%. Corn stunting (3 to 16%) with flufenacet plus isoxaflutole was noted at the one location where the soil sand content was greater than 80% and moisture was received within 48 h of herbicide application. With few exceptions, corn weed control and yield with flufenacet plus isoxaflutole combinations were generally comparable to those observed for the atrazine and acetochlor standard treatments.Nomenclature: Flufenacet; isoxaflutole; Palmer amaranth, Amaranthus palmeri S. Wats. #3 AMAPA; pitted morningglory, Ipomoea lacunosa (L.) # IPOLA; Texas panicum, Panicum texanum Buckl. # PANTE; corn, Zea mays L., ‘AS986’, ‘DK668’, ‘Pioneer 3223’, ‘Pioneer 32K61’.Additional index words: Corn tolerance, weed management.

Weed control and grain sorghum tolerance to flumioxazin

Field studies were conducted from 2002 to 2004 to determine weed control and sorghum tolerance to flumioxazin. Flumioxazin at 0.07 and 0.11 kg ai/ha was applied 30, 21, 14, 7, and 0 days prior to sorghum planting. Flumioxazin at either dose provided excellent control of Amaranthus tuberculatus and Parthenium hysterophorus but provided variable control of Panicum texanum. No sorghum injury was noted with flumioxazin at any application timing. Reduction in sorghum yields were noted where annual grasses and broadleaved weeds were not effectively controlled.

Conservation Tillage and Herbicide Management for Two Peanut Cultivars

To reduce production costs and soil erosion and aid in management of tomato spotted wilt tospovirus (TSWV), many peanut (Arachis hypogaea L.) farmers in Florida are converting to conservation tillage systems. A split‐split plot experiment with six replications was conducted over 2 yr to evaluate pod yield and grass control from five tillage systems, two peanut cultivars (‘Georgia Green’ and ‘Andru 93’), and two postemergence herbicide programs (paraquat plus acifluorfen plus bentazon and imazapic). Peanut planted into rye (Secale cereale L.) with strip‐till management yielded (5280 to 5480 kg ha−1) similar to those in conventional tillage (5140 kg ha−1). Georgia Green (5500 kg ha−1) yielded higher than Andru 93 (5100 kg ha−1). Yields were greater for paraquat plus acifluorfen plus bentazon than for imazapic in 1999, but gross value was equivalent. Yields and gross value were higher for imazapic in 2000. Grass weeds included fall panicum (Panicum dichotomiflorum Michx.), Texas panicum (Panicum texanum L.), and large crabgrass [Digitaria sanguinalis (L.) Scop.], which were controlled more effectively with imazapic both years (18% greater control in 1999 and 52% greater control in 2000). The difference in yields between herbicide treatments for the 2 yr is attributed to replanting and drastically lower levels of grass control in 2000. These results support the claim that reduced tillage systems, with proper cultivar and herbicide selection, provide advantages over conventional tillage systems.

Texas Panicum (Panicum texanum) Interference in Peanut (Arachis hypogaea) and Implications for Treatment Decisions

Abstract Trials were conducted from 2001 through 2003 in Georgia to quantify Texas panicum interference on peanut. One set of trials investigated the effect of Texas panicum densities on peanut yie...

Using diclosulam in a weed control program for peanut in South Texas

Field studies were conducted during the 1997 and 1998 growing seasons to evaluate diclosulam alone and in combination with ethalfluralin for Eclipta prostrata, Ipomoea lacunosa, Panicum texanum, and Cyperus esculentus control. Diclosulam alone or in combination with ethalfluralin-applied preplant incorporated (PPI), preemergence (PRE), or postemergence (POST) at 0.009 to 0.024 kg ai/ha provided at least 93% season-long Eclipta control. Ethalfluralin, in combination with diclosulam-applied PPI at 0.016 or 0.024 kg ai/ha controlled C. esculentus at least 82% season-long. Ethalfluralin followed by diclosulam-applied POST at 0.016 or 0.024 kg/ha controlled at least 90% Ipomoea season long, while ethalfluralin followed by diclosulam-applied PPI or PRE at 0.024 kg/ha controlled 81%. Ethalfluralin in combination with diclosulam at 0.016 kg/ha or ethalfluralin followed by diclosulam at 0.016 or 0.024 kg/ha applied POST controlled greater than 80% P. texanum throughout the growing season. Diclosulam offers more effective Eclipta control than the commerical standards now being used.

Using diclosulam in a weed control program for peanut in South Texas

Field studies were conducted during the 1997 and 1998 growing seasons to evaluate diclosulam alone and in combination with ethalfluralin for Eclipta prostrata , Ipomoea lacunosa , Panicum texanum , and Cyperus esculentus control. Diclosulam alone or in combination with ethalfluralin-applied preplant incorporated (PPI), preemergence (PRE), or postemergence (POST) at 0.009 to 0.024 kg ai/ha provided at least 93% season-long Eclipta control. Ethalfluralin, in combination with diclosulam-applied PPI at 0.016 or 0.024 kg ai/ha controlled C. esculentus at least 82% season-long. Ethalfluralin followed by diclosulam-applied POST at 0.016 or 0.024 kg/ha controlled at least 90% Ipomoea season long, while ethalfluralin followed by diclosulam-applied PPI or PRE at 0.024 kg/ha controlled 81%. Ethalfluralin in combination with diclosulam at 0.016 kg/ha or ethalfluralin followed by diclosulam at 0.016 or 0.024 kg/ha applied POST controlled greater than 80% P. texanum throughout the growing season. Diclosulam offers more effective Eclipta control than the commerical standards now being used.

Annual Grass Control in Peanut (Arachis hypogaea) with Clethodim and Imazapic1

Field experiments were conducted to evaluate possible interactions of clethodim with imazapic applied as mixtures or sequentially for control of broadleaf signalgrass, fall panicum, goosegrass, and large crabgrass. Imazapic at 70 g ai/ha alone controlled grass weeds inconsistently, whereas clethodim at 140 g ai/ha alone controlled the same weeds at least 99%. Imazapic did not affect broadleaf signalgrass control by clethodim. Reduced control of fall panicum, goosegrass, and large crabgrass was observed when clethodim and imazapic were applied in mixture. Antagonism of clethodim occurred when clethodim was applied 1 d before or up to 3 d after application of imazapic (fall panicum and large crabgrass). Antagonism of goosegrass control was noted when imazapic was applied 3 d before or up to 7 d after application of clethodim. In other experiments, large crabgrass and Texas panicum control by clethodim (70 and 140 g/ha) applied alone or with imazapic (70 g/ ha) or bentazon (1.1 kg ai/ha) plus 2,4-DB (0.28 kg ai/ha) either with or without ammonium sulfate (2.8 kg/ha) was evaluated. Texas panicum control by clethodim was reduced by imazapic regardless of the ammonium sulfate rate. However, large crabgrass control by imazapic was not affected in these experiments. Control of both grasses by clethodim was reduced substantially by bentazon plus 2,4-DB, although in some instances ammonium sulfate improved control when in mixture. Ammonium sulfate improved control by clethodim in some instances irrespective of the broadleaf–sedge herbicide treatments.Nomenclature: Bentazon; clethodim; 2,4-DB; imazapic; broadleaf signalgrass, Brachiaria platyphylla (Griseb) Nash #3 BRAPP; fall panicum, Panicum dichotomiflorum L. # PANDI; goosegrass, Eleusine indica L. Gaertn. # ELEIN; large crabgrass, Digitaria sanguinalis L. Scop. # DIGSA; Texas panicum, Panicum texanum Buckl. # PANTE.Additional index words: Ammonium sulfate, antagonism, herbicide compatibility, herbicide interaction, sequential application.

Effect of row spacing and herbicide dose on weed control and grain sorghum yield

Field studies were conducted in 2000 and 2001 near Yoakum, Texas without irrigation to determine the effect of row spacing and herbicide dose on weed control and grain sorghum response. Atrazine or dimethenamid alone or in combination were compared under conventional row spacing (single rows spaced 91 cm apart on a bed) and twin rows (two rows spaced 20 cm apart on a single bed). Amaranthus albus (tumble pigweed) control was 100% with all treatments except dimethenamid at 0.56 kg/ha which controlled at least 96%. Panicum texanum (Texas panicum) control was less than 80% with dimethenamid at 0.56 kg/ha and atrazine at 0.56 and 1.12 kg/ha under the conventional row spacing. Under the twin-row system, P. texanum control was greater than 80% with all herbicides. Cyperus esculentus (yellow nutsedge) control was less than 70% early season with both row spacings but greater than 80% late season under the twin-row system.

Flufenacet and Metribuzin Combinations for Weed Control and Corn (Zea mays) Tolerance1

Field studies were conducted in 1999 and 2000 at seven locations in south Texas to evaluate flufenacet plus metribuzin for weed control and corn tolerance. Texas panicum control with flufenacet plus metribuzin was variable with less than 70% control in 1999 and greater than 75% control in 2000. Palmer amaranth and pitted morningglory control ranged from 41 to 100%. Corn stunting (4 to 13%) was noted in soils with greater than 75% sand. Corn yields with flufenacet and metribuzin combinations were increased up to 19% over the untreated check where stunting was not observed. Nomenclature: Flufenacet; metribuzin; Palmer amaranth, Amaranthus palmeri S. Wats. #3 AMAPA; pitted morningglory, Ipomoea lacunosa (L.) # IPOLA; Texas panicum, Panicum texanum Buckl. # PANTE; corn, Zea mays L. ‘AS986’, ‘Pioneer 3223’, ‘Pioneer 32K61’, ‘DK-668’. Additional index words: Corn tolerance, ivyleaf morningglory, weed management. Abbreviations: POST, postemergence; PRE, preemergence.

Weed Control with Combinations of Selected Fungicides and Herbicides Applied Postmergence to Peanut (Arachis hypogaea L.)

Abstract Experiments were conducted from 1997 through 2001 in Georgia, Florida, North Carolina, and Texas to evaluate compatibility of selected postemergence herbicides and fungicides applied in tank mixtures. Control of broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash], goosegrass [Eleusine indica (L.) Gaertn.], large crabgrass [Digitaria sanguinalis (L.) Scop.], and Texas panicum (Panicum texanum Buckl.) by clethodim applied in tank mixtures with copper-based fungicides, fungicides containing chlorothalonil, azoxystrobin, and iprodione was reduced in 80, 69, 60, and 46% of comparisons, respectively, when compared to clethodim alone. Fluazinam, tebuconazole, and propiconazole did not reduce efficacy of clethodim. Efficacy was reduced more by fungicides when clethodim was applied in 230 L/ha spray volume compared with 94 L/ha. Efficacy of acifluorfen, bentazon, imazethapyr, and 2,4-DB applied with fungicides was also compared. Smooth pigweed (Amaranthus hybridus L.) control by 2,4-DB was reduced in at least two of three experiments when applied with chlorothalonil, copper-based fungicides, tebuconazole, azoxystrobin, and fluazinam. Iprodione did not affect efficacy of 2,4-DB. Control of smooth pigweed by imazethapyr was reduced when applied in combination with copper-based fungicides but not when applied with chlorothalonil, propiconazole, tebuconazole, fluazinam, propiconazole plus flutolanil, or propiconazole plus trifloxystrobin. Smooth pigweed control by acifluorfen was reduced in one of three experiments when applied with tebuconazole. Efficacy of acifluorfen was not affected by chlorothalonil, azoxystrobin, propiconazole, or fluazinam. Yellow nutsedge (Cyperus esculentus L.) control by bentazon was reduced by propiconazole plus chlorothalonil, propiconazole plus flutolanil, and copper-based fungicides. With the exception of fluazinam and chlorothalonil applied with 2,4-DB in one experiment, fungicides did not affect peanut injury following application of acifluorfen, clethodim, imazethapyr, or 2,4-DB.

Weed Management in Watermelon (Citrullus lanatus) and Cantaloupe (Cucumis melo) Transplanted on Polyethylene-Covered Seedbeds1

Studies were conducted from 1998 to 2001 in Tifton, GA, on weed management systems in transplanted cantaloupe and watermelon grown on polyethylene-covered seedbeds. Soil fumigants were metham (748 L/ha) and a nonfumigated control. All metham applications were sprayed in a 61-cm band and incorporated with a modified power tiller. Herbicide treatments were ethalfluralin (0.8 kg ai/ha) premergence (PRE), ethalfluralin plus halosulfuron (36 g ai/ha) PRE, ethalfluralin PRE followed by glyphosate (1.1 kg ai/ha) postemergence POST-SHIELDED, ethalfluralin plus halosulfuron PRE followed by glyphosate POST-SHIELDED, and a nontreated control. Premergence herbicides were directed to row middles not covered in polyethylene, without contacting the transplants. Glyphosate was applied to row middles using a hooded sprayer, just before vine running. Overall weed control was not improved with soil fumigation in either cantaloupe or watermelon, and there was no yield response in either crop. There may be minimal benefit in transplanted cantaloupe and watermelon on polyethylene-covered seedbeds from preplant soil fumigation for weed control, in the absence of other pests. Herbicide systems that included halosulfuron PRE or glyphosate applied POST-SHIELDED improved control of yellow nutsedge compared with ethalfluralin alone. Control of Texas panicum, southern crabgrass, Florida pusley, and smooth pigweed was not improved by halosulfuron or glyphosate. Polyethylene-covered seedbeds provide a mechanical barrier to weed infestation for many species. Integration of these weed control practices gives cantaloupe and watermelon growers effective options for weed management, particularly for a troublesome species such as yellow nutsedge.Nomenclature: Ethalfluralin; halosulfuron; metham; crowfootgrass, Dactyloctenium aegyptium (L.) Willd. #3 DTTAE; Florida pusley, Richardia scabra L. # RCHSC; smooth pigweed, Amaranthus hybridus L. # AMACH; southern crabgrass, Digitaria ciliaris (Retz.) Koel. # DIGSP; Texas panicum, Panicum texanum Buckl. # PANTE; yellow nutsedge, Cyperus esculentus L. # CYPES; cantaloupe, Cucumis melo L.; watermelon, Citrullus lanatus (Thunb.) Mansf.Additional index words: Alternatives to methyl bromide, fumigation, halosulfuron, metham, plasticulture.Abbreviations: POST, postemergence; PRE, premergence; PTO, power take off.

Recovery of Pantoea ananatis, causal agent of center rot of onion, from weeds and crops in Georgia, USA

Center rot of onion, caused by Pantoea ananatis, has been a problem of sweet onions in Georgia since 1997. A polymerase chain reaction (PCR) protocol was developed to screen for populations of P. ananatis on plant surfaces. Plant samples producing a positive PCR reaction were targeted for further processing to culture the bacterium. In a survey of the Vidalia onion-growing region of Georgia, we detected and cultured P. ananatis from 25 asymptomatic weed species, which included commonly occurring weeds such as crabgrass ( Digitaria sanguinalis), Florida beggarweed ( Desmodium tortuosum), Florida pusley ( Richardia scabra), sicklepod ( Cassia obtusifolia), Texas Millet ( Panicum texanum), tall verbena ( Verbena bonariensis) and yellow nutsedge ( Cyperus esculentus). In addition, the bacterium was recovered from crop plants such as Bermuda grass ( Cynodon dactylon), cowpea ( Vigna unguiculata) and soybean ( Glycine max) . Based on the field survey and tests with strains held in storage in the Coastal Plain Experiment Station culture collection, we concluded that P. ananatis was in Georgia prior to 1997, and was distributed widely on weeds and crops throughout southern Georgia.

Weed Management with Diclosulam in Strip-Tillage Peanut (Arachis hypogaea)1

Experiments were conducted at three locations in North Carolina in 1999 and 2000 to evaluate weed management systems in strip-tillage peanut. Diclosulam was evaluated with standard preemergence (PRE), early postemergence, and postemergence (POST) herbicide systems in a factorial treatment arrangement. Preemergence treatments that contained diclosulam controlled common lambsquarters, common ragweed, and eclipta by 100%. Diclosulam PRE controlled entireleaf morningglory by 88%, ivyleaf morningglory by ≥ 90%, pitted morningglory by ≥ 81%, and prickly sida by ≥ 94%. Yellow nutsedge control with diclosulam ranged from 65 to 100% depending on location, whereas POST systems containing imazapic controlled yellow nutsedge by at least 89%, regardless of PRE herbicides. Peanut yields and net returns were reflective of levels of weed management. Systems that included diclosulam PRE plus POST herbicides consistently provided high yields and net returns. Clethodim late POST was required for full-season control of annual grasses, including broadleaf signalgrass, goosegrass, large crabgrass, and Texas panicum.Nomenclature: Clethodim; diclosulam; imazapic; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #3 BRAPP; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; eclipta, Eclipta prostrata L. # ECLAL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; Texas panicum, Panicum texanum Buckl. # PANTE; yellow nutsedge, Cyperus esculentus L. # CYPES; peanut, Arachis hypogaea L. ‘NC 10C’ and ‘NC 12C’.Additional index words: Economic analysis.Abbreviations: EPOST, early postemergence; fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Control of Seven Grasses with a Mixture of Three Fungal Pathogens with Restricted Host Ranges

Abstract Three fungi indigenous to Florida, Drechslera gigantea, Exserohilum longirostratum, and E. rostratum, were isolated from large crabgrass (Digitaria sanguinalis), crowfootgrass (Dactyloctenium aegyptium), and Johnsongrass (Sorghum halepense), respectively. In greenhouse trials, these pathogens controlled the following seven grasses: crowfootgrass, guineagrass (Panicum maximum), Johnsongrass, large crabgrass, southern sandbur (Cenchrus echinatus), Texas panicum (Panicum texanum), and yellow foxtail (Setaria glauca). Four-week-old seedlings were inoculated with spore suspensions of each pathogen (2 × 105 spores/ml) or a mixture of the three pathogens (1:1:1 by volume; total 2 × 105 spores/ml). The spore suspensions as well as the control (water only) were amended with 0.5% Metamucil and the seedlings were sprayed, incubated in a dew chamber for 12 h at 28°C, and then held in a greenhouse. All seven grasses were susceptible to each of the pathogens and the pathogen mixture, each with 100% disease incidence. Two weeks after inoculation, disease severity ranged from 83 to 100% for the different grasses. In a host-range trial, 52 plant species were tested, and all nontarget plant species were safe from the individual pathogens and the pathogen mixture inoculum amended with 0.5% Metamucil. An emulsion-based inoculum preparation of the pathogen mixture was also not injurious to the crop species tested (21 species). Thus, D. gigantea, E. longirostratum, and E. rostratum and a mixture of these pathogens were nonpathogenic to the crop species tested, including Poaceae members. It is preferable to have more than one or even two pathogens in the grass pathogen mixture to achieve a broad spectrum of weed control and provide insurance against any possible failure of one or even two of the pathogens in any given combination under field conditions. More pathogens (at least three instead of two) with different modes of action and/or sites of action in a combination have a much greater chance of reducing potential risk of development of resistance in weed populations than a single pathogen used repeatedly. The use of a mixture of these pathogens appears to have the potential to be developed further as a bioherbicide system to control weedy grasses.