A host-specific fungusColletotrichum truncatumstrain 00-3B1 (Ct) was mixed with herbicides to improve the control of scentless chamomile, a noxious weed in western Canada. The compatibility of Ct conidia (spores) with herbicides was evaluated in vitro, and varying effects were observed with different products on spore germination. Clodinafop, glufosinate, MCPA, and 2,4-D ester were relatively benign and delayed the germination slightly, whereas dicamba, imazethapyr, metribuzin, and 2,4-D amine were noticeably more inhibitive. Bromoxynil, glyphosate, sethoxydim, and Merge®(spray adjuvant) were most inhibitive, showing >50% inhibition after 24 h. To determine potential synergy, Ct was applied at 7 × 106spores/ml in tank mixtures with selected herbicides at 1× and 0.1× registered rates under greenhouse conditions. Combining Ct with MCPA, 2,4-D ester, clopyralid, or metribuzin at 1× rate resulted in synergistic or additive interaction on scentless chamomile, increasing weed control significantly when compared to Ct or herbicides applied alone. Similar applications of Ct with imazethapyr, 2,4-D amine, dicamba, or glyphosate were antagonistic. Treatments with Ct plus 1× metribuzin killed scentless chamomile completely, whereas neither Ct nor the herbicide alone caused plant death, suggesting the value of this tank mixture.
Hair fescue (Festuca filiformis) is a tuft-forming perennial grass of concern in lowbush blueberry (Vaccinium angustifolium) as tufts form dense sods that reduce lowbush blueberry yield and inhibit harvest. Although generally tolerant to ACCase-inhibiting herbicides, injury to some Festuca spp. following clethodim applications has been reported. ACCase-inhibiting herbicides are important for non-bearing and bearing year perennial grass management in lowbush blueberry but have not been extensively evaluated for hair fescue management. The objectives of this research were to 1) determine the relative efficacy of foramsulfuron, fluazifop-p-butyl, sethoxydim, and clethodim on hair fescue, and 2) determine if foramsulfuron tank mixtures with fluazifop-p-butyl, sethoxydim, and clethodim improve hair fescue suppression. None of the herbicides evaluated caused unacceptable injury to lowbush blueberry. Foramsulfuron (35 g a.i. ha-1) reduced hair fescue total tuft density, flowering tuft density, and flowering tuft inflorescence number. Fluazifop-p-butyl (250 g a.i. ha-1) and sethoxydim (495 g a.i. ha-1) caused variable levels of visual injury to hair fescue and did not reduce total tuft density, flowering tuft density, or flowering tuft inflorescence number. Clethodim (91 g a.i. ha-1), however, caused >50% visual injury to hair fescue and reduced hair fescue total tuft density, flowering tuft density, and flowering tuft inflorescence number. Fluazifop-p-butyl and sethoxydim tank mixtures with foramsulfuron did not increase hair fescue suppression relative to foramsulfuron alone. A foramsulfuron + clethodim tank mixture provided equivalent hair fescue suppression as either herbicide applied alone. Foramsulfuron and clethodim should therefore be used in rotation rather than tank mixture to manage hair fescue in lowbush blueberry
Potato producers in the Atlantic Canadian provinces of New Brunswick (NB) and Prince Edward Island (PE) rely on the photosystem II-inhibiting herbicide metribuzin for weed management. Recently, potato producers in the region have reported unacceptable common lambsquarters control following an application of metribuzin. Tissue and seed samples were collected from escaped common lambsquarters populations from across the potato producing regions of NB and PE and screened for the Ser264Gly mutation in psbA. Overall, 46% of sampled populations possessed the Ser264Gly mutation across the region. Cross-resistance testing to atrazine, metribuzin and linuron confirmed populations with the Ser264Gly were resistant to triazines and triazinones but remained susceptible to linuron. Dose response analysis determined a moderate level of resistance to metribuzin in common lambsquarters which would not be controlled in producers fields. A field experiment was conducted in Fredericton, NB and Harrington, PE, to determine if currently registered and unregistered products and tank-mixes would control PSII-inhibitor-resistant common lambsquarters in potato. All evaluated products, with the exception of S-metolachlor, provided control equivalent to the weed-free check without compromising potato yield or quality. This study demonstrates that PSII-inhibitor-resistant common lambsquarters are found in Atlantic Canadian potato production systems, but can be controlled with currently registered herbicides and rates with alternative modes of action.
Scentless chamomile, a noxious weed in western Canada, has a high natural tolerance to many herbicides. Colletotrichum truncatum , a host specific fungal pathogen, is suppressive to scentless chamomile when applied inundatively. A broadcast application was used at 200 L ha (1 to evaluate biocontrol potential of this pathogen under a range of dew temperatures (DT), postinoculation conditions (PIC), and pathogen doses (PD). A DT between 20 and 258C was more conducive to infection, resulting in higher levels of disease and weed suppression as compared to 15 and 308C. Under similar post-inoculation temperature regimes, disease was only slightly more severe in growth chambers than in the greenhouse. There was a positive linear relationship between the PD and weed suppression. An inoculum concentration /1)/10 8 spores mL (1 reduced plant fresh weight by approximately 50% when compared to untreated controls. These results indicate that biocontrol of scentless chamomile using C. truncatum in the semi-arid Canadian prairies will likely encounter frequent non-favourable field conditions.
Colletotrichum truncatum (Ct) was examined in a tank mix with the herbicide 2,4-D, clopyralid plus MCPA (Caurtail M Ò ), or metribuzin (Sencor Ò ) for control of scentless chamomile at 8-(younger) and 11-leaf stages (older) under controlled conditions. In initial trials, Ct at 7 Â 10 6 spores/ml (200 l/ha) reduced the fresh weight of scentless chamomile only slightly. However, its combinations with herbicides improved the efficacy variably depending on the herbicide used and stage of the weeds. Ct plus 2,4-D reduced the fresh weight by about 50% at both leaf stages of scentless chamomile when compared to untreated controls but no plants were killed. The fungus plus Curtail M consistently killed younger but not older plants, and the efficacy was substantially greater than that of the herbicide alone. The herbicide Sencor was highly effective on younger plants, and adding Ct did not achieve additional benefits. On older plants, however, Ct plus Sencor was substantially more effective than the herbicide alone, causing 76% fresh-weight reduction when compared to controls and killing 9 out of 16 older plants in four trials. Sencor applied alone reduced the fresh weight of older plants by 65%, but no plants were killed. Tested at doses ranging from 2 Â 10 6 to 20 Â 10 6 spores/ml, Ct plus Curtail M was most effective at the highest fungal inoculum dose, consistently killing younger but not older plants. In comparison, Ct at a medium dose (7 Â 10 6 spores/ml) plus Sencor killed the majority of older chamomile plants (7 out of 12), whereas the herbicide alone did not cause plant mortality. Further increasing fungal inoculum dose from this medium level did not enhance the weed control by Ct plus Sencor.
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