This study was conducted on two rangeland sites in south Texas with large populations of huisache (Acacia farnesiana (L.) Willd.); the Bush Ranch in Goliad County, and the Hitchcock Ranch in Bee County. The purpose of the study was to evaluate the effect of three herbicide treatments and three seasons of application on 1) apparent mortality of huisache, 2) huisache canopy cover, 3) huisache stem density, and 4) herbaceous ground cover. Herbicide treatments included aminocyclopyrachlor alone at a rate of 0.315 kg a.i. ha-1, aminocyclopyrachlor + triclopyr at a rate of 0.210 kg a.i. ha-1 + 0.420 kg a.e. ha-1, and triclopyr + picloram at a rate of 0.560 kg a.e. ha-1 + 0.560 kg a.e. ha-1. Herbicide treatments were applied over 3 x 30 m plots containing previously mowed huisache in May, July, and October of 2010 with ground-broadcast equipment at a rate of 140 L ha-1. Randomly selected huisache individuals and herbaceous ground cover at randomly selected points were monitored for the duration of the study. Statistical analyses of huisache mortality, canopy area, and stem densities revealed that at both sites one year after treatment, huisache mortality across the three seasons of application was consistently higher in plots treated with aminocyclopyrachlor + triclopyr (50 to 99%) versus those treated with aminocyclopyrachlor alone (16 to 78%) or triclopyr + picloram (4 to 70%). This mixture also provided the greatest reductions in huisache canopy area (60 to 99% reduction) and stem density (61 to 99% reduction). Also at both sites, spring applications consistently provided the greatest huisache control and canopy and stem reductions. Herbicide treatment and season of application had little effect on post-treatment herbaceous ground cover, likely due to extreme drought conditions in 2011. Of the possible combinations of seasons of application and herbicide treatments, the application in the spring of aminocyclopyrachlor plus triclopyr provided the most desirable results in terms of huisache mortality, canopy reduction, and stem density reduction. However, for sites invaded by huisache that are located near to potentially susceptible crops, the application of aminocyclopyrachlor plus triclopyr or aminocyclopyrachlor alone in the fall after the harvest of those crops may be more appropriate in order to avoid non-target injury while still providing acceptable huisache control.

The weed red rice is a major problem in rice producing areas world wide. All of the red rice in commercial rice fields in the United States has traditionally been considered to be the same species as commercial rice, Oryza sativa. However, using DNA markers it was found that most of the red rice with black hulls was sufficiently divergent to be considered a separate species. This includes TX4, a red rice ecotype that has been reported to have considerable natural tolerance to the herbicide glufosinate. TX4 is closely related to samples that have been classified as Oryza rufipogon. However, it was shown that both the TX4-like red rice from commercial fields and most of the Oryza rufipogon accessions in the US National Small Grains Collection are more accurately classified as Oryza nivara. This is significant since Oryza rufipogon is regulated under the Federal Noxious Weed Act, while Oryza nivara is not. Oryza nivara closely related to TX4 was found to be widely distributed across the rice production areas of Texas and was also found in Arkansas, Louisiana, and Mississippi. Of 240 samples from across Texas, 23 samples from six different counties were identical with TX4 with all 18 DNA markers tested. The reported glufosinate tolerance of TX4 is a potential problem since this same herbicide would be used in conjunction with genetically modified (GM) that is being developed as a method of red rice control. Thus, field, greenhouse and tissue culture studies were conducted to evaluate the degree of glufosinate tolerance in TX4. TX4 typically was severely damaged by glufosinate, but not efficiently controlled. Even with the maximum number of herbicide applications at the proposed maximum label rate, TX4 often re-sprouted and produced viable seed. Herbicide tolerance was found to be variable, but appears to be sufficient to present a problem with the use of the GM glufosinate resistant varieties currently under development, particularly when combined with variation in the response of ??sensitive?? varieties.

No description available.

Studies were conducted in 2009 and 2010 under field and growth room conditions to determine a) cultivar tolerance of soybean to preemergence (PRE) applications of saflufenacil and b) the biologically effective rate of saflufenacil/dimethenamid-p for control of annual weeds applied PRE alone and prior to an in-crop application of glyphosate. Environmental conditions following application influenced the amount of soybean injury caused by saflufenacil, as well as the rate of saflufenacil/dimethenamid-p required for the control of annual weeds. Increased soybean injury from saflufenacil was observed when soybean emergence was delayed due to cool, wet conditions following planting. Injury decreased with time; however, sensitive soybean cultivars were unable to fully recover from early season injury under adverse environmental conditions. OAC Hanover was the most sensitive cultivar in both field and hydroponic testing. With adequate moisture and above average temperatures in 2010, between 224 and 374 g a.i. ha-1 of saflufenacil/dimethenamid-p was required for 80% control of common ragweed, common lambsquarters, and green foxtail 4 weeks after treatment (WAT). In contrast, with below average temperatures and excessive moisture in 2009, between 528 and 613 g a.i. ha-1 of saflufenacil/dimethenamid-p was necessary for the same level of weed control. Pigweed species were least affected by environmental conditions after application with only 245 g a.i. ha-1 required for 80% control 4 WAT in both years. Excellent full season control of all weed species was achieved with saflufenacil/dimethenamid-p applied PRE followed by glyphosate postemergence (POST). However, there was no difference in yield when saflufenacil/dimethenamid-p was followed by glyphosate POST compared to a single glyphosate POST application. / BASF Canada

Weed control in chickpea (Cicer arietinum L.) is challenging because of poor crop competition ability and limited herbicide options. Development of chickpea varieties with resistance to different herbicide modes of action would be desirable. Resistance to imidazolinone (IMI) herbicides in chickpea has been previously identified, but the genetic inheritance and the mechanism were unknown. In many plant species, IMI resistance is caused by point mutation(s) in the acetohydroxyacid synthase (AHAS) gene resulting in an amino acid substitution. This changes the enzyme configuration at the herbicide binding site, preventing the herbicide attachment to the molecule. The main research objective was to genetically characterize chickpea resistance to imidazolinone herbicides. Two homologous AHAS genes, namely AHAS1 and AHAS2 sharing 80% similarity were identified in the chickpea genome. A point mutation in AHAS1 at cytosine 675 thymine 675 resulting in an amino acid substitution from alanine 205 to valine 205 confers the resistance to imidazolinone in chickpea. A KASP marker targeting the point mutation was developed and effectively predicted the herbicide response in the RIL population. This same population was used in molecular mapping where the major locus for herbicide resistance was mapped to chromosome 5. Segregation analysis demonstrated that the resistance is inherited as a single gene in a semi-dominant fashion. To study the synteny of AHAS across plant species, lentil (Lens culinaris) AHAS1 was sequenced. The same mutation that confers the resistance to imidazolinone in chickpea was also found in lentil. Phylogenetic analysis indicated independent clustering of AHAS1 and AHAS2 across pulse species. In vivo and in vitro AHAS enzyme activity analysis showed inhibition of AHAS activity in the susceptible genotype CDC Frontier over time and with the increasing imidazolinone concentrations. In contrast, the resistant genotype CDC Cory did not show AHAS inhibition under the same treatments. In summary, the simple genetic inheritance and the availability of KASP marker could aid in the development of chickpea varieties with resistance to imidazolinone herbicide.

A Pseudomonas strain, AI08, which was capable of detoxifying the herbicide acetochlor (2- chloro-N-ethoxymethyl-6'-ethylacet-o-toluide) was isolated from soils. The microbe was isolated using a combination of batch culture enrichment techniques, phenotypic agar plate based assays and a qualitative bioassay for detecting acetochlor detoxification. With the aid of a bioassay developed specifically for the quantification of acetochlor concentrations, it was determined that over a 21 day period Al 08 was capable of detoxifying 20 % of the acetochlor present in a medium containing no other organic carbon and 53 % of the herbicide in a medium containing glucose and yeast extract at concentrations of 0.02 g.l-l and 0.005 g.l-l respectively. A fragment of A108 DNA was cloned in Escherichia coli which produced recombinant cells with both elevated acetochlor resistance and the ability to detoxify 15 % of the acetochlor present in a minimal nutrient medium (containing 0.02 g.l-l glucose and 0.005 g.l-l yeast extract) over a 21 day period. Partial sequencing of the cloned A108 DNA revealed that it encoded an amino acid sequence with significant homology with the dihydrolipoyltransacetylase component of the pyruvate dehydrogenase complexes of Azotobacter vinlandii, E. coli and Alcaligenes eutrophus. Theories are proposed as to the possible biochemical mechanisms whereby expression of the dihydrolipoyltransacetylase gene of Al 08 in recombinant E. coli cells may function in the detoxification of acetochlor. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1995.

Genetically modified (GM) canola (Brassica napus L.) has been widely adopted in Canada since its commercial release in 1995 and now represents over 85% of the canola grown in western Canada. Concurrently, GM canola volunteers have become an increasing management problem in cultivated fields and are ubiquitous in adjacent ruderal (non-cropped disturbed) habitats. However, systematic post-release monitoring is lacking and the ecological and agronomic impacts of escaped GM canola are poorly understood. In this dissertation, I characterize the escape, demography and distribution of GM canola in ruderal habitats in southern Manitoba, at multiple spatial and temporal scales. I characterized GM herbicide tolerance traits in 16 escaped canola populations. The progeny of 129 plants were tested in herbicide trials; 74% of plants produced glyphosate-tolerant progeny, 63% produced glufosinate-tolerant progeny, and 34% produced multiple herbicide-tolerant progeny as a result of gene flow between escaped plants. At the population-scale, four escaped GM canola populations were monitored and periodic matrix models were constructed to describe the dynamics and persistence of flowering plants. Escaped populations were observed to flower in synchrony with adjacent crops and were projected to persist for 2 to 5 years, confirming the potential for gene flow between escaped and cultivated canola populations. At the landscape-scale, the distribution of escaped canola was surveyed in three agricultural regions. Regional factors were important determinants of distribution; escaped canola density was positively correlated with canola cropping intensity and with traffic intensity, and was negatively correlated with distance to grain distribution centres. Local seed dispersal had negligible impact on distribution compared to landscape-scale anthropogenic seed inputs resulting from agricultural transport. These findings suggest that escaped canola persists as a metapopulation, where long-distance dispersal and colonization compensate for frequent extinction of local populations. Escaped populations play an important role in the persistence and spread of GM traits at large spatial scales, with substantial implications for the coexistence of GM and non-GM crops, and especially for organic and reduced-tillage farming operations. Landscape-scale management approaches, designed and implemented collaboratively by multiple stakeholders, are necessary to mitigate the risks of contamination resulting from GM trait escape. Regulation and ongoing monitoring of GM crops must acknowledge and address the dynamic regional nature of seed- and pollen-mediated gene flow.

In 2011, Poa annua L. (Poa) biotypes were collected from greens of two golf courses in Lexington, Kentucky: 1.) The Lexington Country Club (LCC) and 2.) The University Club (UC). The samples were collected based on exhibiting one of two appearances while on the same green: 1.) dark green, with few to no flower heads (dark biotype) or 2.) light green, with numerous flower heads (light biotype). Two PGRs, paclobutrazol and flurprimidol, and two herbicides, bispyribac-sodium and amicarbazone, were applied to the plants both in the field and the greenhouse. Quality ratings were recorded weekly in both the field and greenhouse and grass clippings were collected and measured weekly in the greenhouse. Flurprimidol controlled the dark biotypes and paclobutrazol controlled the light biotypes in the field in 2011. However, only location by treatment interactions were in 2012; flurprimidol, bispyribac-sodium, and amicarbazone controlled the biotypes from the LCC while paclobutrazol controlled the biotypes from UC. In the greenhouse study there was a significant three way interaction between color, location, and treatment for quality. PGRs controlled the light biotypes from LCC and the dark biotypes from UC. Herbicides controlled the light biotypes more than the dark, however, the light biotypes recovered after amicarbazone treatments. PGRs reduced clipping weights of the dark biotypes more than the light and herbicides reduced clipping weights of the light biotypes more than the dark. Both PGRs and herbicides reduced clipping weights of the Poa collected from the LCC more than UC. These results demonstrate both the potential for differential responses between Poa biotypes to PGRs and herbicides and that these differences, like all things about Poa, may be complex. A laboratory experiment was also designed to examine the absorption and potential metabolism of 14C-labeled flurprimidol in creeping bentgrass (Agrostis stolonifera (L.)), bermudagrass (Cynodon dactylon (L.)), Kentucky bluegrass (Poa pratensis (L.)), perennial ryegrass (Lolium perenne (L.)), tall fescue (Festuca arundinacea (Schreb.)), and zoysiagrass (Zoysia japonica (Steud.)) and light and dark Poa biotypes collected from golf greens. Flurprimidol absorption and translocation was greater for warm season grasses than cool season grasses. Only parent flurprimidol was detected in all turf species.

Waterhemp was a sporadic weed in Kentucky soybean production since the 1970’s. Waterhemp’s presence was not significant until the 1990’s after a widespread adoption of imazaquin and imazethapyr herbicides in the late 1980’s by Kentucky farmers which resulted in ALS-resistant waterhemp in some Kentucky areas. The introduction of glyphosate resistant soybeans in 1996 resulted in glyphosate-containing products being widely used by Kentucky farmers. Waterhemp populations resistant to glyphosate have occurred in Kentucky in the past few years. The majority of Kentucky soybeans are produced in some type of conservation tillage system, primarily to conserve soil and water, which is advantageous on Kentucky’s rolling topography. Glyphosate controls a wide range of weeds and popular with farmers because of this characteristic. However, waterhemp resistant to glyphosate developed in some fields with the continuous glyphosate usage. Waterhemp control research trials were conducted in Union and Hancock Counties in Western Kentucky in an attempt to find herbicide combinations to provide season-long control. Waterhemp populations in these studies were resistant and susceptible to glyphosate but the resistant populations were great enough to cause soybean yield loss if not controlled. KEYWORDS: Amaranthus tuberculatus, Herbicide Resistance, EPSPS, PPO, ALS

Our research investigated whether priming switchgrass seeds with water or ethephon would increase stand establishment in the field. ‘Alamo’ seed germinated faster and grew taller than ‘Cave-in-Rock.Seeds primed for six days in water or for one day in ethephon 10 mM had the greatest seedling densities. In growth chamber environments seed priming were tested to hasten germination velocity. Seeds primed for two, four or six days in water germinated faster than unprimed seeds. Ethephon treatments reduced overall germination and germination velocity. Accent and Accent Q herbicides containing nicosulfuron are used to control weeds. To test ‘Alamo’ sensitivity to these herbicides, greenhouse evaluations were conducted. Seedlings treated with Accent Q had lower shoot fresh and dry weights than Accent treated seedlings. Seedling atrazine tolerance was examined in a greenhouse study at various growth stages (1, 2 and 4 true leaves). One and two true leaf were more sensitive to herbicide damage than the 4 leaf seedlings. To investigate difference in atrazine tolerance due to differential atrazine metabolism, 14C atrazine metabolism was examined in 1, 2 and 4 leaf ‘Alamo’ seedlings. 24-48 hours after exposure, 4 leaf seedlings metabolized atrazine at a greater rate than 1 and 2 leaf stage seedlings.