Credit Cards: Weapons for Domestic Violence

The objectives of this study were to describe the intra-specific variation in herbicide response of weed populations when subjected to new vs. well-established herbicides, and to assess distributions of logLD(50)- and logGR(50)-estimates as a potential indicator for early resistance detection. Seeds of two grass weeds (Alopecurus myosuroides, Apera spica-venti) were collected in southern Sweden, mainly in 2002. In line with the objectives of the study, the collections sites were not chosen for noted herbicide failures nor for detected herbicide resistance, but solely for the presence of the target species. For each species, seedlings were subjected to two herbicides in dose-response experiments in a greenhouse. One herbicide per species was recently introduced and the other had been on the market for control of the species for a decade, with several reports of resistance in the literature. Fresh weight of plants and a visual vigour score were used to estimate GR(50) and LD50, respectively. Resistance to fenoxaprop-P-ethyl in A. myosuroides was indicated by the LD50-estimates to be present in frequencies sufficient to affect the population-level response in 9 of 29 samples, and was correlated to response to flupyrsulfuron, while low susceptibility to isoproturon in A. spica-venti populations was not linked to the response to sulfosulfuron. In the study as a whole, the magnitude of the estimated herbicide susceptibility ranges differed irrespective of previous exposure. No consistent differences were found in the distribution of LD50-estimates for new and "old" herbicides, and normality in the distribution of estimates could not be assumed for a non-exposed sample, even in the absence of an indication of cross-resistance.Original Publication:Liv A Espeby, Hakan Fogelfors and Per Milberg, Susceptibility variation to new and established herbicides: Examples of inter-population sensitivity of grass weeds, 2011, CROP PROTECTION, (30), 4, 429-435.http://dx.doi.org/10.1016/j.cropro.2010.12.022Copyright: Elsevier Science B.V., Amsterdam.http://www.elsevier.com

Within-species variation in grass weeds in Sweden

Variation within a weed species enables it to persist through varying conditions and is thus an important component of weediness. In this thesis, intra-specific variation in two agronomically important attributes - herbicide susceptibility and seed dormancy - are studied in Swedish Apera spica-venti (L.) Beauv. and Alopecurus myosuroides Huds., both serious annual weeds in winter cereals, and with many cases of herbicide resistance. Swedish Elymus repens (L.) Gould, a perennial, rhizomatous grass, is investigated for its genetic variability and variation in glyphosate response. The susceptibility to new and established herbicides in greenhouse studies in the two annual grasses ranged 0.5-4 orders of magnitude among populations, which mostly came from fields with no previous suspicion of resistance. The greatest variation was found in A. myosuroides in response to fenoxaprop-P-ethyl (an old herbicide in the sense that it had been used for a decade), with significant correlation with response to flupyrsulfuron-Na (a newly introduced herbicide). One fifth of the A. spica-venti populations were significantly less susceptible to isoproturon (old) than a susceptible reference population, but without correlation in response to sulfosulfuron (new). The findings indicate field evolved resistance at a scale of practical importance with possible cross-resistance to one new herbicide. Both A. spica-venti and A. myosuroides exhibited considerable primary and seasonally variable seed dormancy, with variation between seed collects. Light requirement in A. myosuroides was affected by stratification, and soil disturbance did not greatly enhance the low spring emergence occurring in this winter annual. Swedish E. repens seem to consist of one large, fairly homogeneous group, with a moderate geographic differentiation. Glyphosate dose-response patterns varied greatly between clones but were not linked to type of habitat or to genetic or geographic distance. The results are discussed in relation to methods for assessing herbicide susceptibility, for early detection of resistance, and for weed management

Susceptibility variation to new and established herbicides: Examples of inter-population sensitivity of grass weeds

The objectives of this study were to describe the intra-specific variation in herbicide response of weed populations when subjected to new vs. well-established herbicides, and to assess distributions of logLD(50)- and logGR(50)-estimates as a potential indicator for early resistance detection. Seeds of two grass weeds (Alopecurus myosuroides, Apera spica-venti) were collected in southern Sweden, mainly in 2002. In line with the objectives of the study, the collections sites were not chosen for noted herbicide failures nor for detected herbicide resistance, but solely for the presence of the target species. For each species, seedlings were subjected to two herbicides in dose-response experiments in a greenhouse. One herbicide per species was recently introduced and the other had been on the market for control of the species for a decade, with several reports of resistance in the literature. Fresh weight of plants and a visual vigour score were used to estimate GR(50) and LD50, respectively. Resistance to fenoxaprop-P-ethyl in A. myosuroides was indicated by the LD50-estimates to be present in frequencies sufficient to affect the population-level response in 9 of 29 samples, and was correlated to response to flupyrsulfuron, while low susceptibility to isoproturon in A. spica-venti populations was not linked to the response to sulfosulfuron. In the study as a whole, the magnitude of the estimated herbicide susceptibility ranges differed irrespective of previous exposure. No consistent differences were found in the distribution of LD50-estimates for new and "old" herbicides, and normality in the distribution of estimates could not be assumed for a non-exposed sample, even in the absence of an indication of cross-resistance.Original Publication:Liv A Espeby, Hakan Fogelfors and Per Milberg, Susceptibility variation to new and established herbicides: Examples of inter-population sensitivity of grass weeds, 2011, CROP PROTECTION, (30), 4, 429-435.http://dx.doi.org/10.1016/j.cropro.2010.12.022Copyright: Elsevier Science B.V., Amsterdam.http://www.elsevier.com

Variation in Elymus repens susceptibility to glyphosate

Continuous increase in glyphosate use in Sweden has caused concern about resistance development, not least inconnection with the possible introduction of crops resistant to glyphosate. In Sweden, the main weed targetedby glyphosate is Elymus repens (L.) Gould. We sampled 69 clones of E. repens to assess the magnitude andgeographical distribution of variation in susceptibility to glyphosate. Clones originated from four habitat types:intensively and extensively used arable lands, field vicinities and other habitats, including natural vegetation.Susceptibility varied greatly among clones with GR50 (50% of untreated growth reduction) spanning over atleast one order of magnitude, 17–278 active ingredient ha−1 in a pot experiment setting. There was a strongcovariance between geographic and genetic distance, but there was no evidence of geographic or geneticdifferentiation in GR50. Nor did GR50 vary consistently between habitat types. We conclude that no indicationof past selection was found towards the resistance to glyphosate in E. repens clones in Sweden. The greatvariability in susceptibility suggests that there might be a potential for such selection