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    Efficacy of herbicides for selective control of an invasive liana, old man's beard (Clematis vitalba)
    (Published by Cambridge University Press on behalf of the Weed Science Society of America, 2023-06-02) Jarvis-Lowry B; Harrington KC; Ghanizadeh H; Robertson AW
    Old man's beard is a woody liana that has become an invasive weed in many areas of its introduction, through its vigorous spread and negative impacts on the tree hosts it climbs. Control techniques that improve precision and reduce non-target damage are increasingly preferred for weed control yet have not been compared in published research for use against old man's beard. Field experiments in New Zealand were conducted to: (i) assess targeted herbicide techniques for control of this weed's climbing stems when growing among trees and (ii) assess foliar herbicides for control of creeping stems in ruderal sites. For climbing stems, triclopyr in oil was applied around the circumference of woody stems near their base, which was compared with cutting the stems and applying concentrated glyphosate gel (45% ai) to each cut end. Herbicides were applied in autumn directly to individual stem bases of the weed, thereby protecting tree hosts and other non-target vegetation. The basal application of triclopyr to intact stems was highly effective (>95% mortality) with no damage to nearby trees noted. The glyphosate gel applications to cut stems were less effective (56% mortality by 2 yr after treatment). For creeping stems in grass-dominated ruderal sites, selective foliar herbicide sprays had not been previously juxtaposed to compare control of old man's beard. Three selective sprays that do not damage existing grass cover were applied in autumn at their recommended rates: (i) metsulfuron; (ii) triclopyr; and (iii) a mixture of triclopyr, picloram, and aminopyralid. All herbicide treatments provided effective control, although metsulfuron had a negative effect on grass vigor, which might allow new establishment of old man's beard seedlings by competitive release. These results provide effective options that reduce non-target damage for control of both climbing and creeping old man's beard stems.
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    Trading risk for ambiguity: Production versus health under pesticide application
    (Wiley Periodicals LLC on behalf of Agricultural and Applied Economics Association, 2022-08) Voica DC; Schmitz TG; Hurley T
    Pesticide use reduces the variation in crop yields at the expense of potentially negative consequences to farmers and their family members. This article examines the trade-off between decreasing production risk and increasing health ambiguity because of pesticide use. We find that under ambiguity, pesticide application decreases the variation in health outcomes, whereas under risk, it decreases the expected value of health outcomes. Health insurance protects health from the pesticide damage but not from the ambiguity effect of pesticide application, and the optimal choice of pesticide application does not depend on the farmer's health preferences over risk or ambiguity. However, in the absence of health insurance, ambiguity can increase or decrease the optimal choice of pesticide compared to the risk case. This suggests that public policies around pesticide usage should be designed to reflect and account for the multitude of behavioral responses in the presence of ambiguity and risk.
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    Aspects of herbicide resistance in three New Zealand weed species : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Manawatu, New Zealand
    (Massey University, 2015) Ghani Zadeh, Hossein
    Herbicide resistant weeds have become a challenge in agricultural systems globally. In this thesis, aspects have been studied of three weed species which have evolved resistance to herbicides from different chemical families within New Zealand. Dicamba-resistant fathen (Chenopodium album) was recently reported by researchers in Waikato. In this thesis, the level of resistance to dicamba in two of these populations of fathen was investigated using a whole plant dose-response experiments and it ranged from 5- to 20-fold. Also, a seed-test for rapidly and reliably detecting dicamba resistant fathen has been developed. Seed tests have seldom been used for detecting resistance within weeds to auxinic herbicides. The thesis also investigated aspects of the first reported cases of glyphosate resistance in New Zealand, found in both Italian ryegrass (Lolium multiflorum) and perennial ryegrass (Lolium perenne) from vineyards. Resistance to glyphosate in two populations of Italian ryegrass (Populations A and P) and two populations of perennial ryegrass (Populations J and N) was found to be almost 10-fold, whereas it was almost 30-fold for one perennial ryegrass population (Population O). Three different quick tests (seed assays, excised tiller bioassays and shikimic acid assays) were developed for detecting glyphosate resistance in Italian ryegrass and perennial ryegrass. Of the five populations of ryegrass studied, only Population O had a target site modification at Codon 106 of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). Translocation of radiolabelled glyphosate was studied in four of the populations (Populations A, J, O and P), and movement from treated leaves was significantly reduced in them all compared with susceptible populations (non-target site mechanism of resistance). Therefore, Population O had two mechanisms of resistance, possibly explaining the 30-fold resistance. The studied glyphosate-resistant ryegrass populations were all found to be resistant to glufosinate. Populations A, J and O were also found to be resistant to amitrole. Genetic studies showed that the restricted glyphosate translocation trait is incompletely dominant and can be transmitted via pollen. The restricted herbicide translocation was suppressed under cool conditions in experiments, suggesting that application of glyphosate during winter might improve control of glyphosate-resistant Italian ryegrass and perennial ryegrass infestations. KEYWORDs: Chenopodium album, dicamba, glyphosate, Lolium multiflorum, Lolium perenne, amitrole, glufosinate, glyphosate mechanisms of resistance, target site mechanism of resistance, restricted herbicide translocation.