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March/April 2014

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WESTERN CANADA TURFGRASS ASSOCIATION 33 TURF RESEARCH ARTICLE METHIOZOLIN A NEW ANNUAL BLUEGRASS HERBICIDE FOR TURFGRASSES BY SUK-JIN KOO, KI-HWAN HWANG, MAN-SEOK JEON, SUNG-HUN KIM, JONGSOO LIM, DONG-GUK LEE AND NAM-GYU CHO BACKGROUND: Selective control of annual bluegrass (Poaannual L.) has been difficult in turfgrasses. The potential of methiozolin in this area was investigated. RESULTS: Methiozolin was safe on established zoysiagrass (Zoysia japonica Steud.), creeping bentgrass (Agrostis palus- tris Huds.), Kentucky bluegrass (Poa pratensis L.), and peren- nial ryegrass (Lolium perenne L.) at 1000 g ha, and controlled annual bluegrass with GR50 values of 23, 52, 104, and 218 g ha at PRE, two-, four- and eight-leaf stage, respectively, in the greenhouse. When applied at early flowering, methiozolin suppressed >80% of annual bluegrass seed heads at 2000 g ha. C-Me- thiozolin was readily absorbed by both leaves and roots, but translocation was mainly acropetal. No herbicidal activity re- sulted from application to the leaf only; however, application to the soil surface only showed equivalent herbicidal activity to that of broadcast application to the leaf and soil. Methio- zolin at 500 to 1000 g ha provided 80 to 100% control of annual bluegrass when applied in the fall with acceptable and temporary injury to creeping bentgrass, and about 60% con- trol when applied in the spring with no bentgrass injury in the field. CONCLUSION: Methiozolin is an excellent candidate for an- nual bluegrass management in turfgrasses. INTRODUCTION Methiozolin is a new turf herbi- cide being developed by Moghu Research Center, Korea. The herbicide is in the isoxazoline chemical family and was first invented as a rice herbicide can- didate. The molecule controlled barnyardgrass (Echinochloa spp.) and several other annual broadleaf and sedge weeds from 125 g ha in rice paddies while having good safety to transplanted rice up to 1.0 kg ha. Koo and Hwang reported that the herbicide controlled annual bluegrass and large crabgrass (Digitaria sanguina- lis) effectively in various cool and warm season turfgrasses. The mechanism of action of methiozolin and related chemis- try is not thoroughly understood and appears to be novel. Lee et al. reported several morphological responses in ger- minating barnyardgrass including cessation of shoot and root growth without twisting, colour changes, burning and other symptoms associated with known modes of action. Further, they showed methiozolin inhibited root growth of corn, a suscep- tible grass, at a very low dose with a GR50 of 0.03 μM. Using C-glucose incorporation into corn root cell wall constituents, Lee et al. showed methiozolin inhibited biosynthesis of both cellulose and hemicellulose fractions greatly from 0.1 μM after 24 h of exposure. However, the morphological symptoms did not resemble those of known cell wall synthesis inhibitors such as dichlobenil. Recently, Grossmann et al. sug- gested methiozolin might inhibit tyrosine aminotransferase (TAT), an enzyme in the biosynthesis of plastoquinone, in duckweed (Lemna paucicostata L.). This suggestion was based on feeding of hydroxyphenylpyruvate, the product of TAT, to duckweed, which nullified growth inhibition of methiozolin. They also showed that methiozolin inhibited a recombinant TAT of A. thaliana, but with a very high IC50 value (about 200 μM). Grossmann et al. further suggested that other TAT isoenzymes in Arabidopsis or from other plants could be more sensitive and the primary in vivo target of methiozolin. Although the mechanism of methiozolin was shown to involve inhibition of cell wall biosynthesis and potentially plastoquinone biosynthesis, the primary site of herbicidal action is still unclear. Annual bluegrass is a common and major weed species in both cool and warm season turfgrasses. Annual bluegrass usually behaves as a winter annual, germinating in the late summer to early fall when soil temperatures fall below 21°C, followed by prolific seed head production during the late winter and spring. In addition to the typical annual biotype, P. annua spp. reptans (Hausskn.) Timm, a perennial subspecies of annual bluegrass, is commonly found in creeping bentgrass put- ting greens throughout most of the United States. The perennial biotype shows a stoloniferous prostrate growth habit and has been shown to be difficult to control by herbicides.Annual bluegrass is also man- aged by default as a turfgrass species in many golf courses, but is generally regarded as an undesirable species due to prolific seed head production, shallow root system, and susceptibility to many diseases and less tolerance to heat and cold. In a situation where annual bluegrass persists in more desirable turfgrasses, such as creeping bentgrass, it is very invasive yet relatively intolerant of most biotic and abiotic stresses, often dying unexpectedly, leaving surface voids, requiring higher cultural and chemical inputs to maintain it. Furthermore, it is considered to be the number one weed problem in turfgrass both in frequency of occurrence and difficulty of control. Options for selective chemical control of annual bluegrass are limited, especially in cool season turfgrasses. A few her- bicides, including bensulide and ethofumesate, or plant growth Continued on Page 34 Options for selective chemical control of annual bluegrass are limited, especially in cool season turfgrasses.

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