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PRODUCTIVITY AND PERSISTENCE OF DECLINING ALFALFA STANDS AS INFLUENCED BY THE ALFALFA WEEVIL, WEEDS, AND EARLY FIRST HARVEST IN OKLAHOMA

Published online by Cambridge University Press:  31 May 2012

M.A. Latheef
Affiliation:
Departments of Entomology, Agronomy and Statistics, Oklahoma State University, Stillwater, Oklahoma, USA74078
R.C. Berberet
Affiliation:
Departments of Entomology, Agronomy and Statistics, Oklahoma State University, Stillwater, Oklahoma, USA74078
J.F. Stritzke
Affiliation:
Departments of Entomology, Agronomy and Statistics, Oklahoma State University, Stillwater, Oklahoma, USA74078
J.L. Caddel
Affiliation:
Departments of Entomology, Agronomy and Statistics, Oklahoma State University, Stillwater, Oklahoma, USA74078
R.W. McNew
Affiliation:
Departments of Entomology, Agronomy and Statistics, Oklahoma State University, Stillwater, Oklahoma, USA74078

Abstract

Importance of cultivars, harvest schedules, and pest infestations as determinants of alfalfa, Medicago sativa L., productivity and stand persistence was investigated using the unimproved “OK08” (Oklahoma Common) and the multiple-pest resistant “WL 318” cultivars. Beginning in the 5th year of production, treatments including three first-harvest schedules (early bud, early bloom, and full bloom) were imposed in a factorial arrangement with unsprayed subplots and three pesticide options for control of alfalfa weevil, Hypera postica (Gyllenhal), or weeds such as downy brome, Bromus tectorum L., or both. In addition to estimating population levels of alfalfa weevil and percentage composition of weeds in forage during each year, alfalfa dry matter yield and stem densities (no. per square metre) were determined during the 3-year period from 1986 through 1988. The seasonal forage production (2-year mean) of WL 318 was nearly 5.4 Mg per hectare greater than that of OK08. There was no consistent trend for greater seasonal alfalfa yield with any of the first-harvest schedules. Timely application of pesticides, as well as use of the improved cultivar were essential for maintaining productivity in years 5 through 7 of stand life. At the termination of the study, only the herbicide + insecticide treatment of WL 318 had close to sufficient stem (and plant) numbers remaining for continued production.

Résumé

L’influence de la nature des cultivars, du calendrier des récoltes et des infestations d’organismes nuisibles sur la productivité et la survie des cultures de luzerne, Medicago sativa L., a fait l’objet d’une étude au cours de laquelle les cultivars OK08 (Oklahoma Common) non amélioré et WL 318 résistant à plusieurs organismes ont été utilisés. Au cours de la 5ème année de production, divers traitements, notamment trois calendriers de première récolte (début du bourgeonnement, début de la floraison, faîte de la floraison), ont été essayés. Ces traitements ont été imposés selon un arrangement factoriel sur des grilles-échantillons non vaporisées et sur des grilles-échantillons vaporisées selon trois options d’arrosage au moyen de pesticides destinés au contrôle du Charançon postiche de la luzerne, Hypera postica (Gyllenhal), ou au contrôle de mauvaises herbes telles le brome des toits, Bromus tectorum L., ou au contrôle des deux. En plus de mesurer les densités de population du charançon et la composition en pourcent des mauvaises herbes dans les récoltes chaque année, nous avons déterminé la production de luzerne (masse sèche) et la densité des tiges (nombre par mètre carré) au cours d’une période de 3 ans, de 1986 à 1988. La production saisonnière (moyenne de 2 ans) de luzerne de type WL 318 s’est avérée de près de 5,4 Mg par hectare plus élevée que celle de la luzerne de type OK08. La date de la première récolte n’affectait pas de façon particulière la production saisonnière de luzerne. Deux facteurs, l’application de pesticides à des moments précis et l’utilisation de cultivars améliorés, se sont avérés essentiels à l’obtention d’une productivité stable au cours des années 5 à 7 de la vie de la culture. A la fin de l’étude, seules les grilles échantillons de WL 318 traitées à l’herbicide + insecticide avaient encore des nombres suffisants de tiges (et de plants) pour assurer une production continue.

[Traduit par la rédaction]

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1992

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