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Preharvest sampling plan for larvae of the wheat stem sawfly, Cephus cinctus (Hymenoptera: Cephidae), in winter wheat fields

Published online by Cambridge University Press:  02 April 2012

Christian Nansen ,
Mark E. Payton ,
Justin B. Runyon ,
David K. Weaver ,
Wendell L. Morrill  and
Sharlene E. Sing
Christian Nansen*
Affiliation:
Montana State University, Department of Entomology, 333 Leon Johnson Hall, P.O. Box 173020, Bozeman, Montana 59717, United States of America
Mark E. Payton
Affiliation:
Oklahoma State University, Department of Statistics, 301 Math Sciences, Stillwater, Oklahoma 74078-1056, United States of America
Justin B. Runyon
Affiliation:
Montana State University, Department of Entomology, 333 Leon Johnson Hall, P.O. Box 173020, Bozeman, Montana 59717, United States of America
David K. Weaver
Affiliation:
Montana State University, Department of Entomology, 333 Leon Johnson Hall, P.O. Box 173020, Bozeman, Montana 59717, United States of America
Wendell L. Morrill
Affiliation:
Montana State University, Department of Entomology, 333 Leon Johnson Hall, P.O. Box 173020, Bozeman, Montana 59717, United States of America
Sharlene E. Sing
Affiliation:
Montana State University, Department of Land Resources and Environmental Sciences, 334 Leon Johnson Hall, P.O. Box 173120, Bozeman, Montana 59717, United States of America
*
1 Corresponding author (e-mail: weaver@montana.edu).
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Abstract

The wheat stem sawfly, Cephus cinctus Norton, is the most important insect pest of dryland wheat, reducing both harvest efficiency and head weight. When wheat lodged (flattened) by C. cinctus is straight-cut, harvest efficiency is affected in three ways: (1) lodged stems are difficult to collect with the combine, so mature wheat is lost; (2) the combine has to operate more slowly to collect as many of the lodged stems as possible; and (3) there is increased risk of damage to the combine due to lowering of the combine header to recover lodged stems. An alternative harvest method is to swath the wheat before lodging occurs and place it in windrows prior to combining. When swathing is used, harvest efficiency is not affected by the C. cinctus infestation level; however, this type of harvesting is more expensive and labor-intensive than straight- cutting. Thus, swathing should be used only when the crop is heavily infested by C. cinctus, while straight-cutting should be used when the level of C. cinctus infestation is lower. Adapting harvesting practices to the C. cinctus infestation level requires a sampling plan that can reliably and cost-effectively predict the infestation level in a given field. In this study, we (i) evaluate the relationship between sampling effort along field edges and precision of the estimated average infestation level in 6 wheat fields, and (ii) generate a Gaussian regression analysis of the infestation level up to 200 m into 18 wheat fields using two variables, distance from the edge and average infestation level at the edge, as explanatory variables. We conclude that little additional precision for estimates of infestation level is gained by collecting more than 10 samples along field edges. We also conclude that the average C. cinctus infestation level along field edges can be used successfully to predict infestation levels up to 200 m into winter wheat fields. The proposed sampling should be implemented about one month before harvest to provide growers with enough time to make logistical preparations for harvest.

Résumé

Le cèphe du blé, Cephus cinctus Norton, est le ravageur principal du blé des régions arides et il cause à la fois une réduction de la masse des épis et de l'efficacité de la récolte. L'efficacité de la récolte en coupe directe du blé couché par C. cinctus est affectée de trois façons: (1) il y a une perte de blé mûr parce que la moissonneuse-batteuse a du mal à récolter les tiges couchées, (2) la moissonneuse-batteuse doit avancer plus lentement de manière à récolter le plus grand nombre de tiges couchées possible et (3) il y a un risque accru d'endommagement de la barre de coupe qui est surbaissée pour récupérer les tiges couchées. Une méthode de rechange de récolte consiste à faire l'andainage du blé avant que les tiges ne soient couchées et de le placer en andains avant de le moisonner. L'efficacité de la récolte par andainage n'est pas affectée par le niveau d'infestation par C. cinctus, mais ce type de récolte est plus coûteux et requiert plus de main-d'oeuvre que la coupe directe. On doit donc utiliser l'andainage seulement lorsque la récolte est fortement infestée par C. cinctus et faire la coupe directe lorsque le niveau d'infestation par C. cinctus est plus faible. Afin d'adapter les pratiques de récolte au niveau d'infestation de C. cinctus, il faut un plan d'échantillonnage qui puisse prédire de façon fiable et à un coût rentable le niveau d'infestation dans un champ donné. Dans notre étude, (i) nous évaluons dans 6 champs de blé la relation entre l'effort d'échantillonnage en bordure du champ et la précision des niveaux moyens d'infestation estimés et (ii) nous mettons au point dans 18 champs de blé une analyse de régression gaussienne du niveau d'infestation jusqu'à 200 m vers l'intérieur en utilisant deux variables explicatives, la distance depuis le bord et le niveau moyen d'infestation en bordure. Nous concluons que la récolte de plus de 10 échantillons en bordure du champ ajoute peu de précision aux estimations du niveau d'infestation. De plus, le niveau moyen d'infestation par C. cinctus en bordure du champ peut servir à prédire avec succès le niveau d'infestation jusqu'à 200 m à l'intérieur du champ. On doit utiliser le plan d'échantillonnage proposé environ un mois avant la moisson afin que les agriculteurs puissent avoir le temps de faire les ajustements logistiques requis de leur matériel de récolte.

[Traduit par la Rédaction]

Type
Articles
Information
The Canadian Entomologist , Volume 137 , Issue 5 , October 2005 , pp. 602 - 614
Copyright
Copyright © Entomological Society of Canada 2005

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