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ECONOMIC THRESHOLD FOR PLANT BUGS, LYGUS SPP. (HETEROPTERA: MIRIDAE), IN CANOLA1

Published online by Cambridge University Press:  31 May 2012

I.L. Wise  and
R.J. Lamb
I.L. Wise
Affiliation:
Cereal Research Centre, Agriculture and Agri-Food Canada, 195 Dafoe Road, Winnipeg, Manitoba, Canada, R3T 2M9.
R.J. Lamb
Affiliation:
Cereal Research Centre, Agriculture and Agri-Food Canada, 195 Dafoe Road, Winnipeg, Manitoba, Canada, R3T 2M9.
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Abstract

Plant bugs in the genus Lygus infest canola (Brassica napus L. and Brassica rapa L.) when the crop is producing buds, flowers, and pods. Field studies in cages and open plots show that plant bugs can reduce yield by 20% or more, but have little effect on seed size. A single application of a foliar insecticide when the crop has finished flowering and is beginning to produce pods will prevent most or all of the yield loss. The yield loss of canola that can be prevented by control is 0.007 t/ha per plant bug per 10 sweeps sampled at the end of flowering or the beginning of pod formation. The yield loss that can be prevented by a later application drops to 0.005 t/ha. When precipitation is greater than 100 mm from the onset of bud formation to the end of flowering, the crop may partially compensate for plant bug damage. The economic threshold for control of plant bugs in canola at the end of flowering or at the beginning of pod formation is 15 plant bugs per 10 sweeps, based on crop prices and control costs from 1989 to 1992. If plant bugs are present but control is not warranted when most flowering is complete, plant bug densities should be assessed again 5–7 days later as pods develop, but at this stage the threshold is 20 plant bugs per 10 sweeps. The use of economic thresholds for chemical control of plant bugs will maximize seed yield and minimize unnecessary or ineffectively timed insecticide applications.

Résumé

Les punaises des plantes du genre Lygus infestent les cultures de colza (Brassica napus L. et B. rapa L.) quand les plants produisent des bourgeons, des fleurs et des gousses. Les études en nature dans des cages et dans des champs à découvert ont démontré que les punaises peuvent réduire la récolte de 20% ou plus, mais ont peu d’effet sur la taille des graines. Une seule application d’un insecticide foliaire après la floraison et à l’apparition des gousses peut prévenir les pertes, entièrement ou presque. La perte de récolte qui peut être enrayée par une lutte efficace est de 0,007 t/ha par punaise par 10 coups de filet à la fin de la floraison ou à l’apparition des premières gousses. La perte de récolte qui peut être enrayée par une application plus tardive n’est plus que de 0,005 t/ha. Lorsque les précipitations dépassent 100 mm entre le bourgeonnement et la fin de la floraison, l’importance de la récolte peut compenser partiellement les dommages dûs aux punaises. Le seuil économique qui détermine la pertinence de la lutte contre les punaises dans le colza à la fin de la floraison ou au début de la formation des gousses est de 15 punaises par 10 coups de filet; ce chiffre est basé sur les coûts reliés à la récolte et à la lutte de 1989 à 1992. Si les punaises sont présentes, mais qu’il n’y a pas lieu de les contrôler au moment où la floraison est presque terminée, les densités des punaises devraient être réévaluées 5–7 jours plus tard, pendant le développement des gousses, mais à ce stade le seuil est de 20 punaises par 10 coups de filet. La détermination de seuils économiques dans la lutte chimique contre les punaises des plantes peut maximiser la production et minimiser le nombre d’applications d’insecticide superflues ou mal synchronisées.

[Traduit par la Rédaction]

Type
Articles
Information
The Canadian Entomologist , Volume 130 , Issue 6 , December 1998 , pp. 825 - 836
Copyright
Copyright © Entomological Society of Canada 1998

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