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The Development and Comparison of Visual Damage Thresholds for the Chemical Control of Plutella Xylostella and Crocidolomia Binotalis on Cabbage in India

  • K. Srinivasan
  • G. K. Veeresh
Research Article

Abstract

An economic threshold on fresh cabbage affected by Plutella xylostella (L.) and Crocidolomia binotalis Z., based on visual estimates of defoliation and a determination of this damage on the marketable yield was developed. An initial survey of unprotected cabbage field for determination of general levels of number of holes caused by feeding of both the lepidopterous pests formed a prerequisite for conducting visual damage threshold experiments. Maintaining a low visual damage threshold of up to 1.0 mean hole (mean of two leaves) on the wrapper leaves, after initial protection of primordia, was found to be an effective alternative in reducing present reliance on weekly or fortnightly sprays for the control of both the pests on cabbage. The possibility of eliminating precupping sprays is supported by the study since the larval populations causing damage to either outer leaves or leaves about to cover the head did not reduce the yield to a significant extent. The use of thresholds based on larval counts of either P. xylostella or C. binotalis failed to give enough lead time during scouting and resulted in loss of marketability.

Key Words

Cabbage visual damage thresholds Crocidolomia binotalis Plutella xylostella 

Résumé

Un seuil économique pour le chou marâicher frais atteint par le Plutella xylostella (L.) et le Crocidolomia binotalis Z. a été développé dans cette étude basée sur les estimations visuelles de la défoliation et la détermination de l’effet des dégats sur le rendement vendable. Une inspection préliminaire d’un champ de choux non-protégé pour la détermination des niveaux généraux de nombres de trous provoqués par le nourrissage des deux insectes lépidoptères nous a permis de conduire des études de seuils visuels des dégats. Le maintien d’un seuil visuel des dégats assez bas, de l’ordre de 1.0 trou moyen (moyen de deux feuilles) sur les feuilles extérieures, après la protection initiale des primordes, s’est révélé comme une alternative efficace pour réduire la dépendence actuelle de la pulvérisation hébdomadaire ou tous les quinze jours pour protéger les choux contre les deux insectes. Cette étude a montré également qu’il serait possible d’éviter la pulvérisation avant la formation du calice parce que les populations de larves qui provoquent des dégats aux feuilles extérieures ou bien aux feuilles qui sont en train de couvrir la tête du chou ne réduisaient pas le rendement d’une manière significative. L’utilisation de seuils basées sur les comptes des larves du P. xylostella ou du C. binotalis ne pouvait pas fournier un temps d’avertissement suffissant pendant l’inspection et conduisait aux pertes de choux vendables.

Mots Cléf

Visuelles de la défoliation Plutella xylostella Crocidolomia binotalis 

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Copyright information

© ICIPE 1986

Authors and Affiliations

  • K. Srinivasan
    • 1
  • G. K. Veeresh
    • 1
  1. 1.Indian Institute of Horticultural ResearchBangaloreIndia

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