Farmers' friendly scouting technique for Helicoverpa armigera (Hubner) in Bt cotton hybrids

摘要

Bt transgenic cotton appears to be a new strategy for the management of cotton boll worms. Bollgard cotton is ideally suited to IPM as the level of control of Helicoverpa sp. provided by the plant is usually sufficient to dramatically reduce the needto spray for this pest, especially during the early season. With the introduction of Bt cotton hybrids for commercial cultivation in India, it becomes imperative to develop a farmers' friendly rapid scouting technique as an alternative to know the appropriate time for taking up the protective measures by working out the level of square/ boll damage in the simplest way. Studies were made to know the allometric relationship between the square/ boll damage in the whole plant, with the square / boll damagein two-third of the plant. The results of the field studies conducted in the farmers' holdings during Kharif 2003 revealed that if scouting on square / boll damage is taken between 45 and 60 days sowing (DAS), on top two-third of the plant (t_2) the equation viz., t_3 = 1.2761 t_1~(07492) and t_3 =1.1413 t_2~(0.8731), could be used to arrive the square /boll damage of the whole plant, respectively. After 60 days scouting could be carried out only at top two-third portion of the plant. If it is taken upbetween 60 and 75 DAS, the equation viz., t_3= 1.2100 t_2~(0.8990), would fit to the best to find out the relative square / boll damage of the whole plant. The allometric relationships of the relative square /boll damage between top two-third and the whole plant, during 75 to 90 DAS would fit very well with the equation, t_3 = 1.3160t_2~(08964)