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Title: IPM in Dryland Cotton on the Darling Downs
Authors: Scholz, Brad
Keywords: Beneficial Impact Ratio (BIR)
Trichogramma wasps
broad spectrum chemical sprays
Issue Date: 30-Jun-2002
Publisher: Department of Primary Industries Queensland
Series/Report no.: ;DAQ96C
Abstract: Cotton consultants have been reluctant to monitor levels of egg parasitisin, primarily because of the tiine involved in collecting eggs. A new ratio, called the Beneficial Impact Ratio (BIR) was proposed to assist consultants in understanding in-field mortality due to egg parasitoids without having to collect eggs. The BIR is the ratio of young larvae (Vs+S) to eggs. IdealIy the egg counts that are used in the BIR calculation should be from counts that were completed 2-4 days prior to the larval counts. However same day counts call be used to estimate in-field egg and young larval mortality. The lower the BIR the better, e. g. a BIR of almost zero was recorded when the levels of egg parasitisim were high. On farm sorghum appeared to affect the abundance of egg parasitoids in nearby cotton, as high levels of egg parasitism were found in the sorghum immediately prior to those recorded in the cotton. There were also several plantings of sorghum on the farm. This sorghum provided a regular supply of eggs that supported substantial populations of Trichogramma. The unsprayed INGARD cotton yielded just as well as the sprayed INGARD because: - The Bt. toxin in the plant was effective against very small larvae early-mid season. - The populations of beneficial species built up in the absence of chemical sprays. High numbers of predators (over 20/m) were recorded late season. -Trichogramma were abundant from mid-late January onwards. Cotton plants have a natural ability to compensate for fruit loss. The above factors combined represent successful, sustainable IPM.Intervention with chemical insecticides is not always required. The success of IPM depends on not disrupting parasitoids and predators with chemicals. It is not enough to go soft early, because beneficials really come to the fore until mid-late season. If you are serious about IPM you must strive to avoid multiple applications of organophosphates and synthetic pyrothroids because they are extremely disruptive to beneficials, including Trichogramma. The impact of Trichogramma on the Darling Downs will become more noticeable as the use of broad spectrum chemical sprays throughout the region declines. Some insecticides, such as Dipel and Gemstar, are safe on Trichogramma, and should be used to control heliothis larvae whenever possible. All cotton growers and consultants should try to collect eggs and develop an appreciation for the Trichogramma, they are amazing little wasps!
Appears in Collections:2002 Final Reports

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