Blackfly Larval Control in Irrigation Canals with Bacillus thuringiensis var israelensis, 1981

A wettable powder formulation of B.t. was tested in irrigation canals in south central Idaho to determine mortal ity to S. vitattum larvae. For each treatment the appropriate amount of formulated material to achieve a given concentrate in the canal was mixed with 15 gall of water in a high pressure sprayer. The mixture was sprayed into canals at the rate of 1 gal spray per minute to achieve a 15 minute application period. Blackfly larval populations were monitored on 0.375 inch yellow polypropylene rope. Sections of rope 4 ft long were suspended above the water surface and allowed to trail in the water current at distances 10 m-1600 m downstream from the treatment site. Ropes were placed in the canals 14 days prior to the application dates. Each rope had sections 5 cm long marked along the center. Larval counts were taken from 4 of the marked sections at each distance downstream before and after treating. Larval detachment or moribund, non-mobile larvae were both used in the tests as evidence of mortality. Test numbers 1-4 were applied Aug 6, Sep 28, Oct 2, and Oct 16, respectively.