Trials with the microbial insecticide Bacillus thuringiensis have been continued during the last three years to compare it with carbaryl, the standard control measure for grape leaf folder control (Desmia funeralis Hubner). Carbaryl gives excellent control of grape leaf folder but under some conditions it also produces biological upsets leading to increased spider mite and grape leafhopper populations. The overall evidence of the last three years shows that Bacillus does not increase spider mites or grape leafhoppers, and that it is usually, but not always, as effective as carbaryl. Timing of application is of critical importance with Bacillus treatments, however, whereas carbaryl applications are effective within a fairly broad range of time.