Animal-protein based repellents like BANGBANG work by slowly oxidising and releasing a sulphurous odour that repels through smell as it decays. They do work, but over time will breakdown in air and sunlight which limits their effectiveness. This applies for any animal protein based repellent. That's just the way nature works...protein will naturally decay and rot away. So a 4-6 week effective protection period is about the most you should expect and it will need to be reapplied, especially for new growth. DO NOT BELIEVE the hype from some other animal-protein based repellents (including powdered blood) that claim longer term protection.
Fat-based repellents - and there are none made here in NZ except FATBANG and GREASEBANG - offer a much longer protection period as the coating of fat serves as a natural sticker-spreader. When plants are dormant the fat layer can remain for up to 6 months. Even if the smell has dissipated the fat coating will still offer protection. The coat may have a light white tinge on some leaf margins where the fluid may have congealed when drying.
For these repellents the dormant season will offer more protection as there will be little growth to dilute the coating. For spring/summer a more frequent light spray may be required on new shoots. Because of the huge variety of plants/trees and local conditions we suggest a small trial spray to test for any adverse reaction. ALWAYS SPRAY LIGHTLY...LESS IS MORE!