Focused use of insecticides
Insecticides can help control nuisance fly populations on cattle feedlots or in dairies but they should not be the main control strategy. They should only be used if current manure/spilled feed management and biological methods fail and a fly monitoring program indicates that a predetermined population threshold has been exceeded. Insecticides should not be used on a scheduled calendar basis, and the following application and targeting guidelines should be considered to avoid unnecessary applications. Lower temperatures from March to October will limit fly breeding, so there shouldn’t be any need to use chemical fly treatments during this time.
Use larval insecticides and fly baits in preference to adult insecticides. Larval insecticides will not deliver instant relief, but will provide better control over time. Research demonstrates that the effect of spraying insecticides to kill adult flies is short-lived and generally only gives temporary relief. When targeting adult flies, do not spray the manure as this will kill fly predators and parasites and result in a subsequent surge in fly numbers.
Fly baits are mainly effective against house flies as they contain a house fly attractant. Apply baits either in bait stations, scattered or painted on surfaces where flies rest. Use both larval insecticide treatments and fly baits to delay the development of resistance.
If an adult insecticide must be used, residual insecticides are preferred over knockdown insecticides. Knockdown insecticides are short-lived and fly populations are likely to recover quickly after spraying. Residual insecticides should be sprayed or painted on major resting sites of adult flies. However, the repeated use of residual insecticides creates a high potential for selection for resistance, particularly if a single chemical group is used. Consult product labels for information on resistance management strategies.
Target hot spots rather than broadcast insecticide across the entire feedlot. To control breeding, only apply larval insecticides to major breeding sites, e.g. pen fence lines, drains, sedimentation pond and hospital area. Leaking taps, pipes or troughs or depressions where water accumulates can be major sites of fly breeding. To control adult flies, restrict treatments to resting places, e.g. exterior of feed bunks, pen fences, the underside of shade cloth, trees and other vegetation. Never apply insecticides to feed or areas that come in direct contact with feed.
It is important to protect existing populations of biological control agents in the feedlot. Keep all fly-breeding substrates dry (manure, spilt feed and vegetation), this inhibits fly breeding and promotes parasitic wasp and mite breeding.
Most insecticidal fly treatments also kill parasitic wasps and mites so it is advisable to avoid or minimise the use of these treatments. Fly populations recover more quickly than parasitic wasps due to their shorter life cycle, which can result in surges of fly numbers during this lag period. Biological agents are a softer and slower acting tool for fly control and their use, unlike some chemical fly treatments, has to be carefully planned and implemented well ahead of major fly waves.
An additional strategy to improve the control achieved by these biological agents is to boost the parasitic wasp populations.. Research demonstrates that releasing the parasitic wasp Spalangia endius increases parasitism of fly pupae. Parasitic wasps are commercially available in Australia from Bugs for Bugs (Mundubbera, Queensland).