But individual production and management practices often rule out this method of cultural control. Such an area-wide treatment can substantially reduce heel fly activity the following year. In the absence of regional control programs, individual producers may minimize damage to their own animals by using systemically active insecticides on their young, nonlactating heifers. It is essential, however, that systemic insecticides not be used on lactating animals because of the danger that insecticide residues would appear in the milk. At present no cattle grub treatment is available for lactating animals.
Proper timing is critical for the safe, effective use of systemic insecticides.
Treatment must be made after adult heel fly activity ceases, but before the migrating grub larvae reach the esophagus or spinal cord. This means that systemics should be used in September, and never after November 1.