With record setting temperatures this spring insects are making an earlier appearance this year. Horn flies, face flies and even stable flies have been observed on grazing animals recently.
Normally we do not think about livestock pest control this early in spring, but this year appears to be different. As livestock producers ponder when to send cattle to pasture another consideration is what livestock pest control options are available for this summer. Livestock pest control should be viewed as having a positive economic impact on your livestock operation.
There are three fly species in Nebraska that economically impact pastured cattle: horn fly, face fly and stable fly.
The horn fly, Haematobia irritans (L.) is one on the most important blood feeding pests of pastured cattle in the United States. Losses in the United States have been estimated at about $800 million annually. When horn fly numbers are high, cattle experience annoyance and blood loss (see image at right, click on image for larger view). The result may be decreased milk production, reduced weight gains, changes in grazing patterns and bunching of animals. Significant reduction in calf weaning weights is well documented. Nebraska studies demonstrated calf weaning weights were 10 to 20 pound higher when horn flies were controlled on cows. Other studies around the U.S. and Canada have shown improved weight gains of stocker cattle and replacement heifers when comparing treated to untreated animals. In addition, horn flies have been implicated in the spread of mastitis.
The economic threshold for horn flies is 200 per animal. The animal pictured at right has 314 horn flies and population numbers of several thousand of flies can often be observed during the summer. Monitoring horn fly numbers on cattle is important in making appropriate management decisions. Routine observations will help livestock producers determine when best to initiate control methods and the efficacy of the current program. Cattle should be be monitored weekly for horn flies throughout the fly season. Observations are best taken between the hours of 9:00 AM - 1:00 PM when horn flies are located on the shoulders and sides of cattle. Observations made later in the day are less accurate because the flies will have moved to the belly where it is cooler and where they are harder to count. If the average number horn flies per animal exceeds 200 (Figure 2), the economic threshold has been exceeded and control should be considered.