Horn fly (Haematobia irritans) numbers are starting to go down in many parts of the US and they will soon start entering their winter pupal stage in some Northern States as the cold weather kicks in. These 3/16th inch long pests will winter as maggots underneath manure pads or in the soil. Thus providing cattle with a break from the 20 or more daily blood meals the adults engorge themselves on, at the cattle's expense.
Annual cattle management best practice focuses on ensuring the most pounds are brought to market. Horn flies are an economic pest that dig into those pounds produced and the dollars earned! During the hot summer months horn flies live almost continuously on cattle moving to their lower sides and under belly during extremely hot weather or rain. Horn flies adult stage averages 8-20 days during which the females only leave to deposit their eggs (up to 500) in fresh manure. These pests are particularly troublesome on calves (loss of up to 15 pounds at 200lb weaning weight) and yearling cattle (up to 30lbs) dramatically impacting their weight gain vs. non-protected cattle. There are many different reports you can look up regarding horn fly economic impact, but most peg the number at around $800 million loss per annum in the US.
There are a number of different products ranchers can use to protect their cattle from horn flies with some more efficacious and easier to use than others. The most common has been ear tags (but usage appears to be declining based on sales volume), with dust bags, pour-ons, back rubbers, back oilers, animal sprays and oral larvicides in the mix. All of these products have value and depending on the ranch layout and horn fly problem can be part of an annual integrated cattle management solution.
One of the biggest recent concerns regarding using insecticides to treat horn fly infestation is the level of insecticide resistance that has built up in many parts of the country. With horn fly seasons in the Gulf States almost year round, ranchers have found that some insecticides that worked at times in the past don't work at all now. To combat potential resistance and develop an integrated approach to attack them, here are some Horn Fly Best Practices to consider in your planning:
1) Plan on rotating insecticides throughout the season (using different families of insecticides each time to combat any resistance) before the season starts
2) If using ear tags, wait to apply them until the season starts and rotate them (i.e., change them so the insecticide is different every year or preferably ever time they are replaced)
3) Remove ear tags when control period ends (30, 60, 90 days etc., depending on product tag) - this will reduce ongoing sub lethal dosage to the horn flies which can lead to faster resistance build up (Horn flies have up to 15 generations per annum)
4) Regardless of which product the producer is using be it tags, bags, sprays or pour-ons if it isn't working stop using it, and switch to a different control method / product
5) Use common sense - each ranch is different and there is no one best practice that will fit every ranch. Rotate your insecticide use on a regular basis (regardless of application method), hit them early (when flies reach 50 per side they will often jump to over 200 per cow within 2 weeks) keep track of what insecticides you use, how well / long it performs and keep monitoring the effectiveness of your fly control program adapting as necessary
There is no silver bullet, or one best practice for horn fly control that will work every time, for all ranches. Use these key points as a base best practice starting point, to plan out your annual horn fly cattle management program. Producers utilizing an integrated insecticide management approach with regular monitoring and adaptation, can reduce horn fly dollars from flying out of their pockets!