Horn fly populations are increasing rapidly this year, with some beef cattle exceeding the 200-fly action threshold. These flies cause significant pain and annoyance to dairy and beef cattle, leading to economic losses due to reduced milk production in dairy cattle and decreased weight gain in beef cattle.

Horn flies are biting insects that need a blood meal from cattle to reproduce, with both females and males consuming up to 30 meals daily. They are smaller, about half the size of face flies or stable flies, and primarily infest the back and sides of cattle, moving to the belly in higher temperatures. Horn flies spend most of their lives on cattle, leaving only to lay eggs in fresh manure. Each female can lay up to 20 eggs at a time, totaling around 400 in her lifetime. Maggots in manure can reach high populations.

The horn fly life cycle spans 10 to 20 days, with adults living about a month. They develop only in cattle manure pat on pasture, not in manure from other livestock. In the northeastern United States, there are typically 12 to 14 generations per grazing season.

To determine if control measures are needed, scout the cattle on pasture. Take photos of the cattle where the flies are, count the flies in that area, and estimate the number of horn flies on one side of the cattle. Depending on herd size, count up to 15 cattle, take the average, and compare it to the action thresholds.

Action Thresholds

• Dairy Cattle: 50 horn flies per shoulder, side, and belly.
• Beef Cattle: 100 horn flies per shoulder, side, and belly.

Control Methods

Bruce Trap (Passive Walk-Through Trap)

Horn flies, which dislike enclosed spaces, fly off the cattle as they enter the trap. The trap features strips of old carpet or canvas that brush off the flies, which then move towards the light and are trapped by double screen walls. Data suggests that this trap can control 50 to 70 percent of horn flies over time.

CowVac

The CowVac is an advanced vacuum system designed to remove horn flies from cattle. It generates a strong air current that dislodges flies from the cattle’s body, while a high-powered vacuum sucks up the dislodged flies. This trap has been shown to reduce horn fly populations on farms by 68%, improving cattle health and comfort and reducing the need for chemical treatments.

Flatten Manure Pats

Disrupting breeding habitats by flattening manure pats on pasture can control horn flies. Dragging a harrow or chain over the pasture spreads out fresh manure, causing it to dry out and preventing egg and larvae development. This method is particularly effective in rotational grazing systems but can be labor-intensive.

Shaded Areas

Providing shaded areas, such as sheds or barns, allows cattle to escape flies. Darkened spaces can significantly relieve cattle from the stress and annoyance caused by flies.

Organic Solutions

For organic producers, approved forms of pyrethrum or neem and other natural repellents can offer some relief, though their efficacy may be limited to short durations.

Insecticidal Measures

When infestations are significant, insecticides may be necessary. Use them only when populations exceed the action threshold. Methods include sprays, pour-on, ear tags, back rubbers, and dust bags, targeting areas where face flies congregate.

VetPestX is a valuable resource for selecting suitable insecticides tailored to specific pasture conditions, aiding producers in making informed choices. More information can be found at VetPestX.