Be on the lookout for Blister Beetles in Second Cutting Alfalfa
While harvesting second cutting alfalfa variety plots at the Cimarron Valley Research Station (CVRS) in Perkins, OK (Payne County) earlier this week I noticed several healthy swarms of striped blister beetles (Fig 1).
Figure 1. Striped Blister Beetle Swarm. Photo: OSU
As alfalfa producers gear up for their second cuttings, they should be prepared for potential blister beetle activity. Emergence of adult blister beetles typically occurs after the first cutting of alfalfa is completed in early May.
Striped blister beetles, Epicauta occidentalis (Fig 2) have not been collected by OSU entomologists before May 14 in Oklahoma, and in many years, it is mid-June or later before they become active. This activity can last until early fall.
Figure 2. Striped Blister Beetle. Photo: OSU
Cantharidin is highly toxic when ingested by livestock, especially horses, and may cause illness and even death in these animals. According to some reports, ingestion of as few as twenty-three beetles can cause illness, and consumption of 50-100 can cause death. Irrespective of an exact figure, it is a very stable compound that retains its toxicity to livestock even when dried remains of beetles have been killed in the harvesting process and are fed along with forage.
Blister beetle adults emerge from the soil in late spring or early summer, and large numbers normally will congregate in small areas of fields, usually within fifty yards of field margins.
There are many blister beetle species, but several are commonly found in Oklahoma (Fig 3).
Figure 3. Black margined, spotted, ash gray, black, and stiped blister beetles. Photo: OSU.
Another species found last season in (Payne County) lespedeza (Epicauta conferta) (Fig 4)., was also observed in the Perkins alfalfa plots this week.
Figure 4. Epicauta conferta. Photo: Jonathan Cammack.
However, the predominant species (75%) found in Oklahoma is the striped blister beetle. It has the highest concentration of Cantharidin of all the species and because of its aggregating nature, beetles can be easily killed during the alfalfa harvest operation and can be concentrated in only a few hay bales or small portions of bales.
When infesting alfalfa, blister beetles prefer to feed on blossoms but will feed on leaves if blossoms are not present. Pigweed, goldenrod, goat head, puncturevine, peanuts, soybeans and many other plants also serve as hosts for these beetles.
Swarms of beetles can be crushed by crimper rollers of the swather and are trapped in windrowed hay. If beetles remain alive in the windrows, most of them will crawl out. They also can be trapped and killed in hay if windrows are driven on before beetles have had time to escape.
Therefore, two of the best ways to avoid blister beetle problems in hay from an infested field are swathing without the crimpers and avoiding wheel traffic on freshly cut windows. After swathing, beetles will crawl away on their own to find a new food source.
Other measures alfalfa producers can take to avoid blister beetles in the hay are:
- Maintain weed control within and outside the field.
- Spraying fence rows and field borders can help prevent migration into fields.
- Harvest before bloom, if possible.
- Monitor fields extensively for blister beetle activity before harvest. Swarns can move to other
- locations within the field in a short amount of time.
- Match cuttings and markets (early May and late September cuttings are before and after the major blister beetle season and are the best cuttings to target for horse buyers).
If blister beetles are found or even suspected, do NOT feed the alfalfa to horses or any other livestock. Simply removing the beetles will not eliminate the toxic contamination by cantharidin.
Awareness and proactive management among hay producers and livestock owners is crucial for management of this pest.
Additional information on Blister Beetles can be found in EPP- 2072, Blister Beetles in Alfalfa