Learn how to protect your alfalfa yields from a surge in weevil activity after a mild winter. Are your fields at risk? Discover effective scouting and control tips.
The unseasonably mild winter of 2023-24 has cultivated a sanctuary for a notorious pest in northern regions, triggering a voracious outbreak in alfalfa fields. Rory Lewandowski of Ohio State University Extension indicates that alfalfa weevil infestations predominantly pose a threat before the initial harvest.
Alfalfa Weevils Are Having a “Hayday”
Given that alfalfa weevils overwinter above ground, the hot winter has resulted in a higher-than-usual population poised to exploit new plant growth. An Integrated Crop Management bulletin from Iowa State University underscores that weevils appear earlier due to breaking dormancy during mild fall weather, leading to egg-laying that results in earlier spring hatching.
“This leads to a prolonged feeding period, which might extend past the first cutting of alfalfa,” noted Iowa State Extension education specialist and entomologist Ashley Dean.
Considering this season’s optimal conditions for alfalfa weevils, weekly scouting of first-cutting alfalfa is strongly recommended. Lewandowski outlined that the larvae, which inflict the most damage, are identifiable by their lime-green bodies, jet-black heads, and a distinct white stripe along their backs.
The larvae exhibit a top-down feeding habit, creating a pinhole pattern on the leaves. This notably differs from the clover leaf weevil, which feeds from the bottom up and features a lighter, brownish head.
Scouting and Action Thresholds
According to Lewandowski, effective scouting for alfalfa weevils entails sampling plants from 4-5 distinct areas per 25 acres, as demonstrated in this video. He notes that an action threshold chart detailing the thresholds based on plant growth stages and larval presence is available.
Lewandowski emphasizes the role of natural predators, such as parasitic wasps and fungal pathogens, in managing alfalfa weevil populations. Nonetheless, should scouting activities identify damage and larval counts surpassing the established thresholds, intervention in a rescue insecticide application or early harvesting may be required.
“The most cost-effective control strategy is early harvesting,” he asserted. “However, monitoring regrowth 4-5 days post-harvest is crucial, as larvae can target new crown buds.”
Post-Harvest Considerations
In this video, Bryan Jensen from the Integrated Pest Management program at the University of Wisconsin elucidates the methodology for alfalfa weevil scouting after the first cutting. Jensen underscores that although harvesting typically alleviates weevil infestations, larvae may persist if they are met with cool and wet conditions immediately following the cutting.
A delay in the green-up process might signify the presence of resolute alfalfa weevils. When regrowth appears sluggish due to an early first cut, allowing recovery time may suffice as the sole intervention. “Ensure that alfalfa weevils are responsible for the delayed green-up before resorting to insecticide applications,” he urged.
For those who encountered early-season weevil issues, Jensen advised rigorous scouting of the regrowth phase. As regrowth approaches the 8 to 10-inch mark, larvae are expected to pupate and produce distinct silver-colored cocoons. “These cocoon formations indicate that the weevils are nearing the end of their feeding cycle,” Jensen explained.
The Bottom Line
The alfalfa weevil’s adaptation and resilience underscore the critical importance of vigilant field monitoring and timely intervention. With milder winters enabling early and prolonged infestations, traditional control methods may be inadequate, demanding innovative strategies and proactive measures. Regular scouting, understanding pest behavior, and leveraging biological controls can significantly mitigate damage and minimize economic losses. As climate patterns continue to shift, the agricultural community must remain adaptable, continuously updating pest management approaches to safeguard yield and sustainability.
Key takeaways from this situation highlight the necessity of vigilant monitoring and timely intervention strategies to mitigate the potential damage.
- The mild winter allowed a higher-than-usual survival rate of alfalfa weevils over-wintering above ground.
- Earlier breaking of dormancy and egg-laying contributed to a prolonged feeding period.
- Experts recommend weekly scouting of first-cutting alfalfa to assess larval damage.
- Larval infestation is identified by distinctive pinhole patterns in the foliage and lime-green larvae with black heads.
- Parasitic wasps and fungal pathogens naturally control weevil populations, but severe infestations may require insecticide treatment or early harvest.
Act now to protect your alfalfa yields! Implement weekly scouting practices, identify signs of weevil damage early, and utilize integrated pest management strategies to mitigate losses. Stay vigilant and proactive to ensure a healthy, thriving crop. Your action today secures your harvest tomorrow.
