Understanding the Alfalfa Weevil Menace
Alfalfa weevils, notorious in south-western Ontario, can severely impact forage yield and quality. For the unaware, these pests primarily strike right before the first-cut. The brown adult weevils, just about 4-5 mm long, go dormant in winters. Come April, they resume their destructive journey by laying eggs on alfalfa stems.
Characteristics to Watch Out For:
- Young larvae are pale green with a noticeable black head.
- Mature larvae might reach up to 8 mm and feed on leaf buds.
The Impact on Alfalfa Fields
Once they start feeding, the damage becomes evident. Initial damages are minuscule holes, but over time, larvae feed between leaf veins leading to a 'skeletonized' appearance. This not only reduces the yield but affects the quality of the harvest.
Nature's Own Defense Mechanisms
There’s a silver lining though. Since the 1950s, over a dozen biological controls have been introduced to manage these pests. Parasitoid wasps are nature's warriors against these weevils. They lay their eggs inside weevils, eventually neutralizing them. There's also the fungal pathogen, Zoophthora phythonomi, that can control weevil populations.
Note of Caution: Using insecticides might kill these helpful parasitoids, leading to more weevil outbreaks.
Scouting and Action
Regular scouting can save the day. A simple rule to remember: if 40% of plant tips display damage, and there are 2-3 active weevils per stem, consider taking action.
Cutting vs. Spraying:
- Cutting is preferable as it removes larvae.
- Insecticides have limitations. Remember to always refer to local guidelines and inform nearby beekeepers before application.
Post-Harvest Monitoring
After the first-cut, monitor the regrowth. Weevils can feed on it and jeopardize the entire stand.
Awareness and timely action can ensure a healthy alfalfa yield for Ontario farmers. Stay informed, stay proactive.