Bug of the Month August 2019


The Lygus Bug – a Complex Pest

By Hector Carcamo

The lygus bug is a complex pest in more ways than one. The pest is not just one species but often two or three, although usually one will be dominant in a particular crop depending on the year and region. The tarnished plant bug is usually the dominant bug in the more humid regions in central and northern Alberta, but Lygus keltoni (no common name) is often dominant in southern Alberta. Lygus bugs have one generation in the north and two in the south. They feed on hundreds of broadleaf crops which include most of our major established and emerging cash crops: seed forages like alfalfa and sainfoin, canola, flax, mustards, fava bean, hemp, quinoa, strawberries and many others. The key time to monitor for lygus is at the end of the flower because they cause the main economic damage on the soft seeds. If the crop is within 10 days of swathing it is likely too mature and lygus no longer require control. Thresholds for Lygus were first developed for canola in the late 1990s for open-pollinated cultivars and were 1-2 per sweep. Ongoing research suggests that the thresholds for hybrid cultivars may be higher, around 2-3 per sweep. To assess lygus numbers in canola one should take 10 sweeps at 4 spots along an arc near the edge and repeat that process at other locations in the field. Only the bigger lygus juveniles (nymphs) that have spots on their backs and the adults should be counted because the very tiny lygus are not expected to pierce the pods to damage the seeds. Like other insects, lygus have natural enemies, but more research is needed to enhance biological control options.