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Canola Research

CARP 2001–99–20
Canola and Lygus Bug Damage - Does Canola Compensate for Lygus Bug Damage?

Summary:
(2001) – Canola’s ability to compensate for herbivore damage is essential information for the management of lygus bugs. The objective of this study was to determine the effect on yield and other components of plant compensation of lygus feeding on canola during the bud to early bloom period by manipulation of (1) rates of lygus infestation, (2) duration of lygus infestation, and (3) levels of balanced nitrogen sulfur fertilizer.

At harvest, plants were retrieved for measures of stature and feeding damage. Yields were measured by seed size.

Results:
Density experiments showed that plants became more robust with increasing lygus density. Canola stem diameter, biomass, and branching were significantly increased by lygus treatments. Total seed weight increased at Beaverlodge in 2000, but in all other cases, seed weight was not significantly affected, either in total or by size class. No negative treatment effects on plant productivity were found.

Duration treatments did not affect stem diameter, height, biomass, or total seed yield. Lygus–treated plants produced 23% more buds than controls. The greatest numbers of buds were produced after a 5–day exposure.

These induced defensive responses to lygus feeding were agronomically positive. Yield losses were not found although yield increases sometimes occurred. Bud “blast” was not a useful indicator of potential yield since losses in buds and pods occurred both when yields were improved and when no changes in yield could be detected.

Implications for Farmers:
Insecticidal control of lygus at early growth stages in canola is not a prudent strategy. In this study, plants with lygus bugs were more productive. Where growing conditions allow compensation for bud damage to occur, lygus bugs present in canola during bud though flowering stages do not pose a threat to yield. Early–season populations of lygus bugs are not pests – their feeding benefits canola plants through the release of apical dominance.