ECONOMIC THRESHOLD FOR PLANT BUGS, LYGUS SPP. (HETEROPTERA: MIRIDAE), IN CANOLA

Abstract

Plant bugs in the genus Lygus infest canola (Brassica napus L. and Brassica rapa L.) when the crop is producing buds, flowers, and pods. Field studies in cages and open plots show that plant bugs can reduce yield by 20% or more, but have little effect on seed size. A single application of a foliar insecticide when the crop has finished flowering and is beginning to produce pods will prevent most or all of the yield loss. The yield loss of canola that can be prevented by control is 0.007 t/ha per plant bug per 10 sweeps sampled at the end of flowering or the beginning of pod formation. The yield loss that can be prevented by a later application drops to 0.005 t/ha. When precipitation is greater than 100 mm from the onset of bud formation to the end of flowering, the crop may partially compensate for plant bug damage. The economic threshold for control of plant bugs in canola at the end of flowering or at the beginning of pod formation is 15 plant bugs per 10 sweeps, based on crop prices and control costs from 1989 to 1992. If plant bugs are present but control is not warranted when most flowering is complete, plant bug densities should be assessed again 5–7 days later as pods develop, but at this stage the threshold is 20 plant bugs per 10 sweeps. The use of economic thresholds for chemical control of plant bugs will maximize seed yield and minimize unnecessary or ineffectively timed insecticide applications.

Managing cabbage seedpod weevils (Coleoptera: Curculionidae) in canola (Brassicaceae) – areLygus(Hemiptera: Miridae) affected?

“…Despite the economic significance of insect pests to canola production, there are still only a few validated thresholds for the major pests. For pests with established economic thresholds (or economic injury levels) such as Lygus Hahn (Hemiptera: Miridae) species (Wise and Lamb 1998), there is a need to validate them in relevant ecoregions where the crop is grown. Furthermore, the thresholds need to be tested with modern cultivars that differ in terms of yield and genetics compared to the original cultivars used to develop them.…”

“…Lygus are native pests that attack many crops including canola throughout Canada. Economic thresholds have been developed for Lygus with conventional open-pollinated cultivars that are no longer planted (Wise and Lamb 1998; Otani and Cárcamo 2011; Cárcamo 2012), and are being validated using a combination of cages and commercial farm level sites (H.C., unpublished data).…”

Seasonal occurrence and within-field distribution of Lygus lineolaris on buckwheat in Manitoba

“…The next-generation adults emerge during late August to mid-September. Densities on buckwheat can greatly exceed the economic threshold on canola of 1.5 lygus bugs per sweep (Wise and Lamb 1998) and may cause yield losses in buckwheat. The alfalfa plant bug also can complete one generation on buckwheat.…”

“…Since sampling for nymphs will likely be recommended in buckwheat, based on studies in other crops (Wise and Lamb 1998), growers can be advised to sample anywhere within the field.…”

Damage to wheat seeds caused by a plant bug, Lygus lineolaris L.

“…(Heteroptera: Miridae), are pests of many crops in western Canada, reducing yield of canola (Wise and Lamb 1998) and seed alfalfa (Craig 1983) by damaging developing seeds (Butts and Lamb 1990). These plant bugs or related true bugs are suspected of causing damage to seeds of Canadian wheat, although the causative agent of the damage has not been confirmed.…”