Take Time to Scout for Tarnished Plant Bug in Canola and Beans

I sometimes wonder if you even want to read one more article from me, as it usually means there is another insect pest to watch out for. Let's face it, 2007 has been a busy year for insects. But one more pest should not be missed just because we are all getting a little tired of scouting the crops. Hot, dry weather is ideal for the seed stinging insect, tarnished plant bug.

Tarnished plant bug adults are approx 5 mm in length, are yellowish to reddish brown in colour and have a small triangle shape on its back (Figure 1). The nymph stage doesn't look the same as the adult but is a yellowish-green, wingless and lacks the distinctive triangle shape on its back (Figure 2). They have several different host crops but tend to move into canola and edible beans when alfalfa is being cut.

The adults and later stages of nymphs are the more damaging stages. TPB have piercing-sucking mouthparts that they use to pierce into the plant tissue and inject saliva that breaks down some of the plant tissue. If injury takes place during the pod stages, scarring, malformation and dimpling or pitting on pods can occur. They can also drill directly into the seed.

To scout for them, take 20 sweeps (180 degree arc = 1 sweep) in 5 areas of the canola field. Border rows are apt to have higher populations so ensure that you sweep further into the field to get a good idea of the average number of TPB per sweep. No thresholds have been validated for Ontario, though other jurisdictions recommend spraying in canola when 2 bugs per sweep can be found after petal fall but prior to pod maturity. For edible beans, control is necessary if 1-2 bugs/sweep can be found up to later pod fill stage.

Figure 1. Tarnished Plant Bug Adult (Flax Council of Canada)

Figure 2. Tarnished Plant Bug Nymph (Bauer, USDA ARS)