Scouting for stink bugs

STINK BUGS ARE becoming more prevalent in field crops. Though we don’t often reach threshold in Ontario, this could change as summers become warmer. These shield-shaped bugs have needle-like mouthparts to pierce and suck on plant juices, injecting digestive enzymes into them. They can feed directly on the seed or kernels by piercing through the ear or pods. Seeds/kernels may abort, have dimples, or shrink. Injury can lead to ear moulds and pod disease development. Injured soybean plants may stay green longer, delaying their maturity.

Brown and green stink bugs are most common in Ontario (Figure 1). Nymphs differ from adults; they lack wings and may vary in colour. Green stink bug nymphs are black, orange, and yellow instead of green (Figure 2). Eggs are yellowish-white and barrel-shaped, with a ring of tiny thorns on the top of each egg (Figure 3).

Infestations are more frequent in later-planted, no-till fields bordering wheat. Scout fields weekly during late vegetative and reproductive stages. Focus first on field edges where they aggregate. Seed corn, IP soybeans, and dry beans are most at risk and take fewer bugs to reach threshold.

A sweep net or drop cloth can be used in soybeans and dry beans. In R3 to early R6 stages, control is warranted in crush soybeans if an average of 0.4 bugs per sweep or two bugs per 30 cm (1 foot) of row are found. In IP food-grade, seed soybeans, or dry beans, the threshold is one stink bug per 30 cm of row or 0.2 bugs per sweep.

Scout at least 100 plants in corn, focusing on one leaf above and two below the ear. Control is warranted in corn’s V14 to VT stages if 10 or more adults or nymphs are found on the 100 plants scouted. In R1 and R2, threshold is reached if there are 28 or more bugs found in the 100 plants sampled. Control is not warranted beyond R2. •