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Invasive pest is set to strike field crops

Tracey Baute, OMAFRA field crop entomologist says it’s a question of when, not if, the brown marmorated stink bug spreads into Ontario field and horticultural crops.

Brown marmorated stink bugs are on the march, heading from the Hamilton and Niagara regions inexorably towards Ontario’s crop fields. Once they do arrive in Ontario’s major agricultural region, they will - very unfortunately for the crops they infest - be there to stay.  If there is any good news in this otherwise all-bad story, it is only that ongoing surveillance surveys by the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) suggest the bugs have not moved into crops…yet.

“Given that the brown marmorated stink bug (BMSB) is an invasive species and it has a plethora of hosts including tree hosts, it is just a question of time for it to spread into Ontario’s field and horticultural crops. We didn’t find any in crops this year, but we know they are coming,” says Tracey Baute, field crop entomologist with OMAFRA who is part of a team monitoring the spread of the insect.

BMSB feed on a wide variety of crops. On fruit and vegetables where quality is everything, the disfiguring wounds are a major issue in and of themselves, drastically limiting the marketability of affected product. Like other stinkbugs, BMSB have needle-like mouthparts that pierce through corn husks and soybean hulls to the kernels or beans within. This sting allows a starting place for ear rot and vomitoxin development in corn, and pod diseases in soybean. Additionally, changes to soybean plants’ hormones when under attack can cause stay green syndrome.  In field crops, the sting is less of a concern than the secondary problems that stem from those wounds.

“The typical threshold for any stinkbug in soybeans is one individual per foot of row. We’re looking at lowering that for this pest to 0.5 or 0.75 bugs per foot of row. Initial research conducted in Virginia saw losses of up to 40 bushels per acre in the first 40 feet of the field at a density of one bug per foot of row,” says Baute. “In a soybean crop you can visibly see the impact: when a producer goes to harvest the field, there’s a huge strip that’s still green, which significantly delays harvest.”  

BMSB originate from a large area of southeast Asia including South Korea, Japan and Eastern China. Since it was first detected in Pennsylvania in 2001, BMSB has made a home for itself in 41 States, reaching economically damaging levels in at least six of them. In Ontario, the very first individuals were identified in 2010, but sightings are now commonplace.

“We went from having known sightings in the Hamilton area to finding them overwintering in homes from Ottawa to Windsor, which spans most of the growing region in Ontario. And, in some areas we are now spotting multiple breeding populations (multiple stages of insects) on tree hosts in a single location, which means we’re not only seeing individual insects spreading outside of areas of known establishment, they are now becoming established in more locations,” she says.

“Climatically, it can tolerate anywhere we grow its host crops, and it doesn’t matter how harsh the winter because it overwinters inside homes, making it a homeowner’s headache too. Detection in fields is key to implementing timely control options if growers are to stay ahead of the damage.”

While making an accurate count of BMSB is a far cry from stopping the pest, it is a very necessary first step.

“Our efforts at management are still preliminary. There is a collaborative effort in the mid-Atlantic States to try to develop management strategies and thresholds for field crops. We are quite lucky in that they’ve been dealing with these bugs for some time, so we can work off of the knowledge they’ve already built up,” says Baute.

Though it looks similar to other stink bugs, BMSB has several unique features – white bands along its antennae, white triangles in a pattern on its abdomen, and smooth (non-serrated) “shoulders” – that make it clearly identifiable even to a layman. Simple identification is incredibly important since, because it always overwinters inside a closed building, it is most likely to be first detected by homeowners. As such, OMAFRA conducted an intensive public outreach campaign to educate Ontario residents about BMSB and to help people learn how to identify the pests. Now, much of Baute’s survey and tracking work is based on data phoned in by homeowners.

“It is incredibly vital, I can’t stress enough how vital, for the public to notify us when they find them,” she says. “We researchers can’t be everywhere all the time, so it is incredibly important that farmers, crop scouts, homeowners and the general public let us know when they find them.”

In addition, she and a team of researchers conduct annual field surveys on high-risk crops to monitor the advancing edge of the invasion. Once the pests reach a high enough density on the tree hosts they target first – a reality in the very near future - Baute expects them to start honing in on the host crops they are most attracted to.

BMSB is an edge insect, choosing to stay within about 40 feet of the edge of the corn or soybean field. This may decrease the cost of control for field crop farmers who may be able to focus insecticidal efforts exclusively in that zone.

All growers, particularly growers with fields neighbouring host trees (buckthorn, maples, oaks, elms, cedars, hawthorn, etc.) or horticultural crops (including apples, pears, peaches, blueberries, raspberries, grapes, peppers, tomatoes, snap beans and lima beans) should begin scouting weekly as soon as their corn or soybean starts developing flowers and ears/pods. Because BMSB often catch a ride on vehicles, farmers with fields close to tourist locations or thoroughfares should also be particularly vigilant, as should farmers with fields near any of the towns/cities where BSMB have been identified as overwintering (Windsor, Cedar Springs, London, Hamilton, Kincardine, Paris and Guelph).

New invasive pests are becoming more common, both because of climate change and the way we now routinely transport goods around the world.

“As much as our borders do a good job of detecting invasive species, there are many ways for things to be carried in. And in terms of a changing climate, the more ideal a location starts to become for a pest, the more likely it is to survive when it does arrive,” says Baute. “Finally, when an invasive shows up, there are not a lot of natural predators that recognize it initially, so the  invasive has the upper hand until the natural ecosystem catches up. BMSB have quite a number of advantages in their favour.”

For more information, visit To report a sighting of BMSB, call the Agricultural Information Contact Centre at 1-877-424-1300.

April 10, 2015  By Madeleine Baerg


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