Garlic mustard is an edible, biennial herb that emits a strong garlic odor. It was brought to the United States from Europe as a culinary herb. It has naturalized in many eastern and midwestern states.
In Minnesota, it is widespread in the south and is spreading north. The bad news is garlic mustard is highly invasive. It grows in woodlands, and along trails and waterways. It outcompetes native plants, becoming detrimental to wildlife habitat and biological diversity.
Garlic mustard forms rosettes after seed germination in early spring. In its second year, it forms upright stems that produce flowers in May and June. Seeds begin to develop in slender pods shortly after flowering and are the plants’ primary means of spread.
The plant has distinctive characteristics to distinguish it from other woodland plants. In the rosette stage, the leaves are heart-shaped with toothed margins. When it matures, the leaves along the stem are triangular and the small, white, four-petaled flowers are produced in clusters at the tops of the stems. The plant produces slender seed capsules. Seeds can be spread by water and soil movement on boots and equipment.
Garlic mustard is a restricted noxious weed and cannot be transported, sold, or intentionally propagated in Minnesota. It is recommended that this species be prevented from spreading to new areas and that smaller populations be eradicated.
Managing garlic mustard takes persistence and a focus on preventing flowering, making timing a key component to management.
Regular site monitoring for several years will be required to ensure that new seedlings are destroyed and the seedbank is depleted.
Hand pulling may be practical for small infestations. Pull plants prior to flowering to prevent seed production. Flowering plants can continue to set seed following removal of soil.
Mowing of bolted plants prior to flowering can prevent seed production. All equipment should be inspected and cleaned prior to moving into new areas.
Foliar herbicide applications may be effective. If using herbicide treatments, check with your local University of Minnesota Extension agent, co-op, or certified landscape care expert for assistance and recommendations.
Lisa Behnken of the University of Minnesota Extension Service in Rochester, Minnesota (Photo from Extension website http://r.umn.edu/academics-research/extension/staff/UMR_EXTENSION_STAFF_L_BEHNKEN.html)
“Corn is looking very good across the area,” said Behnken. “That’s the crop that’s probably outstanding. The general region had good planting dates and some very timely rains in most of southeast Minnesota. It has been a little bit wet in certain areas, and some spots did see some hail. Overall, the corn crop looks good and has had a very good growing season.”
Soybeans are a different story. She said the soybeans have had a rougher go of it.
“And they may even have a rougher go between now and the end,” said Behnken. “There are some fields that look beautiful, but there are some different things happening in area fields. Some of it has to do with the amount of moisture we’ve received. In some cases, it’s been too much moisture, and that’s led to some problems for bean here in late August, into early September.”
Weeds are becoming a big challenge in area soybean fields.
“You have some fields that are very clean,” said Behnken, “with maybe a corn spear or weed here and there. On the other side of the equation, we have a lot of fields with Waterhemp coming through in soybeans. In other cases, you may see giant Ragweed, or even a mixture of weeds like Velvetleaf and Lamb’s Quarter, but the big one people are talking about here, and around the state, is Waterhemp.”
So, why is Waterhemp a problem?
“It germinates a little later in the spring,” said Behnken, “but it can germinate all through the growing season. When the canopy doesn’t close right away, the weed will keep germinating through the season.”
Behnken has a theory on why soybean canopies are closing later than they have in the past. She called it a Catch-22:
The bigger question is what a farmer did early in the season to treat fields for weed development.
“What did people do for their herbicide program,” said Behnken. “If you did not use a residual herbicide in your pre-emergence program, or in some cases, come back with a residual in your post-emergence program to keep those herbicides working all season, then Waterhemp has an opportunity to take off.”
According to Lisa Behnken of the University of Minnesota Extension Service, Waterhemp is becoming a challenge in SE MN Soybean fields. (Photo from soilcropandmore.info)
She added, “We’re also talking about resistance issue now. Waterhemp has some resistance to the ALS chemistry, and we’ve just confirmed some resistant pockets to another class of chemistry we call PPO’s.”
Area soybeans are struggling with some disease pressure as well.
“One that’s difficult to manage is white mold,” said Behnken. “I see it going east of Rochester throughout eastern Olmsted County including Winona and Wabasha and even into Fillmore County. If you notice uneven canopy development and walk out into the field, you should see some white mold. White mold likes wet conditions, and east of Rochester saw quite a bit of steady rain.”
Behnken added, “It’s a very difficult disease to treat, and while fungicides control other diseases in soybeans, there are more limited options to take care of white mold. It’s definitely going to cost some yield in certain fields.”
Bean challenges don’t stop there.
“We always wonder when aphids will hit us, and this year they hit us in August again,” she said. “The weather earlier this year kept them at bay. Toward the end of July, we saw a mass migration when aphids came in on westerly winds. Once they arrived and got established, they exploded in numbers really fast. Growers need to keep a sharp eye on their fields.”
The area’s alfalfa crop has turned out well in spite of frequent early season rains.
“We’ve put up a lot of hay this year,” said Behnken, “mostly in between rain storms. The good part of it is if you do have rain, then you have a crop. We know how to deal with hay that gets rained. We chop a lot more hay and we round bale, then you categorize it based on quality and how much rain damage there is. We’ve put up a good crop, so there’s good feed out there.”
If it’s been awhile since you’ve seen white mold in your fields, here’s a good refresher at spotting white mold in soybeans, courtesy of the University of Wisconsin Extension Service: