Weeds & Invasive Plants

All Weeds & Invasive Plants Content

A white and purple seedhead of a Canada thistle with a blurry, bright green background.

Perennial Weed Management in the Fall

Most herbicide applications to manage perennial weeds have already occurred. However, now is the time to consider fall applications for weeds that were not treated or escaped the spring application.

A green Canada thistle with large, round galls throughout.

Galls on Canada Thistle: Biological Management at Work

A common sight this summer on Canada thistle is odd growths (also known as galls) on stems. These galls are a product of thistle stem gall fly attacking Canada thistle plants.

Tall, green grass surrounding a small, green yellow toadflax plant that hasn’t quite flowered yet.

Yellow Toadflax Has Not Flowered in Some Parts of South Dakota

Yellow toadflax is a difficult-to-manage weed that infests pastures and rangeland. In contrast with other weeds, yellow toadflax should be sprayed when flowers are present for more-effective management.

United States Environmental Protection Agency Sign plate outside the agency’s main office.

EPA Issues Emergency Order: Stop Using Dacthal

Following a review of data associated with the use of dimethyl tetrachloroterephthalate (sold under the most-common trade name, Dacthal), the EPA has issued an emergency order to stop using this active ingredient effective immediately.

Small, green grass plant amongst brown soil.

Woolly Cupgrass Management

Compared to other grassy weeds, woolly cupgrass is difficult to manage due to the large seed and tolerance to select herbicides. Proper identification will ensure proper selection of management tactics.

Weeds growing abundantly between rows of soybean in a research plot.

Weeds Are Starting to Flower: Management tactics to minimize seed production in soybean

Flowering weeds are an indication that seed production is about to occur, and viable seeds can soon be produced. Learn a variety of strategies to manage these weeds before they become a problem in your soybean fields.

Two pictures of green sunflower plants amongst brown dirt and tan crop residue. Taller, green corn plants can be seen in the distance.

Would you rather know or assume? A reminder to check varieties before spraying.

No matter how busy you are this growing season or in the future, you should never be too busy to stop and take a few minutes to double check herbicide types and crop varieties before spraying.

A few small, green weed plants among a background of brown dirt, tan crop residue and green soybean plants.

Excess Moisture and Heat Will Likely Increase Weed Growth and Germination

With warmer temperatures on the horizon, crop growth and development is set to rapidly increase, and so is weed growth and germination. Learn some expert tips for scouting and managing later-emerging weeds.

Full plant profiles: Golden alexander and wild parsnip.

Plant Look-Alikes: What’s the Difference Between Golden Alexander and Wild Parsnip?

Golden alexander (Zizia aurea) is a striking native plant in South Dakota. However, another plant in this region often mistaken for golden alexander does not belong here and contains a harmful toxin.

Picture of multiple green plants and tan, corn residue with brown soil in the background.

Reminder: One herbicide in the postemergence application will likely not be effective

The SDSU Extension Weed Science Project is currently conducting a plethora of field research evaluating weed management in soybean. One study is investigating the effectiveness of 2,4-D and tank mixtures applied one time to 4-inch weeds.