The weeds are coming!

March 17, 2016 11:51 AM
Blog Post

Spring seems to have sprung early this year with the beautiful weather and very warm temperatures. I like to take a lap around the office on the Johnson County Fairgrounds a few times during the spring to keep an eye on the weeds, as we have a nice variety of winter and summer annuals, biennials, and perennials in the area. I wanted to share a few of the species I discovered.

ISU weed scientist Bob Hartzler always proclaims that spring is here when the prostrate knotweed (Polygonum aviculare) germinates. Spring must officially be here - bring back the warmth and green on the landscape! Unlike many other plants, this weed grows well in compacted soils, so I often notice it in areas with lots of foot traffic on campus or driveways at the research farms.

This picture is a little strange, but I wanted to show the beautiful flowers already blooming. This is a Veronica spp. It may be corn speedwell (Veronica arvensis), but I found it to be too difficult to key out. This plant can act either as a winter annual or an early summer annual. This one looks like a winter annual - meaning it germinated in the fall and flowers the following spring. The speedwells produce heart-shaped fruit containing seeds for the next generation. Notice the horseweed (Conyza canadensis) on the right side of the picture, another winter or very early summer annual.

The picture below shows some very newly germinated summer annuals. The seedling with the larger, round cotyledons in the center of the picture is probably prostrate spurge (Euphorbia maculata). I'm keeping an eye on the seedlings with smaller cotyledons to determine their identity.

Soon we'll notice the more common summer annual weeds coming up in crop fields - stay tuned for more information about them.


Meaghan Anderson Field Agronomist in Central Iowa

Meaghan Anderson is a field agronomist in central Iowa and an extension field specialist at Iowa State University Extension and Outreach. Educational programming is available for farmers, agribusinesses, pesticide applicators, certified crop advisors, and other individuals interested in...