A weed that I have gotten many questions and emailed pictures about this spring is Pennsylvania Smartweed. This is an annual weed common to central Ohio that is in the same family as Buckwheat. It can produce upwards of 20,000 seeds per plant that can persist in the soil for several years so control of this weed before seed set is critical for the backyard grower, community gardener and urban farmer.
One use of note for this weed is as a trap crop. Japanese Beetles prefer this as a forage to the rest of my desired plantings and will feed on this first before going to my vegetables, fruits and herbs. To make effective use of this weed as a trap crop, make sure to kill the beetles regularly or you have provided them with food and shelter instead.
The flower of Pennsylvania Smartweed including a couple of breeding pollinators. Make sure to mow, herbicide, or use tillage to kill this weed before seed set to prevent large amounts of weed seed from entering your seed bank.
Source fact sheet for background information – Credit: Michigan State University Extension.
Planted new grass and where I used peat moss, I now have lots of smart weed (dark blotch in leaves) I’d like to be rid of it but don’t want to kill new grass. I may try to pull by hand or just mow & collect before it goes to seed. I planned to overseed same area in fall. Any suggestions for weed killer or do I mow it short now or do something else ? Thanks, Ron
Ron, I would not put a weed killer on new grass as that may stress it. I would mow the smartweed which should eradicate it since it is an annual.
Thanks, I did mow it a tad shorter than usual (3.25 vs 3.5) and lots of the smartweed is gone but it’s trying to make a comeback .. I plan to just cut it again. It has no visible seed pods so I didn’t collect cuttings, just mulched it. A new worry is my grass looks a bit pale , almost yellow in some areas. I threw some 10-10-10 down and watered it in. I can’t see if the discoloration is on the new or old growth. Still have straw under so maybe the grass is just thinner in those areas.
I would consider a soil test for your lawn to make sure that the proper nutrition is present. Probably wait until early fall or late summer to check since you just fertilized.