Winter annuals will germinate in the late fall or early winter, then grow to maturity in the spring and complete their life cycle in the summer. Leaves will turn yellow late spring or early summer which is a good indicator that the plant is dying due to heat stress.
Being a member of the mint family, purple deadnettle has the characteristic square stem but does not exhibit the odor when crushed as other mints will. The leaves are opposite, with rounded teeth on the margin.
Towards the apex or tip, leaves have very short petioles or stems whereas towards the base, the petioles are much longer. Leaves at the apex begin with a purplish tint that fades to green as the growing season progresses. Flowers are a pink to light purple and do act as a food source for pollinators in the spring.
This weed is more often found in beds, gardens, or other disturbed soils than in well-established turf. Populations may survive in thin turf, reminding us again that maintaining a thick, healthy stand will help crowd out unwanted weeds.
Purple deadnettle can be easily confused with henbit and also bears some resemblance to Persian speedwell and ground ivy. Henbit leaves have no petiole at the apex and flowers are slightly darker in color.
Persian speedwell is in the figwort family, so it has a round stem which is a good differentiating factor. Henbit and deadnettle are both winter annuals so pre-emergent control strategies will be the same.
Most pre-emergent herbicides will get reasonably good control if applied at the right time in the fall. Post-emergent herbicides formulated with phenoxy (2,4-D, MCPP) Pyridine (Triclopyr, fluroxypyr, clopyralid) and benzoic acid (dicamba) herbicides work well in turf, and non-selectives can be used for control in ornamental beds.
The problem comes in the fact that this weed will be visible in cooler weather when the activity of post-emergent herbicides is fairly slow. Adding products like Octane or Quicksilver will speed up that activity.
Don’t forget to read the label to see if a surfactant is necessary and advise on a tracker dye and tank cleaner.
In closing, we always recommend having a separate sprayer for herbicides to prevent damage from residual material. It never hurts to have a dedicated sprayer.
Please contact the Ewing Technical Services Team with questions and for help with weed identification.