Controlling Perennial Weeds When They Emerge from Seed

Mark VanGessel, Extension Weed Specialist;

Perennials often produce seeds that are adapted to being moved by the wind (hemp dogbane, milkweed, or Canada thistle) or produce large seeds or berries that are eaten by birds and animals and spread around (pokeweed). We conducted a greenhouse study (funded by DE Soybean Board) to examine soil-applied herbicide control of some perennials when they originate from seeds. Perennial seedlings (emerged from seeds), can produce a perennial root system after only 3 to 4 weeks. Being able to select the correct herbicide when you know seeds are coming into your fields can help prevent headaches and frustration in years to come. If at all possible, keep the perennials mowed along ditches and field edges to reduce (or eliminate) seed production. Prevention is the best approach.

Johnsongrass, bermudagrass, Canada thistle, hemp dogbane, common milkweed, common pokeweed, and horsenettle were planted in the greenhouse and sprayed with common soil-applied herbicides (Dual, Prowl, Command, Lorox, metribuzin, atrazine, and Canopy). Next to each weed are the herbicides that provided the best level of control (over 90% control). This study was conducted a few years ago and neither Lumax, Valor, nor Authority were available at that time for testing.

Bermudagrass: Dual, Prowl, Command, and metribuzin

Johnsongrass: Command.

Canada thistle: Command, metribuzin, atrazine, and Canopy.

Hemp dogbane: Command, Canopy, metribuzin, and atrazine.

Common milkweed: metribuzin and Canopy.

Common pokeweed: Canopy, and metribuzin.

Horsenettle: metribuzin, atrazine, and Canopy.