Davey Tree Flipbooks

22 JOHNSONGRASS (Sorghum halapense) perennial PLANT DESCRIPTION Johnsongrass, or Johnson grass, is a 5–8 foot tall perennial grass typically seen in summer in dense colonies with a symmetrical, open, pyramid-shaped seed head. Johnsongrass looks like other grasses while young, but grows rapidly in summer and becomes taller than most grasses with a distinct leaf. LEAF: The leaf blades are 2 inches wide with prominent white center midribs. The leaf wraps around the stem where it attaches, and if peeled off reveals a tattered translucent membrane at the base. STEM: The stems are smooth and grow rapidly after flower formation during the boot-to-head stage. FLOWER: The densely-arranged, tan flower heads emerge in summer. Once mature, the loosely-arranged, symmetrical, pyramidal flower heads help distinguish Johnsongrass from other large grasses. SEED: The seeds are oval shaped, shiny, brown, and covered in coarse hairs. The seeds are produced on open, pyramid-shaped seed heads. A mature plant can produce thousands of seeds that remain viable for up to ten years. REPRODUCTION: Seeds facilitate reproduction with most seeds falling around the parent plants, but the roots of Johnsongrass are the primary means of reproduction. Johnsongrass has rhizomes that spread underground, sprouting up new plants and creating dense colonies. WHY IT IS NOXIOUS: Johnsongrass is a major concern for roadside maintenance due to its mature height. It invades agricultural crops and can be toxic to grazing animals. SEASONAL IDENTIFICATION WHEN TO FIND: The ideal time to find Johnsongrass is midsummer to late summer. Look for tall, dense colonies in flower or seed. SPRING IDENTIFICATION = DIFFICULT Johnsongrass is not prevalent or likely to be visible aboveground in spring, but will be present underground in root form. SUMMER IDENTIFICATION = EASY Johnsongrass grows in patches and can be identified by a white center midrib on the leaf. Flowers emerge in midsummer and the stem grows rapidly, reaching heights of 8 feet tall. Look for dense patches of tall grass and then look for loose, pyramid-shaped flower/seed heads. FALL IDENTIFICATION = EASY As Johnsongrass fades away, the leaf center vein turns pink-purple and the entire plant turns dark brown and eventually light tan. WINTER IDENTIFICATION = DIFFICULT Johnsongrass does not retain an above-ground form in winter but survives in root form. SIMILAR-LOOKING SPECIES SHATTERCANE (Sorghum bicolor) leaves look very similar but are wider than Johnsongrass when held side by side. The main difference is in the flower/seed head. Shattercane has a more dense, tufted flower/seed head similar to a dust broom and much larger, more rounded seeds. CORN (Zea mays) leaves look similar but are actually broader than Johnsongrass. Corn flower head spreads open and has several branches that look like pipe cleaners. LOW HIGH ohio distribution roadside distribution growth seeds ability to dominate difficulty of control WHERE TO FIND: Johnsongrass is not yet widespread in Ohio, but is becoming abundant in the southern half of the state. Johnsongrass can be found in well-drained areas with full sun. Johnsongrass is not controlled by mowing and is most noticeable in areas that are less frequently mowed. With a faster growth rate than other grass, Johnsongrass is easy to notice within weeks after mowing an area. CONTROL METHODS: MECHANICAL: Mow repeatedly from midsummer to fall to maintain visibility, weaken perennial patches, and reduce seed production. Expect rapid regrowth. CHEMICAL: Make directed or broadcast applications to Johnsongrass in midsummer with selective residual herbicide. Make application when grass is at least 18 inches tall and before flower/ seed heads develop. CULTURAL: Plant tall fescue in early fall. RECOMMENDATION SUMMARY: Johnsongrass is a tall, aggressive, difficult-to-control perennial grass. Accomplishing complete control may take several seasons, so be persistent. For best control results make herbicide application in summer during the boot to head stage. Once established patches are under control, broadcast applications with a spray truck and boomless nozzles using grass selective herbicide (sulfosulfuron) to control seedlings that have not formed colonies. Johnsongrass has been reported to develop herbicide resistance, and results should be closely monitored for effectiveness. If a second application is required for control, use alternate herbicides with different modes of action. Mowing provides little to no control of Johnsongrass but can be used to keep plant height down. If Johnsongrass is mowed before herbicide applications, allow it to regrow to at least 18 inches before spraying. Plant tall fescue in the fall and allow to grow tall in late spring to compete with Johnsongrass for space and to reduce seed germination. Failure to control Johnsongrass could allow this very tall grass to dominate the entire right-of- way, creating maintenance, sight distance, and safety concerns. RIVM LEVEL OF CONCERN

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