Davey Tree Flipbooks

32 MUSK THISTLE (Carduus nutans) PLANT DESCRIPTION Musk thistle, or nodding thistle, is a biennial weed that can be seen in summer as an upright, multiple stemmed, 3–6 foot tall flowering plant with pink flowers and spine- tipped leaves. It can also be found as a low-growing seedling or rosette in spring. Round pink flowers are known to bend over or nod downward and are easily noticed in unmowed areas. LEAF: Leaves are hairless, narrow, lobed, and coarsely toothed with sharp spines along the leaf margin. A key identification feature is the winged leaves and spines growing along the length of the stems. STEM: Multiple stems arise from a single base of leaves. Stems are winged, covered in spines, and lack lateral branches. FLOWER: Flowers are produced at the ends of stems. Flower buds are globe shaped with large, lance-shaped bracts. Flowers bloom in early summer, with pink flower petals. The way petals emerge from the flower base resembles the form of a shaving brush. SEED: After pollination, cottony, white and fluffy seeds develop. Seeds and flowers are often present on the same plant at the same time. REPRODUCTION: Seeds are the primary means of reproduction and are dispersed by wind. A mature musk thistle plant is capable of producing thousands of seeds that can remain viable for up to ten years. WHY IT IS NOXIOUS: Musk thistle can create maintenance and visibility issues if allowed to grow near the road and can disperse seeds long distances. SEASONAL IDENTIFICATION WHEN TO FIND: Look for vivid pink-rose colored, globe-shaped flowers and spiny- winged stems from late spring to midsummer. Cottony seed heads can be seen from summer to fall. SPRING IDENTIFICATION = DIFFICULT Basal rosettes can be found as low-growing mounds of spiny leaves. At the rosette stage, distinguishing musk thistle from other thistles can be difficult. SUMMER IDENTIFICATION = EASY TO MODERATE Stems grow long and are covered in spiny wings. Green and pink flower buds are globe shaped with large lance-shaped bracts. Flowers are pink and resemble a shaving brush shape. Seeds are produced by midsummer as flowers continue blooming. FALL IDENTIFICATION = EASY TO MODERATE Fully mature plants are declining. Look for remnant, fluffy seed heads on fully-formed multiple stems with spiked wings along the stems. WINTER IDENTIFICATION = DIFFICULT Musk thistle does not persist into winter after going to seed and dying. However, rosettes that germinated in spring may be found and will survive over winter. SIMILAR-LOOKING SPECIES CANADA THISTLE (Cirsium arvense) leaves and form can be similar. The flowers are purple, small, and grow in groups of multiple flowers. Their stems are smooth with no hairs or spikes. BULL THISTLE (Cirsium vulgare) leaves look similar but the lobes are more pointed or lance shaped. The flowers are constricted where petals emerge. The flower buds or base of emerged flowers are more oval shaped and have needle-like flower bracts. Stems and leaves are covered with dense white hairs. LOW HIGH ohio distribution roadside distribution growth seeds ability to dominate difficulty of control WHERE TO FIND: Musk thistle is common in western Ohio. It is typically found in well-drained fields, slopes, and unmanaged areas in full sun. CONTROL METHODS: MECHANICAL: Mow only to maintain visibility and to reduce seed production. Hand pull with gloves and use caution to avoid spines. CHEMICAL: Make directed applications from spring to early summer with selective herbicide. For best results, make applications before plants grow tall and flowers bloom. CULTURAL: Plant tall fescue in early fall. RECOMMENDATION SUMMARY: Musk thistle germinates in spring, lives for one full season, and overwinters as a rosette. In the second spring, the stems bolt and produce flowers and seeds before dying. Accomplishing control should not be difficult with many opportunities to prevent seed production. For best control results, make herbicide applications in late spring to early summer before plants grow tall and flowers bloom. Fall and early spring applications to rosettes and seedlings can also be effective. Use directed applications for large colonies and broadcast applications for sporadic musk thistle growing in turf. Mow at flower emergence to reduce seed production. Plant tall fescue in early fall and allow to grow tall in spring to compete for space and to shade out seedlings. Failure to control musk thistle will allow this tall-growing, heavy-seed-producing weed to spread into newly disturbed areas along the road and into adjacent private and agriculture properties. biennial x 2 RIVM LEVEL OF CONCERN

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