Listed below are weed species descriptions, distribution, problems, and possible management methods for weeds considered noxious by the State of Iowa and Johnson County. This web page is meant to give general knowledge of these problem weeds, why they are a problem, and common methods of control. Individual weed and management circumstances may vary and these recommendations should be used as changing situations dictate.
The Iowa Department of Agriculture and Land Stewardship and the Code of Iowa have declared the following species of plants as noxious weeds which need to be controlled:
Bull Thistle (Cirsium vulgare)
Canada Thistle (Cirsium arvense)
Field Bindweed (Convolvulus arvensis)
Leafy Spurge (Euphorbia esula)
Multiflora Rose (Rosa multiflora)
Palmer Amaranth (Carduus nutans)
Teasel (Dipsacus species)
All other species of thistles belonging in the genus of Carduus
Iowa Administrative Code, Agriculture and Land Stewardship Department, Chapter 58 Noxious Weeds
This web page also contains very general herbicide control methods. This web page is not intended to promote the sole use of herbicides, rather using herbicides as a tool and as an overall part of an integrated weed management program. Changes in pesticide regulations occur constantly. If you have questions about the usage or legality of certain herbicides, contact your County Extension office, or the Iowa Dept. of Agriculture & Land Stewardship. Always read and understand chemical labels before use. The recommendations for using herbicides included in this web site are incomplete and should not serve as a substitute for herbicide labels. Complete instructions for the use of a specific herbicide are on the herbicide label. The pesticide user is responsible for applying pesticides according to label directions, as well as for problems that may arise through misapplication or misuse of the pesticide. Label changes, product cancellations, and changes in recommendations may have occurred since the production of this web site. Before using herbicides, consider whether possible impacts of chemicals outweigh the benefits of other management techniques, whether there are other appropriate management choices, and also whether the area is appropriate to use herbicides. For more specific information on plant identification or management, consult with knowledgeable professionals before attempting control. Some weed species are nearly impossible to manage without the careful use of some herbicides. The best weed control program begins with prevention. Once weeds are established though, using several management methods in an integrated weed control program will generally give the best results.
A variety of methods are used to control invasive and noxious plants. Their effectiveness will vary with the type of infestation, weed species, and the skill and dedication of the persons controlling weeds. Select a control method, which meets the goals of the particular area (i.e. lawn, prairie, agricultural field, etc.) where weeds have invaded. The majority of these management methods are most effective when used in combination as part of an integrated vegetation management program. For example, much better control of Canada Thistle (Cirsium arvense) can be achieved using mowing, competitive seeding, herbicide applications, and prescribed burning all as management tools, rather than relying solely on just one method.
Identifying noxious weeds correctly and preventing them from establishing is a much more efficient and effective management strategy than is waiting for a weed to reach epidemic levels. With some weed species, such as Canada Thistle, Japanese Knotweed, or Purple Loosestrife, this may be the only real opportunity to "control" the weed. Some noxious weeds are extremely difficult to get rid of once they are established, and long-term management is necessary just to reduce their populations to acceptable levels. Noxious weed management is expensive in terms of dollars, but also in time spent and energy used.
Don’t know what a word means?
Try looking in the glossary of plant terms for help. Here you can find various explanations of terms such as "annual", or "rosette" to assist in correctly identifying characteristics of some of the noxious or invasive weeds of Johnson County.
- Glossary of Plant Terms
Taken from Iowa Noxious Weeds, published by the Iowa Department of Agriculture and Land Stewardship
Alternate: singly along a stem, one leaf or bud at a node.
Annual: lasting but one growing season.
Axil: point where a leaf or secondary branch joins the stem; the upper angle of the junction of the stem and leaf.
Biennial: plant of two years duration. The first year is often a vegetative form such as a rosette and the second year the plant flowers, forms seeds and dies.
Bract: small leaf-like structure surrounding a flower; belonging to an intlorescence, or sometimes a stem.
Carpel: a simple seed bearing organ, or one member of a compound organ (pistil).
Clasping: blade of the leaf extending beyond and surrounding the stem.
Glandular: supplied with glands or similar structures.
Granular: rough surface with grain-like appearance.
Hoary: grayish-white from fine hairs.
Lanceolate: lance-shaped, tapering at both ends, but broadest at the base and several times longer than wide.
Ligule: an appendage on the inside of a leaf at the junction of sheath and blade.
Linear: long and narrow with nearly parallel edges.
Lobe: a division or segment of a leaf or other plant organ.
Node: joint of a stem that is sometimes enlarged.
Noxious: a plant considered to be extremely destructive or harmful to agriculture and so designated by law.
Oblanceolate: lance-shaped, tapering at both ends, with the broadest part at the tip end and several times longer than wide.
Ovate: egg-shaped with the broadest end near the base.
Panicle: loose, irregularly compound inflorescence with the flowers borne on individual stalks.
Perrennial: a plant that lives more than two years.
Petiole: stem or stalk of a leaf.
Pinnate: compound leaf with the leaflets arranged on each, side of the midrib or vein.'Also used to describe leaves which are lobed or cleft to appear pinnate.
Pistillate: flower with female parts but the male parts are absent.
Plume: (plumose) short hairs attached to filaments of the pappus.
Pubescent: covered with short soft hairs.
Raceme: a simple inflorescence of flowers on stalks of equal length arranged on a single elongated stem.
Rhizome: under ground stem which provide means for the spread of some perennial plants. The term root-stock is used in place of rhizome in many instances.
Rosette: cluster of leaves in circular form without descernible upright stem.
Sheath: lower part of the leaf that encloses the stem on grasses.
Spatulate: enlarged rounded apex with a narrowing and elongated base.
Spike: simple inflorescence with flowers sessile or nearly so upon an elongated stem.
Spikelet: a unit of inflorescence of grasses and sedges, consisting of one or more flowers between two empty glumes.
Staminate: flower has stamens but usually no pistils.
Style: part of a pistil connecting ovary with stigma.
Umbel: simple inflorescence of flowers on stalks which radiate from the same point.
Valve: one of the pieces into which a pod splits.
Whorled: three or more leaves or stems occurring at per single node, often arranged around the stem.
Winged: any membraneous extension or in some instances the extension of the leaf blade beyond that normally expected.