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Biggest Problem for Iowa Farmers Missing From Noxious Weed Law

August 3, 2016

Iowa Code 317 is the portion of the Iowa laws and regulations that defines the Iowa Noxious Weed Law. Chapter 317.1 is the piece of legislation that actually defines what weeds are classified as noxious. I like to refer to this piece of legislation as the most out-of-date law in our great state, although I will confess that I don’t know the Iowa Code well enough to know what other gems might be present in the books.

The reason I like to criticize the Iowa Weed Law is not because I think regulation can‘t help manage weeds, but rather that the weeds included in the law are hopelessly out of sync with the current threats to Iowa’s agricultural fields and natural areas. Because the list of noxious weeds is an actual piece of the Iowa Code, it is extremely difficult to make any changes to the weeds defined as noxious. Counties do have the authority to classify weeds as noxious.

Most of the weeds classified as noxious in Iowa are naturalized. A naturalized plant is a species not native to Iowa, but the plant is well established and widely distributed. Because of the wide distribution of naturalized plants, it is unrealistic to prevent its spread or expect eradication of the weed – these are the primary intents of noxious weed laws. In addition, many of the weeds classified as noxious are not a threat to today’s agricultural systems. Examples of weeds too widely established for regulation to impact their distribution include velvetleaf, cocklebur, wild carrot and Canada thistle. Weeds on the list that are remnants of past agricultural systems include sheep sorrel, wild mustard, and buckhorn plantain.

In my opinion, the noxious weed law should include weeds that are either not present in the state, or are currently present in small, isolated populations. These are the weeds where regulation could actually help in their management. In some situations, the law could actually play a role in eradicating a new threat. In the current form, most counties ignore the Iowa Noxious Weed Law unless a citizen complains about an infestation of a noxious weed. In addition, I think the list of weeds should be taken out of the code so that it would be easier to add and eliminate weeds as threats change over time.

Two examples of the types of invasive weeds that the Noxious Weed Law could help manage are Sericea lespedeza (Lespedeza cuneata) and Palmer amaranth (Amaranthus palmeri). Sericea lespedeza is a warm-season, perennial legume that invades pastures, prairies, CRP and roadsides. It was introduced in the south for erosion control and forage. The plant can rapidly take over undisturbed areas of the landscape, and has been moving north into Iowa for at least a decade.

The main difference between Palmer amaranth and waterhemp is that Palmer is much more competitive, thus it poses a much bigger economic threat to producers than waterhemp. Palmer amaranth was first identified in Iowa in 2013, and is known to be present in less than 10 Iowa counties. Classifying Palmer amaranth as noxious would provide counties authority to manage new infestations while they are small enough to be eradicated, and reduce the likelihood of Palmer amaranth being found in seed supplies. Seed used to establish CRP plantings this spring is suspected to be the source of two new Palmer amaranth infestations.

The first noxious weed law in the US was enacted by Vermont in 1795, targeting Canada thistle. While regulation alone will not prevent the invasion of new weeds, it can be one tool to reduce the threat posed by weeds. Regulation can only really be effective on weeds that currently are not widespread across the state. Wisconsin, Minnesota and other states have changed their weed laws relatively recently to better account for current threats and changes in agriculture. It is time for Iowa to play catch up.

Source: Bob Hartzler, Professor of Agronomy and Extension Weed Specialist, Iowa State University