Achoo! August is the start of back-to-school sales and ragweed season, which lasts through mid-October (ragweed season, that is!). Ragweed pollen is one of the most common causes of allergies, often called hay fever. Preen’s webpage addressing Ragweed called it “the champion of sneeze-inducing weeds” (Preen). Many people blame goldenrod for their allergies however all the references used in this article were clear that it is not goldenrod but ragweed that is causing all the misery. 

Symptoms of Ragweed allergies include sneezing, eyes that may be itchy or swollen, a scratchy throat, runny nose, nasal congestion and/or sinus pressure and pain, coughing, and even sleep disruptions (Minnesota ENT). About 10% of the population are allergic to Ragweed. 

Ragweed has been found across the whole country, with 17 varieties identified. There are three kinds of ragweed that grow in Minnesota: Common Ragweed (Ambrosia artemisiifolia), Giant Ragweed (Ambrosia trifida), and Western Ragweed (Ambrosia psilostachya). The three types look different, with Giant Ragweed distinguishable due to its large size, growing up to 17-20 feet. Common Ragweed reaches a height of 2-4 feet, and Western Ragweed grows to a height of 1-3 feet. All three have distinctly different leaves. Western Ragweed leaves are hairy and are oval-lance shaped that are deeply lobed. Common Ragweed’s leaves are fernlike, and Giant Ragweed has palmately lobed leaves. The Common Ragweed has a taproot, Giant Ragweed has fibrous roots with a short tap root, and Western Ragweed has fibrous, creeping rhizomes (Cornell CALS, Minnesota Wildflowers). They all grow in disturbed soil, with Common Ragweed common in both rural and urban settings. 

Common Ragweed seedling

Common Ragweed seed

Common Ragweed’s seed production, per plant, is 3,500 seeds compared to Giant Ragweed’s seed production of 10,300 seeds per plant. Seeds from both plants can live in the soil for up to 30 years, with only 50% depletion seen in 1.5 to two years (Time to Remove Flowers, UMN IPM Extension, Common and Giant Ragweed Identification). The seeds are dispersed through wind, water, animals (rodents and birds), and farming practices. A single Ragweed plant can produce up to a billion grains of pollen (Preen). Ragweed pollen travels! It has been found 400 miles out to sea and 2 miles into the air (Minnesota ENT).

Giant Ragweed

Giant Ragweed seed

Western Ragweed

This graph from the Minnesota Department of Health (2020) shows the types of pollen and their percentages. Ragweed represented almost 60% of the pollens sampled in the air.

Link: Pollen Charts, MN Department of Health

All forms of Ragweed can be difficult to control. The best approach is the manual method of plant removal, especially pulling them out before August to avoid pollen release. You can also repeatedly cut them down to keep them from flowering. Herbicides are not generally recommended unless you are farming, which then requires significant applications. Ragweed plants have developed resistance to many herbicides, so if your preference is to use herbicides, it may require the use of several types and several applications. Because ragweed is one of the earliest plants to germinate in the spring (but don’t start causing problems for humans until they start flowering in August), the best method of control is to hand pull them. It is also important to remove them from the yard quickly as they can re-root if left in a debris pile. 

References: 

Bayer, Crop Sciences United States: https://www.cropscience.bayer.us/articles/channel/common-and-giant-ragweed-identification-and-management 

Cornell College of Agriculture and Life Sciences: https://cals.cornell.edu/weed-science/weed-profiles/giant-ragweed 

Minnesota Department of Health (MDH): https://data.web.health.state.mn.us/pollen_charts 

Minnesota Ears, Nose, and Throat (ENT) Specialists: https://minnesotaent.com/goldenrod-or-ragweed-whats-worse/ 

Minnesota Wildflowers: 

https://www.minnesotawildflowers.info/flower/common-ragweed 

https://www.minnesotawildflowers.info/flower/western-ragweed 

Missouri Department of Conservation: https://mdc.mo.gov/discover-nature/field-guide/giant-ragweed 

Preen: https://www.preen.com/learn/lawn-garden-tips/weed-control/weed-notes/how-to-control-ragweed/ 

University of Minnesota Weed Identification: https://extension.umn.edu/weed-identification/annual-broadleaf-weeds#ragweed%2C-giant-8380611 

University of Minnesota Extension Fruit and Vegetable News: https://blog-fruit-vegetable-ipm.extension.umn.edu/2024/08/why-remove-flowering-weeds.html 

University of Minnesota Extension Yard and Garden News: https://extension.umn.edu/yard-and-garden-news/zero-seed-rain 

Photo Credits: Chris Evans, University of Illinois, Bugwood.org (1),  www.publicdomainpictures.net (2), Strand Memorial Herbarium (3-6), https://www.minnesotawildflowers.info/flower/western-ragweed (7)