Marestail, or conyza canadensis, is a persistent weed that can significantly hinder corn growth and yield. Known alternatively as Horseweed, Marestail is a native North American annual weed.

Its notorious resistance to glyphosate and other herbicides poses a significant challenge for corn farmers. Marestail competes fiercely for nutrients, sunlight, and space, drastically reducing corn yield, especially when it invades fields early in the growing season. Marestail can overshadow corn plants, reducing their ability to photosynthesize. This can lead to stunted leaf growth and smaller corn ears.

Marestail's competition for resources can force corn plants to divert energy from growth and reproduction to survival, resulting in smaller, less productive plants.


Marestail, also known as horseweed, can drastically reduce soybean yields if not effectively managed. It battles with soybean plants for critical resources like sunlight, water, and nutrients, thereby inhibiting their growth and development. Moreover, marestail exhibits resistance to glyphosate, a common herbicide in soybean fields, making its control even more challenging.

Marestail's extensive root system vies with soybean plants for water and soil nutrients. This competition can lead to nutrient deficiencies in the soybean plants, affecting their overall health and productivity.

Marestail's towering growth can overshadow soybean plants, blocking sunlight vital for photosynthesis. This lack of sunlight can lead to the yellowing and wilting of soybean leaves, reducing the plant's food production capability.

The competition for resources can stress soybean plants, affecting their physiological processes such as photosynthesis, transpiration, and nutrient uptake. This stress can lead to reduced pod formation and lower seed count, ultimately reducing yield.

(Image Credit: Doug Doohan, Ohio State University/ OARDC,


How to Identify Marestail


Marestail typically towers between 1 to 6.5 feet, with an erect stem blanketed with fine hairs. The leaves are alternate, linear, and stretch up to 4 inches long. They also bear fine hairs and have smooth edges. The weed flaunts small white or light purple flowers at the stem's apex.

Marestail can be a winter or summer annual weed. The winter annuals germinate in the fall, overwinter as rosettes, and spring back to growth when winter subsides. The summer annuals sprout in the spring and grow throughout the summer.

Rapid growth and the presence of its distinctive flowers are significant Marestail indicators.


Marestail, a winter or summer annual weed, can grow up to 6.5 feet tall. Its unique rosette growth pattern in early stages, with leaves arranged in a circular pattern close to the ground, makes it identifiable. As it matures, it develops a single, erect stem covered with small, hairy leaves that are alternate, linear, and range from smooth to coarsely toothed.

The weed produces small, white flowers at the stem's top, typically blooming from July to October. Marestail seeds are small, equipped with a pappus of white bristles that facilitate wind dispersal.

(Image Credit: Shaun Winterton, Aquarium and Pond Plants of the World, Edition 3, USDA APHIS PPQ,


Geographical Distribution of Marestail


Marestail thrives across North America, particularly in the Midwest and Eastern states. It flourishes in no-till or reduced-till corn fields and other disturbed areas.


Geographically, marestail is prevalent across the United States, particularly in the Midwest and Eastern regions. It commonly appears in no-till or reduced-till soybean fields. Marestail usually emerges in the fall or early spring but can appear at any time during the growing season.

Timing of Marestail Emergence

Marestail can appear at any point in the growing season, but it becomes most problematic when it sprouts early in the season. Early-emerging Marestail competes with corn for resources throughout the growing season, leading to significant yield losses.

How to Manage Marestail in Corn


There is widespread resistance to Group 2 (ALS-inhibitors) and Group 9 (glyphosate) herbicides.




How to Manage Marestail in Soybeans


There is widespread resistance to Group 2 (ALS-inhibitors) and Group 9 (glyphosate) herbicides, limiting effective post-emergence herbicide options in soybeans. Planting glufosinate-tolerant soybeans may offer the most effective marestail control strategy. Effective burndown and pre-emergence herbicide applications are critical for successful weed control.





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Every product that labels MARESTAIL as a weed, pest, or disease the product can be applied against is shown below. Click any product for label and more information.
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