Keep Crops Safe from Broadleaf Weeds

Giant ragweed has rough stems and leaves with leaves
Giant ragweed in the early stages of growth.

Broadleaf weeds compete with crops for water, light, space and nutrients, all factors that can reduce yields.

To protect their profits, growers must be able to first identify and understand the biology of problem broadleaves. Then, its time to design effective integrated weed management programs to control them.


Pigweeds are easy to recognize, but because significant variation can occur between species, correct identification is often difficult. Most pigweed plants are tall, with simple, alternate leaves that are oval to diamond-shaped. The plant structure is erect to bushy, with dense, profuse clusters of small, greenish flowers. Pigweeds thrive in hot, drought-like conditions and compete aggressively with warm-season crops.


Marestail, an annual weed, can follow a winter or summer annual life cycle. It is a fierce competitor for water and exhibits rapid growth. Flowers are arranged in a branched cluster of numerous white and yellow flowers. Marestail leaves are alternate, linear and simple with entire or slightly toothed margins. Stems are erect and tend to be unbranched at the base of the plant.


Velvetleaf, a summer annual broadleaf weed, can grow to such heights that it severely hampers sunlight penetration to crop plants. It may also host several problematic diseases and pests, and seeds can remain viable in the soil for up to 50 years. This erect plant has large, heart-shaped, velvety leaves with pointy tips. Stems are coarse and grow up to 5 feet or taller. Leaves are densely covered with hair, and plant tissue has a distinct odor when crushed.


Chickweed can wreak havoc on crops, especially small grains. Typically a winter annual, common chickweed can become a perennial under certain environmental conditions. Leaves, which are arranged in an opposite pattern, are elliptical and mostly hairless. Stems often root at the nodes and have hairs arranged in vertical rows. Small white flowers appear at the end of stems either alone or in small clusters.


Common knotweed is a short-lived perennial broadleaf that can thrive even on poor and compacted soil. Knotweeds have numerous slender, wiry stems that are highly branched and form mats. This extensive branching gives knotweed a zigzag appearance. The flower heads consist of a cluster of tiny green flowers with white or pink edges, which are found atop short stalks that grow from the leaf base.


Common ragweed is an erect summer annual with a distinctive vertical and branching growth habit. Common ragweed produces small flowers that turn from green to yellowish brown as they mature. The deeply pinnated (featherlike) leaves are one of the most distinguishable features of this plant; these leaves are usually alternate, though sometimes the lower leaves are opposite. Leaves are often hairy but can sometimes be smooth.

Giant ragweed can reach heights of up to 15 feet and thrives in fertile agricultural soils. Giant ragweed has rough stems and leaves with leaves that are commonly palmately divided normally with three lobes but can have up to five lobes or no lobes at all.

Best Management Practices to Control Broadleaves

Growers can keep common broadleaf weeds from affecting their bottom line by using well-designed best management practices. Herbicide programs should consist of a fall and spring burndown treatment to ensure the field is clean at the time of planting, as well as spring-applied residual herbicides to control the weeds after planting. A variety of products have proved successful in controlling broadleaves.

An integrated approach that combines different sites and modes of action along with cultural practices, such as cover crops and equipment maintenance, can protect fields now and prevent resistance in the future. Crop Science has a broad portfolio to combat tough-to-control and resistant weeds.

Learn more about using herbicides with effective modes of action. You can also find information about Respect the Rotation™, the Crop Science resistance management program.

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