Weed Management

Weeds reduce agronomic crop yields through competition for resources. On this page, find recommendations for managing weeds in agronomic crops such as corn, grain, soybeans, small grains, and forages.

Weed Management Best Practices

Agronomic crop weed management requires year-round vigilance and control. Weeds can be broken down into annuals, biennials, and perennials, each of which has its own life cycle. Understanding these life cycles, for example, helps agronomic crop producers decide whether they can control annual and perennial weeds after silage harvest or in fallow areas.

Not only are there different types of weeds, but there are also many different methods for controlling them. Penn State Extension’s Introduction to Weeds and Herbicides covers the important issues surrounding weeds and their control. Weed management plays an important part in agronomic field diagnostics.

The use of herbicides is just one method, with new herbicide products entering the market every year. The Agronomy Weed and Pest Management Tour is one way you can find out about the new herbicide products.

Conservation tillage systems are another way of managing weeds that uses cultural, mechanical, and chemical control tactics.

The effectiveness of any weed control method depends on a number of different things, such as the time of the year, unstable weather conditions, crop injury, and tank-mixing. Mid-season weed control issues also include herbicide drift.

Weed Management in Agronomic Crops: Corn, Soybean, and Wheat

Corn, soybean, and wheat have specific weed management issues to contend with. When spring is approaching, for example, populations of winter annual weeds become prevalent, thereby competing with wheat and barley. Certain herbicides can be applied in nitrogen carriers, but it’s important to get the timing right. There is a temptation, when applying herbicides, to wait until all the weeds have emerged, but this is counterproductive.

Some winter annual weeds are easier to manage in the fall rather than waiting until the spring. There are many options for fall herbicide applications, such as Harmony Extra, a broad-spectrum herbicide. Glyphosate is another broad-spectrum herbicide and is a herbicide option for burndown in no-till corn.

Herbicide-resistant weeds are a common cause for concern, too, with Marestail, or horseweed, being one of the most challenging.

Producers use cover crops as part of their weed management program, but it’s important to remember that some herbicides can persist and potentially influence the establishment of cover crops.

Soybean producers can attend the Soybean Management Workshop and Herbicide Demonstration workshop to learn more about herbicide usages along with variety selection, management strategies, insect, and disease management.

Chemical Free Weed Management for Agronomic Crops

The application of herbicides is not the only way to manage weeds successfully, especially if producers want to “plant green”. Organic producers use cover crops, for example, as well as a number of other non-chemical control strategies in their weed management plans that are cultural and mechanical.

The focus of organic weed management is prevention, crop rotation, crop competition, and cultivation. Hairy vetch, for example, mixed with a winter grain, can be used before corn, and cereal rye is predominantly used before soybean. Hairy vetch would typically be terminated with a roller crimper before planting corn.

Harvest weed seed control using a Harrington Seed Destructor is a way of managing herbicide-resistant weeds. It is used as part of the harvesting process and is currently being tested in Illinois.

Herbicide Application and Timing for Field Crops

Timing is crucial when it comes to the successful application of herbicides. Spring herbicide applications, for example, include Broadworks and Pindar GT, used in stone fruits, and Zeus Prime, which is currently only used for apples.

Certain residual herbicides can also be applied close to the time for planting. However, timing is critical, as Early Preplant (EPP) Herbicide applications that are too early may require a post-application.

As well as timing, there is the problem of herbicide drift and drift-related damage to consider. The issue is a very serious one because if a substantial amount of drift-related damage occurs there are legal ramifications.

Soil persistence or soil residual life is another factor to consider when applying herbicides to crops. Herbicides vary in their potential to persist in the soil. There is a very fine line between controlling weeds for a growing season and then planting a sensitive rotation crop.