For corn growers, a handful of notorious annual weed species seem to wreak havoc year after year, stealing water, nutrients, and yield. These most wanted “weed villains” have evolved and adapted to thrive in the corn agroecosystem. Understanding the biology and behaviour of these usual suspects allows farmers to take them down more effectively through an integrated weed management approach.
Giant Foxtail: An Aggressive Summer Annual Grass
Giant foxtail is undoubtedly the most troublesome of the annual grasses infesting cornfields. This prolific and competitive weed emerges all summer, blanketing fields with its bristly seed heads. Giant foxtail robs moisture and nutrients, slashes yields, and reduces harvest efficiency.
Its tolerance of cooler weather allows giant foxtail to vigorously compete with corn early in the season. Later on, each plant produces hundreds of seeds, ensuring future generations. Attacking giant foxtail through pre- and post-emergence herbicide applications and cultivation is critical to curtailing its spread.
Waterhemp: The Rising Broadleaf Superweed
Few weeds strike fear into the hearts of corn growers like water hemp. Over the past decade, this broadleaf annual has rapidly spread through corn production regions. Waterhemp exhibits aggressive early-season growth, often towering over young corn plants in heavy infestations. Prolific seed production – up to 500,000 seeds per water hemp plant – quickly overwhelms fields. Most troubling, water hemp has evolved resistance to several herbicides, especially glyphosate. New-generation soybean and corn traits will expand options to fight resistant water hemp. But for now, using multiple effective modes of action along with row cultivation is critical for its control in continuous corn.
Velvetleaf: The Late-Season Broadleaf Bandit
Velvetleaf may only emerge later in the season, but this wily broadleaf still manages to steal yields at the worst possible time. One or two velvetleaf plants competing with corn can slash annual profits by approximately 15-20 bushels per acre. Dense infestations spelled even more significant losses.
Unlike many weeds, velvetleaf germinates best in hot soils, often appearing mid-season. This is after other summer annual weeds in corn are already dying off. Once established, its tall, coarse growth shades corn plants while aggressively robbing soil moisture during that all-important grain fill period. Timely post-emergence herbicide applications and cultivation provide the best control against late-invading velvetleaf.
Marestail: An Emerging Glyphosate-Resistant Threat
Recently, marestail’s spring-germinating rosettes have become an ominous sight in no-till corn and soybean fields. With extreme tolerance to cool temperatures, this winter annual establishes early steals moisture intended for crops. And over just the past few years, marestail has rapidly evolved resistance to glyphosate–the world’s most widely used herbicide.
Now, new tank-mix partners and application timings are required to achieve control of glyphosate-resistant marestail. Fall burndown treatments also reduce overwintering weed populations that later compete with corn. Diligent management is necessary to prevent the marestail scourge from spreading rampantly.
Controlling The Usual Suspects
Knowing each notorious corn weed’s unique characteristics and weaknesses facilitates management considerably. Correctly identifying water hemp, giant foxtail, velvetleaf, marestail, and other frequent trespassers informs herbicide selection and timing.
Conclusion
The most effective plan often involves layered pre-plant burndown, pre-emergence, and post-emergence herbicide applications targeting early, mid, and late flushes. Integrating chemical control with timely cultivation further strengthens defense against these wily-yield bandits. We were scouting and record-keeping track escapee weeds while guiding future adjustments. Utilizing these integrated practices keeps the worst-of-the-worst annual corn weeds at bay.
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