Protect Your Yield​​​​​​​​​

Scout and Control Weeds Early

Proactively scout fields and control weeds throughout the season. Application timing, correct use rate for weed size, and environmental conditions are all important for yield and performance. The chart below shows the effect of waiting too long to address a weed problem.

 


Five Weeds to Look Out For

Palmer amaranth, waterhemp and marestail are notorious for spreading quickly, growing quickly, and significantly damaging yields. You must take a proactive approach to weed control, by using residual herbicides and diverse weed management practices (DWMPs), or they may become tough-to-control or resistant. Learn more about the five most common weeds below.

Palmer Amaranth

With up to 1 million seeds per plant, palmer amaranth is highly invasive, and can reduce yield by up to 78%.* This erect summer annual grows taller than any other pigweed — sometimes reaching 6.5 feet or more in height.

Palmer Amaranth

* http://www.cals.ncsu.edu/agcomm/news-center/perspectives/work-continues-on-managing-the-weed-palmer-amaranth/
** Steckel, L. 2007. The dioecious Amaranthus spp.: here to stay Weed Technology vol. 21-567-570

Several characteristics make it difficult to eradicate:

  • It has both male and female flowers, which increases its genetic diversity and its potential to become resistant.**
  • It can tolerate drought relatively well.
  • The seeds can remain viable in the soil for up to two years.

How to identify Palmer Amaranth:

  • Palmer Amaranth has dense, compact terminal flowers and relatively tall stems with petioles that are longer than the leaves.
  • Its terminal panicles can reach up to 1.5 feet in length.
  • Compared to other pigweeds, its terminal spike is smoother, narrower, and less spiky.

Waterhemp

Waterhemp loves the flood plains and other wet, low-lying areas. However, it has also become well-adapted to conservation tillage and no-till environments. With 20 plants per square foot, waterhemp can reduce soybean yield by 44%.*

Waterhemp

* Steckel, et al.: waterhemp seed-bank persistence
** www.weedscience.missouri.edu/publications/ipm1030.pdf

Here are some of the reasons waterhemp is so tough to beat:

  • Each plant can bear up to 250,000 seeds.**
  • Waterhemp seeds can remain viable in soil for up to 4 years.
  • Although its seeds are tiny, waterhemp has a higher growth rate than other weeds. It can grow nearly 1" per day during peak growing season.

How to identify Waterhemp:

  • Seedlings are typically hairless with waxy or glossy leaves.
  • Tall waterhemp has a smooth, erect stem with small, green flowers. It can grow up to 8' tall.
  • Common waterhemp does not grow as tall, but it also has smooth leaves and stems. It can have a yellowish-green, red, or reddish-purple stem.

Marestail

Marestail, or horseweed, is one of the most common weeds in the eastern and central U.S., but it can be found in every state. A proper burndown is critical for controlling this weed, or else it can damage soybean yields by up to 22%*.

Marestail

* Mark Loux, Ohio State University, Bill Johnson, Glenn Nice, Purdue University, "Control of Marestail in No-Till Soybeans," http:agrcrops.osu.edu/specialists/weeds.

** http://weeds.cropsci.uiuc.edu/

Its lightweight seeds — up to 200,000 per plant — are responsible for making this weed such a formidable opponent:

  • Seeds are dispersed on the wind and can travel great distances.
  • Up to 80,000 seeds can germinate immediately after they land in soil.**
  • Once it reaches the rosette stage (fall), marestail can be even more difficult to control, and can potentially develop resistance to several herbicides.

How to identify Marestail:

  • When a marestail plant emerges in the fall, it forms a rosette before overwintering.
  • The weed develops elongated flower stalks in late spring, blooms in mid-July, and produces seed in late summer.
  • It has simple, alternating leaves.
  • Its stems are erect and unbranched at the plant's base.

Common Ragweed

Common ragweed is a summer annual, and is among the earliest emerging weeds. True to its name, it is the most abundant of the ragweed species, and it will greatly reduce yield potential if not managed in a timely manner. The broadleaf weed prefers undisturbed seedbeds (no-till fields) and can thrive even in low fertility fields.

Common Ragweed  

Why is common ragweed such a strong threat?

  • It outcompetes many other annual weeds.
  • It produces an abundance of pollen, which leads to genetic diversity.
  • Common ragweed can grow to more than 6' tall, branching frequently when populations are low.

How to identify common ragweed:

  • Common ragweed is a shallow-rooted annual with variability in plant size, leaf shape, and the amount of hairs found on the plant.
  • It has compound leaves that are nearly smooth, thin, and finely divided into a number of lobes.
  • Its leaves are usually wider at the base than at the tip.

Giant Ragweed

Giant ragweed emerges early and grows rapidly to an average height of 5'. If left untreated, it can be one of the tallest summer annuals that plagues farmers. It prefers cultivated soils, and typically emerges early and in a continuous flush.

Giant Ragweed  

Giant ragweed is a serious contender:

  • It can reach up to 17' tall.
  • It produces an abundance of pollen, which leads to genetic diversity.
  • In the eastern Corn Belt, it emerges later and over a more extended period, making it harder to manage.
  • One giant ragweed plant per 3 feet of row can reduce soybean yield by 80%.

How to identify giant ragweed:

  • This broadleaf weed has a relatively short taproot and a hairy stem.
  • It has large leaves with 3 to 5 distinct lobes.
  • You can see "spoon-shaped" cotyledons as it emerges from the soil.
  • Flowers are produced in greenish heads, and each head contains only female or male flowers.
  • If it matures enough to produce seeds, the seeds will be crown-shaped with points and ridges on the tops.

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