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large seeded broadleaf weeds

A new herbicide from Syngenta called Acuron contains Lumax EZ (27, 15, 5) + bicyclopyrone (27). Bicyclopyrone is an HPPD-inhibitor herbicide that enhances large-seeded broadleaf weed control and also has grass activity. Acuron (27, 15, 5) has enhanced control of giant ragweed, common ragweed, common cocklebur, and velvetleaf, along with improved morningglory control over Lumax EZ. An herbicide just registered in 2016 is called Acuron Flexi (27, 15) which is basically Acuron without atrazine. Acuron Flexi (27, 15) and Zemax (27, 15) which is basically Lumax without atrazine (5) were developed for areas where atrazine generally isn’t used or is prohibited. Without the atrazine (5), less broadleaf weed control is expected.

Phenylurea family (7) – Lorox, Karmex, Spike

Aryloxyphenoxypropionate family – Fusilade DX, Assure II, Fusion, Targa

Imidazolinone family – Arsenal, Plateau, Pursuit, Raptor, Scepter, Contain, Beyond

Cyclohexanedione family – Poast, Poast Plus, Select, Volun­teer, Section, Arrow, Tapout

Figure 3. Giant foxtail, Setaria faberi, a summer annual grass weed. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Figure 2. Velvetleaf, Abutilon theophrasti, a large-seeded summer annual broadleaf weed with relatively long-lived seeds. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Invasive perennials—also known as wandering or spreading perennials—reproduce by one or more types of vegetative structures such as stolons (prostrate stems along soil surface), rhizomes (belowground, root-like stems), bulbs, and tubers, as well as by seed. Stolon or rhizome fragments as small as one inch long can regenerate new individuals, often from depths of 3–12 inches. Thus, a single tillage pass may simply spread propagule of these weeds. The lifetime of an individual plant is long and difficult to delineate owing to its vegetative propagation. Many of our most serious weeds are in this category. Examples include johnsongrass (Fig. 7), Bermuda grass, quack grass, nutsedges, horsenettle, milkweed, bindweeds, and Canada thistle.

Summer Annual Grass Weeds

Figure 5. Wild carrot, Daucus carota, also known as Queen Anne’s lace, is a biennial that remains vegetative and forms a deep taproot during its first growing season. The following spring, it sends up the white umbel inflorescence shown here. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Figure 7. Johnsongrass, Sorghum halepense, a wandering perennial that reproduces through thick, fleshy rhizomes. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Knowledge of a weed’s life cycle and modes of reproduction is especially important in designing effective prevention and control strategies. Weeds can be classified into several major groups based on their life cycles.

Simple perennials or stationary perennials typically have deep, heavy taproots (most broadleaf species) or strong fibrous root systems (grasses, plantain) from which the plant regenerates after the top is destroyed by mowing, cultivation, or winter freezes. These weeds reproduce by seed shed annually from mature plants. Seedlings grow slowly at first, then become strong competitors once established. Simple perennials are most problematic in pastures and perennial crops, though they sometime occur in reduced-tillage annual cropping systems. The lifetime of an individual plant is usually several years. Examples include broadleaf dock (Fig. 6), curly dock (which may grow as a biennial in some areas), dandelion, chicory, and tall fescue.

The best approach to large-seeded broadleaf weed control in corn is to start clean with a burndown application or a burndown application followed by an application of Acuron® or Acuron Flexi corn herbicide. Both Acuron brands contain multiple, effective modes of actions including bicyclopyrone (group 27), which was developed to complement Callisto® herbicide (group 27) and provides improved control of large-seeded broadleaves.

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Cocklebur, giant ragweed and morningglory are often referred to as “large-seeded” broadleaf weeds because they produce larger seeds than their small-seeded counterparts: lambsquarters, marestail and waterhemp. While large-seeded broadleaf weeds tend to produce fewer seeds, the seeds are heartier and often remain viable in the soil for decades. Due to their larger size, the seeds often emerge from deep within the soil profile and present a larger plant mass when they appear, making them more established and difficult to control. To complicate matters, they often appear in flushes, which makes choosing a herbicide with strong residual control a must.

All photos are either the property of Syngenta or are used with permission.

Since large-seeded broadleaves often come in flushes and residual is important to maintain season-long control, we recommend applying Acuron or Acuron Flexi in a 2-pass system: a foundation rate of Acuron or Acuron Flexi followed later by the remaining rate. This approach incorporates multiple, effective modes of action and helps ensure long-lasting residual control.