Sulfonylaminocarbonyl-triazolinone family – Olympus, Osprey, thiencarbazone
Cell Membrane Disrupters
Benzothiadiazole family (6) – Basagran
ALS-AHAS inhibitors (2):
Large-seeded summer annual broadleaf (dicot) weeds emerge from slightly deeper in the soil profile (typically 0.5–2 inches), grow rapidly, compete aggressively with crops, and set seed within a single season. They often become major weeds in conventionally tilled agronomic crops like corn, but they may also occur in vegetables. Seed production is less prolific (a few hundred to a few thousand per plant) but seeds of some of these weeds may survive for decades in the soil. Examples include velvetleaf (Fig. 2), common cocklebur, and morning glory.
Winter annuals emerge in late summer or fall and are winter hardy in all but the coldest parts of the United States. In cool–temperate regions like the mid-Atlantic and southern New England, they typically overwinter as low, compact plants or rosettes, resume growth in late winter or early spring, form one or more flowering shoots or stalks, and reproduce by seed in late spring or summer of their second season. In warmer climates from the Gulf Coast up into Oklahoma, they may grow actively through the winter. These weeds are most problematic in winter and early spring vegetables and in winter grains; they have little direct effect on warm season crops. Examples include wild mustards, common chickweed, horseweed, henbit, and purple deadnettle (Fig. 4).
Large-seeded Summer Annual Broadleaf Weeds
Figure 6. Broadleaf dock, Rumex obtusifolius, a simple perennial with a deep, heavy, winter hardy taproot, from which the weed’s foliage and flower stalk emerge each growing season. 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.
Small-seeded summer annual broadleaf (dicot) weeds emerge from seeds at or relatively near the soil surface (mostly from the top inch of soil), grow rapidly, and produce prolific amounts of seed within a single season. They are often major weeds in vegetable crops. The seeds usually germinate in response to one or more stimuli associated with soil disturbance, such as light and increased concentrations of nitrate N. When buried deeper in the soil, the seeds of many of these weeds remain dormant but viable for years, germinating when brought to the surface again by tillage. A few, such as galinsoga, have short-lived seeds that will deteriorate when buried. Examples of small-seeded summer annual broadleaf weeds include pigweeds (Fig. 1), common lambsquarters (Fig. 1), common purslane, galinsoga, and smartweeds.
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.
Caption: Urbana, Ohio: Acuron applied pre-emergence at 2.5 qt/A with 1 qt/A atrazine in a field with a history of giant ragweed pressure. Application made on May 28, 2016. Photo taken 88 days after treatment.
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.