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Lecture 8: Postemergence Broadleaf Weed Control in Landscapes

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Selective: Few Options

  • Basagran, Goal, Lontrel, Image, Asulox, Casoron

Non-Selective:

  • Roundup-Pro, Finale, Scythe, Reward

Selective Postemergence Broadleaf Weed Control

  • Limited product selection
  • Most effective only on seedling weeds
  • Most have a limited spectrum of weeds controlled
  • Generally not particularly useful in landscapes, except for Lontrel, Casoron & triclopyr

Basagran, Goal, Image and Asulox have limited uses in landscape plantings because they injure many ornamentals and must be used as directed applications. Since directed applications are required – why not use a broader spectrum herbicide such as Roundup-Pro? However, Lontrel and Casoron are used in landscape plantings for specific purposes. Casoron controls perennial broadleaf and grass weeds that no other selective herbicide can control. Applied in the winter, in a granular form, it can control many weeds including mugwort, horsenettle, bamboo, and Florida betony. However, it can also be very injurious to any herbaceous ornamental, many woody ornamentals and turfgrasses. Lontrel selectively controls legume and aster weeds. Directed applications around woody ornamentals are recommended. But, avoid herbaceous ornamentals and woody plants in the legume family (Fabaceae) such as honey locust, red bud and mimosa.

Lontrel / Stinger (clopyralid)

  • Postemergence control of Legumes, certain Asters and a few other species
  • Labeled for use in Christmas trees, and field-planted woody ornamentals
  • Key weeds controlled: Legumes and asters incl. clovers, vetch, black medic, thistles, goldenrod, nightshades, groundsel, galinsoga
  • Suppression: mugwort, smartweed
  • Not controlled: evening primrose, plantain

Lontrel — Do not use on or near:

  • Legumes (Fabaceae): redbud, locust, mimosa, or
  • Asters / composites (Asteraceae): sunflower, daisies, artemesia, liatris, or
  • Linden (Tilia sp.). Some damage has been observed on crepe myrtle

Pre/Post Weed Control With Casoron (diclobenil)

  • Controls many perennial, hard-to-kill weeds **
  • Safe on certain established trees & shrubs
  • Significant potential to injure non-labeled species – including hemlock, fir, & spruce
  • Apply in late fall or early winter due to volatility **
  • Residual lasts until early summer (then late season weeds can emerge)
  • Other trade names: Dyclomec, Barrier
  • Positional selectivity (basically non-selective)
  • Recommended dose: 2.3 to 3.4 lb / 1000 ft2
  • Weeds controlled: Florida betony*, dandelion, red sorrel, clover, mugwort*, Equisetum*, winter annuals, and most cool season perennials
  • Weeds suppressed: bindweed, nutsedge, quackgrass, and other rhizomatous perennials*
  • Weeds not controlled: most woody weeds such as black locust sprouts, mulberry, catbriar, brambles and late germinating summer annuals
  • It is fairly expensive

Triclopyr (Ortho Poison Ivy / Oak Killer, Brush B Gon, Brush Control, etc)

  • Same active ingredient as Garlon 3A – used for brush control on roadsides and in conifer forests
  • Better than many other herbicides for controlling woody weeds – woody vines (such as poison ivy, VA creeper, Japanese honeysuckle), tree seedlings / sprouts, etc.
  • Synthetic auxin. Labeled for broadleaf weed control in turf under other trade names
  • Caution – this will kill desirable trees, shrubs and flowers.

Study Questions:

  1. Contrast selective vs. non-selective.
  2. Why do we rarely use Basgran, Goal, Image and Asulox, in landscape bed maintenance?
  3. When would you use Garlon?
  4. On what types (families) of weeds is Lontrel particularly effective?
  5. Name a few common ornamental species that are likely to be injured by Lontrel.
  6. What kinds of weeds isCasoron used to control?
  7. Name at least 3 species that Casoron controls.
  8. Name three reasons Casoron is not more widely used.