Problem Weed Series for Orchard & Vineyards - Quackgrass

Problem weed: Quackgrass

Other names: Agropyron repens, couch grass, quitch grass, twitch or twitchgrass, devil's grass

Growth habit: Perennial, with extensive underground growth in spring and fall. Tends to grow in ever-thickening patches.

Spreads by: Seed or underground rhizomes. Cultivation often breaks rhizomes at the nodes and starts a new patch where the broken piece falls.

Reasons for concern: Very competitive with crops. Crop losses from 25 to 85% have been reported from the competition from quackgrass. It grows in all soil types, and most crops, infesting more than 50% of all farmland in Canada.

May be confused with:

1. Smooth brome grass - another common perennial grass in orchards, and a species that is often used in pastures. However, smooth brome has a denser seed head with branches, and no auricles. Quackgrass has distinctive clasping auricles wrapping around the stem, and a slender, unbranched seed head.
2. Wire-stemmed muhley which is also perennial, but which has small scaly rhizomes in a tangled mass growing from its crown, instead of the long, much branched rhizomes that quackgrass is known for. Wirestem starts growing much earlier in the spring and grows in very dense patches. As its name suggests, the stems tends to be sharp and wirey, especially when it is mown. Also, wirestem tends to require higher rates of glyphosate to control it.

Chemical control:

• Note that quackgrass in orchards/vineyards has undisturbed root systems and will be more difficult to control than quackgrass in cultivated fields.
  
• A systemic herbicide like glyphosate or amitrole (for apples only) is needed for long term control. Spring or fall applications work best applied at 4-6 leaves. Note the mid-range rate of glyphosate (4.75 to 7 L/ha) required for quackgrass. Lower rates will give one season's suppression only.
  
• Some soil-applied herbicides (where registered) like simazine (at higher rates), Casoron, Kerb and Sinbar can also suppress quackgrass.
  
• Mid-summer burndown herbicides only work well if quackgrass is actively growing. In dry summers, it's better to mow and wait for fall regrowth
  

Cultural control: Mechanical control methods (eg cultivation, flaming,) can reduce quackgrass if done early, thoroughly and repeated frequently. Mowing needs to be done frequently, and will often encourage other more desirable grass species to flourish. Mulching can be effective on quackgrass if applied very thickly and maintained at this level for several years.

Caution: Use of cultivation can spread quackgrass rhizomes over large areas very quickly. Avoid cultivating through patches of quackgrass or do them last, and clean equipment thoroughly.

References and Pictures:

• Ontario Weed Gallery online
• Publication 505, Ontario Weeds, p. 31

Related Links

• Ontario Weed Gallery online
• Publication 505, Ontario Weeds
  

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