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:
- 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.
- 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
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