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Grass-weed Problem
The Perennial Grass-weed Problem
Perennial grasses have different patterns of growth and maturity, but all survive over winter because of perenating organs packed with carbohydrates that support new foliar growth each season. These can take the form of rhizomes, bulbils or stolons.
Many have sufficient reserves to survive for years underground, and can re-establish when brought to the surface by ploughing.
Couch
Couch is a serious threat to wheat yields. There are two true Couch species among the many grasses collectively referred to as Couch grass.
Common Couch, also known as Scutch, Rack and Twitch, has deeper roots and greater drought tolerance than most other perennial grasses. It tends to mature later, and its large underground rhizomes allow it to survive between seasons.
Onion Couch is a rapidly spreading perennial grass, reproducing by both seed and bulbils which remain viable in soil for up to two years.
Couch identification
Common Couch and Onion Couch look remarkably similar to Yorkshire Fog, Creeping Soft-grass and the Bents. But there are clear differences in the way these grasses grow and survive from one season to the next.
Risk assessment
Where perennial grasses are present in the spring in a winter wheat crop, consider using Monitor to reduce yield loss and ease harvesting. The product suppresses Common Couch and Onion Couch.
Couch risk factors
| LOW RISK | MEDIUM RISK | HIGH RISK | VERY HIGH RISK | |
| Couch Population |
None |
0-10 shoots/mē |
10-15 shoots/mē |
>15 shoots/mē |
| Previous crop |
Cereals |
OSR, linseed, peas, beans |
Sugar beet, potatoes, veg. |
|
| Present crop |
Cereals |
Winter OSR, beans |
Spring linseed, OSR, peas, beans |
Fallow |
| Next crop |
Cereals |
Winter OSR, beans |
Spring linseed, OSR, peas, beans |
Fallow, Sugar beet, potatoes, veg. |
| Soil type |
Heavy |
Medium |
Light |
|
| Cultivation practice |
Plough |
Direct drill |
Reduced cultivations |
|
| Weather Autumn/winter 2 years ago |
Dry |
Moist |
Wet |
|
| Weather last Spring/Summer |
Dry |
Moist |
Wet |
Couch management
The ideal time to control perennial weeds is between July and October, when they are most susceptible. The optimum timing for Common Couch is usually late September to November, when new rhizomes have come to the surface and produced leaves. Use Roundup at this stage to ensure good control.
Rhizomes with too few leaves at the time of spraying may not be eradicated, and further rhizomes may emerge. Use Monitor in the spring to suppress Couch growth.
Monitor reduces Couch by 80% of its volume, and gives a yield benefit in the year of treatment. The long-term efficacy of Monitor depends on the infestation level and the Couch growth stage at application, as well as the spraying conditions.
For best results, apply Monitor between crop GS 23 to GS 39 in a weed control programme containing Roundup. The efficacy of follow-up Roundup treatments is not compromised by using Monitor.
