PASTURE Topics- WEEDS
The first addition of pasture topics will look at weeds in your pastures. What are some of the common weed types, why they grow and how you can control them. This time of the year is a great indicator for weeds and assessment of how good your pastures are and plan to eradicate the weeds and possibly sow some more preferred species in their place next autumn.
Weeds are really an indicator plant. They can indicate problems such as poor soil fertility and soil structure, soil acidity, poor drainage and possibly salinity. They can become a problem in a pasture due to cultivation, hay cutting, overgrazing (common with horses) and even under grazing. They can also appear due to climatic reasons such as a wet summer or drought.
Common grass weeds.
Barley Grass - often occurs when pastures are bare, with patches of soil, grows well with lack of competition from preferred species of pasture plants. They are very quick to germinate in the autumn, which at this stage are the first green pick, it is later on in spring /summer they are a real pest. They are a high fertility weed so love manure, high organic matter, gateways etc.
What can you do to control - Don't bare your pastures out through overgrazing
- Stop the seed head setting seed in the spring/summer. The seed head can be nasty as it can get in the horses eyes or stuck in the throat. Light rates of glyphosate when the seed head is green in the spring is a great way to control the spread of the weed. If you were to do this for 1-2 years and plant competitive pasture species you can beat barley grass quite easily.
- You may choose to slash the seedhead in the spring, the barley grass plant is very smart and just keeps trying to set seed closer to the ground, every time you cut it. If you have old dry seed heads run a harrow or mesh over the pasture to smash the seedhead to the ground so to avoid problems for the horse.
Bent Grass - is a sign of low fertility in the pasture. Soils are often acid (low pH), and the paddocks are poorly drained and may suffer from waterlogging. It is a matted type of weed which can take over a pasture. Undergrazing a pasture can cause it to take over and also can be spread by cultivation.
What can be done to control bent grass - firstly fertilise your pastures to get fertility higher - the main elements are phosphorous and sulphur. This may also involve applying lime to improve the soil pH.
- A further method of control is like barley grass is to spray the weed in end of October early November with glyphosate at light rates to control seedset of the grass. Then back it up with heavy grazing, horses are very selective so this might need some other animals to help like sheep or cattle.
- If really bad a pasture renovation program is the best form of control. Spray with heavy rates of glyphosate in the spring/early summer, then cultivate (dead material at this point so won't spread weed) and sow in the autumn with improved pasture species and fertiliser.
Fog Grass - again a low fertility weed, acid soil weed. Loves wet waterlogged areas, very little nutrition value. This weed does send out toxins to prevent other grass species growing around it. It can be controlled quite easily with improving soil fertility with fertilisers and sowing preferred competitive pasture species.
What can be done to control fog grass – spray top pastures in the spring with glyphosate to stop it setting seed
- fertilise pastures
- pasture improvement through sowing improved pasture varieties
- always do a soil test to gauge your soil status in regards to soil fertility and pH
- slash or graze heavily spring summer
Silver Grass - again often occurs in a poor pasture with low fertility. It comes in with overgrazing and takes over bared out areas. Very competitive grass.
Control of silver grass - spraytop in the spring
- improve soil fertility with fertisiliers
- resow paddocks to improved competitive pasture species
Paspalum - active summer rainfall weed. Loves heavy wet soils with poor drainage. Loves to be undergrazed. Stock can get the staggers from a fungus that can appear on this plant at certain times of the year. Very common in irrigation areas.
Control of paspalum - graze heavily over spring and summer (may need cattle or sheep for this)
- spraytop to stop seed set.
- pasture renovation by sowing competitive grasses to compete against it
Broadleaf weeds
Bathurst Burr - a summer active weed that germinates in the spring, grows in areas where stock heavily use, waterways, dam banks, flood ways, fence lines. It is a nasty weed which has spikes and can get stuck in horses legs, vehicle tyres and anything that touches it.
Best control - is spray by spot spraying or pull plants out and dispose of them
Capeweed - very common broadleaf weed with a distinct yellow flower. Loves bare areas which it quickly takes over. Grows well where ever there is high fertility . Spreads easily by overgrazing paddocks and cultivation. It also is a remover of calcium from the soil
Control - the best form of control is selective herbicides in early winter. Be careful of witholding periods of sprays that you do not introduce the horses back into the pasture following spraying as nitrate poisoning can occur.(nitrate levels in the plant increase dramatically when sprayed and can be toxic to horses)
- the other form of control is sowing of improved pastures to compete against the weed
Heliotrope - summer active weed that occurrs due to lack of competition by other species
- it can be harmful to the liver which can result in jaundice and copper toxicity control - spray with selective herbicide
- sow improved pastures to compete against it
Dock - occurs mainly in waterlogged soils with poor drainage or heavy clays
- it has a large tap root which helps its survival.
- if stock do graze it it can induce calcium deficiency control - can be sprayed with selective herbicide
- pasture improvement
Sorrel - generally it is a weed of low soil fertility and acid soils, and lack of competition in the pasture
- is very bitter for livestock to eat so they will avoid it where possible control - improve pH of soils through liming (find out through doing a soil test)
- improve soil fertility
- spray out and resow improved pasture
Onion Grass - occurs where there is very low soil fertility (generally phosphorous)
- can cause stomach concerns if horses are forced to graze it as it balls up inside the stomach like a ball of string.
control - high rates of fertiliser (phosphorous and sulphur base) to improve fertility levels in the soil
- re sow paddocks to improved pastures. If pastures have a good mix of perennial pasture species but a lot of onion grass both fertiliser use and selective herbicides can improve the pasture quickly without having to re sow
Wild Raddish/Turnip - can grow quite and tall with a white (raddish) or yellow flower (turnip)depending on the variety.
Generally not toxic to horses unless it is sprayed and horses are forced to eat it, they may suffer from nitrate poisoning.
If allowed to set seed the resultant seed can last in the ground for years. (upto 25yrs)
Control - again improved pastures
- selective herbicides
- if only a few plants simply pull them out and remove from the paddock
Deadly Nightshade - there is quite a lot around this year with ample moisture
- again a summer active weed that can grow upto 60cm tall.
- the important thing to watch is that horses do not eat the berries that can be toxic
Control - again competition from other plants
- herbicides
The next issue will look at soils and pasture species for horses.
