Now is an ideal time to assess and plan a, sometimes overlooked, key element of grass growing– weed control, writes Jack Friar, Beef & Sheep Adviser, CAFRE
Economic losses caused by weed infestation in grass swards, for example chickweed, thistles and docks, include competition with grass for nutrients, light and water, reduced area availability for grazing and lower palatability and quality of silage or hay.
Weed control
As ground temperatures start to rise, weeds will start to grow and reach the optimum stage for control quickly. You need to be prepared to implement control at the correct time to improve the success rate.
A good start is to think back to last year about what fields had a weed problem. You should walk these fields and assess them for signs of weed growth again.
Weed infestations should be measured and as a general rule of thumb, for every 1% infestation of the sward, such as thistles and docks, grassland productivity and forage quality will be reduced by 1%.
At weed infestation levels between 10%-20%, or higher, action should be taken.
The best defence against weeds is ensuring an establishment of a well-managed, dense sward making it more difficult for weeds to establish.
Ensuring soil pH is it least 6.3 and phosphorous (P) and potash (K) levels are at the correct indexes play a crucial role in promoting grass growth. Avoid over or under grazing and poaching of ground as these provide ideal conditions for weed seeds to germinate.
Topping weeds is a short-term management practice, and can stimulate active regrowth which results in the problem becoming worse in the longer term.
Docks
The most common and troublesome weed in grassland, it thrives on fertile ground, especially soils with high potash levels.
One plant can produce up to 60,000 seeds a year, which can remain viable within the soil for 50 to 70 years. Docks have only 65% of the feed value of grass and are unpalatable to livestock. Cutting will not control them as new shoots will regenerate.
Spraying can be an effective treatment, with best control being achieved when docks are actively growing and transporting nutrients to new foliage and roots (late April or early May and again in late August or early September).
Repeat sprays in same or subsequent years with products based on fluroxypyr and triclopyr (such as Doxstar Pro) give much better control, but care must be taken not to exceed maximum annual dose rates. Clover safe sprays are available where clover establishment and protection is important.
Chickweed
There are two types of chickweed, common chickweed (most commonly found) and mouse-eared chickweed. Common chickweed has a smooth leaf and mouse-eared chickweed has a larger leaf with a hairy surface and stem.
Both types of chickweed will be an issue in swards this year due to the wet autumn and winter months and cool temperatures during the start of 2020 that benefitted the growth of chickweed more than grass.
Products containing both fluroxypyr and florasulam (such as Leystar and Envy) are good to use during early cooler spring conditions (5°c) or when temperatures rise just straight fluroxypyr is an option.
These products will not stunt the growth of immature grass plants, again these are not clover safe. Clover safe options are available.
Bare patches left after removal are ideal for more weed seeds to germinate, so ensure the grass sward is established quickly to block out chickweed and other annual weeds from establishing.
Thistles
Thistles are common in older swards that are low in nitrogen and phosphorus, but high in potash. The two types of thistles are creeping (perennial) and spear (biennial).
Best control is achieved when the majority of plants are actively growing at the full rosette stage.
Products based on triclopyr and clopyralid (such as ThistleX) will give a high degree of root kill or alternatively products containing MCPA may be applied, though this will give good control of leaf growth but limited root kill.
None of these products are clover safe. Clover safe options are available.
Ragwort
Ragwort is poisonous to livestock. Small infestations can be managed by hand-pulling and ensuring root stock is removed.
With regard to large infestations, spraying is highly effective. Ragwort should be sprayed in early spring, or as soon as there is active growth. Leaving it too late may let the plants start to shoot and control will be slower.
Once sprayed, ragwort is more palatable to stock, so ensure ground is not grazed for at least 4 – 6 weeks after spraying to allow poisonous decaying material to die.
The product Forefront is effective against a wide range of grassland weeds, but must be used only on grazing ground, and following manufacturer’s instructions.
Advice
Before using any plant protection products, consult a registered agronomist for the latest information on product availability and application advice.
Anyone supplying plant protection products will have access to a qualified Adviser at the point of purchase, either directly or by phone. There will also be a helpline number on the label for technical queries.
Always read the label and product information before use and adhere to label recommendations with regard to product application rate, cutting and grazing intervals etc.
Local supply businesses have put in place good working procedures which greatly reduce COVID-19 risk and enable you to purchase, collect or have farm supplies delivered. It is important that you work with your suppliers and avoid panic buying or stockpiling.
Anyone who uses pesticides for use in agriculture is legally required to have a Certificate of Competence in the Safe Use of Pesticides (PA1, PA2A Boom Sprayer, PA6A Knapsack etc.). Contact CAFRE Industry Training on 028 9442 6880 to register your interest on a pesticide training course.
