Troublesome Grassland Weeds That Will Soon Need Treating

Now is the time to consider grassland management and control of some key weeds.

Chickweed – The early starter

Chickweed is likely to be the earliest broad-leaved weed to be emerging in grassland as it can grow at very low temperatures. It can use nitrogen in the soil very rapidly and can smother out grass very early in the season. Its prostrate growing habit allows it to rapidly colonise any gaps in the sward. It will aggressively compete with grass species for space, light, water and most importantly nutrients and so it needs to be controlled.
Chickweed will be found in new leys and established grassland. It can be particularly problematic in new leys which were untreated prior to the winter. Young grasses are normally dormant at the time that chickweed growth commences in the spring, so chickweed has a head start of several weeks! Controlling chickweed in young leys allows productive grasses to tiller out. In this situation, it is important to choose a herbicide which can be used early in the season to minimise the damage that chickweed will do. Many herbicides do not work well in cooler conditions, or in fluctuating temperatures where the temperature overnight is low. However, Envy® is not affected in this way which means it can be used as early as 1st February when conditions allow. Depending on weed size and density, Envy® can be applied at between 1.0 and 1.5L/ha in 200L water in new leys. It is very safe to grass and has a stock exclusion period of just 7 days. However, it will kill clover so where there is a heavy population of chickweed, spray the ley and plan to re-introduce the clover 12 weeks later.

Untreated                                       Treated with Envy®

The picture shown above shows a ley sown in June 2019 which was treated for chickweed control in July 2019 with Envy® at 1.0 L/ha in 200L/ha water. The photo was taken in September 2019. Whilst Envy® did kill the clover present, as expected, the chickweed killed most of the clover and the grass in the untreated part of the field.

Chickweed is also a big problem in established grassland. Where late autumn grazing has caused poaching or where the grass is killed by slurry smother and leaves a bare patch, chickweed will be the first of the broad-leaved weeds to colonise the bare soil. Over-seeding may be necessary in situations where chickweed has become strong and smothered larger areas.  If other weeds are present, Envy® can be applied in established grass at up to 2.0L/ha in 200l/ha water.

The picture above shows how chickweed will colonise an area such as a poached area.

Each chickweed plant can produce up to 2500 seeds and it only takes five to six weeks from germination to seed dispersal. Plants are capable up to five generations a year in good conditions and seed buried in soil can remain viable for more than 5 years. It’s an important weed to control.

Envy® can be sprayed until the end of November, so it is also a great product to protect new-sown leys sown now onwards.

Envy® has excellent grass safety, is rainfast in two hours and has a stock exclusion period of just seven days. Envy® is also an excellent herbicide for controlling buttercups and dandelions.

Weed control in new sown leys

Reseeding is an important part of grassland management. However, it is expensive with costs typically of £500/hectare being quoted, meaning that it needs to be done successfully.

Grass re-seeds typically take place from mid-March onwards and spraying early in the life of a sward will ensure a clean start and allow grass to establish quickly without competition from weeds. It is more economical and effective to treat weeds at this seedling stage rather than when they are large and established.

Many grassland herbicide product labels stipulate that grass should be ’established’, i.e. over 12 months old at the time of treatment. The number of available herbicides for newly sown leys is limited. Leystar® and Envy® both have approval for use in new sown leys. Leystar® is a particularly good choice for spring sown leys, as its broader spectrum means that it controls important spring germinating weeds, such as thistles, whilst its very low dose rate of 1.0 L/ha makes it very cost effective. If docks are present and are growing from root fragments rather than seed in the new ley, then the higher 1.5 L/ha rate of Envy® might be more appropriate.

For best results apply when weeds are small and actively growing.

Both Envy® and Leystar® will kill clover, so if having clover in the seeds mixture is important, it may be necessary spray out the weeds first and then stitch clover back in after 12 weeks.

Plan Dock Treatments Ahead of First Cut Silage

Farmers should spray dock infestations in silage leys in April, three to four weeks before the mower goes in. Most grassland farmers have a target date for first cut silage, but they may not have a similar date in mind for an early season dock spray. 

Reasons for controlling docks before the 1^st silage cut include:

• Docks are usually healthy and showing rapid growth, so translocation of herbicides is optimised
• Grass is better able to recolonise small bare patches following weed removal at the start of the growing season
• Extra grass yield can be achieved for the whole growing season
• Grass silage without weeds will produce better quality silage than grass with weeds present

If a spray contractor is used, a date should be booked in now to avoid missing the ideal spray opportunity ahead of silage-making.

Docks have only 60-65% of the feed value of grass and can restrict silage fermentation, leading to lower dry matter intakes.

It can be tempting to spray docks when they are too small. They may be healthy and actively growing, but in established grass they are most likely growing from established roots. It is important to get enough herbicide onto the leaves to kill the roots. This can’t be achieved if the docks are too small.  The ideal time to spray docks with an effective product that kills down to the roots, such as Doxstar® Pro, is when the plants are actively growing, the size of a dinner-plate (approx. 20cm across) and before they begin the flowering process. Spraying three weeks before cutting allows the spray to kill the docks and for the leaves to decay ahead of the silage cut, meaning that they won’t be taken into the clamp causing a reduction in silage quality. Spraying early in the season also means docks are likely to be at the same stage of growth, making it easier to treat them effectively.

Apply Doxstar® Pro at 2 litres/ha in at least 300 litres of water, or up to 400 litres of water if dock numbers are high or the grass sward is particularly dense. Water volume is very important to achieve good coverage of the weeds. It is very tempting to reduce water rates, but this is likely to result in shorter term dock control. If the water rate is too low, the chemical may scorch the weed leaf and this will potentially reduce or even stop the uptake of the chemical into the leaf, which means it will never get to the roots resulting in top-kill only.

The picture above shows a dock at the ideal size (20cm across) for treatment

Buttercups

Controlling buttercups can be an important component of rejuvenating tired old grassland and to lengthen the life of the pasture.

Buttercups seem to be present in ever-increasing numbers in permanent pasture. These are often in fields which are not due for a full re-seed either in the short or mid-term. They add to the demise of the grass species present and prevent any other remedial activities. Control of buttercups and other weeds, such as dandelions and daisies, in these fields can both improve the quality of the existing grass and offer an opportunity to stitch in some new grass resulting in an improvement in the quality and extended life of the pasture.

Whilst the optimum time to control buttercup is before they flower, all is not lost if it is treated post-flowering. Corteva Agriscience looked at this precise issue and found that a post flowering treatment still gave good levels of control.

Untreated - Photo Taken June 2017

Treated with Envy® 2.0L/ha – 02.08.17 - Photo Taken June 2018

Dandelions

April is an ideal month for controlling dandelions in grassland where they are unwanted. Dandelions are one of the earliest weeds to be seen in pastures.

Dandelions typically come into flower once temperatures start to rise in early spring, and it is during flowering that their presence is noticed. Trials work we have undertaken in the last few years has shown that, just like with buttercups, you will get good control of dandelions post-flowering.

If dandelions are the main weed to be controlled, use Envy®. If there is a mixed population of dandelions and docks, use Doxstar® Pro.

Spot spraying grassland weeds

Weed control in paddocks and other specific problem areas will often require use of a knapsack sprayer – typically when the weed infestation is 5% or below. Grazon® Pro is the market leading knapsack applied weed control. It kills down to the roots, meaning it gives lasting control and lessens the need for repeat spraying. Grazon® Pro controls docks, thistles, nettles, brambles, gorse and broom. Use Grazon® Pro at 60 ml per 10L water.

You will find all the products discussed here, and more, available from Welland Valley Feeds. Information sheets are also available in store. For further specific advice on your weed control scenario, please contact Rob Sheets – Agrovista agronomist on 07768540953.

Use plant protection products safely. Always read the label and product information before use. For further information including warning phrases and symbols refer to label.

Corteva Agriscience Limited, CPC2 Capital Park, Fulbourn, Cambridge CB21 5XE. Tel: 01462 457272.

®, ™ Trademarks Corteva Agriscience and its affiliated companies. All other brand names are trademarks of other manufacturers for which proprietary rights may exist.

Doxstar® Pro contains fluroxypyr and triclopyr

Envy® contains fluroxypyr and florasulam

Grazon® Pro contains clopyralid and triclopyr

Leystar® contains fluroxypyr, clopyralid and florasulam