Product choice and timing are key when controlling docks

Dock leaf

Sinéad Devaney

June 03 2019 10:06 AM

Docks must be the most despised and best known persistent weed problem on many intensive grassland farms.

Docks will seriously limit grassland output and productivity unless controlled.

A heavy infestation of docks in a silage crop can reduce yields by up to 10%. Docks have a wonderful survival mechanism. The dock has huge root reserves; its tap root can reach a metre deep in mature plants.

Seed Production & Survival: It has been estimated that one mature dock plant can produce up to 60,000 viable seeds per year. The other extraordinary fact is the longevity of dock seeds. Scottish data indicates that dock seeds can remain viable for 50 to 70 years if buried in soil and will germinate when conditions of light and soil temperature are suitable.

In Grassland: Best control of docks will be achieved in good growing conditions when docks are actively growing and nutrients are actively being transported to new foliage and roots.

If seed stalks are seen on the plant or if the dock has diseased leaves or is under pest attack it is better to cut/top or graze and allow re-growth of the docks before applying chemical.
Treat when the docks are actively growing, in the rosette stage up to 25cm high or wide.
Do not apply chemicals in a period of drought as the chemical will not be taken up by the plant leaves in sufficient quantities.
Use the highest water rates on the manufacturer’s label for best effects.
Allow adequate time between spraying and cutting silage for the herbicide to work.

Season Long Dock Control

Use of herbicides based on aminopyralid, dicamba, triclopyr, fluroxypyr, etc., (Dockstar Pro, Forefront T, Bandock EW, Starane 2, Reaper etc) will give at least season long control (possibly 2-3 years significant reduction in numbers and re-growth of docks) plus a wide range of common grassland weeds. These products will eliminate clover.

Dock leaf

Where Clover is of consequence

Eagle or Prospect may be applied. These products do not harm clover but Prospect may have some effect on the constituent grasses in the sward. These are best applied in good growth conditions and will give season long control. Use highest label rates where rootstocks are well established.

Control in a Reseed

Teagasc trials have shown that longer term (up to 5 years) control of docks can be achieved by applying a suitable herbicide onto small docks shortly after re-seeding. Applying the herbicide at this stage of the docks development results in almost complete elimination of the docks. The trials have also shown that docks that emerge in the following years rarely establish due to competition from the grass, as the dock seed does not get the correct light signal to germinate. Always spray seedling docks at 4-6 weeks after re-seeding.

Cultural Control

The best control of all for docks is good grassland management. Maintaining a dense, leafy grass sward will smother out emerging docks. In this regard, having a fertile soil with adequate levels of Nitrogen, Phosphorous and Potassium along with a suitable pH for grass growth is hugely important. Avoiding poaching and overgrazing will limit the space for docks to emerge. Tight grazing and heavy regular silage cuts leave open swards. Open swards promote docks. The dock seed needs light, air and plenty of nutrients to establish. A harvested silage field is a good environment for the dock. Docks are associated with slurry. Teagasc research has shown that docks germinate and thrive better where there are high potassium (K) levels. Regular slurry applications build up or provide K for dock establishment.

Sustainable Use Directive

Finally ensure you are cross compliant when using sprays. Only a registered Professional User using a registered sprayer is approved to apply pesticides. Spraying guidelines must be followed and the spraying details must be recorded. You may be required to supply this information if you are selected for a cross compliance inspection.

The following precautions should be taken with all pesticides:

Read and follow the product label
Don’t spray if rain or strong wind is forecast in the next 48 hours
Mark out a minimum 5-metre buffer zone from any river or lake
Containers should be triple rinsed and washings put in the sprayer
All sprayers that are more than 5 years old having a boom width of >3m, must have passed a Pesticide Application Equipment Test by a DAFM approved inspector.

Sinéad Devaney, Teagasc Adviser, Galway/Clare Regional Unit