Controlling weeds in autumn reseeds

Applying a post –emergence herbicide to a new grass reseed is the most cost effective spray you will use on that field. Control of docks, thistles and chickweed etc. is much easier when these broad-leaved weeds are seedlings.

Product choice is based on whether you wish to protect clover in the new ley as some of these sprays are not clover-safe. The clover-safe chemicals designed specifically for use in new leys principally contain 24D and MCPA. Other products containing fluroxypyr as the active ingredient are not safe to use on clover.

There is a practical difficulty with applying sprays to autumn reseeds in that ground can be too wet to travel without causing damage. However if it is at all possible to do so post-emergent broad-leaved weed control sprays should be applied.

Research has shown that the best method of dock control in subsequent years is achieved by applying post-emergent sprays on the original reseeds.

Spraying will also help your grass to establish as the grass plants will not have to compete for space with other broad-leaved weeds such as chickweed or redshank.

In other words applying a post-emergent spray maximises your investment in the new reseed. Compared to other inputs associated with reseeds applying post-emergent sprays are not expensive.

If weeds are not sprayed in the autumn it is possible that they can become dominant in the sward between now and next spring. This could result in the very undesirable situation of needing to re-cultivate and reseed once more next spring!

In order that post-emergent spraying is effective it should be carried out on a well-established, even, and relatively vigorously growing sward.

Carry out spraying 6-8 weeks after re-seeding when there are 3 leaves on the grass and 1 true leaf on the clover. With respect to the weeds these should be actively growing seedlings. For example the dock weed leaf size should be the size of a €2 coin.

Avoid spraying in very dry or cold conditions as uptake will be poor due to poor plant growth. It is also recommended to keep water rates high - 220-350l/ha (20-30 gallons/ acre). As with all cases of herbicide applications remember to follow the product label and to keep to correct cross-compliance and Sustainable Use Directive procedures.