Should I plough in my heavy blackgrass burden?
I am a farmer in Kent. My land is a mixture of light land on one side of the farm, and heavy clay on the other. Last year, with the wet autumn, the sprayer would not go near the field. As a result, weeds, especially blackgrass, have really got going.
How can I get rid of these weeds without using too many sprays, and should I definitely plough, for at least this year (at the moment the field is in untouched stubble).
Where blackgrass is the main (key) target, autumn control is essential. The single most important timing is when the majority of blackgrass are at the 1-2 leaf stage (none larger than 3 leaves).
A well-timed application of a reliable and effective contact and residual herbicide mix should give good control. Hawk (clodinafop-propargyl + trifluralin) with Lexus (flupyrsulfuron-methyl) is a good example.
Where blackgrass resistance is an issue, the above should be used as part of a sequence, including a pre-emergence application of either Avadex (tri-allate) or Crystal (pendimethalin+flufenacet).
Application timing where resistance is present is THE critical issue. Trying to control resistant blackgrass in the spring (after February) is usually a waste of time.
These options will also control most of the other commonly occurring autumn germinating grass and broad-leaved weeds.
Ploughing is not essential for blackgrass control, but can be a useful tool where there has been poor control in the preceding crop, resulting in a high level of seed return.
Full inversion will bury seeds below their 1-2 inch germination depth. Assuming good control is achieved in the current season, or where previous control was good, reduced cultivation techniques can be used.
It is essential in such situations to use stale seedbed techniques in order to allow blackgrass to germinate and then be removed before drilling using a total herbicide such as glyphosate.
Whatever the situation, a combination of cultural techniques (e.g. rotation, drilling date, cultivation) and chemical mixes/sequences are the best long-term strategy for blackgrass management.
If you are just starting with lo-till then I would plough, on the understanding that what you are about to bury is less than what you could potentially bring up.
If you are already in lo-till I would plough as well, BUT with hindsight I would advise you do things differently in future as a routine.
If you have a high seed return in any year then you need to adopt a strategy to lower the seed bank at every opportunity.
From what you have said I am assuming that this field is going into a spring crop (stubble untouched).
I would look to cultivate as soon as possible after harvest to allow germination of these weeds and spray them off repeatedly with low rates of glyphosate (which is very cheap now) to lower the seed bank.
This would then allow you to plant your spring crop confident that you have reduced the weed problem.
My advice would be to avoid lo-till if you have a grass weed problem unless you are prepared to work at the system.
Conventional tillage will keep the lid on the problem, but in my opinion will never get rid of it. But a well managed min-till system, using effective stale seed beds, rotating cereals with broadleaved crops and the occasional spring sown crop, can go a long way to getting the problem back to manageable levels again.
It takes time and patience. Further information on the subject is available from the Soil Management Initiative (SMI).
Ask for A Guide to Managing Crop Establishment. It covers weed control and gives detailed case studies of farms where lo-till has been used to overcome grass weed problems.
You could also try Revised Guidelines for Preventing and Managing Herbicide-Resistant Grass Weeds on the Home Grown Cereals Authority website.
Spray off with glyphosate & plough. Its too late to start min-tilling and waiting for a greening up.