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The purpose of this article is to outline some mechanical methods of controlling weeds in organic cereal crops. What follows should not be regarded as the organic alternative to herbicides, as weed control in biological agriculture is achieved because of the system as a whole. Rotations, manure management, green manures, choice of varieties, etc. . ., all play a part in weed control, a fact which should be borne in mind whilst reading this article.
A full fallow was one of the traditional methods of weed control. Fallowing a field for a full growing season and working it continuously is undoubtedly beneficial. However, it seems prohibitively expensive under today's conditions. Michael Rust in Elm Farm Research Centre's Report No. 1 (The Research Needs of Biological agriculture in Great Britain) estimated in 1980 that a full fallow would cost £91.25 per acre. Such a financial burden rules out a full fallow for most farmers whatever the benefits of weed control and improvement of soil
Fallowing a field for part of a growing season however, is advantageous and less costly. Barry Wookey who farms on chalk and heavy loam in Upavon, Wiltshire uses a bastard fallow to great effect following grass before winter wheat. After a haycut the field is chisel ploughed twice, then chain harrowed twice. These operations are done over a period of time which allows the sod to rot down and weeds to germinate. The field is then ploughed and a seed bed worked down. Ideally, it is then left for ten days before drilling at the end of the first week in October. This allows further weed germination. The whole process is designed to germinate and destroy as many weeds as possible.
There is not enough time between harvest and sowing another winter cereal to have a bastard fallow. However, the creation of a false seedbed on which weeds germinate can be an effective method. Barry Wookey places great importance on allowing time between the creation of the seedbed and drilling the crop to enable an effective weed strike to take place through the drilling and subsequent harrowing operation.
This is the practice of harrowing just prior to the emergence of the crop. The ideal time is about 24 hours before the crop can be seen. Spring Tined harrows, chains and drag harrows can be used. This method is commonly used in Germany. The University farm at Kassel for example blind harrows all its arable crops provided the weather and soil conditions are satisfactory. They stress however, that blind harrowing at the wrong time can produce more weeds. It is necessary to look at the weed seeds and see whether the first tiny white roots have emerged. If they have then the operation can proceed. If not, then harrowing may well cause them to germinate at a time when the emergence of the immature cultivated crop prevents further passes.
Harrowing established crops sounds a little daunting but under the right conditions can be effective with minimal damage. The ideal implement is a spring fined harrow with long, thin tines. A German firm Rabewerk designed the Hackstregel especially for this purpose. Once the crop is established and is at 2/3 leaf stage, then harrowing can be done effectively. Passes can be made across and along the cereal rows. It is a quick operation and provided the ground is not too wet, little damage will be done although the crop does look sorry for itself immediately afterwards. However, wet conditions will cause damage from tractor tyres and many plants will be torn out if the operation is attempted then.
This technique is effective against immature weeds that can be ripped out by the tines. If, however, the weeds themselves are well established, then this harrowing has little effect on them. Details of the Rabewerk Hackstregel can be obtained from Rabewerk, 4515 Bad Essen - Linne, West Germany. The 'Tearaway Weeder' is a similar implement and can be purchased from Organic Farmers & Growers Ltd., 9 Station Approach, Needham Market, Ipswich, Suffolk.
Although inter-row hoeing of root crops is common practice in Britain, very few people use the method in cereal crops. In other parts of Europe however, there is a good deal of experience in hoeing cereals. Precision drilling is vital and the establishment of a good seed bed which the drill can penetrate is a prerequisite for successful hoeing. The British tradition of harrowing seed in can move the seed enough to alter the width between rows and so make hoeing extremely difficult and cause high plant damage. Depending upon the type of hoe used, it is likely to be necessary to use unconventional row spacings.
A mid-mounted tractor hoe is used at Kassel University and elsewhere in Germany. We are also using this approach with Fendt Toolcarrier. This is similar to conventional tractors at the back. However, the engine is placed below the cab, allowing various implements to be placed in the middle of the tractor body. This is especially good for hoeing as the driver can see ahead of him. Further information on the Toolcarrier is available from Bill Bennett Engineering Ltd., Horton, Chipping Sodbury, Bristol. However, as long as the row spaces can be worked out, rear mounted or steerage hoes will also be effective.
It is well to remember in this mechanical age that hand rogueing is still an effective and acceptable method of weed control. The odd dock or thistle or that patch of weeds in a crop of wheat can be the cause of tremendous problems in the future. Localised weedy patches spread into and across the field rapidly. The damage caused by walking into a standing cereal and hand rogueing a weedy area is minimal compared to the problems of allowing the weeds to seed. In some cases, cutting a particularly bad patch may be a wise preventative move.
It is useful to consider leaving a strip along the field sides that can be cultivated during the season. This will provide a barrier against colonisation from the sides. Furthermore, it would enable any hedgerow bottoms to be cut before weeds seed into the field.
All the above are meant to be suggestions, they may not be suitable for all farming situations. There are three points to remember however, that do have general application:
1. Any mechanical operation within a cereal crop inevitably results in some plant losses. Increasing the seed rate is a wise precaution.
2. Do not attempt to grow cereals in a field that is so dirty that the weeds are uncontrollable. A crop that is overwhelmed by weeds is not only uneconomic and unsightly but multiplies the problem and makes it more difficult to solve in the future.
There is no one organic alternative to herbicides. The farming system itself - rotations, manure management, tillage methods, etc., - is the most important factor in controlling weeds on an organic farm.
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