Black-grass continues to be a key issue for UK wheat farmers – the first step in controlling the problem is understanding the scale and spread of the problem.
You can use field mapping to identify all areas of black-grass, and see the nature, extent and precise location of weeds throughout your farm.
There are different methods of field mapping – the best option will depend on the size of your farm and resources available.
The standard way of mapping is by walking fields and marking on plans where there is significant black-grass.
As it is not viable to count black-grass in every spot, you need to make a visual assessment of how much there is. Usually, a 3- or 4-point scale, from zero to high-level, is the easiest way to mark out the map. Take care to identify any particularly bad patches, as these should probably be controlled with robust measures such as patch spraying (link to article) or hand-rogueing.
Once completed, you should ideally transfer the maps into your farm management software.
The main drawback of mapping by hand is the time it takes and the reliance solely on your judgement to assess black-grass. However, many farmers have mapped this way for years to good effect, so don’t automatically assume you need a technological solution. On larger farms, though, it may not be realistic to map the whole area by hand, so technology such as drones is an alternative option.
Mapping black-grass infestations using technology means larger areas can be mapped with much more speed and accuracy than doing so on foot, or from personal memory.
Technology in this area is moving at a rapid pace, and software can now pick out black-grass in a field of wheat using images from Unmanned Aerial Vehicles (UAVs) or drones. Cameras can also be mounted onto sprayer booms, on the windows of tractors, or in combine cabs, which capture geo-referenced, timestamped images which are fed back into farm management software to create a detailed map of infestations.
However, as technology is still being developed, results can vary, and growers should be mindful of factors that could influence results. Patch sprayed and hand-rogued weeds will not be picked up by field mapping technology but may have still returned seeds to the soil depending on when the weeds were treated. Furthermore, cultivations including ploughing will change the distribution pattern of buried seed which could still be viable into areas not recognised as affected by mapping software.
Initial identification of black-grass in cereals remains challenging with mapping best carried out at wheat T3 stage when black-grass ears are most noticeable. Consequently, it is difficult to use mapping technology to control black-grass in season because by the time black-grass is easy there is little time to react before seed is shed.
Of course, such technology has a cost, so it is worth considering what benefits it will give you over and above field-walking. With attention to detail, sight specific weed management using mapping technology could see herbicide use for black-grass fall by up to 79% (link to study).
You can compare the maps created by drones or by field-walking with other information, such as yield, soil or other data on your farm management software. This can then be used with precision farming technology to apply treatments to just one area, rather than spraying the entire field, for instance. Field data obtained can also be used to compare the performance of difference black-grass control methods, and the costs related to production.
Use of UAVs on your farm should always be in line with UK aviation laws.
UAVs used for field mapping generally fall under small unmanned aircrafts and are defined as having a mass of no more than 20kg without fuel, but inclusive of all other equipment used during the flight such as cameras.
The Air Navigation Order 2016 states that the operator of the UAV must not:
Failure to comply can result in a prison sentence.
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