Mention variable rate fungicides and many farmers think of adjusting rates across a field based on crop biomass measured using a tractor-mounted sensor.
However, fungicide rates could also be varied through a season, as plants are much smaller at the T0 or T1 fungicide timing than at the T2 or T3 stage.
Current pesticide labels state a maximum dose rate and latest application timing.
“Effectively you can have the same rate for different surface area, or biomass,” says Toby Waine, lecturer in applied remote sensing at Cranfield University.
Therefore, he believes there is scope to cut back the dose used on smaller plants and still deliver the required amount of active ingredient to the leaves.
“If the plant only needs a fraction to achieve the required effect, why waste more chemical. This not only reduces costs for farmers, it is beneficial to the environment,” he says.
PhD researcher Alex Ansell highlights published work showing a potential reduction in fungicide use of 37%. “There are potentially some big savings.”
Dr Waine adds precision technology for varying rates is already here, but what is lacking is the data to tailor rates to growth stage. And it’s not just growth stage, biomass can also vary for the same stage.
To address this, a new project has kicked off with the ultimate aim of creating a new model that can calculate fungicide rates according to growth stage.
However, it is not as simple as looking at differences in crop surface area, as a proportion of the active applied will also go on to ground or simply evaporate.
So the first stage, Ms Ansell has started on, is to develop a new method of studying spray patterns using laser scanning and imaging at the unique covered gantry facility at Cranfield University (see ‘Glasshouse offers greater control for imaging system research’, below).
It generates very accurate 3D images of wheat plants, down to 0.25mm detail on the plant’s surface. She explains that current methods of measuring spray coverage require destructive sampling so you cannot take the plant to a later growth stage.
She is using two different varieties, Claire and Skyfall with contrasting growth habits.
The next stage will quantify variation across a field. “Farmers are well aware of variability in fields, especially when assessing growth stage for spray timings,” she says.
“But they are not looking at variation in terms of spraying and the amount of active ingredient that is needed by the plant. So we are looking to quantify this using remote sensing with drones or tractor-mounted sensors.”
Recommended fungicide rates
The eventual result will be a new model that will generate recommended fungicide rates for the different growth stages without affecting efficacy.
“This will help secure the longer-term future of fungicides,” adds Prof Ron Corstanje, head of the Centre for Environmental and Agricultural Informatics at Cranfield University.
“If we can use pesticides more efficiently, there is a stronger case to legislators that they are being used sensibly. Reducing overall use will also reduce resistance pressure.”
Glasshouse offers greater control for imaging system research
There are only three high-accuracy crop-imaging gantry systems in the world, two of which are in the UK at Rothamsted Research and Cranfield University.
However, Cranfield’s is the only one in the world stationed in a glasshouse, enabling unique research such as Ms Ansell’s work looking at how fungicide sprays interact with the wheat plant’s canopy.
“Being in a glasshouse means you can fully control the conditions,” says Dr Waine.
The £2m facility is part of Agricultural Engineering Precision Innovation and Crop Health and Protection, which are two of four recently established Centres for Agricultural Innovation and a key component of the government’s Agri-Tech Strategy.
Another valuable role is that the imaging gantry will help plug the gap between the lab and the field.
“When imaging crops for signs of disease, a very expensive spectrometer in the lab can detect the colour change of an individual leaf when infected by a specific disease,” Dr Waine says.
“But as you transfer this into the field with a drone or tractor-mounted sensor, it is more difficult to distinguish between healthy and unhealthy leaves. This is because you also have reflectance from soil as well as the effects of shadowing.
“You get more noise in your measurement and it is difficult to detect small changes in leaf colour that are early signs of disease.”
Therefore, the gantry will allow researchers to refine the system before moving into the field.
In addition, Dr Waine believes the gantry will also help in the development of drone sensors. The £100,000 hyperspectral cameras cover a wide spectrum (visible to shortwave infrared) and researchers will be able to investigate specific wavelengths that will enable detection of that disease.
“Then you can develop a much cheaper camera, making it feasible for routine disease detection using remote sensing,” he says.