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18.03.2019 - Hermann Leithold (Send email to Hermann Leithold)

Site specific application of fungicides

Basic and nitrogen fertilization has been carried out on professional farms for around twenty years with partial precision. The specific determination of the optimum and the variable distribution of the necessary amount of fertilizer in real time have become good professional practice for them. The variable application of growth regulators has also been indispensable for modern farmers for more than ten years. These practitioners quickly extended the application of the system to the field of fungicides. They were unanimous in their opinion: fungicides should be as variably dosed and adapted to the crop as fertilizers and growth regulators! On this basis, Agricon and its partners developed an agronomic module for the variable dosage of fungicides. In order to evaluate this module, a three-year test series was set up, the results of which are now available.
Plant populations never develop evenly

The growing conditions for plants vary from sub-area to sub-area. Nationwide evaluations of more than 600,000 ha show that 90 % of the shoots have greater differences in N uptake than +/- 25 %. This means that some areas have already absorbed more than twice as much nitrogen as others. The fresh cuts vary even more. Strongly developed sub-areas have produced up to six times as much fresh mass as weak stands on the same field. Biomass cuts make it easy to check this in one's own fields.

What happens to the active ingredients during constant application?

This can be illustrated by an example of winter wheat at the beginning of the shoot phase. In a medium population at GS 31/32, the N uptake varies from 20 to 60 kg N/ha (Fig. 1). This corresponds to a difference in the fresh cuts to be protected of 0.5 to 3 kg/ha. The change in the leaf surface to be wetted (relative spray area) must also be taken into account. In thick stands more active substance adheres than in thin stands. Due to the saturation effect of the leaf area index (LAI), however, this should not be considered linearly. This means that the differences in the spray quantity relative to the fresh cuts are retained.

What exactly happens when injection is constant (Fig. 2)? The average dosage on the average population should be 1 l /ha (100 %). This dosage corresponds to the manufacturer's recommendation.


With a general dosage, the active ingredient concentration in thin and weakly developed populations increases to 400 %. Instead of the calculated 0.05 ml active ingredient per kg fresh cuts, 0.2 ml active ingredient per kg fresh cuts is applied. On the well-developed partial areas, where the highest yields tend to be harvested, the dosage is reduced to 67%. Instead of the 0.05 ml active ingredient per hectare, only 0.033 l active ingredient per hectare is applied. This problem becomes even more critical if we apply this general logic to the usual, i.e. often reduced, quantities of active ingredients. Assuming a typical reduction to 70 % of the manufacturer's recommendation, the following picture emerges: In the weak popua, 280 % are still being injected. However, pesticides are still given away, which corresponds to unnecessary costs. On the other hand, the dosage in dense stands drops to 47%!

The potential high-yield zones thus receive less than half of the manufacturer's recommendation. The fact that, in addition to the poor fungicide effect, possible maximum yields are poorly secured is one side of the coin. This weak fungicide protection, however, also results in a massively increased risk of resistance on the best partial areas.


The differences in the active ingredient content not only change the strength of the fungicide protection, but also its duration. Within a field, it depends significantly on the concentration of the active ingredient per fresh mass. Degradation in the plant occurs much faster at low doses (uniform area and dense stands) than at high doses (uniform area and thin stands). If one consistently thinks ahead, the best crops are faster without fungicide protection than the weaker ones. If spraying sequences build on each other, a negative spiral develops. This is precisely where the process of stock-dependent application of fungicides comes in and solves this problem.

Escape the vicious circle with adequate spraying

Dosing according to population means taking up the challenges and treating populations according to their needs. The aim must be an even concentration of active substances per kg of fresh cuts on each section of the field. This ensures a uniform protection performance as well as a long-term permanent effect on every part of the field. The technical implementation of a fungicide application with partial area accuracy can only be carried out with a Yara N-Sensor® or a P3-Sensor ALS as well as the agronomic module for fungicides. This includes all information and algorithms relevant to crop cultivation. On the one hand, the system complies with the legally permissible maximum quantities and,
on the other hand, with minimum dosages to avoid resistance.

Agronomical control algorithms

The measured absolute N-uptake is the basis for the agronomic control functions. Absolute measured values and control functions prevent the spraying technology from being over- or understeered. An overdrive causes such a high degree of variation that an excessive reduction in the spray rate on weak parts of the surface can no longer guarantee a sufficient fungicidal effect - the risk of resistance increases. With understeering, on the other hand, the full potential of a variation is not exploited. Only validated control curves ensure the optimal distribution in the area. Long-term tests have shown that this is correct not only from a plant cultivation point of view but also from an economic point of view.


Accurate subarea fungicide usage at trials

Together with practitioners and Bayer Crop Science AG, Agricon conducted a three-year trial series from 2014 to 2017 in Germany, England and France. A total of 21 farms took part. The 79 field trials resulted in a trial area of 3,240 hectares. Winter wheat and winter rape were investigated as the most important arable crops in terms of area. The trials were designed and evaluated in accordance with the strict OFR guidelines (reference box). The question posed by the experiments was to quantify the effects of fungicide application on practical areas with partial precision. The parameters were examined:

  • Yield,
  • fungicide expenditure and
  • occurrence and intensity of disease before and after treatment.

The participating farms were selected in such a way as to ensure the widest possible range of growing regions. Both family farms and agricultural cooperatives took part. The farm sizes varied from 150 ha to over 2,000 ha LN, the soil values from 40 to over 90 BP and precipitation totals from 400 to over 1000 mm. At all locations the usual operational technology was used. All companies use Yara N-Sensors® or P3 sensors in their daily operations. All trials were recorded with yield mapping.

Depending on the location, one to four applications were carried out. In wheat, very early treatments (BBCH < 30, T0) and ear treatments (BBCH > 49, T3) were performed consistently and uniformly. Thus one to two applications with variable application rates were available according to test elements. The variants differed in each case into a healthy variant and the sensor-supported variant. The pesticides used were always identical. The dosage differed depending on the sensor values both in the distribution in the field and in the average dosage. The fungicide module complied with the statutory approvals on the one hand and the lower limits for resistance prevention on the other.

The trials were carried out separately for clean separation: First a so-called sensor scan of the field was carried out, then the application was calculated based on the fungicidal algorithm of the Agricon. The result was a plot-specific spraying plan, which was applied with the usual spraying technique. Each application was accompanied by on-site bonitures. At regular intervals, disease occurrence and intensity were credited at previously defined points. At the beginning, the sites were selected in such a way that the most varied conditions possible were covered. Based on the initial heterogeneity of the populations, points with high, medium and low N uptake were selected.

It's a fact that the weather and the incidence of disease are closely linked. For this reason, temperature, precipitation and leaf humidity were recorded with a professional weather station at each test site and the data were taken into account in the evaluation. The recommended spraying date was dynamically calculated for each experiment from the weather and inventory data.

What's the use of area specific fungicide usage?

The experiments on a total area of more than 3,240 ha show a natural dispersion between the sites and years. Three quarters of the trials were statistically significant at a significance level of 95 %. The results can be summarised as follows: Average increase in revenue of € 33 per hectare on average + 2 % Reduction in the use of funds by an average of -12 % No differences in the incidence of disease between the uniform and the variable option.


Higher yields


We were able to prove that the specific use of fungicides in the partial area is economically worthwhile: Compared to the 100 % variant, the variable variant generated additional revenue of + 33 €/ha (Fig. 3). Fungicide savings of up to 20% and yield increases of up to 6% were measured. Accompanying bonituren showed no significant differences in the occurrence or strength of infestation between the variants. Even if the proof of a reduction of the resistance risk through stock-adjusted dosage was not sufficiently investigated, it must be assumed that this form of application makes an enormous contribution. Thus, the results clearly speak for the use of the Yara N-Sensor® or P3 sensors in plant protection from an ecological point of view.

Finally, this technology can also be recommended from a social point of view, as agriculture can present itself to society as a solution provider when it comes to reducing environmental impacts.

Important annotation: The results refer only to the presented sensors and algorithms. All data and results refer only to the technologies used. Therefore, no statements on other sensor systems or image information sources can be derived from the data.


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