Targeting Fungicide Inputs According to Need

Abstract

Fungicides should be used to the extent required to minimize economic costs of disease in a given field in a given season. The maximum number of treatments and maximum dose per treatment are set by fungicide manufacturers and regulators at a level that provides effective control under high disease pressure. Lower doses are economically optimal under low or moderate disease pressure, or where other control measures such as resistant cultivars constrain epidemics. Farmers in many countries often apply reduced doses, although they may still apply higher doses than the optimum to insure against losses in high disease seasons. Evidence supports reducing the number of treatments and reducing the applied dose to slow the evolution of fungicide resistance. The continuing research challenge is to improve prediction of future disease damage and account for the combined effect of integrated control measures to estimate the optimum number of treatments and the optimum dose needed to minimize economic costs. The theory for optimizing dose is well developed but requires translation into decision tools because the current basis for farmers' dose decisions is unclear.

Identifying when it is financially beneficial to increase or decrease fungicide dose as resistance develops: An evaluation from long‐term field experiments

“…These three options for adjustment of the treatment programme are interrelated (as discussed below) and an underlying question is whether the total dose of the fungicide in the treatment programme should be increased or decreased when resistance is developing. In many European crops, doses less than the maximum permitted individual dose (the dose per application) and maximum permitted total dose (the dose per season) are used routinely (Jørgensen et al , ). It is therefore possible for growers to increase or decrease the total dose applied, whilst remaining within the legal limits of the authorization of the fungicide product.…”

“…In many European crops, doses less than the maximum permitted individual dose (the dose per application) and maximum permitted total dose (the dose per season) are used routinely (Jørgensen et al, 2017). It is therefore possible for growers to increase or decrease the total dose applied, whilst remaining within the legal limits of the authorization of the fungicide product.…”

Using epidemiological principles to explain fungicide resistance management strategies: why do mixtures outperform alternations?

“…Alternation was also optimal at full doses in our model of grapevine powdery mildew (Figures 10a and 10b). While performance at full doses of both chemicals is a simple comparison, it is now common practice in some countries for fungicides to be used at lower doses (Jørgensen et al , 2017). Additionally, the comparison depends strongly on model parameterisation.…”

“…Given the high level of year-on-year variability typical of real disease systems (te Beest et al , 2008) and the extent to which available models do not necessarily capture the complex dynamics of epidemics accurately enough to make such a precise prediction (Gent et al , 2013), this might be rather difficult in practice. There would also be questions raised surrounding the risk-aversion of growers and/or agronomists, who might – reasonably enough – wish to use higher doses of fungicides than are necessary on average to avoid failure of control in years with high disease pressures (Jørgensen et al , 2017), although in principle this might be mitigated via a sufficiently well-calibrated decision support system (Carisse et al , 2010). We have also not considered the economic aspects of our recommendations (te Beest et al , 2013), nor the potentially confounding effects of varying the timing of fungicide sprays (van den Berg et al , 2013, 2016), nor the emergence phase of resistance (Hobbelen et al , 2014; Mikaberidze et al , 2017), nor of spatial heterogeneity in coverage (Shaw, 2000; Parnell et al , 2005, 2006).…”

Protocol for the evaluation of data concerning the necessity of the application of fungicide active substances to control a serious danger to plant health which cannot be contained by other available means, including non‐chemical methods

“…Therefore, the decision on the classification of impacts on plant health as 'serious' should be taken by the risk managers (e.g. European Commission) on a case by case basis (Jørgensen et al, 2017).…”