Measures to cut Danish fungicide use

In December 1986, the Ministry of Environment adopted a pesticide action plan because of growing concerns about the environmental effects of pesticides. Lise Nistrup Jørgensen examines the impact of this plan on the levels of fungicide use in Denmark.

The action plan contains a target to reduce pesticide usage by 50% by 1997. The Danish authorities calculate reduction by the amount used (by tonnage) and a 'treatment frequency index' (TFI)(1). They then compared changes in these levels with an average base-line usage figure from 1981-85.

Cereal fungicide use
Fungicide use on cereals has reduced over the last 10 years due to widespread use of disease-resistant varieties and the precise timing of low-dose fungicide application in the initial stages of disease development. These measures have been possible without affecting the farmers' gross margins. The fungicide TFI for cereals has reduced from 1.09 (the average 1981-85 figure) to 0.61 in 1995.
    The Department of Plant Pathology and Pest Management has devoted much research time to reducing dosages. To reduce fungicide doses, it is essential to treat the epidemic early in its development, or during the latent period of the disease. We have had success with both herbicides and fungicides.
    Based on data from AIM-Farmstat (which takes information from 700-1,000 farms 30 ha or above), the total average fungicide TFI in cereals has decreased from 1.6 FU in 1986 to 0.6 in 1996(2). In spring barley a similar situation has occurred. The TFI was 0.6 FU in 1986, decreasing to 0.25 in 1996. During the same period, in both spring and winter cereals, the average dose rate used has reduced from one full dose to a third dose. One product, Tilt Top (propiconazole and fenpropimorph), now occupies more than 90% of the Danish cereal fungicide market.

The importance of resistant varieties
The choice of crop variety is without doubt the most important decision to minimise the risk of disease development. Danish farmers can rely less on fungicide input because they use new high-yielding disease-resistant varieties of both spring barley and winter wheat (about 80% of the cereal area). The required fungicide input can vary quite dramatically according to the variety. The most susceptible ones require just over a full dose (divided into 3-4 applications), whilst the least susceptible needs only a third dose. Vigilance and continuous development of new resistant varieties are important considerations. In 1996, a severe mildew attack in winter wheat, and breakdown in the efficiency of resistance genes, meant there was a higher fungicide input (0.71 FU) compared with the previous year (0.60 FU). Mildew is the most important disease in spring barley in Denmark. The widely used m-lo resistance gene has reliably controlled mildew for the last 10 years, leading to a reduced need for fungicide input.

PC-plant protection
Researchers in Denmark have produced a computer-based decision support system called PC-Plant Protection that helps farmers to decide whether to spray or not, as well as recommending the product and dose to use. The PC-Plant Protection programme calculates a threshold for disease and insect control based on growth stage, susceptibility of variety grown, agronomic factors and, in some cases, weather records. A further dose calculation takes into account the pesticide's specific efficacy. This reliable system allows for significantly less fungicide use, whilst not affecting the farmers' gross margin. The system is now available to all advisors, agricultural schools, and about 2,000 farmers have bought it.

Fungicide use on potatoes
Today Danish growers treat potatoes on average six times per season with fungicide (mainly maneb or mancozeb), representing an increase on the four applications a season in 1986. The change was caused by greater potato production for industrial starch which has a longer growing season and therefore greater fungal protection. Growers normally treat these potatoes 5-7 times per year while potatoes for human consumption receive 3-5 applications.

Conclusions
The farming community believes they have lost out to EU competitors who have a wider range of products available. In particular there is a serious shortage of minor use pesticides. The authorities have recently banned many minor crop pesticide uses because they have exceeded health and environmental criteria. This may lead to a halt in some minor crop production.
    Denmark has almost attained the goals set out in the action plan. By 1994, pesticide use had dropped by 44% compared with the 1981-1985 average. Reducing the TFI, however, is extremely difficult. The switch from spring to winter cereals has made targets more difficult to reach. Spring cereals use about 60% of the treatments of winter cereals. In 1985 the winter cereal area was 32% of the total cereals area-by 1995, this proportion had increased to 60%.
    Taking account of these changes in the cropping systems in the final evaluation, there was a 20% reduction in the overall TFI by 1994.
    There are no clear signs yet what will happen beyond 1997, although assessing the health and environmental effects of pesticides will remain an important issue. The re-evaluation of pesticide active ingredients is almost complete (see table). At present, farming organisations define their own voluntary concept of IPM. In the future, the Danish government may require a mandatory approach, compelling farmers to take up IPM.

1. TFI = number of full-dose treatments/crop/season
2. 1 FU = one full approved fungicide dose

Lise Nistrup Jørgensen works for the Department of Plant Pathology and Pest Management, Danish Institute of Plant Science and Soil Science, DK-2800 Lyngby.

[This article first appeared in Pesticides News No. 34, December 1996, page 7]