Pesticides Research, 58, 2002

Effects of reduced pesticide use on flora and fauna in agricultural fields

01-05-2002

In this large scale project, related to the Danish Pesticide Action Plan I, responses of flora and fauna in arable fields to reduced dosages of herbicides and fungicides were investigated. After pilot studies the investigations were carried out 1997-1999 at five farms where three dosage plots of 6 hectare or more could be placed in each of the crops spring barley, winter wheat and sugar beets, rotated as mentioned. The dosage levels were normal (by definition the farmers choice of chemicals and dosage), half and quarter. In beets the reduced herbicide levels were obtained by applying normal dosage in narrow bands plus supplementary mechanical weed control. The reduced dosages opened for higher plant densities, at quarter significantly higher than at normal. Beside this more plant species were found at the reduced dosages and the proportion of flowering species increased with decreasing dosage. Samplings of insects proved in general higher abundances at reduced dosage. As for plants this came out very clearly at quarter dosage in barley. An over-all analysis of non-carnivores and carnivores in the three different crops strongly supported a general improvement at quarter dosage. Counts of birds revealed that Skylarks, Whitethroats and "small seed-eaters" all occurred significantly different in response to dosages with higher numbers towards quarter dosage. The effect of half dosage was less clear but the estimates indicate that half of the improvement through quarter dosage is also obtained by half dosage. Investigations of yield and economy revealed limited losses. The economical calculations indicate that on short term yield reductions are generally counterbalanced by reduced pesticide costs. The effect not properly covered is the risk of accumulated weed problems in case on ongoing reduced dosages on the same area. In conclusion both quarter and half dosages will improve the "nature element" of fields. However, the gain at quarter dosage is much more marked. Modern GPS technology combined with a more sophisticated planning open for this option and hence the reestablishment of more flora and fauna in arable fields still supplying sufficient yields.

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