Interview with Jens Erik Jensen, senior agronomy adviser, SEGES Technical Institute.
It is an important part of our crop rotation strategy. Of the 2.6 million ha of farmland in Denmark, 175 200 ha are oilseed rape (174 000 ha is winter rape and 1 200 ha is spring varieties). The average winter rape yield over the last five years was 39 dt/ha. Oilseed rape is particularly important because it is useful as a crop to precede cereals. Specifically it allows for easier work flow throughout the year and also helps to control weeds and manage resistant grasses. A key factor is that herbicides with different modes of action can be used compared to the ones used on cereals.
Oilseed rape fields are particularly affected by broad-leaved weeds such as mayweed, poppy, crane’s bill and shepherd’s purse. Farmers also need to control grasses, annual meadow grass, ryegrass, blackgrass and more recently, rat’s-tail fescues.
Danish farmers generally treat pre-emergence with a mixture of clomazone and pendimethalin, followed by a specific grass control herbicide in the autumn. In recent years, we have had exemption registrations for propyzamide, which is important to delay resistance development in grasses.
Very useful indeed. In fact many Danish farmers are interested in using this strategy between September and November when their workload is significantly lighter than immediately after planting.
Another advantage is that farmers are able to visibly check for weeds and if they find them, they can be targeted. For more than 30 years now there has been a great deal of pressure in Denmark to reduce the use of plant protection products. Indeed pesticide taxes here are the highest in the world! It is therefore in the farmers’ best interests to optimise the use of herbicides to control weeds in their oilseed rape fields.
Post-emergence weed control would also add a bit of flexibility in terms of application dates. For example, in August, oilseed rape can germinate quickly leaving very few days for application of pre-emergence herbicides. And the benefit of post-emergence treatment is that it wouldn’t require additional work for farmers as they already need to make autumn applications of other plant protection products.
SEGES coordinates national variety and plant protection trials and new production methods. It also engages in advisory work through agricultural technicians and consultants and its website, www.landbrugsinfo.dk.