Physical and Cultural Weed Control Working Group of - European ...

9 th EWRS Workshop on Physical and Cultural Weed Control 4
Samsun, Turkey, 28 – 30 March 2011
Highlights from recent research in physical and
cultural weed control at Aarhus University
B. Melander
Aarhus University, Faculty of Agricultural Sciences, Department of Integrated Pest Management,
Research Centre Flakkebjerg, Slagelse, Denmark
The perennial species, Tussilago farfara and Cirsium arvense, are problematic weed problems
in organic farming. Especially, T. farfara is poorly studied and there is an urgent need for better
management strategies. However, several perennial species often occur in the same field
simultaneously and weed control strategies need to address a mixed occurrence of perennials. A
field study on a sandy soil showed that p.t.o.-driven rotary cultivators used twice, with a 3 week
interval between treatments, in the stubble period after harvest of spring barley markedly reduced a
mixed stand of T. farafara, C. arvense and Elytrigia repens. If the treatments were followed by
cultivation in spring - and the whole strategy was repeated again following the subsequent crop - an
accumulated reduction of more than 95% was achieved for the mixed stand.
For the control of E. repens, we are also investigating an innovative approach: effective
uprooting, exposure and destruction of rhizomes in one go using new machinery. We are looking
for new tool configurations that ensure an effective uprooting of rhizomes including methods that
instantly can destruct the sprouting ability of exposed rhizome buds. This will allow the return of
nutrients imbedded in the rhizomes but with now risk of re-infesting the soil with E. repens.
Thermal destruction using hot water is effective, but energy demanding, and removal of rhizomes
from the field for composting and then returning the compost is too laborious and costly. However,
crushing rhizome buds using pressure appeared promising.
Band-steaming is now used commercially for organic carrot production in Denmark and the
performance of two band-steamers has been investigated. It was concluded that a maximum soil
temperature of 80ºC should ensure satisfactory weed control under moist soil conditions, especially
if the soil is cultivated prior to steaming. Surprisingly, the rapidity of cooling from the maximum
temperature did not affect the efficacy of the treatment on weed seed mortality. Temperature
measurements clearly revealed that successful performance of the two band-steamers strongly
depended on their ability to disperse the heat evenly in the soil volume in order to reach target
maximum temperature homogenously.
Two new robotic weeders, Robocrop (www.garford.com) and Robovator
(www.visionweeding.com), for intra-row weed control in row crops are now operating on a
commercial basis. At this stage, the technology is only useful in transplants, such as cabbage and
lettuce. Experiences from practise are promising and growers claim that 70-100% of the labour
normally needed for hand weeding can be saved with robotic weeders. We compared Robovator
with non-selective mechanical methods in transplanted onion in 2010 and found no clear differences
in weeding effectiveness provided that the non-selective tools were steered accurately. However,
the two robotic weeders have more operational advantages than current low-technology solutions.
Selected references
Graglia E, Melander B and Jensen RK (2006). Mechanical and cultural strategies to control Cirsium arvense in organic
arable cropping systems. Weed Research 46, 304-312.
Van der Weide RY, Bleeker PO, Achten VTJM, Lotz LAP., Fogelberg F and Melander B (2008) Innovation in
mechanical weed control in crop rows. Weed Research 48, 215-224.
Melander B and Kristensen JK (2011). Soil steaming effects on weed seedling emergence under the influence of soil
type, soil moisture, soil structure and heat duration. Annals of Applied Biology, (in press).