Libère Nkurunziza

Project	Phenology and Source Sink Dynamics in Relation to Management of the Perennial Weeds, Cirsium arvense and Tussilago farfare
Supervisors	Professor Jens C. Streibig, KU/LIFE Senior Scientist Ilse Rasmussen, AU/DJF Flakkebjerg
University	Copenhagen University, Faculty of Life Sciences
Work place	Copenhagen University Faculty of Life Sciences, Department of Agricultural Sciences Højbakkegård Allé 13, 2630 Taastrup
E-mail / phone	/ (+45) 3533 2240
Aim	The PhD project is aimed at following the phenology of Cirsium arvense and Tussilago farfara and finding the best time of control in the context of organic farming system. With repeated measurements of carbohydrates reserves in aboveground and belowground parts, we will establish their most vulnerable time to different physical disturbances. The hypothesis is that the time corresponds to when roots or rhizomes are depleted of carbohydrates reserves and the aerial parts commence exporting carbohydrate to underground parts Therefore, controlling perennial weeds at that time would impair further development of the plant
Background	Perennial weeds are the most troublesome weeds in organic farming systems. Their vegetative regeneration ability facilitates the infestation in dense patches and makes them ill-suited to the current management strategies. Cirsium arvense and Tussilago farfara are problematic among creeping perennial weeds in organic farming thus causing severe constraints on the food production. They are characterized as plants with high tolerance to tillage and strongly regenerative due to the structure of the roots (C.arvense) and the rhizomes (T.farfara). Several management strategies have been investigated, especially for C.arvense, but the results are still unsatisfactory. The presence of roots and rhizomes in the deeper soil layers excludes control by uprooting whereas the repeated mowing or the fragmentations of regenerative structures by soil cultivation are much energy consuming and costly. Even though, the latter are to give relatively good results, they are in conflict with the objectives in organic farming to retain nutrients in the upper soil layer by keeping the soil plant-covered during autumn and winter. Therefore, fewer and better-timed treatments would be more effective. We think that this could be achieved by the understanding of carbohydrates source/sink dynamics in response to growth disturbances. It is known that the process of vegetative regeneration starts, early in spring, with the dormant belowground parts (roots and rhizomes) that allocate stored carbohydrates to the formation of new aerial structures (stems and leaves), thereby depleting they reservoirs. At a certain development stage, photosynthetic assimilates are allocated to belowground parts, again increasing the nutrient reserves. These allocations of carbohydrate reserves have been studied for T.farfara, only in undisturbed conditions. Much information would be gained when understanding the regeneration capacity explained by sources/sink dynamics.
Status	Status reports
Time table	Start: 09.07.2007 End: 08.07.2010

Sofie Kobayashi, - last update:26 June 2009