Resistance against uprooting in carrots (Daucus carota) and annual weeds: a basis for selective mechanical weed control.
Trials were carried out in order to investigate ways in which to achieve selectivity in mechanical weed control. The influence of soil type (pure sand, commercial peat, loamy sand and organic), uprooting angle and development stage on the uprooting force of some annual weeds and carrot (cv. Bolero) was studied. Spergula arvensis, Urtica urens, Chenopodium album and carrots were sown in soil bins filled with the four different soil types. The plants were uprooted when they had two true leaves. Soil type significantly influenced the uprooting force needed by all four species. The forces required to uproot U. urens and C. album differed significantly between peat and loamy sand. In loamy sand, Capsella bursa-pastoris, Stellaria media, Chamomilla suaveolens and Viola arvensis could all be uprooted by less force than it took to uproot carrots. The uprooting angle (0°, 45° and 90°) had no significant influence on the uprooting force for carrots at the studied developmental stage. Chenopodium album, Spergula arvensis, U. urens, Matricaria inodora [M. perforata], Thlaspi arvense and carrots could all be uprooted by less than 1 N when they had two true leaves. Carrots required a greater uprooting force than weeds at the three early developmental stages studied. This indicated that it should be possible to develop selective mechanical weed control methods.