UNTERSUCHUNGEN üBER öKOLOGIE UND BEKäMPFUNGSMöGLIGHKEITEN DES HUFLATTICHS (TUSSILAGO FARFARA L.) *

Summary. The effect of herbicides on coltsfoot (Tussilago farfara L.) varies according to the plant's constitution resulting from different environments. 4‐CPA‐ester had the best effect of all the auxin‐type herbicides. The application of 4‐CPA in cereals is not possible because of its phytotoxicity, but this chemical could be promising for the control of coltsfoot in grassland. Fenoprop (2,4,5‐TP) is somewhat less effective but cereals, especially wheat (Triticum setivum L.) and oats (Avena sativa L.), are more tolerant. All the other auxin‐type herbicides, including mecoprop (CMPP) and 2,4,5‐T were unsatisfactory. Control of coltsfoot after harvesting the cereals was most satisfactory with amitrole (7.5‐10 kg/ha in one application or two applications of 4 and 6 kg within 3‐4 days). Shallow ploughing 4‐6 weeks after spraying increased the effect as did the addition of Nad (10‐20 kg/ha) to the spray‐fluid. Good results with amitrole can be obtained only when the plants are growing vigorously and have a sufficient amount of large and healthy leaves at che time of application, not damaged at harvest and without fungus infection. There should be dry weather 2‐3 days prior to the application. The regrowth in the following spring is usually so weak that it cannot compete with the crop plants. The soil should be cultivated immediately after harvest, so that the still living remains of coltsfoot plants can also be killed and re‐establishment prevented. It is advisable to plant root crops after the chemical control of coltsfoot, so that the weak regrowth can be killed by the normal cultivation practices of these crops. The residual effect of amitrole in the soil can vary widely. Under conditions in the Rhine Valley the residues are partially broken down biologically, partially leached during autumn (and winter), so that the following summer crop can be grown without risk.