Tekohormonien merkityksestä öljypellavaviljelyksien rikkaruohontorjunnassa

Authors

• Otto Valle Maatalouskoelaitoksen kasvinviljelysosasto, Tikkurila
• Juhani Paatela Maatalouskoelaitoksen kasvinviljelysosasto, Tikkurila
• Jaakko Mukula Maatalouskoelaitoksen kasvinviljelysosasto, Tikkurila

DOI: https://doi.org/10.23986/afsci.71272

Abstract

Investigations of the importance of artificial hormones with regard to weed control were begun in Finland at the Department of Plant Husbandry of Agricultural Research Institute Tikkurila, in 1946. Investigations were continued in 1947 and 1948. As is generally known, artificial hormones, if given in suitable amounts, destroy many herbaceous plants, but do not usually have injurious effects on graminous plants. All herbaceous plants, however, are not equally susceptible, and as well among cultivated plants as among weeds there are some rather resistant species. Oil flax is one of these herbaceous cultivated plants, which is more susceptible than graminous plants, but at the same time is more resistant to artificial hormones than most weeds. Thus it is possible to use artificial hormones for weed control in oil flax cultivations. The safety margin between resistance and injury, however, is for oil flax smaller than for cereals. The results of the experiments, which were carried out at the Department of Plant Husbandry and which deal with the resistance of oil flax, have already been published (10). In this study, which is based on other experiments with artificial hormones conducted at the Department of Plant Husbandry in 1947 and 1948, attention is paid mainly to the effect of different preparations on some species of weeds occurring in oil flax cultivations. Following conclusions, among others, may be drawn from the experiments; 1. Of the preparations used Weedone (ethyl ester of 2,4-D) had so injurious an effect on the yield of oil flax that it is almost impossible to use it in oil flax cultivations. On the other hand, none of the other preparations used, whether 2,4-D or 2M-4K compounds, caused any reduction in the yield. On the contrary, in 1947 when the experimental area was heavily infested with weeds, especially with Chenopodium album, all treatments resulted in distinct increase in yield (103—363 %, p. 98). For 2M-4K the results thus agree with earlier investigations (3, 6, 10, 14), but not for 2,4-D. According to the above-mentioned investigations 2,4-D compounds usually have injurious effects on the yield of oil flax. That they (with the exception of Weedone) did not result in injurious effects in the present experiments may be due to the fact that pure aqueous solutions of 2,4-D are not sufficiently absorbed by oil flax (cp. 10, pp. 41—45). 2. Sprays (applied at the rate of 1000 1. per ha.) were on the whole more effective than dusts, though in 1948 the applied dusts contained twice as much effective substance as the sprays. Evidently dusts cannot penetrate into plants as easily as sprays, in which the effective substance appears in dissolved state already at the time of treatment. Besides, as the price of dusts is 4—5 times that of sprays, their use cannot be recommended to farmers at least not in the present form. 3. There are significant differences in the effectiveness of different sprays. In our experiments 2,4-D compounds (with the exception of Weedone), which are generally considered more effective than 2M-4K compounds, did not eradicate weeds so effectively as 2M-4K compounds. So in 1947 about kg. of sodium salt of 2,4-D per ha. applied as an aqueous solution (Veith, Hormotox) destroyed 95 % of Chenopodium album and 31 % of other weeds, about 1 kg. per ha. correspondigly 96 and 58 %. In 1948 0.8 kg. of the sodium salt of 2,4-D per ha. applied as an aqueous solution (Hormoxol) destroyed 65 % of the weeds occurring in the experimental area. The reason for this is probably the same as the one mentioned under the first item: deficient absorption of the compounds by plants. On the other hand, all the 2M-4K compounds used seem to contain substances which reduce surface tension, and they have been very effective. In 1947 y 2 kg. of 2M-4K per ha. (Acodrin) destroyed 100 % of Chenopodium album and 68 % of other weeds, 1 kg. per ha. correspondingly 100 and 80 %. In 1948 0.8 kg. of 2M-4K per ha. (Acodrin, Agroxone, P 46) destroyed 68—85 % of the weeds occurring in the experimental area. 4. The eradication percentage of weeds seems to be essentially dependent not only on the compounds used, on the stage of development and on the rapidity of growing of the plants, but also on the species of weeds occurring in the area. If the main weed is some species which is easily eradicated (e.g. Raphanus, Chenopodium, Erysimum, Capsella, Thlaspi), ½ kg. of the effective substance per ha. may be sufficient to kill it. If more resistant species occur among them (e.g. Cirsium, Sonchus, Stachys, Equisetum, Galeopsis, Spergula, Stellarid), larger amounts of effective substance must be used, especially as oil flax is well resistant up to 1 kg. per ha. (cp. 3, 10). If very resistant species form the main part of the weed vegetation (e.g. Polygonum, Viola, Fumaria, Lapsana, Galium, Tussilago), it is uncertain, whether artificial hormones give such results as to cover the expenses caused by the use of artificial hormones. It is namely impossible to eradicate very resistant species in oil flax cultivations, their growth can only be retarded, and their flowering and seed formation prevented.