Unweeded Plots Research Articles

TRIAZINE HERBICIDES ON MAIZE AND THEIR RESIDUAL EFFECTS ON FOLLOWING CROPS*

Summary. Pre‐emergence application of 2–5 kg/ha (a.i.) of atrazine or simazine was the most effective treatment for control of broad‐leaved weeds in maize. Other triazines injured maize at all rates tested. Among the crops following maize treated with atrazine or simazine at 2–5 kg/ha, sugar beet was injured whereas wheat, oats, vetch, onions and soybeans were not.Post‐emergence application of triazine herbicides was not effective and did not increase maize yields significantly over those of the unweeded plots. Wheat, oats, vetch and sugar beet were injured when following maize treated with post‐emergence sprays; onions and soybeans showed no visible injury except from atrazine or simazine at 5 kg/ha or more, and from mixtures of atrazine+prometryne or atrazine+ametryne at 12–5 kg/ha.Les triazines herbicides sur le mais et leurs arrière‐effets sur les cultures suivantes

EXPERIMENTS ON THE CONTROL OF WEEDS IN GROUNDNUTS IN TRIPOLITANIA

Summary. Studies on weed control in groundnuts grown with summer irrigation in the sandy coastal plain of Tripolitania (Libya) are described. These conditions favour rapid vigorous weed growth which competes severely with the crop; nearly 10 tons/ac of herbage was gathered from unweeded plots, on which groundnut yields were under half those from land kept effectively weeded. Early planting is desirable but may aggravate weed problems, due to inadequate time for cultivation and labour for weeding, through conflicting demands of other crops. It was therefore decided to investigate the possibilities of chemical control. Herbicides applied pre‐emergence included TCA, PCP, monuron, propham and 2,4‐D‐esters. Control of the predominant annual dicotyledons (Portulaca oleracea, Thlaspi arvense and Amaranthus retroflexus) comparable to that from hand‐weeding during early growth was obtained from PCP (10 lb/ac), the crop was not damaged by rates up to 20 lb. and the highest groundnut population was consistently established on plots treated with this herbicide. Effective control was obtained from 2,4‐D‐ester at 0.5 and 1.5 lb/ac, but the higher rate severely checked the groundnuts. Crop damage also occurred from monuron (3 lb/ac) which destroyed all vegetation, TCA (24 lb/ac) which was effective only against Cynodon dactylon; and propham (up to 10 lb/ac) which failed to control weeds. Post‐emergence treatment with MCPB (1.8 lb/ac) and 2,4‐DB (2.5 lb/ac) controlled some 50% of broad‐leaved weeds, but was slow to act and also damaged the crop. A combined PCP + 2,4‐D spray applied pre‐emergence proved to be the best chemical treatment, but maximum persistence was only about 10 weeks; after this, perennial monocotyledons such as C. dactylon and Cyperus sp., not effectively checked by any of the selective herbicides, became a serious problem. Under these conditions good yields depend on weed suppression late into the growing season and excellent results were achieved when an efficient pre‐emergence herbicide was followed, as its persistence waned, by careful handweeding. Early cultivation often damaged the crop, and a comparison of plots where this was omitted and the initial weeding delayed over several weeks, with those hand‐weeded throughout growth, showed no significant advantage from the extra operation. If no pre‐ernergence herbicides can be applied it may therefore be better to postpone the first cultivation for 5–7 weeks after planting. Observations on varieties representing the four broad morphological groups of groundnuts suggest certain differences in susceptibility to herbicides; further studies are required on this subject.Expériences sur le désherbage des Arachides en Tripolitaine

Test of the control of weeds on the paddy field by the use of 2.4-D (1)

Various foreign sources of information have recently shown us that the application of 2.4-D (2.4-dichlorophenoxy acetic acid) is effective for the weed control. Therefore, the writer tested a possibility of adopting this method in paddy condition. From several varied experiments, a spray of 0.05-0.1 percent 2.4-D in the form of either sodium or ammonium salt in water at the rate of 75-150 liters per 10 ares on weeds between the growing rice plants on well-drained paddy field in the mid-or late July has given desirable results, this method was so effective that, with the exception of Echinochlon Crusgalli Beauv. all kind of weeds such as Aneilema Keisak Hassk., Monorkoria vaginalis presl., Lindernia Pyxidaria all., Rotala indica Koehne. ver. uliginasa Miq. cyperus difformis L. Fimbristylis miliacea Vahl., Elatine orientalis Makino, Echipta alba Hassk., Hleocharis acicularis R. Br., etc., were killed within 1-2 weeks, nevertheless no injury to the rice plants was recognized. It may be recommended for the control of weeds on th paddy field to apply 50-75gr of 2.4-D per 10 ares, as it gave as much rice yield as that of the ordinary weeded plot. 37.5gr per 10 ares (0.05 percent solution at the rate of 751. per 10 ares) seemed to be too small doses and 150 gr. per 10 ares too much dose, each of which decreased the rice yields 15 percent and 10 percent respectively as compared with the ordinary weeded plot, although the rice yields of both plots was superior to that of the unweeded plot which about 35 percent less yield than the control.

Test of the control of weeds on the paddy field. : (1) Effect of mulching on the paddy field to the control of weeds.

1. Effects of the straw or compost mulching of rice field being managed as following ways on the growth of weeds and rice yield were investigated. 1). Rice being directry seeded on the ridge ef wheat. (Bakkan Unetate Jikimaki) 2). Rice being directry seeded on flat wheat field. (Bakkan Hiraune Jikimaki) 3). Rice being transplanted on the ridge. (Unetate Ishoku) 4). Riee beihg transplanted in row on the ordinary field. (Namikiue) 2. When 37.5k.g. of wheat straw per are were applied only on the ridges of rice field (1&3), the quantity of weeds reduced to 1/4∼1/5 as compared with unweeded plot, and the rice yield were increaced 5∼9% more than that of commonly weeded. Appliation of compost at the rate of 75∼82.5k.g. also decreased the weeds to 1/2∼1/4, but 3∼7% of the rice yield decreased. 3. 37.5k.g. of wheat straw or 75k.g. of compost per are were applied all over the paddy field (2&anp;4), but they had little effects, which may be due to the soil surface being incompletely coverd in these cases.

Test of the control of weeds on the paddy field. : (2) Chemical control of weeds on the paddy field.

1. It was attempted for the control of weeds that dusting of CaCN3 at the rate of 5.63k.g. per are all over the paddy field well prepared were made 5 days before the rice trans-planting into it. This proved to be effbctive for this porpos, the quantity of weed beeing reduced to one quarter of that of unweeded plot. More than 10% of the rice yield of that plot, nevertheless, was decreased as compared with that of the oridinary managed plot, the reason of which may be due to the unrationality of the apilication of CaCN3 as the manure. 2. Application of CaON3 at the rate of 2.81∼5.63 k.g. per are between rows of rice plants in the middle of late ef July was effective for the control of weed. The rice plants were, however injured at the same time, and the yield was consequently decreased about 20% as compared with the contro1, so this method is not practicable. Here, it may bc noted that the rice yield are sometimes increased by the application of CaCN3 at the rate of 1.88k.g. per are with a caution not to fall on the leaves of rice. 3. Weeds of rice field were also killed by the 2% solution of H2SO4 or 20% solution of FeSO4 7H2O, but the rice yield were decreased 5∼lO% by these spraying.