The present studies were undertaken to clarify a few questions of chemical control, the injury and herbicidal effect of a few herbicides on the mechanical transplanting culture of young rice seedlings.
The results were as follows:
(1) Emergent periods of weeds were long on the paddy field of transplanting culture of young rice seedlings.
As the emergent period of barnyardgrass that 90% of all numbers emerged was about 40 days after pudding, young rice seedlings met stronger and longer competition with the barnyardgrass than adult rice seedlings.
For the above facts, herbicides should be applied twice. We consider that the first application time is either a few days before or after transplanting, and the second time is 20th-25th day after the first application.
(2) The herbicide of first application is CNP granular and the herbicide was harmful to the young rice seedlings at deep transplanting condition combined with low temperature and deep flood. But twofold dosage of CNP did not caused the injury of young rice seedlings on transplanting of 2cm depth and shallow flood (1cm depth).
The injury of young rice seedlings at flooted transplanting of 0cm depth were severe in either ease of non-treatment and treatment.
(3) Swep+MCPA mixture and benthiocarb+simetryne mixture granular were used as the second application herbicide. Swep+MCPA mixture was harmful when was used before the 5.3th leaf stage of rice on shallow transplanting and deep flood conditions.
Benthiocarb+simetryne mixture granular was harmful on deep flood consition (6cm depth), but the herbicide was mild comparatively to young rice seedlings.
(4) Properties of swep+MCPA mixture and benthiocarb+simetryne mixture granular on paddy field were tested practicaly. As the results, swep+MCPA mixture caused the decrease of rice dry weight at the 4.5th leaf stage seedlings of rice, but benthiocarb+simetryne mixture did not. As concerns weeding effect, swep+MCPA mixture granular was not effective to the 2.5th leaf stage plants of barnyardgrass, but it was remarkably effective to other species of weed. Benthiocarb+simetryne mixture granular was effective comparatively to the 2.5th leaf stage plants of barnyardgrass, but it was not effective to Hardstem bulrush (Scirpus hotarui Ohwi) and Monochoria. (Monochoria vaginalis Presl).
But as this field test was undertaken at very late transplanting date, the test have to be studied at normal transplanting date.

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We investigated the influences of depth of submerged water (1, 5 and 9cm), water percolation (0, 3 and 5cm at the next day of the treatment), depth of planting (1 and 3cm) and time of application (3 and 12 days after transplanting) on the damages to young rice seedlings of some herbicides in pot experiment. CNP, NIP (nitrofen), benthiocarb+CNP, simetryne, benthiocarb, benthiocarb+simetryne, TOPE (HE 314), trifluralin and PCP were tested.
(1) Damages by some herbicides were affected by the depth of water, especially CNP caused much greater damage in the deeply-submerged condition than in the shallowly-submerged.
CNP, simetryne and benthiocarb+simetryne, especially the last two, caused greater damages in the non-percolated condition than in the percolated. Trifluralin showed the opposite tendency. The influence of percolation was little with benthiocarb, TOPE and PCP.
(2) TOPE and benthiocarb were safe in both application times. The other herbicides tended to cause greater damages in the earlier application. At the earlier application time, CNP, benthiocarb+CNP, simetryne and benthiocarb+simetryne caused greater damages in the deep planting than in the shallow planting, while trifluralin and PCP caused less damages in the deep planting.

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Knotgrass (Paspalum distichum) has been a serious weed under a humid soil condition, regardless of crop and cropless lands. Recently in southern Japan, Kyushu, this weed is invading in rice fields without satisfactory tillage and/or winter cropping. Once when it invades in rice, it is very hard to weed out perfectly. Thus, we have studied the ecological and anatomical characteristics of this grass weed, concerning its control, and have made the preliminary evaluation test of several herbicides. The results are summarized as follows:
1) Knotgrass can root easily from the nodes of a runner and elongate rapidly. High temperatures are more suitable for elongation than low temperatures, showing the elongation velocity of 15 to 20cm per week under the most favourable condition. The velocity may be about two times or more of rice in the summer season. However, the sunlight control of about one-fifth to one-eighth provides no effect on the elongation of regrowing shoots.
2) The emergence of knotgrass in the soil is made from deeper sites in a dry condition than in a flooded one, but there is no essential difference between sandy and silt-clay soils. Generally speaking, this grass weed seems to be rather shallow emergeable, when compared with other perennial such as perennial cyperaceaes found everywhere in Japan. The depth of emergence is 3.25cm on the average. This fact indicates us that this grass should be controlled by deep-plowing.
3) Some anatomical natures in matured stems which tell us resistability against chemical substances were found. That is to say, thickening of the cell membrance of epidermis, cortex, and central portion, poor development of vascular bundles in the central portion, no air capacity in the central portion, and much accumulation of starch grains in the cortex and central portion.
4) In the cross section of a leaf, distinct differentiation of bundle sheath cells surrounding a vascular bundle is found. This indicates the strong competition ability of this grass with rice.
5) Several herbicides were evaluated at soil-, foliage-, and soil and foliage treatments. Acute action on foliage was found in paraquat, dalapon, NaClO₃, and AMS+2, 3, 6 TBA. Strong suppression of regrowing shoots after cutting was seen in 2, 4-D+2, 4, 5 T and 2, 4-D+amitrole besides the herbicides named above. Generally speaking, promising herbicides in practice may be considered as follows: dalapon, 2, 4-D+amitrole, NaClO₃, AMS+2, 3, 6 TBA, paraquat.

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To compare with longevity of buried weed seeds in different species, three hundred seeds of 15 species mixed with soil, were put in cylinders made of bamboo and they were buried at 10 to 20cm below the ground level. Seeds were removed and tested for germination six times during four and half a year.
The following 10 species gave 80 to 100% germination after half a year: Chenopodium album, Polygonum nepalense, Rumex obtusifolius, Stellaria media, Spergula arvensis var. sativa, Amaranthus retroflexus, Digitaria violascens, Elsholtzia ciliata, Rorippa islandica and Solanum nigrum. But of these, former 5 species had 40 to 70% of germination and latter 5 species only 0 to 7% of germination respectively after four and half a year.
The 4 species, having 60 to 70% of germination after half a year were Commelina communis, Polygonum lapathifolium, P. longisetum and Setaria faberi, and occured to germinate 32, 44, 16 and 10% respectively after four and half a year.
With Echinochloa crus-galli var. praticola germination which amounted to 27% after half a year was especially low and it showed 3% of germination after four and half a year.

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The authers studied the herbicidal activity, crop selectivity, behavior in the soil of four very similar chloroacetamide compounds and herbicidal action of one of them, CP-53619, which showed very excellent properties in the paddy field conditions.
Test Compounds are
A (CP-52223): 2-chloro-N-(isobutoxymethyl)-2′, 6′-acetoxylidide,
B (CP-53619): 2-chloro-2′, 6′-diethyl-N-(butoxymethyl) acetanilide,
C (CP-50144): 2-chloro-2′, 6′-diethyl-N-(metoxymethyl) acetanilide,
D (CP-44939): 6′-tert-butyl-2-chloro-N-(metoxymethyl)-0-acetotoluidide.
The results worth noting in the research of the authers are
(1) All compounds are pre-emergence, soil treatment herbicides and have not any-contact toxicity on stems and leaves.
(2) They are generally effective on graminaceous>>broad-leaved weeds and their order of activity on crabgrass is D>A, B, C, but A has considerable action to broad-leaved weeds.
(3) Crop tolerance was tested in severe conditions. Soybean, radish, cotton and buckwheat are similarly resistant, and rice and cucumber are sensitive to these chemicals, but B is exceptionally low toxic to rice.
(4) The order of leaching of the compounds by water in the soil is A>>C>D>B. The order of residual activity of these compounds in the soil is D>A>>B>C, and B has considerable toxicity ever 60 days after the treatment.
(5) In paddy field condition, B is the only practical compound which has low toxicity to transplanted rice and is very effective on barnyardgrass, broad-leaved weeds and slender spikerush, hence it was found to be promising herbicide for transplanted rice culture.
(6) In paddy field condition, herbicidal effect of compound B is perfect if water is more than 1cm deep, when barnyardgrass seed is emerging; and appropriate period of its treatment can be extended two times longer than that of PCP. B is easily diffusable in water and rapidly adsorped in soil even in the form of granule. B can penetrate into seeds of barnyardgrass in 0.5-1 hour and inhibits the young shoot growth.

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The combination effect of solan with carbaryl was tested on the preemergence and postemergence herbicidal effects and the selectivity for the purpose of brodening selectivity of solan.
(1) Additions of 0.02 to 0.1 percent (2 to 10g per are) of carbaryl to 0.45 to 0.9 percent (45 to 90g per are) of solan continued the preemergence effect for 10 to 30 days as compared with the check (no addition of carbaryl).
Generally, it was appeared that the continuance of preemergence effect increase for long time according to addition of carbaryl.
(2) The persistence of herbicidal effect in soil by combining solan with carbaryl was more longer in sandy clay than silty clay loam.
(3) The postemergence effect of solan by foliar application increased according to addition of carbaryl.
(4) When the ratios of concentration in percent of solan to carbaryl 0.45 to 0.2, 0.75 to 0.05 and 0.9 to 0.05 at postemergence treatment, no injury was observed in the tested tomatoplants.
(5) As above results, the most adequate combination-ratios of concentration in percent of solan to carbaryl for expecting sufficient pre- or postemergence herbicidal effect and the persistence in soil, -were 0.25 to 0.1, 0.45 to 0.06-0.1 and 0.9 to 0.02-0.04 at application.
From a economical standpoints, it was assumed that most controled combination was when the ratio of concentration in percent of solan to carbaryl is 0.45 to 0.1.

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Chlorella elipsoidea assay was investigated to perform comparative activity-tests of herbicides. Chlorella cells have many good characters to fulfil our aims. The cultivation of the cell is possible all the year round, the growth speed is so rapid that the cell numbers become about ten times for 24 hours, and the growth inhibition can be determined colorimetrically. From our results, it may be concluded that this method involves assessment at the 50 percent toxicity level and utilizes certain concepts of probit analysis to herbicides, especially photosynthesis inhibitors.

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An attempt has been made to survey the inhibiting action of N-phenylcarbamates, swep and CIPC, on the respiration which has been thought to be other site (s) of growth inhibition by these herbicides than photosynthesis.
Swep showed the inhibitory effect on the straight growth of avena coleoptiles by decreasing the respiration. In the case of the excised roots of rice plant and barnyard-grass, the respiration of the roots was also inhibited by swep. The oxygen uptake of the roots was much more decreased by treating with swep simultaneously with insecticides, carbaryl, diazinon and fenitrothion, than by treating with swep only. Swep and propanil showed a similar inhibitory activity to the respiration of sweet potato mitochondria.
Although it has been reported by other workers that the primary action of swep was the inhibition of photosynthesis, the results above mentioned suggested that this compound should also inhibit: the respiratory process of plant.

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