The effects of dry heat and torching on seed germination in exotic morningglories (Ipomoea triloba, I. lacunosa, I. purpurea, I. hederacea var. integriuscula, I. coccinea) were investigated; we also studied seed survival after torching and subsequent immersion in water. When seeds were dry-heated at 80°C for 30minutes, germination was 21.1∼97.8%. Germination rates after this treatment were low for I. lacunosa and I. purpurea (21.1% and 47.8%, respectively), but much higher in the other 3 species (72.2∼97.8%). When the seeds were torched for 3 seconds, all five species exhibited almost complete germination (94.4∼100.0%). The seeds of the five morningglories were completely killed by water immersion for two months following torching. These findings suggest that by flooding fields with water following burning of the soil surface after seed dispersal it is possible to effectively manage Ipomoea species.

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We studied the effect of soil sterilization with hot water on the germination and viability of paddy weed seeds. Laboratory experiments showed that seeds of Echinochloa oryzicola, Scirpus juncoides var. ohwianus, and Oryza sativa (weedy rice) lost their ability to germinate after heat treatment at 70°C for over 30min or at 60°C for over 180min in hot water. Soil was sterilized with hot water at about 90°C sprinkled at the rate of 120lm⁻² on soil covered with plastic film under the field condition. The treatment increased the soil temperature at 6cm depth to 73°C and maintained it at over 60°C for 150min. One month after the treatment and following the transplantation of rice seedlings, the heat treatment depressed the number of emerged weeds as much as typical herbicide treatment did, and neither treatment harmed the growth of the transplanted rice.However, at harvest time, the total fresh weight of weeds collected from the heat-treated plot was 2 to 3 times as much as that of weeds collected from the herbicide-treated plot.We investigated the survival rate of weed seeds buried in the soil after the harvest. About 50% of S. juncoides seeds survived in the herbicide-treated plot, but the rate had no correlation with the depth of burial. On the other hand, up to 5% of S. juncoides seeds survived at depths of 3, 6 and 9cm, and about 60% survived at 12cm in the heat-treated plot.

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The water beetle Hydrophilus affinis inhabits paddy fields where it uses the leaves of weeds for constructing cocoons within which it lays its eggs. Recently, abundance of H.affinis has decreased markedly in many regions of Japan and some prefectures have classified it as an endangered species. We considered whether this decline in abundance had occurred in response to the reduced occurrence of weeds in paddy fields and along the paddy levee separating fields. In order to acquire basic data for the conservation of this species, the relationship between H.affinis and weeds was investigated with particular emphasis on cocoon production. Weed leaves drooping from paddy levees were most frequently used for cocoon production with the cocoon found in plots along paddy levee numbering 9.3m^-2, which was significantly greater than the 0.5m⁻² observed for inside-paddy plots (Mann- Whitney U test, P<0.01). Forty weed species belonging to 18 families were found growing along the paddy levee, of which 16 species belonging to 11 families were used for producing cocoons. Analysis using Jacobs' selectivity index showed that H.affinis exhibited a highest preference for Commelina communis, Phalaris arundinacea, etc.
The site of cutting the leaves ranged from between the water surface to 1cm below. The size of the leaves used for producing cocoons ranged from 23mm to 34mm in length and 9mm to 20mm in width with the numbers of eggs in a cocoon ranging from 69 to 81. The number of eggs did not vary with weed species or leaf size.

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