Hideo Chisaka

On Experiments for Assessing the Interaction in Herbicide Combinations with Isobole Method

To assess the interaction in combinations of the herbicides which are applicable to paddy rice, the isobole method was applied in pot experiments with barnyardgrass and rice.Three combinations (benthiocarb+simetryne, butachlor+simetryne, benthiocarb+propanil) among the seven tested combinations showed the synergistic effect, and the others were probably the additive effect. Interactive effects varied possibly with the testing factors, e. g. the response level defined for isobole and growth stage of test plants.Experimental arrangements for the isobole method were discussed.

On the Phytotoxicity of Several Herbicides to Young Seedlings and Weeds in Transplanting Rice Culture

水稲稚苗移植栽培の初期雑草対象除草剤を選定するために, ポット試験および圃場試験に各種除草剤を供試して殺草性について検討した。CNP粒剤およびNIP粒剤は, 田植前後の表面処理でマツバイに対する除草効果がやや劣るが, 一年生雑草には効果が大きい。稚苗に対する薬害はCNPおよびNIPとも比較的小さいが, 薬害発生の危険性は, NIPがCNPより大きい。CNPは適使用量幅が広く, 田植前土壌混層処理剤としても比較的安定している。TOPE粒剤は, 田植後処理でマツバイに効果がやや劣るが, 一年生雑草には除草効果が大きく, CNPやNIPよりも処理適期幅が広い。薬害発生の危険性はCNPよりさらに小さい。シメトリン粒剤は, 田植後処理で一年生雑草に除草効果が大きく, 残効期間も長いが, マツバイにはやや劣る。薬害は使用量が多いと発現するが, 水深・漏水条件によっても変動するおそれがある。TDW-43・シメトリンA粒剤は, 田植前・後の表面処理でマツバイ以外には除草効果が大きいが, シメトリンの薬害が発生する条件下では薬害発生の危険性がある。その他の供試除草剤については, 稚苗に対する薬害の面からさらに検討を要する。

Optimum Application Time of MCC [Methyl-N-(3, 4-dichlorophenyl) carbamate; Swep] in Dry-seeded Rice Culture

水稲に対して, 播種後～1葉展開前の処理では薬害はない。2.0葉期・3.0葉期の処理では著しい薬害を生ずる。ノビエに対する土壌処理効果は, 発生抑制および生育抑制として現われ, 残効期間は50g/aで2～3週間程度とみられる。雑草処理では, 50g/a の薬量で3.5～4葉までのノビエをほぼ完全に枯殺する。ノビエ以外の一年生雑草にも, 全般に高い土壌処理効果・雑草処理効果を有する。乾田直播栽培におけるMCCの処理可能時期は, 水稲播種後～出芽期 (1葉展開前) である。雑草の発生期間が長いことを考慮に入れると, 出芽期の処理が最も合理的である。その場合, 40～50g/aの薬量で, 抑草期間は播種後25日前後とみられる。PCP, NIP などの播種後処理にくらべると, 処理適期幅の長いことや除草効果の高い点ですぐれている。しかし, 乾田期間の短いときや雑草の発生が初期に集中するときなどの場合を除いて, MCCのみで乾田期間発生雑草を防除することは難かしく, 一般的にはDCPAとの結合が必要である。

Studies on Chemicals Effective for Breaking Seed-dormancy and for Killing Dormant Seed of Barnyardgrass (Echinochloa Crus-galli Beauv. var. oryzicola Ohwi) : 3. Activity of several chemicals used in contact with soil

Effectiveness of four chemicals, NIP (2, 4-dichlorophenyl-4-nitrophenyl ether), 1-isothio-cyanato-2-bromopropene (U-3), 1-thiocyanato-2-bromopropene (U-4) and DNBP (4, 6-dinitro-o-sec-buthylphenol), which showed high activity in the soaking treatment, was examined under the presence of soil using petri-dishes or 1/5000 a pots. Three methods were used for the treatment: spraying of the chemical solution to the seeds placed on the surface of water-drained soil, applying of the chemical solution to the seeds placed on the surface of water-submerged soil, and incorporating of the chemical solution to the upper layer of water-drained soil with the seeds. The results obtained were as follows: 1. Effectiveness of each chemical varied according to the method of treatment. NTP, U-3 and U-4 were more effective in the following cases: in case the effect of breaking dormancy by the method of treatment itself was higher, or in case the concentration of chemical solution in contact with the seeds was higher. This fact was especially remakable in NIP. DNBP was most effective when it is sprayed directly to the seeds. 2. The effectiveness in these treatments in contact with soil, in general, was markedly less than in the soaking treatment. Therefore, it was assumed that the treatment given under the presence of soil might have several factors decreasing the activity such as the adsorption and decomposition by soil or the vaporization of chemicals. 3. Generally speaking, such dosages as above 400 g/a in NIP, 200 g/a in U-3 or U-4 and 400 g/a in DNBP were required for full activity. 4. In order to establish the technique for breaking the dormancy or for destroying the germinability of dormant barnyardgrass seeds in soil by chemicals, it is important to find out not only chemicals with higher activity but also methods or factors which will improve the permeability of such chemicals into the seeds.