Summary. 1. Laboratory methods of evaluating herbicides were developed to determine their relative effectiveness as inhibitors of seed‐germination, seedling growth and juvenile plants under photosynthetic conditions.
2. Chemicals such as dinoseb, PGP and diquat were found to be very toxic to seeds, all of them having an MDso lower than 4 × 10−5 for both radish (Raphanus sativus L.) and Sudan grass (Sorghum sudanense Stapf).
3. Of the chemicals examined, the most toxic to radish seed were dinoseb, PCP, octochlorocyclohexenone, tetrachlorophenol, 2,4‐dinitrophenol, hexachloro‐2,5‐cyclo‐hexadiene‐1‐one and pentabromophenol in that order. Nitrophenols were more toxic to the seeds than the corresponding chloro‐derivatives but pentachloronitrobenzene was inactive.
4. 2,6‐Dichlorobenzonitrile and chlorpropham (CIPC) were found to be especially toxic to Sudan grass seed.
5. 2,4,5‐T, 2,6‐dichlorobenzonitrile and diquat were extremely toxic to germinating cucumber (Cucumis sativus L.) seeds, while the latter two and chlorpropham were very toxic to Sudan grass seedlings. Other herbicides which were quite phytotoxic to plants in this stage are 2,4‐D, 2‐methoxy‐3,6‐dichlorobenzoic acid (cucumber), dinoseb, PGP, EPTC and 2,3,6‐TBA (Sudan grass).
6. Diuron, atrazine, monuron and simazine were found to be quite inactive on the seeds and seedlings tested but extremely phytotoxic to young cucumber plants grown in. the light. Molar concentrations from 10−7 to 10−8, applied only to the roots, were found to be lethal under the conditions employed. Ametryne, prometryne, 2,4,5‐T, JV‐(3,4‐dichlorophenyl)‐N'‐methoxy‐JV'‐methylurea and EPTC were also lethal at this dosage while fenac, 2,4‐D and fenuron were lethal from 10−6 to 10−5 M.
7. In all the tests, 2,4,5‐T was found to be quite effective being especially toxic to germinating cucumber seeds.
Evaluation au laboratoire de quelques herbicides
Résumé
1. Des méthodes d'évaluation des herbicides au laboratoire ont été créées pour déterminer leur activité comme inhibiteurs de la germination et de la croissance des plantules et des jeunes plantes dans les conditions de la photosynthèse.
2. Des produits tels que le dinoseb, le PCP et le diquat ont été reconnus comme très toxiques pour les semences. Ils présentent tous une DLso inférieure à 4 × 10−5 pour le radis (Raphanus sativus L.) et le Sudan grass (Sorghum sudanense Stapf).
3. De tous les produits examinés, les plus actifs furent, dans l'ordre, le dinoseb, le PCP, l'orthochlorocyclo‐hexanone, le tetrachlorophenol, le 2,4‐dinitrophénol, l'hexachloro2,5‐cyclohexadiène‐l‐one et le pentabromophenol. Les nitrophénols furent plus toxiques pour les semences que les dérivés chlorés correspondants, mais le pentechloronitrobenzène fut inactif.
4. Le 2,6‐dichlorobenzonitrile et le chlorpropham (CIPC) se révélèrent particulièrement toxiques pour les semences de Sudan grass.
5. Le 2,4,5‐T, le 2,6‐dichlorobenzonitrile et le diquat furent extrémement toxiques pour les graines en germination de concombre (Cucumis sativus L.) cependant que les deux dern...
