Summary: Résumé: Zusammenfassung Sand‐culture techniques for determining the tolerance of fruit crops to herbicides applied to the roots were investigated. Of the methods examined, a single application to pots with a closed drainage system was the most useful provided they were protected from rain. A semi‐automatic system for applying herbicides was developed for use where repeated treatment was required. Visual scoring of plant condition was the most informative method of assessing response and was reliable. Results correlated well with weight measurements of leaves, shoots or whole plants. For each herbicide ED50 values were derived from dose‐response curves and used to express relative tolerance. The slopes of these curves provided an indication of the rate of change of response with dose. The relative tolerance of a range of fruit crops to simazine corresponded to known relative tolerance in field conditions in the U.K. It is concluded that sand‐culture techniques can be used as a preliminary screen to find new soil‐acting herbicides for perennial crops and to detect differences in tolerance between cultivars. They also enable the direct influence of plant and seasonal factors on response to root‐applied herbicides to be studied. Large numbers of treatments can be tested in a small area with the certainty of obtaining positive results. Evaluation des techniques de culture sur sable pour l'étude de la résistance des cultures fruitières aux herbicides agissant par le sol Les auteurs ont étudiè les techniques de culture sur sable pour déterminer la résistance des cultures fruitiéres aux herbicides racinaires, Parmi les méthiodes examinées, celle comportant une seule application, avec un systéme clos de drainage, s'est révélée la plus pratique, à condition qu'elle comporte une protection contre la pluie. Un systéme semi‐automatique pour l'application des herbicides a été mis au point pour les cas où des traitements répétés sont nécessaires. L'observation visuelle du comportement de la plante s'est montreée la méthode la plus instructive pour apprécier les réactions; c'est aussi une méthode súre. Les résultats ont montré une bonne concordance avec les mesures pondérales des feuilles, des pousses, ou des plantes entiéres. Pour chaque herbicide, les valeurs de la E.D. 50 ont étć déduites des courbes de réaction en fonction de la dose et utilisées pour exprimer la résistance relative. La pente de ces courbes a fourni une indication sur le taux de modification de la réaction en fonction de la dose. La résistance relative d'une série de cultures fruitiéres ȧ la simazine a correspondu ȧ la résistance relative constatée au champ dans les conditions du Royaume‐Uni. Il en est conclu que les techniques de culture sur sable peuvent être utilisées comme tests de sélection primaire pour découvrir de nouveaux herbicides agissant par le sol pour le désherbage des cultures pérennes, ainsi que pour déceler les différences de résistance entre cultivars. Ces techniques rendent ègalement possible l'étude de l'influence directe de l...
The success of dicamba-tolerant soybean [Glycine max(L.) Merr.] has revived concerns about plant growth regulator (PGR) herbicide exposure to conventional soybean. In laboratory studies, soybean root nodulation is inhibited by excess auxin, which is the mechanism of action of PGR herbicides. Soybean exposed to PGRs in a field environment may have a similar response, and if nodulation is compromised, nitrogen (N) fixation may be reduced, with subsequent seed yield or protein content decreases. Many soybean–N studies report minimal impact to soybean yield. However, if soybeans show foliar PGR injury symptoms, could N application compensate for a potential nodulation inhibition response? This study examined the response of non–PGR tolerant soybean to N after exposure to low doses of 2,4-D and dicamba applied once (at soybean growth stages V1, V3, and early reproduction [R1 or R2]) or twice (V1 + V3 or V3 + R). N was either foliar or soil applied at early (∼5 d after PGR application) or late (10 d after PGR application) timings. Nodulation and plant growth were evaluated at R3, and grain yield and seed protein and oil content were quantified at maturity. Plant biomass and nodulation were reduced by 10% with some PGR treatments, and early foliar N application after PGR injury resulted in reduction up to 25%. N applications to non–PGR treated soybean did not increase yield. Soybean treated with PGR at V1 or V3, with or without N, had yields similar to control treatments. However, yield reductions of up to 20% were observed when PGRs were applied at V5 or R stages or when double PGR applications were followed by early foliar N application. Seed protein and oil content were not affected by PGR or N treatment.
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