Among The Crops

Press, Volume XCVII, Issue 28701, 26 September 1958, Page 9 (Supplement)

Among The Crops

A wide range of weeds is encountered in crop production. Weeds of cereal crops are generally susceptible to the ordinary hormone materials, the crops themselves being unharmed by these herbicides.

Wild turnip, for example, is readily killed by hormone application and although Californian thistle may not be eradicated by one treatment, its ability to compete with the crop being sprayed is destroyed. Until the introduction of the phenoxybutyric acid derivatives, green pea crops were sprayed with semi-selective phenols which gave satisfactory control of most annual weeds if applied at the correct rate and stage of growth. The new MCPB has the advantage that rate of application, stage of growth of weeds, and weather conditions are not such critical factors in its use as they are when phenols ire employed. - However, certain weeds found in peas are not very effectively controlled by MCPB and the extent to which it will replace the phenols is not yet clear. Because root crops and most market garden crops are susceptible to the application of weedkillers in the usual way, a technique known as pre-emergence weed control is being evolved. Research work is continuing on this method and briefly it consists of applying a weedkiller such as TCA or CIPC to the surface of the ground after the crop has been sown. Annual weed seedlings germinating near the surface are killed, allowing the deeper-rooted seedling to establish relatively free of competition from annual weeds. Since* the selective grass-killing chemicals T.C.A. and Dalapon have been available much trial work has been done oq the removal of grassy weeds such as

browntop and Poa annua from lucerne stands. However, before using weedkillers for this purpose, the farmer .should satisfy himself that the reason for the invasion of grass weeds is not a reduction in lucerne vigour due to some soil fertility factor.

Young lucerne stands can be sprayed ,for the control of weeds with one of the new hormones, 24D8.