Crowdy: Symposium on Systemic Fungicides. Part 1 225

Symposium on Systemic Fungicides. General Discussion Part 1 Chairman: Professor S. H. Crowdy

Professor S. H. Crowdy (University of Southampton) :- What do we know about how seed dressings get into the plant? Is it taken into the seed for later distribution through the plant or is the material taken from the soil by the roots, in which case is movement through the soil at about the same speed as the growth of the roots?

Dr. R. B. Maude (National Vegetable Research Sta- tion) :-In tests of the penetration of non-systemic (thiram) and systemic (benomyl) compounds into pea seeds we found that one of the main features of this penetration of the systemic compound was that of mobility. Benomyl could be detected deep in the cotyledon tissues and in the plumules which emerged from treated seeds. These results were not obtained for thiram which was quickly immobi- lised in the seed tissues.

Dr. K. J. Bent (I.C.I. Ltd., Jealott’s Hill Research Station):-We know little about this yet but studies of the pathways and kinetics of uptake of ethirimol from seed dressing into barley plants are in progress at Jealott’s Hill and elsewhere. The efficacy of control of barley mildew

by ethirimol dressings appears to depend upon the amount applied per acre rather than the amount applied per seed: this suggests that diffusion into and through the soil followed by root uptake is the dominant pathway of absorption.

Mr. E. Ramand (Pan Britannica Industries, Waltham Abbey):-The advantages of seed dressings of any kind whether fungicide or insecticide are (1) convenience of dressing the seed in the factory; (2) placing the chemical completely around the seed - a job very difficult to carry out in the field; (3) in case of a seed-borne or seedling disease the chemical is taken up by the seed or early root system to protect the germinating plant.

Soil application, on the other hand, is time consuming at a time when the work load is very high on farms. There is also the possibility of applying the chemical and not getting it in the zone of activity nearest to the seed. Finally there are problems of highly organic soils which increase adsorption and leaching by rainfall, in case of soluble materials.

Pestic. Sci., 1971, Vol. 2, September-October