THE CONTROL OF LOOSE SMUT IN WHEAT AND BARLEY

Loose smut ( Ustilago nuda ) has become increasingly troublesome in some widely grown wheat and barley varieties in recent years. The usual control of the disease is hot water treatment of the grain, and experiments have been carried out to find the most satisfactory treatment. Variations in times and temperatures for each stage of the treatment were made. In preliminary small‐scale experiments, the moisture content of the grain after different periods of soaking in water was determined, together with the effects on such grain of subsequent treatment at increasing temperatures. Wheat was able to withstand higher temperatures than barley. After presoaking in cold water for 4 hr. a draining period of 3 hr. helped considerably in controlling the disease. After a warm presoak ( c. 90° F.) for 4 hr. the long drain was not necessary. The temperature of the grain in the hot tank must rise as rapidly as possible. Following the presoaking periods, 10 min. in the hot tank at 127–129° F. for wheat and 124–126° F. for barley were found to give control. Single tank treatments, e.g. 4 hr. at 113° F., also gave control. In general, the higher the temperature at any stage of the treatment, the greater the reduction in germination. The reduction in vigour was reflected in the percentage germination after j days. When sown, the plants from hot‐water‐treated seed were a few days later in appearing above ground compared with plants from untreated seed. After a week or two, however, no differences were visible. The tiller populations after earing were not closely related to the original germination percentage of the seed; plots which were thin in the early stages often tillered well. The effects of soaking in chloranil (Spergon) suspensions and in water alone was also investigated, the recommendations of Tyner being followed. No control was achieved in wheat by either treatment, but for barley both treatments gave control, but sometimes with serious reduction in germination.