TREATMENTS FOR THE CONTROL OF SMUTS IN CEREAL CROPS

New Zealand Journal of Agriculture, Volume 63, Issue 3, 15 September 1941, Page 221

TREATMENTS FOR THE CONTROL OF SMUTS IN CEREAL CROPS

uiiiiiiiiiiiiiiiiiiiiiiiiiiiiin By milt imuimiin

D. M. E. MERRY,

1 Instructor in Agriculture, Nelson =

r T"’HE cereal smuts of oats, wheat and J, barley cause heavy annual losses, barley cause heavy annual losses, which now more than ever must be prevented. Smut fungi are of two types, perpetuated by (1) spores carried on the exterior of the seed or (2) fungous threads (hyphae) embedded in the tissues of the seed. These differences govern methods of treatment.

Oat Smut

The oat is susceptible to loose-smut (Ustilago avenae) and covered-smut (JJstilago kolleri) , both of which are readily controlled by treatment with organic mercurial dusts. The fungous spores producing loose-smut of the oat are carried by the wind from smutted to clean heads, usually at about the time the grain in the healthy ears is 1 nearing maturity. Infection arises through one or more spores lodging in the enveloping husk, where the spore remains, if untreated, until the next sowing season. It then germinates along with the germinatinggrain, and the fungous hyphae penetrate and grow along with the oat plant. Infected plants may indeed be wholly indistinguishable from others, although in some cases they are said to grow even more vigorously. ” At about the time the grain in the ear should be maturing the familiar brownish-black smut heads appear in the diseased plants, and the smut spores are wind-borne to continue the fungous life cycle by reinfecting

Siititiimimtmtmmmiiiiimiiiiiiiiimmiiiiitmiiimiitiiiii? healthy ears. Eventually, only the bare and barren oat straws remain. Covered-smut of the oat replaces the grain by a mass of smut spores, but, unlike loose-smut, the spores of which are carried away on the wind, coveredsmut spores are spread at threshing when the smut masses are broken and distributed through the grain. As both infections are carried externally and do not develop further until the next sowing season, dusting or pickling is an effective means of control.

Loose-smut Of Wheat

in contrast, loose-smut of wheat (Ustilago tritici) differs in its mode of infection in that the spores, while also wind-spread, are liberated principally in the early flowering stage of the crop. They lodge on the floral parts of healthy ears, immediately germinate, and produce hyphae, which penetrate the ovarian tissues, remaining there, in a dormant state while the grain matures normally. Such infected grain is indistinguishable from healthy grain. When infected seed is sown the fungus grows parasitical-' ly along with the wheat plant, and converts the developing grain into masses of black smut spores. Once

again the wind disperses the spores to - other plants, leaving barren stalks. Loose-smut of barley is caused by the same fungus. The covered-smut of wheat (Tilletia foetens ■ and T. caries) and barley (Ustilago jensenii) , familiar from the masses of spores held within the skin, which in healthy plants envelops the grain, are recognisable by their offensive and fishy odour. From this characteristic they are commonly known as “stinking-smut.” Infection seriously lessens the value of the. crop for milling purposes. The masses of spores are liberated at threshing, and contaminate healthy grain. As the spores adhere to the outer seed coating and do not develop further until sowing time, they are readily controllable by surface treatment with organic mercurial or copper carbonate dusts. Because they are internally seedborne infections, the control of loose-

smut of wheat and barley is more difficult. In practice, it has been found that the only satisfactory method of treatment is to immerse the grain before sowing in water heated to a ternperature sufficient to kill the hyphae without injuring the embryo. Treatment often lowers the germinating vigour of the seed, and increases the time it takes the seedling to appear above ground.

Clean Seed Lines

In the main cereal growing districts of New Zealand much work has been done in freeing the principal varieties of wheat and barley from loose-smut infection, and relatively clean seed lines are now available either in certified (wheat) or commercial lines of wheat and barley. These may be several times removed from an origi-

nally hot-water treated line yet show high smut-freedom, as they have not sub i eco reinfection . - ' In the Nelson district, where milling wheat is not grown, the variety Major is commonly sown as a feed wheat, Seed has for many years been saved from crops containing appreciable percentages of loose-smut, but control of this disease is now being undertaken.

A small acreage has been sown in Nelson of suitably hot water treated Major wheat seed, which should provide a nucleus line for more widespread sowings of clean seed in subsequent seasons. As may be appreciated from the foregoing description of smut diseases, the wise farmer will either purchase oats, wheat, and barley which have been given a fungicidal treatment (dust or pickling solution) for the checking of these diseases, or will treat the seed himself. Freedom from in wheat and barley can be assured only by sowing lines known to be from disease-free stock, or which are recently removed from, or have received, hot-water treatment.