One of the most common of the head smuts of grasses is caused by Ustilago bullata. It complicates the cultivation and production of several of our best forage grasses. More than 60 species of grasses have been reported as hosts to it, among them wheatgrasses, bromes, fescues, wild- ryes, and barley grasses. In 1946 it was thought that head smut in mountain brome, one of our most valuable forage grasses, was under control through the release of a new variety, Bromar, which was developed jointly by the Department of Agriculture and the Washington Agricultural Experiment Station. In repeated tests the new strain had remained resistant to the various races of the head smut fungus. In 1950, however, an entirely new and very virulent strain of head smut made its appearance and caused some very badly smutted fields of Bromar mountain brome. There are 12 known races or strains of the head smut fungus, each of which is specialized to different species of the wheatgrasses, bromes, wild-ryes, and barley grasses. None of the cereals is susceptible to it.

Several dozen other head smuts of grasses constitute a potential problem among economically important forage or range grasses. Practically nothing is known concerning the life history and methods of controlling most of them.

LEAF SMUTS are of two types: The spot or blister smuts (Entyloma species) and the stripe smuts (Urocystis and Ustilago species).

The spot or blister smuts appear as flat or slightly raised, blackish, round or oval spots in the leaves. Although rather widely distributed, they seldom cause great losses. Once in a while spot smut develops in a bluegrass lawn to such an extent as to cause premature yellowing and death of the leaves. With the stripe smuts, however, it is quite a different matter.

The stripe smuts are evident in the leaves as black stripes, which contain the smut spores. The spores are shed and dispersed into the wind. Afterwards the affected leaves take on a shredded and curled appearance and soon wither. Affected plants quite frequently are dwarfed and contorted and produce abnormal, sterile heads, if any at all. Seedlings of grasses affected with stripe smut are predisposed to drought injury and root rot. Mature plants often are so weakened that they cannot survive severe winters.

Most of the stripe smuts of grasses cannot be told apart by the unaided eye, but they are different enough under a microscope. One of the most common and most virulent is known as flag smut. Many grasses and cultivated wheat are its hosts. Flag smut has several strains, each capable of attacking different groups of grasses.

Another of the common and destructive stripe smuts is the one that has long gone under the name of stripe smut or leaf smut. It has the same effect on its grass hosts as does flag smut and affects many of the same grasses, including some of our best forage grasses the wheatgrasses, bromes, wild-ryes, fescues, and barley grasses. None of the cereals is known to be susceptible to it. Stripe smut is carried on the seed and can be controlled by seed treatment.

Still another type of leaf smut is the "sausage" smut of the grama grasses. It produces small but conspicuous blisterlike (often sausage-shaped) black Pustules on the leaves of the grama grasses, which make up a valuable component of our western ranges. It is restricted to the grama grasses, but often is widespread and undoubtedly results in reduced forage. Its life history is not known. Methods of control therefore have not been developed.

STEM SMUTS (Ustilago species) are represented by several species that develop in significant abundance on economic grasses. All are marked by the development of conspicuous, dusty, brown or black layers of smut around the internodes of the stems. Sometimes nearly all the internodes seem to be smutty. Sometimes only the top one or two seem so. At first the smut is hidden by the leaf sheath that envelopes the stem, but as the stem elongates, the smut is exposed.

The stem smuts occur on some of our most valuable forage grasses the wheatgrasses, wild-ryes, some of the bluegrasses, the needlegrasses, Indian ricegrass, and a few of the fescues.

Quackgrass is commonly infected. It might indeed furnish a supply of smut for the infection of more desirable grasses such as crested wheat-grass, big bluegrass, and blue wild-rye. A peculiar feature about the quackgrass stem smut is that an incubation period of 2 or 3 years is required after infection before the smut appears. The smut is perennial in the plant once it becomes infected. After the incubation period, the plant will produce a crop of smutty stems each year as long as it lives. Infection takes place in the vegetative tissues and thus spreads from plant to plant in a field.

THE CONTROL OF GRASS SMUTS is accomplished mainly in two ways: Chemical treatment of the seed in the case of seed-borne smuts and through the use of resistant varieties or strains.

Not all of the grass smuts can be controlled by seed treatment; but most of the head smuts and the stripe smuts can be. Among the grasses that could be expected to respond favorably to seed treatment for the control of smut are the various wheatgrasses, mountain brome, rescuegrass and related bromes, tall oatgrass, Canada wild-rye and other wild-rye grasses, big bluegrass and perhaps other of the bluegrasses, and the barley grasses. Such seed treatment for the control of smut will also help protect the seed and seedlings from seed decay and damping-off.

The procedure of treating grass seed with chemicals for the control of smut is much the same as that employed with cereal seeds and thus consists in principle of thoroughly applying a certain amount of a seed-treatment chemical to a certain weight of the seed and thoroughly mixing the two. However, comparatively little is known of the effectiveness of such control for many of the grass smuts. This is probably because intensive grass cultivation is relatively recent and the need for such knowledge has not been strongly felt.

The organic mercury dusts and some of the organic sulfur dusts generally are effective in the control of some of the grass smuts. New Improved Ceresan and Ceresan M, 1 ounce to a bushel, have given excellent control. Over-dosage, however, hurts the seed and reduces the stands.

The organic sulfur dusts, Arasan, Arasan SFX, and Tersan, at 3 to 4 ounces to a. bushel, likewise have given good control but not so consistently as organic mercury materials. They have an advantage, however, in that danger of overdosage is less. In fact, these three fungicidal dusts can be applied at maximum dosage (that is, all that can be retained by the dry seed) with little or no seed injury. This tolerance of grass seed to maximum dosage of certain of the fungicides is an advantage if small lots of seed are to be treated. Then it is not practical to attempt to weigh out minute quantities of fungicide, as needed on an ounce-per-bushel basis. Therefore, it is convenient to be able to apply an excess of the fungicide to the seed and, after mixing thoroughly, shake off the excess fungicide and not have to worry about overdosage. Others of the newer fungicides appear promising and eventually testing may show them to be as reliable as the ones here mentioned or possibly even superior.

Better results are had if the seed is stored in the treated condition for a few days. As much as 8 weeks will do no harm. It is possible therefore to treat the seed well ahead of the rush of planting time.

Comparatively little progress has been made toward the control of grasssmuts through the use of resistant varieties. In the various studies that have been made of head smut, stripe smut, stinking smut, and others, and in nursery row observations, it has been noticed repeatedly that resistant lines or strains do exist, but very few attempts have been made to combine that resistance with superior agronomic qualities by the process of hybridization and selection. It is a neglected field of endeavor that merits attention, especially with regard to certain smut-susceptible species of forage grasses.

Certain it is that the smut diseases of grasses are going to come more and more into prominence as our grassland agriculture is extended. We should not delay, therefore, to make studies of the life histories of the grass smuts for which this information is lacking, because only on such a basis can intelligent control measures be devised.

GEORGE W. FISCHER is chairman of the department of plant pathology in the State College of Washington.

Fungus fruiting body.