28o YEARBOOK OF AGRICULTURE 1953 rusts of importance on grasses that can thus be controlled to any practical degree. Elimination of the alternate host has another advantage: It is on that host that hybridization between strains of rust takes place, often with Smuts That the result of new^ and more virulent strains capable of attacking varieties of grasses and cereals that previously Parasitize w^ere resistant. The development or selection of grasses resistant to rust has lagged Grasses behind such projects in the cereals. Strains have been noted in timothy, orchard grass, crested wheatgrass, blue George W. Fischer bunchgrass, big blucgrass, and others that are resistant to their particular Nearly 140 different species of smuts rusts. It is usually true, however, that attack approximately 300 species of those resistant strains are valid only in grasses in the United States. restricted regions and arc not generally The common name smut derives from resistant to the various and numerous words meaning to besmirch or smudge races or strains of rusts in all localities. and refers to the presence of sooty, The individual State colleges can best dirty, black, or brownish masses on the give advice on such local problems. affected plants. The fact remains that genetic resist- All the smuts are plant parasites. ance does exist in strains of most of Most of them occur on grasses and our forage grasses and can be used cereals. As wdth the rusts, the average in breeding work w^hen necessary or person is much more familiar with the desirable. destruction wrought by smuts on ce- reals than on grasses. Familiar ex- GEORGE W. FISCHER, a native of amples of destructive cereal smuts are Indiana, has degrees from Butler Univer- bunt or stinking smut of wheat, oat sity^ Northwestern University^ and the smuts, barley smuts, sorghum smut, University of Michigan. From ipj6 to and boil smut on corn. In everyday ^945 h^ ^^^ plant pathologist with the practice, the name smut is used to division of forage crops and diseases, designate the disease as well as the Bureau of Plant Industry, Soils, and fungus responsible for the disease, Agricultural Engineering. In ig4^ he although the latter is more correctly became chairman of the department of spoken of as the smut fungus. plant pathology at the State College of The smut fungi have much less com- Washington, plicated life histories than do the rust fungi and generally are easier to con- trol. The familiar dusty black smut masses are made up mostly of millions of tiny cells or groups of cells—spores, w^hich serve the same purpose to the smut fungi as seeds do to the seed- bearing plants, namely, for reproduc- tion and dissemination. Some smuts destroy the flow^ering structure. Others are restricted only to certain parts of it. Some are con- fined almost exclusively to the stems Germinating ergot sclerotia. of grasses. Others produce galls or SMUTS THAT PARASÎTIZE GRASSES 281 tumorlike structures in various parts Some of the smut fungi are not of their host plants. limited to seedling infection. Apparent- As with the rust fungi, many smut ly they can infect any succulent or fungi exhibit a remarkable degree of rapidly growing part of their host specialization not only to certain plants and thereby make them smutty species of plants but also to certain in time. The time between infection varieties or strains within those host and the appearance of smut varies species. Likewise, there are often rather widely. In the stripe smut of strains or races of the smut fungi to grasses, for example, seedlings often contend with. The common stinking show smut within 6 weeks of the time smut, for example, has nearly 30 the smut-contaminated seed is plant- known strains or races, each capable ed. Other smuts are not evident until of attacking different varieties of wheat their hosts head out. One of the stem and different strains or varieties of smuts, to be described later, requires wheatgrasses and related grasses. 2 to 4 years after infection before smut The smut fungi are not entirely actually appears. obligate parasites as are the rust fungi. Spores of the smut fungi generally In fact, some smuts can easily complete are much more durable than are their entire life cycle on an artificial those of the rust fungi. It is hard to medium if it contains the nutrients maintain viability of rust spores for essential for growth. Some smuts more than a year; usually it is much apparently persist indefinitely in the less than that. In the case of the smut soil or in old manure piles. They are fungi, it is unusual for viability to be fully capable, however, of attacking maintained for less than a year. For their host plants when the plants are most smuts viability is maintained for available under the requisite condi- two to several years, especially if tions for infection. humidity is low. Some smuts have The smut fungi have a more adverse been known to retain at least some effect directly (and perhaps indirectly) viability for 25 years. on their hosts than do the rust fungi. The cultivation of grasses seems to The smuts that attack all or parts of have much to do with the develop- the flowering structures generally de- ment of smut in them: Often cultiva- stroy the seeds entirely. The leaf tion practices, including harvesting smuts and the stem smuts, while only and threshing, disperse the smut and occasionally involving the flowering contribute toward an increase in the structures, do nevertheless generally amount of smut in succeeding crops. suppress these structures and likewise Any of the grass smuts therefore is a result in a more or less complete loss potential threat to the welfare of its of seed on affected plants. Thesmuts grass host if the grass comes under that attack the vegetative structures cultivation. (that is, the leaf smuts and stem smuts) Some of the grass smuts are the same have a decidedly weakening effect on as those that are destructive parasites their host plants and make them more of our cereal crops. susceptible to other sinister factors in their environment. SEED SMUTS or bunt {Tilletia species) Many of the grass smuts are seed- are terms used here to designate the borne. The wind carries millions of smuts of grasses in which the normal smut spores, which [)ecome lodged in seeds are replaced by smut ''balls." or on the developing seeds of healthy The balls retain somewhat the shape plants. When the seeds germinate, of the normal seed and are even the smut spores also germinate and encased by the seed wall; actually, infect the young seedlings. Then the though, the inside of the seed is a solid plants that arise from the seedlings are mass of spores. smutted. About 25 of these grass seed smuts 202 YEARBOOK OF AGRICULTURE T953 occur in the United States. Several of the grasses, I)ut only a few pose an have actual or potential importance in economic problem, probably because cultivated grasses. One of the poten- grasses have been cultivated only to a tially most important is the one that on limited extent. wheat is commonly called stinking One of the most common of the smut or bunt. Three species of fungi head smuts of grasses is caused by are involved in it, including what is Ustilago búllala. It complicates the commonly known as dwarf smut. cultivation and production of several These smuts are well known on w^heat of our best forage grasses. More than because of the very extensive losses 60 species of grasses have been re- they have caused for a long time the ported as hosts to it, among them world over. Besides wheat, tall oat- wheatgrasses, bromes, fescues, wild- grass and several of the wheatgrasses ryes, and barley grasses. In 1946 it was are known to be susceptible, including thought that head snuit in mountain crested wheatgrass, slender wheatgrass, brome, one of our most valuable for- and intermediate wheatgrass. Care has age grasses, w^as under control through to l^e taken to keep those grasses from the release of a new variety. Bromar, falling prey to the cereal smuts. which was developed jointly by the The dwarf bunt is soil-borne. It has Department of Agriculture and the thus far presented a knotty problem Washington Agricultural Experiment of control except when resistant vari- Station. In repeated tests the new eties are used. The other two species, strain had remained resistant to the being mostly seed-borne, may be various races of the head smut fungus. controlled by seed treatment and the In 1950, however, an entirely new and use of resistant varieties. very virulent strain of head smut made Some of the i^entgrasses are suscep- its appearance and caused some very tible to another of the seed smuts, badly smutted fields of Bromar moun- especially on the east and west coasts tain brome. There are 12 known races where considerable smut infestation is or strains of the head smut fungus, each vSon"ictimes encountered in harvested of which is specialized to different seed crops. The life history of this smut species of the wheatgrasses, bromes, is not known. wild-ryes, a.nd barley grasses. None of - Various other groups of grasses, for the cereals is susceptible to it. example the bromes, fescues, wild- Several dozen other head smuts of ryes, hairgrasses, velvctgrass, and grasses constitute a potential problem others, are prey to similar seed smuts. among economically important forage or range grasses. Practically nothing is HEAD SMUT (species of Sorosporium^ known concerning the life history and Sphacelotheca, and Ustilago) applies methods of controlling most of them. loosely to a variety of rather conspic- uous smuts that occupy all or part of LEAF SMUTS are of two types: The the flowering structures but do not spot or blister smuts {Entyloma species) replace the seeds themselves as do the and the stripe smuts {Urocystis and seed smuts I mentioned. By virtue of Ustilago species). prevalence, severity, wide distribution, The spot or blister smuts appear as and their very numbers, this group of flat or slightly raised, blackish, round smuts probably comprises the most or oval spots in the leaves. Although economically important group of the rather widely distributed, they seldom several here discussed. Familiar ex- cause great losses. Once in a while spot amples are loose smut of w^heat and smut develops in a bluegrass lawn to barley, loose smut of oats, covered such an extent as to cause premature smut of barley and oats, and kernel yellowing and death of the leaves. smut and loose smut of sorghum. Many With the stripe smuts, however, it is similar types of smuts occur on many quite a difl'erent matter. SMUTS THAT PARASITIZE GRASSES 283 The stripe smuts are evident in the brown or black layers of smut around leaves as black stripes, which contain the internodes of the stems. Sometimes the smut spores. The spores are shed nearly all the internodes seem to be and dispersed into the wind. After- smutty. Sometimes only the top one or wards the afifected leaves take on a two seem so. At first the smut is hidden shredded and curled appearance and by the leaf sheath that envelopes the soon wither. Affected plants quite fre- stem, but as the stem elongates, the quently are dwarfed and contorted smut is exposed. and produce abnormal, sterile heads, The stem smuts occur on some of if any at all. Seedlings of grasses our most valuable forage grasses—the affected with stripe smut are predis- wheatgrasses, wild-ryes, some of the posed to drought injury and root rot. bluegrasses, the needlegrasses, Indian Mature plants often are so weakened ricegrass, and a few of the fescues. that they cannot survive severe winters. Quackgrass is commonly infected. Most of the stripe smuts of grasses It might indeed furnish a supply of cannot be told apart by the unaided smut for the infection of more desir- eye, but they are different enough able grasses such as crested wheat- under a microscope. One of the most grass, big bluegrass, and blue wild- common and most virulent is known rye. A peculiar feature about the as flag smut. Many grasses and culti- quackgrass stem smut is that an incu- vated wheat are its hosts. Flag smut bation period of 2 or 3 years is re- has several strains, each capable of quired after infection before the smut attacking different groups of grasses. appears. The smut is perennial in the Another of the common and de- plant once it becomes infected. After structive stripe smuts is the one that the incubation period, the plant will has long gone under the name of stripe produce a crop of smutty stems each smut or leaf smut. It has the same year as long as it lives. Infection takes effect on its grass hosts as does flag place in the vegetative tissues and thus smut and affects many of the same spreads from plant to plant in a field. grasses, including some of our best forage grasses—the wheatgrasses, THE CONTROL OF GRASS SMUTS is ac- bromes, wild-ryes, fescues, and barley complished mainly in two ways : Chem- grasses. None of the cereals is known ical treatment of the seed in the case to be susceptible to it. Stripe smut is of seed-borne smuts and through the carried on the seed and can be con- use of resistant varieties or strains. trolled by seed treatment. Not all of the grass smuts can be Still another type of leaf smut is the controlled by seed treatment, but most *'sausage" smut of the grama grasses. of the head smuts and the stripe smuts It produces small but conspicuous can be. Among the grasses that could blisterlike (often sausage-shaped) black be expected to respond favorably to pustules on the leaves of the grama seed treatment for the control of smut grasses, which make up a valuable are the various wheatgrasses, moun- component of our western ranges. It tain brome, rescuegrass and related is restricted to the grama grasses, but bromes, tall oatgrass, Canada wild- often is widespread and undoubtedly rye and other wild-rye grasses, big results in reduced forage. Its life history bluegrass and perhaps other of the is not known. Methods of control bluegrasses, and the barley grasses. therefore have not been developed. Such seed treatment for the control of smut will also help protect the seed STEM SMUTS {Ustilago species) are and seedlings from seed decay and represented by several species that damping-off. develop in significant abundance on The procedure of treating grass seed economic grasses. All are marked by with chemicals for the control of smut the development of conspicuous, dusty. is much the same as that employed 284 YEARBOOK OF AGRICULTURE 1953 with cereal seeds and thus consists in smuts through the use of resistant va- principle of thoroughly applying a cer- rieties. In the various studies that have tain amount of a seed-treatment chem- been made of head smut, stripe smut, ical to a certain weight of the seed and stinking smut, and others, and in nurs- thoroughly mixing the two. However, ery row observations, it has been no- comparatively little is known of the ticed repeatedly that resistant lines or effectiveness of such control for many strains do exist, but very few attempts of the grass smuts. This is probably have been made to combine that resist- because intensive grass cultivation is ance with superior agronomic quali- relatively recent and the need for such ties by the process of hybridization and knowledge has not been strongly felt. selection. It is a neglected field of en- The organic mercury dusts and some deavor that merits attention, espe- of the organic sulfur dusts generally are cially with regard to certain smut-sus- effective in the control of some of the ceptible species of forage grasses. grass smuts. New Improved Ceresan Certain it is that the smut diseases and Ceresan M, i ounce to a bushel, of grasses are going to come more and have given excellent control. Over- more into prominence as our grassland dosage, however, hurts the seed and agriculture is extended. We should not reduces the stands. delay, therefore, to make studies of the The organic sulfur dusts, Arasan, life histories of the grass smuts for which Arasan SFX, and Tersan, at 3 to 4 this information is lacking, because ounces to a bushel, likewise have given only on such a basis can intelligent con- good control but not so consistently as trol measures be devised. organic mercury materials. They have an advantage, however, in that dan- GEORGE W. FISCHER is chairman of the ger of overdosage is less. In fact, these department oj plant pathology in the State three fungicidal dusts can be applied College of Washington. 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 advan- tage if small lots of seed are to be treated. Then it is not practical to attempt to weigh out minute quanti- ties of fungicide, as needed on an ounce-per-bushel basis. Therefore, it is convenient to i)e 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 lungicides appear promising and even- tually 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 grass Fungus fruiting body.