Another of the wheatgrass varieties of leaf rust (P. rubigo-vera agropyrina) is like the first one I described, but it occurs outside of the mountainous areas. Besides wheatgrasses, it attacks bromes, meadow foxtail, alkali-grass, mannagrass, the wild-ryes, and many others. The numerous alternate hosts are all in the buttercup family.

The wheat variety of leaf rust (P. rubigo-vera tritici) is restricted to various wheats and apparently will not infect grasses. The alternate host is meadow-rue.

The sixth variety, the leaf rust of rye (p. rubigo-vera secalis), is restricted to rye. Its alternate host is the wild forget-me-not or bugloss (Lycopsis). Leaf rust frequently is as destructive as stem rust. Occasionally infection is so heavy that the infected plants are literally dusty red with rust and may even be killed by it. As a species, leaf rust is widespread from coast to coast, although some of the varieties are limited by geography or climate.

STRIPE RUST (Puccinia glumarum) is quite different in appearance from stem rust and leaf rust. The individual pustules, instead of being orange red, are yellow and arranged in long rows or stripes. A cool-weather rust, it makes its best progress in the spring and early summer before hot weather sets in. It is restricted to the Rocky Mountain States and westward.

Stripe rust is found commonly on the various wheatgrasses, wild-ryes, bromes, and barley grasses, besides wheat, barley, and rye. Some grasses, such as crested wheatgrass and blue wild-rye, frequently are infected to the extent that plants are killed outright or are rendered easy prey to drought and other diseases.

The alternate host of stripe rust is unknown. Being a cool-weather rust, it overwinters easily without an alternate host.

CROWN RUST (Puccinia coronata) is really a leaf rust and to the unaided eye looks just like true leaf rust. The difference between the two lies in the black spore stage and in its alternate hosts. Under the microscope its black spores (teliospores) are seen to bear a crown of long projections at the top (hence the name crown rust); these are lacking in the leaf rust spores. Also, it has only a few alternate hosts cascara buckthorn (chittum bark) and related species of buckthorn (Rhamnus).

Crown rust occurs on oats, wild oats, and many grasses velvetgrass, English ryegrass, Italian ryegrass, meadow fescue, tall fescue, orchardgrass, and some of the bentgrasses, among them. It is of economic significance more in the Mississippi Valley than east or west.

BLUEGRASS LEAF RUST (Puccinia poaesudeticae) is common only on grasses. It does not occur on any of the cereals. As the name indicates, the chief grasses affected are the bluegrasses, but occasionally others (such as meadow fescue and alpine timothy) are infected. It occurs chiefly in the leaves and produces numerous, minute, orange-red pustules, but frequently stem infections occur. Of the bluegrasses, Kentucky bluegrass is by far the most commonly infected. It rarely develops in epidemic proportion in lawns and pastures, however, probably because of too frequent mowing or grazing, but in nurseries or other undisturbed stands heavy developments often occur. Several other valuable bluegrasses are commonly infected, sometimes very badly. Bluegrass leaf rust does not have a known alternate host. It over-winters easily and effectively in the red spore stage.

STEM RUST is controlled by eradicating the alternate host, the common barberry (Berberis vulgaris). In the interests of controlling stem rust on wheat, oats, barley, and rye, an active barberry eradication campaign has been in force in 18 States. The campaign also is in the interests of susceptible forage grasses. For example, in eastern Washington, before that State joined the eradication campaign in 1944, stem rust could be found on numerous grasses and sometimes in epidemic quantity. By 1951, with the barberry all but eliminated (except for numerous small seedlings), it was unusual to find stem rust in anything more than trace amounts.

In the States where crown rust is a problem, its alternate host, buckthorn, has been eradicated along with the common barberry. Those are the only 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 the result of new and more virulent strains capable of attacking varieties of grasses and cereals that previously were resistant.

The development or selection of grasses resistant to rust has lagged behind such projects in the cereals. Strains have been noted in timothy, orchardgrass, crested wheatgrass, blue bunchgrass, big bluegrass, and others that are resistant to their particular rusts. It is usually true, however, that those resistant strains are valid only in restricted regions and are not generally resistant to the various and numerous races or strains of rusts in all localities. The individual State colleges can best give advice on such local problems.

The fact remains that genetic resistance does exist in strains of most of our forage grasses and can be used in breeding work when necessary or desirable.

GEORGE W. FISCHER, a native of Indiana, has degrees from Butler University, Northwestern University, and the University of Michigan. From 1936 to 1945 he was plant pathologist with the division of forage crops and diseases, Bureau of Plant Industry, Soils, and Agricultural Engineering. In 1945 he became chairman of the department plant pathology at the State College Washington.

Germinating ergot sclerotic.