Net blotch and kernel blight incited by Pyrenophora teres (Helminthosporium teres) occur on barley only. The characteristic symptoms are netted blotches or irregular stripes on the leaves, brown discoloration on the culm, and light brown, indistinct blotches on the kernels. The size of kernels is reduced, but badly shriveled grain is uncommon. The sexual stage of the fungus is produced abundantly on the old stubble and straw.

At least two distinct races of the pathogen have been identified. They react differently on the two general groups of barley. C. W. Schaller, of the California "Agricultural Experiment Station, and R. G. Shands, of the Department of Agriculture and the Wisconsin Agricultural Experiment Station, found that resistance to the western race is concentrated in the Manchurian-Oderbrucker group of barleys, including Peatland (C. I. 5267), whereas resistance to the eastern race is concentrated in the North African and Abyssinian barleys. Only a few in the Manchurian-Oderbrucker group are resistant.

Stripe disease incited by Helminthosporium gramineum occurs on barley only. The sexual stage of this fungus is not found in nature and the life cycle differs from that of other species. Seedling infection results in fungus invasion of all plant parts, and spores are produced during the period of barley flowering. Seed infection occurs from wind-borne spores.

All leaves of a diseased plant generally are affected. Chlorotic stripes appear on the young leaves as they unfold. The stripes turn brown and spread to the leaf sheath also when the leaves reach full development.

All spikes of affected plants are blighted and brown in susceptible barleys of the Manchurian type. Diseased plants of the Coast barleys in California frequently develop some seed. Spores are abundant on the striped plants during and after flowering. Kernels infected from wind-borne spores do not show the disease in the dormant seed.

Several physiologic races of the pathogen occur, but practical resistance to the known races has been obtained and incorporated into commercial varieties. Inheritance of resistance is conditioned by two or more factor pairs with resistance dominant or partially dominant. Several genes for resistance are reported. Those used most extensively for breeding are from Lion (C. I. 923), Peatland (C. I. 5267), Chevron (C. I. tilt), Brachytic (C. I. 6572), and Persicum (C. I. 6530.

Leaf blotch and kernel blight incited by Pyrenophora avenae (Helminthosporium avenae) occurs on oats and several related grasses. The disease and its pathogen resemble those of net blotch of barley. Small, brown spots or irregular blotches, which may spread over the entire leaf blade, are the characteristic symptoms. Defoliation occurs in winter oats in the Southern States and on very susceptible spring oats in North Central States. Kernel infection is not conspicuous. Yields are reduced when the leaf blighting is severe.

Crop rotation, plowing under crop residues, seed treatment with organic mercury compounds, and using resistant varieties are the recommended control measures.

Most of the commercial oat varieties are moderately resistant to the disease. Yellow leaf spot of wheat (Helminthosporium tritici-vulgaris) was reported first in Pennsylvania and Virginia, the eastern part of the region where soft red winter wheat is grown. It has since spread westward into the hard red winter wheat area of Kansas and Nebraska. It is of minor importance.

Leaf spot and blight of rye incited by Pyrenophora secalis (Helminthosporium secalis) first shows as a small brown spot, which spreads until the leaf blade is yellow and dry. Sexual spore cases are abundant on old rye straw. The disease is of minor importance if crop rotation and seed treatment are practiced. The first general occurrence of the disease was in North Central States in 1940.

Leaf spot (culm blight and kernel blight of barley, wheat, and grasses) is caused by Cochhobolus sativus (Helminthosporium sativum). The damaging seedling blight and root rot caused by the fungus is described on page 321. The brown leaf spot phase is common on barley. The spots spread to cause yellowing and the death of the leaves. Diseased kernels of barley and wheat are dark brown or almost black, especially near the germ end of the kernel. That condition sometimes is called black point. Kernels infected early are shriveled and light in weight. The sexual stage of the fungus has been produced readily in culture through mating of compatible lines of the fungus by two Canadian scientists, R. D. Tinline and P. M. Simmonds.

The disease is controlled by maintaining good fertility of the soil, crop rotation, seed treatment with organic mercury compounds, and the use of resistant varieties.

D. C. Arny, of the Wisconsin Agricultural Experiment Station, found resistance in barley to be controlled by a single factor pair when using Lion (C. I. 923) as the susceptible parent and races of the pathogen found in the North Central States. The more resistant barleys are in the Manchurian group including Peatland and Chevron. Mars (C. 1. 7015) and Moore (C. 1. 7251) are resistant commercial varieties.

Victoria blight of oats, incited by Helminthosporium victoriae, a relatively new disease, has nearly eliminated several high-yielding, rust- and smut-resistant varieties that had been obtained from crosses with Victoria. It is primarily a seedling and culm disease. Leaves show a reddish-brown striping or spotting. The straw breaks over as the crop is heading. The grain is shriveled and chaffy, largely because of infection at the base of the culm. The pathogen is carried over on the seed. The straw and stubble of susceptible varieties are darkened by the mass of conidia (asexual spores), which are produced at the nodes as the plants are killed and cover the surface of the straw in late fall and the following spring. Infected seed and crop residues spread the pathogen to the crop the following year.

Seed treatment with organic mercury compounds reduces seedling loss but does not control the later culm, blight. Apparently only oats derived from Victoria hybrids are very susceptible to the disease. Investigations at the Iowa and Wisconsin Agricultural Experiment Stations and at the Dominion Rust Laboratory, Winnipeg, Canada, indicate that susceptibility to Victoria blight is not completely linked with the Victoria type of crown rust resistance and that a factor for resistance to crown rust can be used without bringing in susceptibility to Victoria blight.

SEPTORIA LEAF AND CULM blights are common on cereals and grasses. The leaf blotches and spots frequently are indefinite in color, shape, and margin. Usually the leaf and culm tissue surrounding the lesion bleaches slowly and turns straw color or brown, depending somewhat on the host. As the leaves bleach or as the diseased plants approach maturity, the small, regular spore cases (pycnidia) develop beneath the leaf surface of the diseased areas. These are globe-shaped, with a definite opening to the surface and light golden brown to brown in color. The abundant spores borne in these spore cases are slender to threadlike and colorless to light yellow. The different species are based largely on the length of the spores and on the hosts upon which they develop. The slender spores are wind-borne.

The damage they cause results largely from shriveled kernels and lodging. Shriveled kernels and reduced yields are common in susceptible varieties. The damage in susceptible varieties of wheat, barley, and oats is similar to that caused by stem rust.

Control is difficult as the spore cases are produced in abundance on the old straw and stubble. Crop rotation, plowing under old straw, and the use of resistant varieties offer the only means of control. Many of the older varieties are moderately resistant to the disease. Some of the newer varieties of wheat, oats, and barley are susceptible. Cereal breeders, in their search for better rust resistance, sometimes have used septoria-susceptible varieties as parents, but that has meant an increase in damage from this group of diseases.

The septoria blights of grains and grasses are incited by several different fungus species. Each is restricted to a particular grain crop and its closely related grasses. I list the common species on the grain crops.

Wheat: Two species are common on wheat, Septoria tritici, a long-spored species that attacks mainly leaves and is widely distributed; and S. nodorum, a very short-spored species that attacks leaves, culms, and heads.

Barley: S. passerinii has thin, medium-long spores and occurs on cultivated barley and some of its wild relatives. Varieties of the Manchuria-Oderbrucker type are susceptible or moderately susceptible. Dorsett (C. 1- 4821), Valentine (C. I. 7242), and Jet (C. I. 967) used extensively in breeding are resistant. North African and Egyptian types often show considerable resistance. Atlas (C. I. 4118) and Atlas 46 (C. 1. 7323) are resistant commercial varieties of the Coast type.

Oats: S. avenae has medium-narrow, short spores and produces the sexual stage abundantly on susceptible varieties. The varieties from Bond are relatively susceptible to culm rotting by this species, and perithecia develop on the old diseased straw. A relatively large number of grasses including wheat are attacked by this species and its varieties. Most of the commercial oat varieties other than those derived from Bond are relatively resistant.

Rye: S. secalis has slender, medium-short spores. This species and variety occur on rye and related grasses especially in the north central area.

RHYNCHOSPORIUM LEAF SCALD and kernel blight is primarily a leaf scald of barley, rye, and numerous grasses, although kernel blight is common in the southwestern barleys grown during the winter. The leaf scald appears as oval to irregular areas, which at first are water-soaked and gray green and later become zonated and yellow or brown and gray green. The pathogen produces a mat of tiny colorless asexual spores in the gray-green surface of the lesion. The spores are scattered by rain and wind. Spores are produced abundantly on crop residues especially during cool weather. The pathogen has specialized races, which are restricted closely to the different small grain and grass species. Experiments at the California Agricultural Experiment Station indicate losses in yield of barley up to 20 percent when leaf scald is severe. Early development of scald reduces the number of kernels; later infection reduces kernel weight. Atlas 46 (C. I. 7323), Trebi (C. I. 936) and some experimental varieties are highly resistant. Many of the Manchurian barleys are relatively resistant.

JAMES G. DICKSON is professor of plant pathology in the University of Wisconsin and an agent of the division of cereal crops and diseases of the Bureau of Plant Industry, Soils, and Agricultural Engineering. He has been engaged in investigations of field crops and their diseases since 1915.