It has been confused with one or another of the blights of celery and with brown check and cracked stem but differs from them in several important respects. M. A. Smith and G. B. Ramsey, of the Department of Agriculture, have described the chief symptoms of brown spot as irregular, light-tan or reddish-brown, shallow lesions, which occur on any of the above-ground parts of the plant. The lesions may unite to form a scurfy brown streak all the way up the inside surface of the stalk. Transverse cracks may develop across the large lesions and the fungus fruits in the cracks as well as on the surface of stalk and leaf spots.

A certain amount of distortion of growth may occur. The fungus produces many small, elliptical or elongate, one- and two-celled spores on the surface of infested areas. Although the fungus was first found and is much worse on the Utah Pascal types of celery, it occurs also on the Golden Self Blanching types and has affected as high as 85 percent of the plants in a field.

Growers are concerned about this disease for several reasons. Because its fungus is a rapid, heavy sporulator, it probably requires more frequent applications of fungicides if satisfactory fungicides can be found. Because it often attacks inner stalks and heart leaves, the plant cannot always be trimmed down to a sightly, marketable product. Furthermore, plants from diseased fields, which look fairly free at harvest, when packaged at the wash house directly from the field for retail markets may develop unsightly reddish-brown freckles in transit or in storage.

The spores of Cephalosporium apii germinate best between 68 and 75 F. and not at all above 90 or below 45 . The fungus grows best at 75 .

Bordeaux mixture is more effective than wettable sulfur in inhibiting spore germination in the laboratory, but control measures have not been worked out in the field. Growers in New York up to 1952 failed to get very good control with either a low-soluble copper or a liquid Dithane spray applied as for blight control.

First attempts to isolate Cephalosporium from seed have failed. Fortunately a number of varieties are apparently resistant. These include Summer Pascal, Utah 52-70, Utah 15, a Department of Agriculture plant introduction 176789, and Tall Fordhook. Very susceptible varieties include Cornell 19, Golden Plume, Top Ten, Ten Grand, and Non Bolting Green Nos. 12 and 13 (from Hart and Vick), according to 1952 tests made at Cornell University by Ralph Segall.

STEM CHECK, brown check, or adaxial crack stem is another new disease of celery which has caused heavy losses from coast to coast since the introduction, in 1943, of the splendid variety Utah 10B. It begins as light-tan, shallow, sunken, greasy-looking spots on the inner surface of leaf stalks after plants are half grown. The spots or streaks turn dark brown and open up with a series of unsightly horizontal cracks. Sometimes typical symptoms of crack stem (known to be boron deficiency symptoms) occur on the outer ridges of the stalk but not always.

Affected plants are not stunted; in fact, the disease seems to be worse where ample fertility increases growth rate. The disorder has been traced by P. A. Minges, J. T. Middleton, and other California workers to a deficiency of boron in the presence of excessive supplies of potash within the plant. Susceptible varieties seem unable to take up as much boron as needed to protect them. This inability is probably an inherited character as certain strains of Utah, notably 10B and Utah Special, are very susceptible. Utah 16-5 and Top Ten are also moderately susceptible, while Utah 52-70, Utah 16-8, Utah 16 PC, and Summer Pascal, in field tests by the California scientists, were practically free from the disease.

Control is only a matter of avoiding the use of susceptible strains, or if they are grown, then withholding of potash and excess nitrogen, or spraying with boron solution, or both, may be desirable.

AT LEAST NINE VIRUS DISEASES attack celery. Three or four of them are widespread and cause heavy losses. None is seed-borne. None remains in the soil after infected roots decay. Most of them have several common wild or cultivated plant hosts, which act as perennial reservoirs of infective virus. Aphids are the usual vectors, but thrips carry spotted wilt and leafhoppers carry virus yellows.

Cucumber mosaic virus, of which there are a number of strains, is common from coast to coast. The first symptoms are vein clearing and mottling of inner leaves. The most prominent symptoms develop about a month later and include stunting, fern-leaf growth of some leaflets, and raised, dark-green, blisterlike areas on others. A closely related virus, causing southern celery mosaic, is established in Florida, Cuba, and Puerto Rico. It also occurs in the Northern States, where it caused heavy losses in 1950.

Often buff-colored and translucent, sunken spots develop on outer petioles. F. L. Wellman correlated the spread of the disease in Florida with east winds and the spread of winged forms of the melon and cotton aphids. The corn leaf aphid and others also can transmit the virus. The disease has often been observed to start nearest to weeds or diseased economic plants. Eradication of Commelina nudiflora dayflower or dewflower in the Sanford area of Florida gave a large measure of control. The more than 140 host plants of the cucumber mosaic virus belong to more than 3o families, among them pokeweed, groundcherry, milkweed, and catnip.

Western celery mosaic occurs in California and Colorado. Its symptoms resemble those of southern celery mosaic, except that the leaf mottling is usually followed by necrotic spotting. On the petioles white spots or streaks develop instead of brown sunken ones. The disease became destructive in Los Angeles County, Calif., in fields where celery was grown continuously. It can be controlled if growers in an area observe a 3-month celery-free period beginning in September each year. The virus is restricted to umbelliferous hosts; celery, carrots, celeriac, dill, caraway, coriander and wild weed hosts are unimportant. At least 11 different aphids carry the virus.

The viruses that cause southern and western celery mosaics apparently belong to the nonpersistent group of viruses. They are easily transmitted mechanically. A vector does not retain for long the ability to transmit it. This ability may be lost during the first feeding or in less than 15 minutes.

Spotted wilt occurs on celery chiefly in the cooler, coastal fog belt of California, where the virus attacks a wide range of truck crops and ornamentals.

Symptoms of spotted wilt on celery are most pronounced on the outer rather than inner stalks and begin on older leaf blades as numerous small yellow spots, which later become necrotic. Internal pockets of dead brown tissue develop inside the petioles and become more or less visual from without as sunken brown patches, which may rot and result in death of the entire leaf. Plants are stunted and worthless.

The vectors of spotted wilt virus are the tiny thrips, Thrips tabaci and Frankliniella insularis, which must pick up the virus while still a nymph and in which a period of 5 to 9 days must elapse before the insect can transmit it. Once infective, the insect remains so throughout pupation, emergence as an adult, and often until death. The virus is not transmitted through eggs of the infective female.

Control is through elimination of the host plants, including ornamentals, that harbor the virus in the off-season when celery is not being grown.

Spraying with one of the newer organic insecticides may be helpful in some cases. Tomatoes have been bred for resistance, but attempts to do that for celery have not been undertaken.

Celery virus yellows is caused by the aster yellows virus so common on lettuce and carrots. It is not to be confused with fusarium yellows, which is caused by a fungus in the soil. The symptoms on celery include shortening, twisting, yellowing, and delicate mottling of inner petioles and leaves, later many new shoots develop, and there is some stunting and a general yellowing. In California, 23 to 100 days may elapse before symptoms begin showing after inoculation of celery.

The vector is the six-spotted leafhopper. That insect overwinters in the egg stage on winter barley and to some extent on native grasses. After developing into adults, the leafhoppers begin in June to migrate to more succulent host plants; they do some feeding on infected plants, among them wild carrot, plantain, dandelion, chicory, perennial sowthistle, and some species of wild aster. After the insect has picked up the virus, an incubation period of 10 days must elapse, during which time the virus multiplies within the vector. The incubation period can be lengthened by heating the leafhoppers for periods up to 11 days at 91 F. After 12 days at this temperature they are no longer infective unless they feed again on a diseased plant. That accounts for the slower rate of spread of virus yellows during a hot summer.

Other celery virus diseases of less economic importance have been described in California under the names of western- cucumber mosaic, celery calico, celery yellow spot, crinkle leaf mosaic, and tobacco ring spot.

CONTROL OF VIRUS DISEASES depends upon doing away with the wild host plants harboring the virus, destruction of insect vectors, or use of resistant varieties. The first has been used in the control of the southern celery mosaic with considerable success in Florida. Destruction of weed hosts around celery seedbeds and plant houses in the north is being employed to reduce losses in the field. It is well known that when hay is cut, when pastures dry up, or when weeds mature, great migrations of aphids and leafhoppers take place when the weather is warm and the air calm.

R. C. Dickson in the Imperial Valley of California calculated some 40 million winged aphids on a mile front may pass in an hour and flights may keep up for many days or weeks. He found that an individual aphid may feed for less than a minute, before flying on to another host, so each plant may play host to many aphids a day.

Weekly spray or dust programs against the insects after the diseases appear have been disappointing in California, probably because the migrating females that bring in the viruses are not killed quickly enough to prevent their first feeding.

CELERY is also subject to attack by several parasitic nematodes such as the root knot nematode (Meloidogyne species), the sting nematode (Belonolaimus gracilis), the stubby root nematode (Trichodorus species), and the awl nematode (Dolichodorus heterocephalus), as well as to damping-off disease (Pythium species), pink rot (Sclerotinia sclerotiorum), black crown rot (Centrospora acerina), rhizoctonia crater spot, a fusarium seedling root rot, a bacterial soft rot (Erwinia carotovora), bud failure, and two or more physiogenic diseases, such as black heart, crack stem (boron deficiency), and a pale-yellow mottle leaf (magnesium deficiency).

A. G. NEWHALL is a graduate of the University of Minnesota and Cornell University. He has made research contributions in the fields of vegetable seed treatments; fungicide testing; and soil sterilization by heat, chemicals, and volatile fumigants. He is research professor of plant pathology at Cornell University.