Also necessary is sanitation the elimination of the sources of spores. The diseased leaves and old flowers should be removed in home gardens. Many growers also have found it desirable to remove the flowers from commercial plantings. If all debris is destroyed at the end of the growing season, a major source of infection is eliminated. It has also been suggested that the basal rosette leaves of L. candidum be cut off just below the ground line in midwinter. This variety should be separated from less susceptible ones and all types should be replanted in a different location whenever dug.

Control measures therefore for lily blight are nothing more than the application of general good growing procedures, supplemented with fungicidal sprays when necessary.

ONE OF THE MOST POPULAR lilies is Lilium longiflorum, the Easter lily. Of the several varieties, the one usually seen in florists' shops at Easter is the Croft, which was developed in the West Coast States, where the center of production still exists. At the time of its introduction and for many years thereafter Crofts were grown in greenhouses without much trouble from diseases. Then a puzzling leaf spotting or scorching began to be reported occasionally in different parts of the country. Finally, in the 1947-1948 forcing season it became prevalent on Croft lilies in many greenhouses in the East, and since has become increasingly serious in many sections.

The condition has been called leaf spot, leaf burn, tip burn, and leaf scorch. The last is the generally accepted term. The symptom usually seen begins near the end of the leaf as a semicircular spot, which may enlarge until the entire tip is affected. Such spots develop most often on the upper part of the plant and after the flower buds appear. Usually only a few leaves are affected, but in severe cases nearly all may be spotted. The condition is usually most severe on plants with light-colored leaves or on those forced rapidly. It appears more frequently following bright sunny days than cloudy ones. Such spots so disfigure the plants that the leaves may have to be trimmed with scissors before they can be marketed.

Although fumigation with nicotine for insect control had produced somewhat similar injury, leaf scorch sometimes appeared where nicotine had never been used. The disorder also resembled botrytis blight in many respects, but the usual blight control measures were ineffective. It differed from the blight in that the spots regularly occurred on the margins of the leaves, usually an inch or two from the tip, and never on the flowers; the botrytis spots were scattered on the leaves and numerous on the blossoms. The possibility that it was caused by a fungus was discarded when research workers demonstrated that the fungus could not be detected in typical scorched spots. So it appeared to be a physiological problem, and investigations since have proceeded on that basis.

Neil W. Stuart at the Plant Industry Station at Beltsville, Md., noticed in 1945 that lilies fertilized with nitrogen during forcing showed fewer scorched leaves than unfertilized plants. He followed the observation with experiments in the greenhouse, using various types of fertilizers. He found that under his conditions nitrogen fertilizer alone reduced the leaf burning, but the inclusion of phosphorus and potash in the mixture counteracted the beneficial effect of the nitrogen. He reported the experiments in 1949 with the statement that "more than one factor is concerned in the leaf-spotting problem."

The soundness of the statement has been emphasized by later work. The beneficial effect of nitrogen has been substantiated generally by experiments by John G. Seeley at Pennsylvania State College and A. N. Roberts and his associates at Oregon State College. Many treatments have responded quite differently in various parts of the country, however. Deficiencies of boron and magnesium, for instance, appeared to increase scorch in one sand-culture test and and not in another. Results with nitrogen have not always been consistent.

Some of these variable results can perhaps be explained now as a result of cooperative tests made by Stuart at Beltsville and William Skou and D. C. Kiplinger at Ohio State University. One of their treatments gave particularly interesting results. Ammonium sulfate at a rate of 1 ounce in 2 gallons of water was applied every 2 weeks to lilies in the greenhouse. At Columbus the treatment produced the least scorch. The total numbers of scorched leaves were much below those occurring on unfertilized plants. The treatment produced the most scorch at Beltsville, however, and nearly three times as much as occurred on the unfertilized plants.

The average number of scorched leaves per treatment was 32 at Ohio and 188 at Beltsville. What factors could be responsible for such different results? The investigators suggest that perhaps they were due to the differences in soil acidity and water. At Columbus the unfertilized soil had a pH value of 7.3; the water had a pH of 10.5; the soil after treatment with ammonium sulfate had a pH of 6.7. At Beltsville the original soil had a pH of 5.8; the water had an average pH of 7.3; and the soil after treatment with ammonium sulfate had a pH of 3.9. Thus, the soil acidity was markedly different at the two locations. They also reported that in another experiment at Beltsville the least scorch was present on plants grown in quartz sand with a complete nutrient solution plus 25 grams of calcium carbonate per pot. A similar benefit was obtained by adding dolomitic limestone to infertile acid soil.

The effectiveness of lime in preventing scorch of Croft lilies during forcing was investigated by A. N. Roberts, R. E. Stephenson, and S. E. Wadsworth at Oregon State College in 1950 and 1951. Although an application of nitrogen alone completely prevented scorch, the plants were poor and were apparently severely affected with a deficiency of phosphorus or potassium or both. Plants that received a complete fertilizer (nitrogen, phosphorus, potash, and sulfur) and lime at a rate of 8 tons an acre grew very well with only a small amount of scorch. The complete fertilizer without lime resulted in a high rate of scorch, especially in the presence of high amounts of manganese and aluminum. Lime at a rate of 5 tons an acre was less effective than at the 8-ton rate. Also, a high rate of lime overcame the scorching tendency of an unbalance of nitrogen and sulfur in one combination and phosphorus plus potassium in another combination. The lime naturally changed the pH of the soil somewhat; generally the scorch was more severe in the most acid soils. V. A. Clarkson at Oregon State College showed that typical scorch could be induced within about 10 days by the addition of dilute sulfuric acid to the soil.

Such data indicate that the pH might be the determining factor, but some of the additional data from Oregon show that there was no significant difference in scorch on two soils, one with a DH of 6.2 and the other with a pH of 5.0. They raise the question whether the value of the lime is in its neutralizing effect or in its ability to supply calcium to the plant.

In those studies and others it was noticed that plants grown from bulbs produced on different farms varied in the amount of scorch. In the 1950-1951 season, F. P. McWhorter assembled bulbs from 21 growers in California! Oregon, and Washington. The bulbs were forced at Beltsville, Ohio State University, and Oregon State College. Not only was there a different response by different stocks the relative performance often was different at the three locations. It was evident that the field "history" of the bulbs had a marked effect on the amount of scorch that developed when no fertilizer was used during forcing.

Mr. Roberts and others at Oregon State College in 1948 began studying the possible carry-over effect of fertilizer treatments in the field on forcing performance and scorch development in the greenhouse. Their experiments demonstrated also that the field "history" of the bulbs had a definite bearing on the amount of scorch that developed but that none of the field treatments tested prevented subsequent scorching in the greenhouse. One field treatment containing nitrogen, phosphorus, potassium, sulfur, and manganese actually increased the number of scorched leaves in the greenhouse. A field treatment with nitrogen, potash, potassium, sulfur, and lime was ineffective in reducing scorch, but in that test the lime was used at a rate of 3,480 pounds an acre, which may have been too low. In general, they found that the more complete the nutrition was in the field and the better the growth, the greater was the likelihood that scorch would appear in the greenhouse.

In addition it may be more of a field problem than has been realized heretofore, since F. P. McWhorter and C. J. Anderson in Oregon pointed out in 1951 that "it is probable that a considerable portion of the injury formerly attributed to Botrytis blight may have been due to the physiological disease, scorch."

Our knowledge of the cause and control of scorch is far from complete, although the studies I have reviewed have helped greatly. Apparently scorch follows unbalanced nutrition. The disorder is generally most severe in very acid soils and can be prevented to a great extent in them by heavy applications of calcium and nitrogen. In moderately acid soils it can apparently be alleviated by the use of nitrogen fertilizers alone. But the exact role of nitrogen and calcium and the possible influence of aluminum, manganese, and magnesium are not entirely clear.

Finally, in developing a suitable treatment, commercial factors other than leaf scorch must also be considered height of the plant, color of leaves, number of flowers. The control program ultimately based on the cause must be one that not only prevents the development of scorch but also one that promotes a good culture.

C. J. GOULD is a plant pathologist at the Western Washington Experiment Station (State College of Washington). He has been investigating diseases of ornamental bulbs since 1941. Dr. Gould has degrees from Marshall College and Iowa State College. He has studied bulb diseases in Holland under a Fulbright grant and has received with Dr. Neil Stuart the Society of American Florists' Award for outstanding research in 1950.

a, Fusarium spores; b, asci.