DIAGNOSIS OF DISEASES BY DR. GEORGE H. HEFTING (l)

Diagnosis is well defined by Webster as "the art of recognizing a disease from its symptoms." In animals many diseases can be identified and their course predicted (prognosis) without knowing the cause. Such is the case with cancer, gout, mononucleosis, and many other familiar diseases for which the cause is not known, In the case of plant diseases, none of which are psychosomatic, diagnosis virtually requires determining the cause, Having told you what diagnosis is, I would like to tell you--with respect to forest --one thing that it isn't. It is not, for most of us, a field to which the brave slogan, "Do it yourself" applies. If today's diagnosing physician had to trade places with a forest pathologist here are some of the things that he would discover: 1. Instead of one host species, Homo sapiens, he has to deal with 150 or more species. 2. The patient cannot say where, when or how it hurts. 3. He has no sophisticated techniques such as x-ray, electrocardiogram, blood sugar, and urine analysis, etc., at his disposal. 4. He is expected to cope with everything from awart to a cataract to leukemia. 5, He has over a thousand potential pathogens to consider among the causes of plant disease. Now you see where we are and why we need all the joint effort we can get from each other. Now we will look at how we go about diagnosing plant diseases. The sequence of steps is usually as follows: 1. What is the host plant? Genus and species? Exotic or native'/ In its normal environment or not? 2. 1-Jhat is the host organ involved? Do the symptoms indicate disease of the organs you have in the specimen at hand, or that the probably injury was to organs not represented·/ For example, all you see may be a dying of foliage, but the cause might well be a which you do not see. 3. What are the symptoms? Use visual, hand lens, dissection microscope, sections, and examination by compound scope. Do they suggest a pathogen or a non-biotic influence such as cold, , or .

(1) Principal Research Scientist, Southeastern Forest Experiment Station, Asheville, North Carolina. - 2 - 4. Examine for signs (structures of a pathogen) such as fruiting bodies, felts of , bacterial ooze, etc. 5. what are the diseases of this host? (See USDA Plant Disease Index, Hepting's Diagnosis of Diseases, Boyce, Westcott, and other books.) Do your symptoms and signs tally with those of known diseases well enough to stop at this point in diagnosis? If not, then: 1. Culture from plant tissue (from margins of lesions, from vascular dis­ colorations, from fruiting-bodies.) 2. Incubate the specimen or the culture to obtain well-developed growth and fruiting of fungi, or to obtain bacterial ooze. Don't incubate longer than a few days in the laboratory because of molding. One can incubate on water and straw agar outside for weeks, and sometimes it takes outdoor conditions of diurnal variation in light, temperature, and humidity to bring a fungus to normal fruiting. Is a primary pathogen involved at all? Leaf pathogen, vascular fungus, canker fungus, etc. If there is no evidence of a pathogen you may have an abiotic or the pathogen may not occur in the plant parts avail­ able to you. If a potential pathogen is uncovered, can you identify it, using the literature and making herbarium comparisons? Here is where you stop doing it yourself. You may think you have identified a Nectria sp., or a known rust, or a pathogenic Fusarium, or a needle blight fungus. That's fine, but now, unless you are very sure of your identification, send your specimen or culture for confirmation to whomever has expertise in the taxonomy of this group. There are several helpful tests and smaller general publication on diseases that the practitioner should have at hand. The main one are: Anonymous. 1960. Index of plant diseases in the United States. U. s. Dept. Agri., Agriculture Handbook 165. 531 p. Baxter, Dow Vawter. 1943. Pathology in forest practice. 618 P• New York: John Wiley and Sons, Inc. Boyce, John Shaw. 1961. Forest Pathology. Ed. 3, 572p. New York: McGraw-Hill Book, Inc. Hepting, George H. 1964. Diagnosis of disease in American forest and shade . Part I. Diseases of coniferous species. 378 p. Asheville, N. C.: U.S. Dept. of Agri., Forest Service. ( Hepting, George H. 1966. Diagnosis of disease in American forest and shade trees. Part II. Diseases of non-coniferous species. 371 p. Asheville, N. C.: U.S. Dept. of Agri.,Forest Service. - 3 - r Peace, T. R. 1962. Pathology of trees and shrubs. 753p. Londcn: Oxford Univ. Press.

Pirone, P. P. 1948. Maintenance of shade and ornamental trees. Ed. 2, 436 P• New York: Oxford Univ. Press. westcott, Cynthia. 1960. Plant disease handbook. Ed. 2, 825 p. New York: D. Van Nostrand Go. Other smaller publications are the bulletins by \Jaterman and Marshall on shade tree diseases, by Renting and Fowler on eastern forest diseases, and the Forest Leaflet series of the U.S. Forest Service. Anyone doing much diagnostic work also should be aware of the monographs on certain genera. These include Booth on Nectria, Lohman and Watson on Nectria, Arthur and Cummins on rusts, Fun1c on Galiciopsis, Guba on Pestalotia and Monochaetia, Groves on Dermea, Groves on Tympanis, Darker on the Hypoderma­ taceae or needle cast fungi, Hahn on PeaysoyphA, Hunt on QP-ratooystis tn­ cluding most wilts and blue stain fungi, Waterhouse on , Middleton on Pythium, Lohman and Cash on Atropellis, Miller on Hypoxylon, Chupp on Gercospora, and Trappe on mycorrhizal fungi. Other useful publication are Christie's text on , Dowson 1s on , and Gill's monograph of the dwarfmistletoes. Examples of leading laboratories for the identification of certain organisms are Berkeley, California, for Fusarium spp.: Riverside Galifornia,for Phytophthora; Purdue for rusts; Syracuse for rot fungi; Delaware, Ohio, for elm fungi; Wisconsin for bacteria; N. G. State and Cornell for nematodes; Quebec for Nectria; and Beltsville for fungi in general and for rot fungi in culture. The Forest Service has experts on many important organisms, and we should make full use of men such as w. A. Campbell on Pythiums, Ruehle on nematodes, Toole on hardwood fungi, Hodges on cedar and nursery fungi, Powers and Gzabator on Southern tree rusts, and Verrall on products fungi. Finally, try to see the area of forest involved, especially if information is needed on the soil, the air, associated hosts, etc. In this way you can also see examples of the whole sick plant, or many sick plants. A warning I can't overstress is to watch for false leads, and guilt-by­ association, especially in dealing with secondary needle and twig fungi. A bad diagnosis can lead to a lot of trouble and expense. It can lead to the wrong treatment, to loss of valuable trees, litigation, descrediting of the pathologist, and other unpleasant situations. If the case is important it is better to say you don't know the cause than to guess at it.

New techniques such as the use of selective media and living trap plants (e.g. apple and avocado for ,) and such as new types of mi­ croscopy including phase, dark-field, incident light, x-ray diffraction and electron, mean that everyone can't have the knowledge and equipment to deal with every problem. The answer? Do your best; don't ge ashamed to ask for help, and seek confirmation if there is any question of correctness. REDUCING LOSSES CAUSED BY FOREST DISEASE.'!

BY

DR. JOHN s. BOYCE, JR. (1)

A conventional approach to the subject of reducing losses cause by forest diseases is to describe methods for controlling each major disease. I am not going to do this today. Instead, I invite you to consider some other ideas.

We can begin by observing that reduction of disease losses is a nacessary part of even though it may be overlooked in practice. The peculiar nature of the forest and its diseases dictates that disease control be accomplished through where it is possible. Direct control treatments are properly regarded as emergency measures because of their high cost. Occasionally there may be outbreaks where promptly taken direct steps may result eventually in much lower damage losses. Hopefully, this is the case with oak wilt in some of the so-called 0 fringe areas" in the East.

It is worth stressing again and again that the annual increment of the managed forest has a relatively low value. This makes it important to consider carefully the adoption of any control measure that is not part of silvicultural practice. It is fortunate that most diseases do not increase rapidly to damaging epidemic proportions as is frequently the case with outbreaks. Usually there is sufficient time to delineate the disease problem and then to deal with it deliberate­ ly as part of silviculture.

What I have said so far has been so obvious that I have almost hesitated to say it. Yet I have said it because I do not think that the reduction of disease losses through silviculture is being given the emphasis in practice that it deserves. The impact of most of our major forest diseases can probably be lessened by adjust .. ing silviculture to take into account their characteristics.

In this connection let us look briefly at an important southern disease, fusiform rust. Its control can be approached silviculturally in several ways. These include site selection, stand density or spacing, choice of species, and sanitatiott cuttings. Although site evaluation for rust hazard needs more refinement, it is possible even now to pick out local areas where rust damage is likely to be higher than an accept­ able standard. We can look for an abundance of susceptible oaks on which the alternate stages of the rust will develop as well as for the prevalence of rust on pines already growing in the locality. In addition we may be able to judge whether bad infection years have occurred frequently in the past by the positions of galls relative to the heights of older trees. By using such guides we ought to be able to tell where it is not sensible to grow loblolly and slash pines because of future rust damage.

Where rust hazard is high but susceptible pines are to be planted anyway, it has been suggested that close spacing will help (Siggers 1955.) There are two expected benefits from this. First, close spacing leads to earlier natural of side branches so that fewer rust infections reach the stem, Second, higher initial stand density will allow the removal of more cankered stems while leaving enough healthy stems after for a commercially operable stand. Close spacing is not a new idea. Nonetheless I have not found published reports that it works. I

(1) Marion, s. c. think tests of several spacings such as 4 x 4, 6 x 6, and 8 x 8 feet in localities where the amount of rust infection is high would be worthwhile. They s·10uld be followed to determine net yield over the rotation as affected by actual losses due to rust.

Selection of the proper species for planting involves a consideration of the sus­ ceptibility of the pines to rust infection. We all know that shortleaf and longleaf pines are more resistant to rust damage than loblolly and slash pines and should be used where they are adapted to high hazard sites. There seems to be little differ­ ence between loblolly and slash pines so that they may be regarded as one specie with respect to rust injury.

However, a new development is the finding from the Southwide Pine Seed Source Study that there is considerable variation within loblolly pines in rust suscepti­ bility. During the first ten years loblolly pines from western sources, that is, east Texas and Arkansas, were consistently least affected by fusiform rust (Wells and Hakeley 1966.) There may be significant differences between seed sources that are geographically close to one another. In a Louisiana study although the four loblolly pine seed sources were witl1in 2UO miles of the test planting site the amount of stem cankering and rust-caused mortality differed sharply between some of them (Crow 1964).

There remains the question of how to deal with stands that are already badly in­ fected. What effect does the removal of cankered stems have on the .composition of the remaining stand? Does cutting cankered stems result in taking out relative­ ly more of the larger, vigorous trees than of the smaller pines? A study of old field slash pine in south Georgia showed that occurrence of stern cankers was not related to tree size as expressed by D. B. H. (Dell and Driver 1963) So it is likely that sanitation for rust will have little effect upon the distribution of tree sizes in the residual stands.

If we consider all of these measures, it appears that we possess a flexible approach to fusiform rust control through silviculture. It would seem that, if practice what pathologists preach, the inroads on forest productivity due to rust ought not to be great in managed areas. However, I question that these measures are as widely used as possible.

Mayby foresters would be more interested in reducing disease losses through silviculture, if two things were done. The first is to set up more and better field studies to establish the worth or the worthlessness of silvicultural control methods. The spacing study mentioned above is an example. The practicing forest pathologists should work with foresters in these investigations for they will often require considerable expertise in pathology that many foresters cannot supply by themselves •. Such practical studies would have come under the aegis of research not long ago.

Regardless of whether action or research groups carry out such tests, they would be time consuming, costly, and often of a long nature. They cannot be carried out adequately without land, manpower, and money resources. The Forest Service is conducting some studies of this kind in connection with F omes annosus control by means of stump treatments and season of cutting. Paper and timber companies are in favorable positions to conduct such studies too.

After obtaining data from these investigations, the results must be presented so as to stimulate foresters to try more effective methods. A primary objective should be to make them readily available to foresters. Even now I think a kind of "i;;-,for­ ( mation gap" exists between research and management. One reason may be that the pathologists who conduct forest disease research tend to publish their results in journals such as Phytopathology and the Plant Disease Reporter that circulate mostly among other pathologists. We should aim at getting more articles about pathology into vehicles like the Journal of which does reach a large audience of foresters. A recent encouraging development in this respect is the creation within the Society of American Foresters of a subject division on entomology and pathology. Hopefully this will lead to greater participation by both entomologists and patholo;;ists at the annual meetings as well as in the affairs of the Society.

Another problem in connection with this information gap is that of interpreting research results for the non-specialist. A valid criticism has been made that "when research does offer information, it is presented in language not easily understood." (Macon 1967.) Perhaps we can get more mileage from research results in pathology by putting ourselves in the shoes of the . He needs and should have responsible and responsive help from specialists in making his decisions. This means better communications and it involves an appreciation by the researcher of the box that the forester is often in.

Tha gist of what I have said is that in order to promote the silvicultural control of forest diseases I think that we need more extension type activities. They might consist of more field tests of the various silvicultural methods as they affect disease losses. They might also include translating results of pathology investi­ gations into the language of the forester.

LITERATURE CITED

Crow, A. B. 1964. Ten-year results from a local geographic seed source study of loblolly pine in southeastern Louisiana. La. State Univ. Forestry Note 57. 4 P•

Dell, T. R. and c. H. Driver. 1963. The relationship of D. B. H. to fusiform stem cankering in old field slash pine plantations. J. Forestry 61:872.

Macon, J. w. 1967. On connections between research and forest management. J. Forestry 65:24-28.

Siggers, P. v. 1955. Control of the fusiform rust of southern pines. J. Forestry 53:442-446.

Wells, O. o. and P. c. Wakeley. 1966. Geographic variations in survival, growth and fusiform-rust infection of planted loblolly pine. For. Sci. Monograph 11. 40 P•