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Plant

Adapted by Edmond L. Marrotte Consumer Honiculturist Depattment of Science

@;,~r,.'i' ~ -====:::..... -.' :.;;.ncJ •• ~.::,"f:::=== UNfVERSITY OF CONNECTICUT COOPERATIVE EXTENS ION SYSTEM • C-/br-..r AK""'U~ff .nJ NJ,,, ..III,,.,,ra, · Table of Contents What is a Plant ? . . How are Diseases Classified? 1 How Do Work? 2 What Causes Plant Diseases? 3 Major Groups of Fungi .. 6 7 and -like Organisms 7 ...... 8 Parasitic Plants 8 How are Diseases Recognized? 8

How to Diagnose Plant Diseases 9 Steps to Follow ...... 10 How Do Diseases Develop? . . . 12 How are Plant Diseases Controlled? 16 Cultural Control of Plant Diseases 16 What to Plant . . . . 16 How to Plant 16 Routine Care of Plants 17 Chemical Control of Plant Diseases 17 When is the Best Time to Apply Chemicals? 17 How Should rhe Chemical be Applied? . 18 Used in Plant Disease Control 18

Adapted from Plant Di"am by Otis C. Maloy. Extension Plant Parhologist. Washington State University

Isn«ti in forthtrona ofCoopt:rarive Ex~nsjon work. Acts ofMay 8 and Junr 30, 1914. in coop­ eration with the U.S. D~artmenl ofAgriculture . Kirltlyn Kur, Dirtftor, Cooptrative Extmsion System. The UnilJmity ofConn«ticut . Slam. The Conn«ticul Cooptrotive Exunsum sys~m offm itJ programr to jJn'$ons r~ardksJ of . cowr, n4tWnA/ origin. so: or disability and ;s an eqU4i opportunity employ". ( Plant Diseases

What is a Plant Disease? taneollS effect of an injury. It is necessary to dis­ tinguish between disease and injury and not con­ Many attempts have been made (0 define what a fuse normal life processes, such as maturation plant disease is. but all definitions have to be and falling of , with diseases. One common qualified CO some extent. A plant disease IS not a confusion is that causal agent and disease are the tangible object as is an or, a . Ie ~~ same. Some believe that a , bacterium or not have absolute, fixed dimensIOns but vanes In is a disease, but it is not. It is a causal its appearance in a great many ways. agent of a disease. Broadly defined. a plant disease is any condi­ The agent causing a plant disease is called a rion in which a plant is different in some way plant whether the agent is living (para­ from a normal (i.e., healthy) plant in either struc­ sitic) or nonliving (nonparasitic), but mually the ture or funccion. The diseased plant may be term pathogen is resuicted to the former. shorter, have more branches or fewer leaves man normal- it differs in structure. It may wilt and die prematurely, or not produce or ffuic­ it differs in function. Plant diseases affect all plants to some extent. They generally cause minor damage, bur when all of the required interacting and contributing faclOcs are present. they can be cawlrophic. Famines caused by blights and mildews are recorded from biblical times. Late blight of porawes led [0 the in Ireland in the mid-lSDDs. and blight eliminated the American chestnut as a commercial in the in a few decades. In commercial , even minor losses to disease can be serious. The science thar deals with the n3Wfe and con­ trol ~ f plant diseases is called plant . also involves other sciences, such as . bacteriology. . nematology, virology. etc. Although disease is sometimes referred to as a Figure 1 condition, it is not a static, constant condition Disease Symptoms but an ever-changing one. Disease is a series of changes in the plant caused by some agenc. It is How are Diseases Classified~ physiological. affecting all or part of the func­ Plant diseases can be classified or categorized in a tions of the plant. It is abnormal to the plant and number of ways. One of the earliest and most not the normal termination of some particular popular ways is to separate diseases on the basis function (for example. normal dropping of of the affected. Thus. there are diseases of leaves). Diseases are always harmful to the plant tree , small fruits, vegetables, , in the long run even though there have been cereals and grasses, ornamentals, etc. Another sys­ attempts to benefit from certain diseases. Exam­ tem is to categorize diseases on the basis of the ples are the virus-induced color break in causal agent. In this system we have fungus dis­ and [he virus-caused shortening ofinternocles of eases, bacterial diseases, virus diseases, nematode cherries. diseases, nutrient deficiencies, etc. Other ways The causal agent of a disease has a prolonged diseases can be classified are on the plant part influence as compared to me sudden, instan- affected, e.g. , diseases, stem diseases or

Plant Diseases diseases; or on the symptom or symptoms produced. such as blights. mildews. decays or ( mosaics. The name applied to a given plant disease generally includes three significant pieces of infor­ mation: (I) the plant attacked. (2) the plant part affected and (3) how it is affected. For example. leaf curl. alfalfa . potato leaf roll and black of wheat. are names that help to develop a mental image of how a disease affeces a plane. Figure 1 illustrates some of the ways that me name of a disease is often derived from the way the plant is affected.

How Do Plants Work? Figure 2 Since plant diseases modify or interfere wim Pans of the Plant the normal functioning of a plant, we must have some idea of how a normal plant works. Figure 2 role co elevate leaves from the ground where they is a simplified diagram of the major parts of a arc effectively exposed to sunlight. In and their components. Cenain types of plants. there is a layer of meristematic cells called cells and tissues do certain kinds of jobs in a the cambium which gives rise to , or water­ plant. Knowing how a plant functions will often conducting , on the inside and to , aid in the diagnosis of plant problems. Briefly. or food-conducting tissue, on the outside. Bark the main parts of the plant are: develops from the outer cells of the phloem. --Anchor plant: absorb water and The leaf is the food factor of the plant. The nucrienes; score food. nutrients from the move upward in the Stern-Supports foliage and conducts xylem and into the leaf veins. These veins ter­ nucrienes from roocs co leaves; water and minate at the leaf margin as special structures nuuienes move upward through the xylem; called hydathodes. The nutrients diffuse out of manufactured food moves downward through the xylem in the veins inco the palisade and the phloem. mesophyll cells. These cells contain the green pig­ Leaves--Absorb C02 and light; synthesize ment called . The plant surface is . covered with a one-cell-thick layer called the . On the leaves and some stems, the -Sexual organs of the plant. epidermis is covered by a waxy cuticle. Also, on - Reproduce the plant. the leaf surface. especially on the underside. are For a plant to grow and develop normally. natural openings called stomata. through which mineral nutrienes must be obtained from the soil. gases are exchanged with the atmosphere. Carbon These nutrients are dissolved in the soil water and dioxide in th e air moves through the stomata inco absorbed by rOot hairs which are simply exten­ the openings in the spongy mesophyll and dif­ sions of the epidermal cells. The dissolved fuses inco these cells. Here, carbon dioxide and nucriencs then diffuse inward to the xylem cells water, in the presence of light, are converted into where they can move upward in the plant. (he simple sugar, glucose, with oxygen as a by­ Secondary roots originate from the peri cycle product. This process is called . which is meristematic tissue Ilke the cambium of The glucose diffuses through the cells into the the stem. These secondary roots force their way phloem of the leaf vein. From here it is trans­ through the cortex and cause small natural ported to various parts of the plant to be used for wounds through which some disease agents can growth and energy, or it is stored as glucose or enter. one of many other compounds. The oxygen dif­ Nutrients move up the plant in the xylem of fuses back into the chambers of the mesophyll the stem. The stem serves mainly a supporting and our inm the atmosphere.

2 Plant Diseases Seven major plant funclions can be identified plant communities are [feated in which there are ( that are affected by disease. Table 1 lists these combinations of different plants in a natural asso­ functions and some of the cypes of diseases affect­ ciation even though the larger of the control ingthem. measure is a single plant species. The highest level In considering how diseases affect plants and of plant organization is the biome. This includes how control measures are brought into play, it is all of the plant life (and many include the ani­ necessary to have some idea of how plants and mals) in a large geographic area. For example, the their parts are organized. Figure 3 illusuates the western coniferow comprise a biome. It is various levels of organization of plants. Diseases rare when the biome is considered in the concrol are usuaUy described in terms of how they affect of a plant disease. cells, tissues or organs. Cells are killed, tissues are over- or underdeveloped. and leaves and other or­ What Causes Plant Diseases? gans are blighted, curled, chlorotic, and so on. The basic unit in the plant is the cell. Cells of The definition of plant disease is very broad and a given type are united to a tissue which is includes all possible causes, as long as the four an aggregate of cells which perform a similar func­ criteria previously listed are satisfied, i.e., a tion, such as xylem, phloem or cambium. Dif­ process, physiological, abnonnal and hannful. ferent tissues combine to form organs, which are The causes can include a wide range of nonliving usually recognizable parts of the plant. In an agencies, such as toxic chemicals or adverse organ such as the leaf. me tissues contained are weather conditions as welJ as a variety of living epidermis, phloem, xylem, mesophyll, etc. organisms. Finally, (he various organs (leaves. stems, roots, For example, that produce galls on blossoms, fruit) make up the individual plant. plant parts are true causal agents of diseases. To control a plant disease, consideration may Insects, however, are generally omitted from the be given to the individual plant, especially if it is field of plant pathology and covered in the an ornamental tree or , but more often a science of entomology. population of plants such as a field or an Plant diseases can be divided into rwo broad is treated. groups based on their cawe. A population is an aggregate oflike individ­ Nonparasitic diseases are induced by some uals. In some cases, as in foreses or rangelands. nonliving agency such as nutrient deficiency,

Table 1 Plant Function Affected by Disease PUl1lt FU1Jcti01J Afficted Diseases Involved Food smrage-smrage organs with Soft cors, decays high sugar and content Mobilization-conversion of starch Damping off, blights to sugar and movement to growing paines Root growth-roots develop and absorb Root rots. nematodes water and nutrienes from soil growth-development of stems, Galls, cankers, blights branches, leaves Water transfer-movement of water and Vascular wil ts nutrients from roots to leaves Photosynthesis- manufacture of food in Leafblights, mildews, mosaics leaves Translocation-movement of food manu­ Stem ruses, yellows viruses factured in leaves to growing points and storage organs

PlantDi s ~ 3 extreme cold or heat. chemicals (air poll mants. and do not cause plant diseases. Most are benefi­ . excess , etc.), mechanical cial to people. Many plant live primari­ damage. lack of water, soil compaclion and many lyas parasites on live tissue but under some ochers. These diseases cannot he rransmincd (0 circumstances they have the ability (or faculty) to healthy plants and their control depends almost develop on dead tissue. They are called facultative entirely on correcting the condition (usually saprophytes. The scab fungus is a typical ex­ something in (he environment). ample. Parasitic diseases are caused by living organ­ Another large categoty of plant pathogens live isms which derive their food by growing in close mainly as saprophytes bur have the faculty to association with plants. The most common develop on live tissue in some cases. causes of parasitic diseases are fungi. bacteria, solani is a good example of a facultative parasite. viruses, , and nemawcles. A This group of organisms can survive for long few seed-producing plants, such as the miSllcr0e5 periods of time without a live host plant and, and dodder. can also cause plant diseases. therefore, is more difficult to control than an Although the definition of disease may include organism more dependent on live tissue. all plant difficulties regardless of the cause. most Organisms that can live, or at least can only plant pathologists are concerned with those complete their developmental cycle. on living tis­ diseases caused by living agents. especially fungi. sue are called obligate parasites. They are obliged bacteria. viruses or nematodes. Organisms that to live on this type of substrate. All obligate obtain their food from other organisms may be parasites, by meir nature. are plant pathogens. classed as saprophytes or parasites. Saprophytes This group includes all of the rust and smut are organisms that derive their food from dead fungi. as well as the downy and powdety mil­ organisms. Parasites derive their food from living dews. all viruses and some seed-producing plants organisms. such as the dodders. Figure 4 illustrates the inter­ The degree to which organisms depend on live relationships of these categories. or dead tissue for nourishment affeccs meir abilicy The concept of how plant pathogens act on co survive and cause plant diseases, and the ease their substrate (food material) to cause a disease is with which they are controlled. sometimes difficult to describe. The development Organisms that can live only on dead or­ of disease is an undesirable side effect of the ganisms (or substrate) are obligate saprophytes process of the pathogen deriving nutrients for its growth and development. It may help to compare the way plant pathogens get their nourishment with the way animals do.

Individual ...... ---<;Ior'-..!~ Population

Figure 3 Levels of Organization of Plants

4 Plant Diseasa: ing the animal. In this way the waste products are ( scattered or diluted and eventually decompose and are recycled. This is illustrated in Figure 5A This procedure is almost reversed with plant OCCASIONALLY disease agents because, instead of engulfing their SAPROPHYTIC 11 {FACULTATIVE food material. they are surrounded by it, as SAPROPHYT shown in Figure 5B. In the process of extracting nutrients, the organism excretes enzymes into the DECAY PLE.~ANT ~fblv~8 !.~ANT DISEASE food substrate, and the material is dissolved to 8~TISSUE ~SUE some extent. Nutrients are absorbed by [he organ­ OCCASIONALLY ism and used for growth and energy. Waste pro­ PARASITIC· (FACULTATIVE ducts are excreted into the surrounding substrate PARASIT where, rather than being diluted, they may be ALWAYS /; concentrated. These wastes may include hor­ SAPROPHYTIC· 'i (OBLIGATE I, mones, enzymes and [Oxic substances that bring SAPROPHYTQ '/' II ,", about the death or malformation of cells and tis­ SAPR~HYTE ~::- ~ sues, thereby producing the symptoms of disease. Figure 4 The fungi probably comprise the largest single Categories of Plant Diseases group of causal agents of plant disease. Fungi are plants that lack the green coloring (chlorophyll) Mos[ animals ingest their food-take i[ into a found in most seed-producing plants and, there­ cen[raI recep[acle. Here enzymes act to break it fore. cannot manufacture their own food. There down. and nutrients are absorbed by [he sur­ are approximately 100,000 species of many types rounding tissues of the animal. Waste products and shapes. Only about 8,000 species cause plant pass from the tissues into the central cavity and diseases. Most are microscopic. but some, such as are discharged into the air, water or soil surround- the mushrooms, are quite large.

/I

for growth and energy 4t~

Organism

Enzymes

~~\ Nuuicnu Metabolic wastes FJ (, hormones) Figure 5 Comparing Ways of Getting Nourishment

Plant Diseases 5 Most fungi reproduce by , which vary fungi and all of the powdery mildews are ascomy­ greatly in size and shape. When spores germinate, cete. (Figure 7). they usually give rise to threadlike filaments The phycomycetes, or water molds. are asso­ known as hyphae. ciated with cool, Hyphae are the Germinating spore wet conditions growing structures and cause anum· of fungi excreting o c== ber of serious plant enzymes, absorbing 112500 inch diseases. These nutriencs and releas­ include darnping­ ing chemical mat­ Figure 6 off of , all erials that induce How Fungi Reproduce of the downy mil­ diseases. In mass, dews, late blight of the hyphae are called mycelium (Figure 6) . pocato and collar rot of fruit trees. The mycelium of many phycomy-cetes is nonsepcarc and some Major Groups of Fungi spores are motile (Figure 8). The basidiomycetes or club fungi, produce The fungi are divided into four groups on the their sexual spores on small clublike structures basis of their vegetative growth (mycelium) and called basidia. Many basidiomycetes have septate how their spores are produced. The relationship mycelium that also hear clamp connections. As of a fifth group, the myxomycetes, to the other with the ascomycetes, the sexual spores of the fungi is questioned by some and, at basidiomycetes are important in development most, they are distant rel atives. Only one disease me of new races of pathogenic fungi (Figure 9). of importance in Connecticut is caused by a myxomycete. This is club root of cabbage and Spo=gia related crops. Fungi are classified mainly on the basis of microscopic features and are clifficult to identifY in the field. The ascomycetes are called sac fungi because their sexual spores are produced in sacs called asci. In addition they often produce nonsexual Saual resting spocc:s spores cal led conidia. Both spores often playa part in the life cycle of the fungus and the sexual stage is especially important, because it provides a means by which new pathogenic races of a fungus can develop. The mycelium of ascomycetes has Figure 8 simple crosswalls (septa). Many leaf and stem Phycomycetes

There are two large groups of basidiomycetes. Mycdium The first group, which contains and • • Fomls, causes roar rots and trunk decays of trees and produces mushroomlike structures from ~ Ascospore: which the spores are produced. The other group S~pta comprises the rusts and smuts that affect many plants. Fruiting body O ne large group of fungi for which no sexual stage is known is called the Fungi Impe1ficti. When a sexual spore stage is found, it is almost always an ascomycete. Many fungi will be known by cwo different scientific names, one based on the imperfect stage and the other on the perfect or sexual stage. Many plant diseases are caused by Figure 7 Ascomyceles imperfect fungi (Figure 10) .

6 Plant Dis~ases various horticultural crops. Agrobactmum tum,­ ( .'1'. .~.To .g:: . jacims causes crown gall of roses, fruit uees and other woody plants. species cause soft rots offrui ts and vegetables, and one species causes fire blight, a serious disease of and pears. One organism, Str'Ptomy", scabies, is classed as a higher bacterium and is the only one of this \ Fruiting body group to cause a serious plant disease, common scab of potato. Bacidiosporcs

Figure 9 Basidiomycetes

Mycdium

Figure 11 Typical Bacteria Viruses and Virus-like Organisms Viruses that cause plant diseases number only Figure 10 about 300 species but these cause some of our Fungi imperfecti most destructive plant diseases. Viruses are so Bacteria small that they cannot be seen with the ordinary and are generally detected and Bacteria (Figur< 11) are very small, one-celled studied by their effects on selected indicator organisms that reproduce by simple fission. plants. Viruses are considered by most scientists They divide into fWO equal parts, each of which to be living organisms while a few think of them becomes a fully developed bacterium. This 'Ype only as highly organized molecules. Structurally, of reproduction may lead to a rapid buildup of a they can be either rods or spheres. Both forms population under ideal conditions. For example. consist of a central core of nucleic acid and an if a bacterium divides every 30 minutes- a gener­ outer coaring of material. The infective ation time not especially short for some bac­ portion of the virus particle is the nucleic acid teria-a single cell could produce core with [he protein shell serving as a protective 281,474,956,710,656 offspring in 24 hours. cover. Because of their limited size and development. Viruses can reproduce only in living cells and bacteria are unable to penetrate the protective sur­ must be moved by some means from plant to face of the plant and must enter through natural plant. Many viruses are transmitted by sucking openings. such as stornates. nectaries or insecrs, such as and . Some hydothodes, or through wounds. viruses are easily transmitted mechanically by rub­ About 200 species of bacteria cause plant bing leaves of healthy plants with juice from dis­ diseases. Several species of Psrodomonas and Xan­ eased plants or by tools. A few viruses thomonos cause leaf spots and shoot blights of are cransmincd in . Big vein of lettuce virus

Plant Diseases 7 is transmitted by a soil-borne fungus. and a few largely on soil temperature and moisture. There­ viruses are uansmi tted by nematodes. Viruses fore, nematodes are usually more of a problem in cause very serious problems in plants that are warmer areas of the country. propagated by , roots and cuttings, because Young nematodes molt four times before the virus is easily carried in the propagation reaching maturity. All are worm- or eel-shaped material. early in their development. and most remain that In recent years, several diseases previously shape. The females ofsome, such as the rootknot thought to be caused by viruses have been shown and cyst nematodes. swell and become pear- or to be caused by very small bacteria-like organisms lemon-shaped. The eggs of the rootknot nema­ called mycoplasms. These organisms differ from tode are laid in a mass outside the body, but the the true bacteria in not having a rigid . eggs are retained inside the body of cyst nema­ and [hey differ from the viruses in being inhib­ todes. The body wall dries and provides an effec­ ited by the antibiotic substance tetracycline. So tive protective shelter for the eggs. Many of these far. aU of the -associated diseases are eggs will hatch only when stimulated by excre­ of the yellow type and include aster yellows and tions from roots or susceptible plants. western-X disease of . Some plant nematodes remain on the outside of the plant and feed on exterior plant cells. Nematodes These are called ectoparasites. Most of these migrate freely over the root surface, while others Nematodes (Figure 12) are small, worm-like are more sedentary and remain at one point to animals that can attack plants and cause diseases. feed. Other nematodes move into the plant tis­ There are many different kinds of nematodes. sues to feed. These are termed endoparasites. some anacking animals. some free-living in soil and water. About 1.000 species are known to attack plants. While nematodes vary greatly in Parasitic Plants size, those causing plant diseases are relatively Several seed-producing plants are parasitic on small. barely visible to the unaided eye. All plant other plants (Figure 13). The best known of parasitic nematodes possess a hard, piercing spear these are dodder and the . of or srylet by which they puncture plant cells and these plants germinate on the host surface or in feed on the cell contents. In the process offeed­ the soil and penetrate the plant surface with an ing. the nematodes inject toxic material into the infection peg. The vascular or conductive system plant and cause symptoms of disease. of the parasite fuses with [he vascular elements All plant nematodes reproduce by laying eggs. of the host and the parasite is able to siphon off The number of eggs produced by one female and for its OWn use food material manufactured by (he number of generations in a season depend the host. Dodder is the only serious seed-producing parasite in Connecticut. It is treated as a weed rather than a plant pathogen.

How are Diseases Recognized? When a pathogen acts upon the host cells or tis­ sues, changes begin to take place. Some of these are submicroscopic and not easily observed. As the changes in the host plant become more obvious. visible syrnpwms become apparent. Symptoms of disease are wilted foliage, death of cells and tissue. enlarged or stems, yellow foliage, etc. Symptoms by themselves may not allow an accurate diagnosis of a plant disease because Figure 12 several distinctly different causal agents may pro- Nematodes

8 Plant Diseases menr of cells. tissues, or organs which produces ( such specific symptoms as stunting of a plant or , which is the failure of chlorophyll to develop. This category of symptoms is often the least easily recognized. Hypertrophy is the over­ development of cells, tissues or organs and often is quite conspicum.,LS. especially when the specific symptom is a large gall or witches' -broom. More than one type of symptom may com­ prise the symptom picture (or syndrome) of a disease. The primary symptom may be hypo­ trophy but a secondary symptom may be necrosis. The pathogen frequently produces structures as part of its growth and these are called signs of the disease. They are more specific than symp­ [Oms and are more valuable diagnostic aids. pro­ vided they can be correctly identified. The bacterial ooze associated with fire blight and wilt and the sclerotia of the white cot­ tony mold (Sclerotinia) ofb.. ns are signs of disease. Unfortunately, the detection and iden­ tification of signs often requires specialized knowledge and techniques. This is nor always available in the field, and specimens must be taken or sent to a diagnostic laboratory for fur­ ther examination. Control measures are directed at the causal agent rather than the diseased plant, therefore, it is important that the cause by correcdy iden­ tified. Symptoms and signs alone are not always enough for such a diagnosis and additional, some­ times complex. teslS must be made.

How to Diagnose Plant Diseases When something goes wrong with a plant, whether it's in a field, a forest or a flower pot. someone wants to know what is me matter and Figure 13 how the problem can he corrected. In most cases, Parasi,ic Plants it is [00 late to conuol a disease on a plant once duce identical symptoms. However, symptoms the disease appears, but conuol measures may he used with other evidence, plus experience, can started to keep the disease from spreading to often produce a satisfactory diagnosis. other plants. Even if control measures are not available, there is a sense of well-being in simply The type of symptoms produced often indi­ knowing what the problem is and what its future cates not only how the plant is affected but also development might be. may suggest the type of pathogen involved. There are three general types of symptoms. Before control measures can be applied, the Necrosis involves the death of cells, tissue or cause of the problem must be determined. It organs and may result in specific symptoms such would be useless to apply a to a plant if as blights, leaf spots, cankers and ,he like. the problem is caused by an insect or nematode. Necrotic symptoms are probably those most Accurate diagnosis of a plant disease usually readily seen. Hypotrophy is the underdevelop- requires correct identification of the causal agent.

Plant Diseases 9 Similarities of symptoms produced on me same tributed or localized in certain spots? Definite plant by completely different agents frequently patterns of distribution. such as at the edges or make me use of symptoms alone inadequate. Yet, the center of a bench, or along the specialized techniques and knowledge roadways. fences, corners or low spots in a required to isolate and identify many disease field, frequendy indicate climatic. soil factors, agents force us to rely largely on symptoms. or toxic chemicals but do not necessarily ex­ Most diagnosis of plant diseases, and especially clude parasitic causes. If an examination is not diagnosis in the field, must be based on reactions possible, ask questions. of the plant rather (han on (he presence and iden­ Is only one type of plant affected or are tification of the causal organism. because of (he many unrelated plants involved? If more man microscopic nature of me organisms that cause one type of plant is affected, parasitic diseases plant disease. are probably not involved. Rather, one should Despite the limitations of symprorns for the suspect climate or chemicals. diagnosis of many plant diseases, certain cate­ Are all of me plants in a field or planting gories of sympwms are definite clues to cenain affected? Parasitic diseases progress with time types of plant diseases. (It should be noted that and rarely amiCI 100 percent of me host plants there are always exceptions.) at one time. Diseases are usually at a relatively low level (less than IO percent). When a prob­ Steps to Follow lem affects all, or almost aU, of a plant popula­ In the diagnosis of a suspected plant disease tion, the cause of me problem is likely a soil there is a logical and convenient series ofsteps to condition (deficiency or toxicity), result of follow. adverse climate (, , , etc.), I. IdentifY me plant affected. If possible, include toxic chemical (air polluntant, , the scientific name as well as the common excess fertilizer) or unfavorable cultural name because the same common name may practices. have been used for several distinctly different How did the disease develop in the affected plant species. The common name cedar is an area? Did it appear overnight? If so, suspect a example of the same common name being climatic factor such as frost or the application applied to several genera of plants. Eastern red of a roxie chemical. However, if the condition cedar is Junip~rns, western red cedar is Thuja, started at one point and spread slowly in Port Orford cedar is Chamaecyparis, incense extent and severity, a parasitic disease is cedar is Libocedrus and Auas cedar is Cedrus. probably responsible. Here are five different genera of plants, all of Obcain a record of environmental condi­ which carry the common name of cedar. tions that preceded the appearance of me Many times it is useful to know me variety disease. Check for short periods of below­ of the plant in question because some varieties freezing temperature or prolonged drought are resistant to certain diseases. For example, periods. Did hail or lightning occur? Air pol­ some varieties of tomatoes are resistant to cer­ lutants might have been involved. If so, infor­ tain strains of the soil-borne wilt diseases macion on air inversions and prevalling caused by and V(rticillium. There­ will be helpful in explaining me pattern of fore, it makes good sense for people with small damage. to plant only wilt resistant varieties. Has there been any treatment that could Rutgers and Big Boy, though popular varieties, have resulted in plant injury? Some types of are susceptible to both diseases, whereas Better herbicides can distort foliage on plants some Boy and Rutgers VF are resistant. Some of the distance away from me site of application varieties are resistant to only one of the because their root systems have intercepted the wilt diseases. This is noted on the seed packet. downward movement of the . Exces­ 2. Carefully examine the diseased area, whether a sive amounts of can cause similar bench in a greenhouse or a large field. Note damage to plants, especially if the soil is dry. how the diseased plants are distributed over 3. Determine the appearance of a typical diseased the affected area. Are mey uniformly dis- plant. Do not base me symptom picture

10 Plant Diseases entirely on the early stages of disease nor on a 4. Determine the primary symptoms of the condi­ ( plant that has deteriorated to a point that tion under srudy. Symptoms are expressions of secondary organisms have obscured the the affected plant that indicate something primary cause of the problem. Ideally, the abnormal and are grouped into three general symptom picture should be a composite based cw.ses. on the progression ofsymptoms from earliest Underdevelopment of tissues or organs. to latest, Examples are stunting of plants resulting from Always compare the typical diseased plant shortened internodes, failure of chlorophyll or with a healthy or normal plant. since normal other pigments to develop, failure of flowers to plant pans are sometimes mistakenly assumed develop or misshapen leaves. to be evidence of disease. Examples are the Overdevelopment of tissues or organs. brown, spore-producing bodies on the lower Galls and witches' -brooms are good examples surface ofleaves of . These are the normal of overdevelopment. The profuse flowering of propagative organs of ferns. Also in this plants suffering from root diseases is another category are the small, brown, clublike tips type of overdevelopment. that develop on arborvitae foliage in early Necrosis or death of plant parts. This is the spring. These are the male flowers, nO( most noticeable of the three types of symp­ deformed shoots. Small galls on the roots of toms. Examples are shoot and leafblights,leaf legumes. such as beans and peas, are most lik­ spots and fruit rots. ley nitrogen-foong nodules essential to normal Diagnosis of a disease up CO this point development and are not roo£i{flO( nematodes. requires no special equipment O[her than a The leaves of some plants, such as syca­ hand lens and knife. more, or some species of are 5. Disease signs provide clues. Signs of disease are covered by a conspicuous fuzz. This is some­ structures produced by the causal agent of that times thought to be evidence of disease, hue it disease. Since signs are more specific than is a normal part of the leaf. Varieties of some symptoms, they are much more useful in the plants i.e., ivy and euonymus, have variegated accurate diagnosis of a disease. For example. foliage that may resemble certain mosaic distortion of leaves and shoots usually points diseases. These examples illustrate the impor­ to damage from a hormone-type herbicide tance of knowing what the normal plant is such as 2,4-0. but similar symptoms can be before attributing some characteristic to produced by frost. viruses, some fungi. insects disease. and nutrient deficiencies. Premature dropping of needles by Discovery and identification of signs of dis­ frequencly causes alarm. Conifers normally ease may require special equipment and retain their needles for two to six years and knowledge, but many signs can be found with lose the oldest gradually during each growing only a hand lens and a knife. season. This normal needle drop is usually noc noticed. However, prolonged drought or ocher The presence of spore-producing bodies on facmrs may cause the tree as a whole to take cankers; mycelial mats of the shoestring fun­ on a yellow color for a short period and may gus. Armillaria meilett; bacterial ooze from a accelerate needle loss. If the factors involved wilted cucumber stem; masses of rust spores; are not understood. this often causes alarm . and the gray-white mycelium of powdery mil­ The needles that drop or turn yellow are dew are all signs of different diseases. actually the oldest needles on the tree, and 6. Isolate and identify causal agent. Sometimes their dropping is a defense mechanism which neither sympcorns nor signs are specific or char­ results in reduced water loss from the foliage as acteristic enough to pin down the cause of a a whole. disease. Then additional specialized techniques Note the portion or parts of the plant are required to isolate and identify the causal affected. Is it the roots, leaves. stem, flowers or agent. fruit? Is the entire plant involved? Isolation of bacteria and fungi usually requires that small pieces of diseased tissue be placed on a nureient medium. The organisms

Plam Diseases II growing out of the tissue are then isolated in darions made to control similar diseases. Diseases pure culture. However, many disease.produc­ new to a region have often been studied in other ing organisms (especially rhose called obligate parts of rhe world and sufficient information on parasites) cannot grow on artificial media, but which to base control measures may be found in can grow only on living tissue. Obligate rhe reports of rhese studies. parasites require other special methods for their isolation. How Do Diseases Develop? Invasion of diseased tissue by saprophytic organisms often makes isolation of the primary The development of any parasitic disease is criti­ cause of disease difficult, if not impossible. cally dependent on rhe life cycle of the parhogen. Because of their ability to grow rapidly and The life cycles of all disease organisms are greatly utilize me artificial substrate more efficiendy influenced by environmental conditions affecting than can many disease organisms, these borh rhe host and rhe parhogen. Temperature saprophytes may rapidly overgrow and crowd and moisture are probably rhe most important out the primary pathogen on synthetic media. factors rhat affect rhe severity of plant diseases. They not only influence rhe activities of the dis­ Experienced plant pathologists overcome this difficulty by isolating from rhe margins of the ease organism, but also affect the ease with which diseased tissue and by employing selective a plant becomes diseased and rhe way rhe disease media which favor growth of rhe parhogen. develops. Assuming that isolation has been successful The development of a parhogenic organism to and there is reasonable certainty the primary initiate a disease follows the same general steps cause of the disease is isolated, there is still the whether the pamogen is a fungus, bacterium, problem of identifYing the organism. There virus, nematode or seed-plant, or whether it is an are 20,000 to 40,000 species of bacteria and obligate or facultative parasite or saprophyte. Fig­ fungi, as well as many viruses and even higher ure 14 gives a typical disease cycle. plants that cause disease. The characteristics A5 an example, start with a diseased leaf rhat upon which their identification is based are has carried a fungus over the winter. In the often complex and not easy to determine. Fre­ spring, as the temperature becomes warmer, this quently only a specialist who deals with a very fungus will begi n to develop and form spores. small group of organisms can correctly identifY This mass of spores is called inoculum. the disease organism in question. A5 the fungus spores mature, rhey are dis­ Viruses are especially difficult to identifY charged into the atmosphere where they are dis­ because their submicroscopic size makes them tributed by or water. Some eventually land too small to be seen except by an electron on healthy leaves of a susceptible host plant. microscope. Their identification usually is This step of moving inoculum to the infeclion based on rhe reactions (i.e., SY'flptoms) of couct, or point where infection can occur. is selected hosts called indicator plants and on called inoculation. Until rhe inoculum begins to their physical and chemical properties. The grow, it is fairly resistant to the action of toxic determination of all characters requires special chemicals or other adverse conditions. Once the knowledge and techniques. inoculum arrives at the infection court. several The primary interest of the grower is things may happen to it. Conditions may be usually to control a given disease. Only after extremely adverse and the inoculum is killed, or positively identifYing the disease can the best it may be washed off by rain. It may start to comrol measures be employed. develop and be affected by adverse conditions. After all of the previously mentioned informa­ If environmental conditions are favorable. the tion has been successfully collected, the available inoculum will begin to develop; spores germin­ literature should be consulted to determine what ate, eggs hatch and bacterial cells multiply. It is is already known about this disease. In some during this incubation stage mat the inoculwn is cases, litde or no information may be available on most vulnerable to chemicals or other unfavor­ the particular disease in question. In such able conditions. It should be mentioned that the instances, control efforts are based on recommen- term incubation is used here to indicate the development of rhe parhogen, but in plant pathol-

12 Plant Diseases • . . . (

L-______JI m~tion

Inaabaoon

Infection

Disease:

Figure 14 Typical Disease Cycle

ogy, incubation is also used to describe mat phase cells having various functions. These cells. at least of disease development from infection to in their early development. are alive and contain sympwffi expression. cytoplasm. a nucleus and , all com­ At some point in the development of [he inoc­ ponents of living cells. This is shown as the stip­ ulum. the pathogen penetrates the plant's protec­ pled areas of the cells and illustrates that the tive harriers and invades me plant tissues [Q begin cytoplasm of one cell can be connected to that of the stage called infection. This is the real begin­ adjacent cells through small pores in the cell ning of disease. but the plant is not yet diseased. walls. It is by this means that virus particles move Only when the plant responds to the invasion of from one cell to anomer. the pathogen in some way, i.e., ceUs die or multi­ The cell wall is made up of and some­ ply abnormally, has disease developed. times contains lignins or other materials. The Once the pathogen is inside the plane, it is pro­ tected from outside influences by the plant itself Therefore, it is imponant that control measures, especially chemicals, be directed at the vulnerable stage of the pathogen. This is usuaUy during incu­ bation. How pathogens enter and affect plant cells and tissues is shown by illustrating a cross section of a leaf. Figure 15 is much simplified but shows the major features. The outer protective coating ofleaves and other plant pares is a waxy cmiele. Under this is a single layer of ceUs which makes up the upper and lower epidermis. Some of these epidermal cells may be modified or give rise (0 leaf hairs of various types. There are also specialized epider­ mal cells that form openings called stomates or stomata into the leaf tissue. Berween the two Figure 15 epidermal layers may be one or more kinds of Cross Section of a Leaf

Plant Diseases 13 cells are held together by pectic substances which form the middle lamella. Pathogens produce enzymes that break down cellulose. lignins. pec­ Spore I tins and other constituents and in the process cause disease. • • Since bacteria are limited in size and structure, (hey are unable to penerrarc the protective bar­ riers of the plant surface and must enter through some opening in this harrier. Wounds are com­ mon enrry points. but bacteria can also enter through natural openings such as scornates. Fig­ ure 16shows bacteria entering through stomata. Many fungi are capable of direct penetration of plant surfaces (Figure 17). The inoculum

Figure 17 FWlgi Directly Penetrates the Plant Surface gus disappear from the outside of the plant and the fungus continues to develop entirely wiellin the plant tissues until it reaches maturity and produces spores. A specialized type of infection takes place with the fungi (Figure 18). The spore germinaees. an appressorium and infection peg is produced and peneuation occurs as in Fig­ ure 17. The fungus remains confined to me epidermal cells where it forms specialized absorb­ ing structures called haustoria. Instead of the external myceliwn disappearing. jt continues to Figure 16 develop and expand. forming new infection pegs Bacteria Entering Through Stomata and extending the infection. Whereas most patho­ genic fungi de·/elop within the protective surface develops for a brief period of time on the plant of the plan t. the powdery mildews develop on the surface, and then an infection apparatus begins to form. This is commonly a swelling at the end of the spore germ tube. This swollen structure is called an appressorium and tightly adheres to the Spore Apptessorium plant surface. From the center of the appres­ 1 sorium and next [0 the plant surface there develops a very small infection peg that can exert Haustoria great pressure on the cuticle and wall of the epidermal cell. In addition to the mechanical penetration. this infection peg oftcn excretes enzymes that aid in the penetration by softening or dissolving the cell wall. Once the fungus is inside the plant. the fungus strands which are called hyphae or mycelium. develop within and between the cells. As the hyphae elongate. they excrete enzymes and other mctabolic materials that bring about the disease. Figure 18 Eventually the spore and other parts of the fun- Powdery Mildew Infection

14 Plant Diseases outside and, thus, are subject to chemical control ingredients is not present lUlder otherwise favor­ ( after infection has occurred. Most fungus diseases able circumstances, the circles do not overlap are difficult or impossible £0 control once inside (Figure 1911) and no disease occurs. the plants. Each of these three rmin components of The concept that a disease is not a tangible disease consists of many variables. The host plant object but is a process resulting from the interac­ may vary in it susceptiblity to disease. It also tion of a pathogen upon a host plant is impor­ serves as a source of inoculum that can infect tant. Equally important is the concept that this other plants. Its age, vigor and stage of growth interaction muse take place under favorable condi­ may influence the development of disease. The tions for disease to occur. It is generally recog­ host plant, by shading the soil or removing nized that three ingredients must be present for a nutrients, may modify the environment. The disease to develop. There must be a host plant host plant, by acting as a genetic screen, is also susceptible (0 disease, there must be a causal essential in modifYing the pathogen and giving agent and (he environment must be favorable for rise to new races and strains. The population or disease co develop. This concept also illustrates density of plants may be a deciding factor the basic principles of plant disease control, since whether a disease remains minor or explodes to eliminating anyone of the three ingredients will epidemic proportions. Even the nature of the prevent disease development. Using resistant rootstocks on a grafted plant may influence dis­ varieties or nonsusceptible species, eliminating ease development in the top. the causal agent with chemicals or other protec­ The causal agent may vary in its ability to tive barriers or modifying the environment so cause disease or in its relative aggressiveness as a that it is less conducive to disease development pathogen. The length of time a pathogen survives will do much in reducing diseases. away from the host plant and its ability to repro­ To illustrate the interrelationships of the three duce are important to its survival and subsequent ingredients. imagine three overlapping circles, development of disease. each representing one of the three ingredients. Host plants can vary in their genetic makeup, These three circles are free to move in any direc­ and so can causal agents. Pathogenic variation is a tion. Only when the three overlap will disease common occurrence in some pathogenic fungi. develop (Figure 19). If all conditions are ideal, such as rusts and smues. The quantiry or mass the circles will be almost one on top of the other that a pathogen produces may be a critical factor (Figure 19c). This would represent a very severe in its ability to cause disease. The Armillaria root disease situation or epidemic. If conditions are rot fungus must build up on dead substrates such average or moderate, only a small portion of each as roots and stumps before it can invade living circle would overlap the others (Figure 19b) and roots. Sometimes associations of certain organ­ the disease situation would be mild. This would isms will produce a different or more serious be an endemic disease. If one or more of the disease than can be produced by either alone. A B C Host

Cawal agent Environment Causal agent Environment

Causal agent Environment Figure 19 Diagram Showing the Interaction of Host, Causal Agent and Environment where (A) there is no disease. (8) there is a low level or endemic disease. and (e) where there is severe or epidemic disease

Plant Diseases IS The environment consists of many compo­ Cultural Control of Plant Diseases nents, but temperacure and moisture are probably ( Many diseases can be controlled by cultural prac­ the two most consistently influential factors. tices alone. Such practices include: Selection of resistant or tolerant varieties of How are Plant Diseases plants. Controlled? Proper establishment of plants. The ultimate concern about a plant disease is to Rotating planting locations. reduce or eliminate the economic or aesthetic loss Maintenance operations, such as raking and it causes. This is caJled the control of a disease. destroying fallen leaves, , pruning and Plant disease control involves one, or more, of regulating fertilizer and water. four basic principles. These are exclusion, eradica­ These are things every should do. tion, protection and resistance. They can also be very effective ways to control Exclusion involves measures to prevent a plant diseases. disease organism from becoming introduced into and established in an area where it does What to Plant not occur. Plant quarantines are one means of exclusion. Some plants do well only in certain areas. Always Eradication is the elimination of a pathogen be sure that a plant is adapted to the area. Avoid from an area, usually when it has limited or planting exotics that have special requirements or restricted distribution. limitations. Temperature is usually the most Protection consists of the placement of a limiting of these requirements, but other factors such as moisture. soil type and soil acidity must protective barrier, usuaUy a chemical, between also be considered. the plant and the pathogen. Resistance involves the use of plants that are The establishment and survival of plants not susceptible to the disease. Immunity is the depends largely on the vigor of the pl.nting ultimate degree of resistance and is usually not stock, whether it is a seed, or plant. Always obtained in genetic programs aimed at develop­ buy healthy material. ing resistance in a given plant. The level of resis­ tance may vary considerably depending on a large How to Plant number offactors, such as age of the host plant, A little extra time spent in establishing a plant aggressiveness of th~ pathogen, relative favora­ will pay dividends in reducing replacement and biJiry of the environment. etc. Very often, a plant maintenance later. Prepare a good seedbed or variety or selection that is resistant to disease planting hole. Don't just dig a hole, throw the lacks desirable qualities wanted for commercial seed or plant into it and cover it up. Sloppy plant­ purposes. ings may survive but are not reliable. In most cases, plant diseases are controlled by Plant in a location suitable for the plant. one of the following measures: Do not put shade-loving plants in exposed situa­ The use of disease-resistant plants on which tions or sun-loving plants in the shade. Avoid the disease organism cannot grow or will extremely wet or dry locations or use plants that develop poorly, i.e. wilt resistant tomatO are suited to these conditions. Many root diseases varieties. are favored by wet . Creating good drainage The creation of environmental conditions un­ may reduce the severity of these diseases. favorable for disease development--often Some diseases, such as the powdery mildews referred to as cultural control. Lowering the and sclerotinia and botrytis blights, are favored pH of the soil to control potato scab. by high hutrtidiry in plantings. Losses can be Placing a protective chemical over the surface reduced by not crowding plants. Also, thin the of the plant--often referred to as chetrtical con­ plants (0 permit free air circulation and allow sun­ trol. light to reach the lower parts of the plant and soil. Plant at the most suitable time of the year to insure survival and good growth of the plant.

16 Plant Diseases Check with local nursery operators or Coopera­ kill all or a large range of organisms are some­ ( tive Etension personnel as to the best planting times called biocides. time. The ideal should have at least the fol­ lowing four characteristics. although these ideals Routine Care of Plants are not always satisfied: The lethal dosage of chemical used should be Diseased branches and shoots should be removed low. This minimizes the amount of material and destroyed before the pathogen can spread. that must be applied and reduces the chances In roucinc pruning. always remove diseased or of causing damage to nontarget organisms and unthrifty growth first and then prune to develop reduces the amount of any persistent chemical and shape the tree or shrub. in the environment. Many disease organisms carry over from onc The chemical must be noninjurious to the season [0 the next on fallen leaves. It is advisable host. Many fungicides can damage plants to collect and dispose of diseased foliage. Do not under certain conditions such as high or low include diseased material in the heap temperatures, stage of plant growth. reaction because of the danger of survival of disease organ­ with other chemicals. etc. Recommendations isms and their subsequent spread. artempt to take this possibiliry into account Maintain a balanced fertilizer and watering and try to use the most efficient concentration program and avoid extremes of either. Some that will result in the least plant damage. diseases. such as certain cankers. are more The material should adhere to the plant sur­ prevalent on plants that are underfertilized or suf­ face. Since protection frequently is required fering from drought. However, other diseases, continuously for a prolonged period. a chemi­ such as rusts and powdery mildew, are more cal that sticks well to the leaf or other surface severe on succulent growth. High nitrogen levds will lessen the number of times that a pesticide and abundant moisture will favor these diseases. need be applied. However. even if adhesion is Excess soil moisture may also lead to excellent. new growth develops and some problems. leaves and other parts already sprayed will expand to produce unexposed surfaces. There­ Chemical Control of Plant fore. applications usually need to be made Diseases more or less periodically through the period of possible infection. A large number of chemicals are used to fight plant diseases. bur some of these are not suitable The chemical should be inexpensive. This is a for home use because they are exrremdy relative value but since the need for controlling poisonous or very costly. However, there are a disease often is decided by economic justifica­ some very effective pesticides that are safe and tion, cost of treatment may be the determining economical for use in the home . factor. The control of many plant diseases is not simple. To do an effective job we must have the When is the Best Time answers to four questions: to Apply Chemicals? What organism is causing the disease? The basis for mOst chemical disease control What chemical (0 use? programs is to apply a protective film of the When to apply the pesticide? chemical to the plant surface before the disease How to apply it? organism has had a chance to invade the plant Chemicals used to control plant diseases are tissues. Once it has invaded, it is usually unaf­ generally called fungicides but correctly these fected by the chemical. Dusts and sprays must include only those chemicals that kill or retard not be applied too early or else the protective the development of fungus pathogens. Those that covering may be lost by washing, aging or new control bacteria are bactericides and those con­ growth. Understanding the life history of the trolling nematodes are called nematocides (or disease agent is essential for good disease control nematicides). Chemicals that are nonsdective and practice.

Plant Diseases 17 The development of most diseases is related to Fungicides Used in Plant the growth of the plant and to the weather. Con­ sequently, a protective chemical should be kept Disease Control on the plant from the time the inoculum is The chemicals used for controlling plant diseases present until it is no longer of economic impor­ a.re many and varied and a.re categorized in tance. In addition, spray after each period of wet several ways. One way is to group them accord­ weather, if the disease is a serious problem. ing to their use, i.e., seed treannent, foliar sprays, While most diseases are controlled during the dusts. soil fumigants. etc. However. it is useful to active growing period of the plant, a few diseases, know something of the chemical nature of the such as peach leaf curl, can be controlled effec­ material and grouping these pesticides may be tively only by spraying when the tree is com­ based on either their active chemical component pletely dormant, usually between leaf fall and or their chemical base. i.e., copper fungicides. car­ before break in the spring. bamates. etc. The most widely used method of classifying How Should the Chemical disease control chemicals is by the active or basic element or ingredient. Copper fungicides are be Applied? among the oldest with being The right amount of chemical must be used to the first. Its fungicidal value was discovered about get good control, but too much can injure the one hundred years ago and it is still used to some plants. eX£ent today. Bordeaux mixture illustrates how · The equipment to be used will depend on fungicides work. It is a mixture of copper sulfate and lime to form copper hydroxide. Copper sul­ what is available. Whether to use a dust or spray will depend on the equipment available and the fate alone is very soluble in water and if a solu­ rion is sprayed on a plant. it is very phyto-toxic disease to be controlled. In general, sprays are (toxic to the plant). Copper hydroxide, however, cheaper, easier to apply and more effective than is practically insoluble in water and will not cause dusts. damage to the sprayed plant. However, enough Regardless of whether a dust or spray is used, it copper goes into solution from the copper is important to completely cover the plant, espe­ hydroxide to kill fungus spores and will control cially the lower and inner leaves and the under­ plant disease organisms without harming the sides ofJeaves. plant. Most chemicals used to control plant diseases Elemental sulfur is actually the oldest of the are protectants and must be applied before infec­ fungi,cides on record and reference to the ­ tion occurs to protee[ the plant from invasion by averting sulfur occurred as early as 1000 B.C. It is a pathogen. A few are classed as eradicants since Still used today, mainly for the control of pow­ they can eliminate an established infection to dery mildew. Sulfur can also cause plant injury, some extent. These materials generally remain at especially at warm temperatures. The polysul­ the point they are applied and do not move in fides, particularly lime-sulfur, are used both as the plant. protectants and eradicants. There recently have been developed a number The mercury fungicides were developed in the of systemic fungicides that can be absorbed by early 1900s and had been widely used: the inor­ the foliage or other parts of the plant and move ganic mercuries primarily as disinfecr.ants and the within the plant to some degree. These systemics organic mercuries as protectants and eradicants. may be prorectants or eradicants, or both. These are no longer available. Fumigants are chemicals that are applied The carbamate fungicides are all built on a car­ usually as a liquid or solid bur which conven to a bamic acid base, primarily as ethylene dithiocar­ gaseous form. They are most commonly used to bamates. They vary depending on the metallic control soil-borne fungi and nematodes. These element associated with them. Ferbam is the iron are not available to the nonlicensed person in salt, zineb and ziram are zinc salts, maneb con­ Connecticut. Any questions on their use should tains manganese and nabam is the sodium salt. be referred to a specialise Thiram is a nonmetallic carbamate fungicide.

18 Plant Dise2Ses Fungicides. as do other pesticides. may have at Everyday use of this name is impractical. and so ( least three names for their identification. These zineb has been adopted as the common or coined. are the chemical name, common or coined name, name. On the market. zineb can be found under and trade or proprietary name or names. For a number of trade names including Dithane Z- example. the fungicide. zineb. has the chemical 78. Panare C. Polyram Z and several others. name of zinc ethylenebisdithiocarbamare.

Th~ infonnation in this 17Ultai41 is for ~ducationa' purpoJ(s. Th~ r~commnu1atiom contained are baud on the best availahk knowkdge at the time ofprinting. Any rif""'c~ to commaci4/ products, IrtUU or brand names is for infonnation only, and no mdorsmzmt or approval is intnuud. The eODpn-alive Exumion System does not guarantu or warrant the standard ofany product rif(1'mced or imply approval a/the product to the aclusion ofothers which also may be availabk. All agrichmzicalslp(ShCUUS Ii.Sled art! TegisttTt!d for suggested uus in accord4nu with fide-al and Connecticut state i4ws arul regulations (lJ ofthe date ofpriming. Ifthe infonnation does not agree with current i4beling, follow the label instructions. The klb,/ is rh, klw. Warning! Agrichmricalslpmicuus are dangerous. Read and follow aU instructions and safety precautions on labels. CarefoUy handk and store agrichmricalslpesticidrs in originaUy labekd containers out ofthe reach ofchildrm, pets and . Dispose ofmrpty containm immediately in a safe manner and plaC(. Contacr the Connecticut Department ofEnvironmmtai Protection for current regulations. The user ofth i; infonnation assumes aU rislrs for pn10nal injury or propmy damage.

Plane Diseases 19