Fungal Diseases

Characteristics of Fungi „

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While they are not plants fungi are often grouped with plants However there are important differences between fungi and plants, especially in the processes of cell division and reproduction often called ‘alternation of generations’

Alternation of Generations „

Many pathogenic fungi have two morphological stages „

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Asexual stage often called the “vegetative” stage where the fungi multiplies in the host causing disease Sexual stage which is true reproduction

Rusts, smuts and woody fungi have an intermediate stage called the dikaryon

Disease-causing Stage „

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In higher plants mitosis always occurs in diploid cells In fungi mitosis occurs in the haploid stage where fungi multiply by conidia which can initiate disease

Diagram of Fungal Life Cycle Gamete n

Zygote Dikaryon

Gamete

n

Gamete

n

n 2n n

n

Haploid

Gamete

Diploid

Haploid

Two gametes either fuse and form a zygote, or join and form a dikaryon. The nuclei in the dikaryon eventually fuse to form a zygote. The zygote matures, divides by meiosis and forms new gametes. The diploid stage does not cause disease.

Fungal Growth When a viable spore or conidium is in the presence of moisture and the proper temperature it will germinate. It may swell but eventually forms a small tube called the germ tube. Hyphae develop from the germ tube and penetrate the substrate. Once established the hyphae produces acids and enzymes which cause the breakdown of host cells and provide the fungi with food. Mycelium (masses of hyphae) of most plant pathogens is mostly inside the host and can be seen at a magnification of 100x to 200x. In a few fungi such as the powdery mildews most of the hyphae are outside the host. Rhizomorphs, pycnidia, conks and mushrooms are formed when compatible mycelium join and form a dikaryon and eventually a zygote.

Damage Caused by Fungi „

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Acids and enzymes kill plant cells destroying roots, stems and leaves Decay of dead plant cells can allow other organisms to thrive and produce additional toxins or clog vascular systems Damage to leaves may cause defoliation Growth of mycelium can clog the vascular system Starvation due to fungal use of nutrients

Common Fungal Diseases „ „ „ „ „ „ „ „ „

Anthracnose Black spot of roses Botrytis blight Brown patch on lawns Cankers Damping off Dollar spot on lawns Dutch elm disease Juniper twig blight (Phomopsis twig blight)

Common Fungal Diseases (2) „ „ „ „ „ „ „

Leaf and bud gall Leaf spots Oak wilt Pine blister rust Powdery mildew Root rots Scabs of apples and crabapples

Anthracnose „

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Anthracnose is the term used for a group of diseases caused by related fungi It is most common and severe on sycamore, white oak, elm, dogwood, and maple Other hosts that are usually only slightly affected include linden (basswood), tulip tree, hickory, birch, and walnut

Anthracnose (2) „

Each species of anthracnose fungus attacks only a limited number of tree species. The fungus that causes sycamore anthracnose, for example, infects only sycamore and not other tree species

Anthracnose Symptoms „

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Killing buds, which stimulates the development of many short twigs or "witches' brooms" these may spoil the shape of the tree Girdling and killing of small twigs, leaves, and branches up to an inch in diameter Repeated early loss of leaves, which over several successive years weakens the tree and predisposes it to borer attack and winter injury Premature leaf drop, which lessens the shade and ornamental value of the tree

Anthracnose on Sycamore „

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Leaves and growing tips of the twigs may die as they emerge from the bud, often confused with late frost injury Sudden browning and killing of single leaves or leaf clusters as the leaves expand Later in the season, irregular brown to nearly black, dead areas between or along the main leaf veins and extending to the margin Infected leaves fall when the petiole is girdled or when several lesions enlarge and coalesce to form large, dead blotches

Anthracnose on Sycamore (2) „

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After defoliation from spring infections, the tree may appear bare except for tufts of leaves at branch tips. Regrowth appears by midsummer Sunken cankers form on larger twigs during cooler weather in fall, winter, and spring. Twigs may die as a result of canker formation When terminal twigs are killed, lateral twigs take over as leaders. Repeated twig dieback results in the formation of crooked branches

Anthracnose on Sycamore

Anthracnose on Sycamore

Sycamore anthracnose shoot and leaf blight

Sycamore anthracnose canker on stem

Anthracnose on Dogwood „

Two different anthracnose diseases may occur „

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Symptoms of spot anthracnose include tiny leaf and bract spots, about the size of a pinhead, with whitish centers and purplish borders Symptoms of Discula anthracnose (dogwood anthracnose) include irregular, small to large brown blotches with purplish borders on leaves and bracts, lower branch dieback, and trunk cankers that culminate in death of the tree

Anthracnose on Dogwood

Anthracnose on Dogwood

Canker on stem

Pycnidia on stem

Anthracnose on Dogwood „

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Reproductive structures of D. destructiva form underneath leaf spots and on the surface of twig cankers Huge amounts of asexual spores are formed inside and, in the spring, ooze out in slimy beige clusters Dispersal of the spores occurs by splashing rain Dispersal may also occur via insects and birds Spores of the fungus land on shoots or leaves penetrating them directly causing the quick death of the plant tissue due to the production of several toxins by the fungus

Anthracnose on Oak „ „

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Most severe on white oak and burr oak Small scattered brown spots or large light brown blotches form along veins The leaves look scorched

Anthracnose on Oak

Anthracnose on Maple „

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Purplish brown areas form along the veins or larger, irregular, light to dark brown spots form along or between veins, extending to the leaf margin Often confused with leaf damage resulting from adverse environmental conditions Young developing leaves are sensitive to freezing temperatures, high winds, or other sudden weather changes

Anthracnose on Maple

Anthracnose on Ash „

Large, irregular, light brown spots appear, most often along leaf margins

Anthracnose on Linden „

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On linden, large brown areas with black margins appear, especially along main leaf veins The areas are small to large and circular to elongate

Anthracnose on Birch „

On birch, small, irregular, circular, brown spots with dark brown margins are apparent.

Anthracnose on Walnut „

On walnut, irregular, circular, dark brown to black spots are visible on leaves

Anthracnose Control „

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Anthracnose diseases are usually not fatal on healthy, vigorous trees Proper cultural practices are the best way to control the disease

Anthracnose Cultural Control „ „ „ „

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Use resistant plant and proper siting Rake and remove infected leaves in the fall Prune burn or bury dead twigs and small branches Prune to thin the crown. Thinning improves air movement and promote faster drying of the leaves Fertilize in the fall about a month after the average date of the first frost or in early spring about a month before the date of the last frost to increase tree vigor

Anthracnose Chemical Control „

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If chemical control is desired, spray with a fungicide containing mancozeb (e.g. Manzate 200, Dithane M-45) at budswell and twice again during leaf expansion (10-14 day intervals) Because Discula anthracnose is often fatal to the tree, control of this anthracnose disease on dogwood is a special case

Discula Anthracnose Control „

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Because Discula destructiva causes cankers, this disease is difficult to control A combination of cultural and chemical methods is recommended for most effective control Once cankering is severe on a tree, the tree can not be saved

Black Spot of Roses „

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Rose black spot, caused by the fungus Diplocarpon rosae, is the most common cause of defoliation of landscape roses Small, round spots, ranging in size from 1/16" to 1/2" in diameter, appear on the upper sides of leaves Leaf tissue adjacent to the spot turns yellow. Whole leaves eventually turn yellow and fall prematurely Black spot can be distinguished from other leaf spot diseases of rose by the generally fringed margins and the darker and consistently black color of the leaf spots

Black Spot Disease Cycle „

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The fungus overwinters in infected canes and fallen leaves Spores are spread to the highly susceptible, young, unfolding leaves in spring by splashing water Infection takes place only when water remains on the leaves for seven or more hours The fungus tolerates a wide range of temperatures, symptoms can continue to develop all season long if moisture is adequate

Black Spot of Roses

Black Spot Cultural Control „ „

Use resistant varieties Begin in the fall with a thorough sanitation program „

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Diseased leaves on the ground should be raked and burned or removed All diseased canes should be pruned back to healthy wood

During the growing season overhead irrigation should be avoided If plants are overhead irrigated, watering should be done in the morning rather than the afternoon so that leaves dry quickly.

Black Spot Chemical Control „

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Fungicides should be applied preventatively to susceptible roses before the new leaves become spotted The plants should never pass through a rainy period without a protective coating of fungicide on the leaves Fungicides registered for black spot include „ „ „ „ „ „ „

propiconazole (e.g. Banner) thiophanane methyl (e.g. Cleary 3336) chlorothalonil (e.g. Daconil 2787) mancozeb (e.g. Fore, Dithane, or Maneb) thiophanate methyl + mancozeb (e.g. Zyban) trifloxystrobin (e.g. Compass) myclobutanil (e.g. Systhane)

Botrytis Blight „

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Botrytis blight or gray mold is a fungus disease which infects a wide array of herbaceous annual and perennial plants There are several species of the fungus Botrytis which can cause blights; the most common is Botrytis cinerea

Botrytis Hosts „

Botrytis cinerea can infect many ornamental plants „

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anemone, begonia, calendula, chrysanthemum, dahlia, dogwood, fuchsia, geranium, hawthorn, heather, hydrangea, marigold, pansy, periwinkle, petunia, rose, snapdragon, sunflower, sweet pea, violet, zinnia

Two other damaging Botrytis blight fungi have strict host preferences „ „

Botrytis paeoniae infects peony Botrytis tulipae infects tulips causing the disease known as tulip fire

Botrytis Symptoms „ „

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Botrytis tends to infect flower tissue The leaf spot phase of Botrytis blight often appears when infected flower petals or other plant parts fall on the leaves and the pathogen invades healthy tissue The resulting lesion often assumes the outline of the fallen, infected tissue Brown or spotted plant material develops during wet weather

Botrytis Symptoms (2) „

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Masses of silver-gray spores on the dead or dying tissue, may appear as a dust coming off heavily infected plant material Infected plants wilt or collapse at or near the soil line from a soft, tan to brown, watersoaked rot (damping off or bed rot) Some species of Botrytis form tiny black resting stuctures called sclerotia that may be evident on dead plant tissue in late summer

Botrytis Disease Cycle „

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Conidia produced on germinating sclerotia, on infected plants, or on infected plant debris are dispersed in large numbers by air currents to new plants The optimum temperature for germination of the conidia of B. cinerea is 72( to 77(F (22( to 25(C) with free moisture or high relative humidity (90 to 100 percent) also necessary for spore germination

Botrytis Disease Cycle (2) „

Germinating conidia seldom penetrate actively growing tissue directly since they need an outside nutrient source „

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Penetration of green tissue is common through wounds, such as cutting stubs, and tip-burned leaves Aging flower petals and dying leaves are very susceptible to conidial infection.

Botrytis

Botrytis on poinsettia

Botrytis on roses

Botrytis Cultural Control „

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Avoid water on the foliage, surface irrigation and watering in the morning is recommended Strict sanitation is of the utmost importance. The fungus readily attacks aging or dead tissue and then produces tremendous quantities of airborne spores „ „

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All old blossoms and dead leaves should be removed All fallen leaves and plant debris on or under greenhouse benches and in plant beds should be carefully collected and burned or hauled away Ideally, all diseased plants and plant parts should be removed and destroyed

Botrytis Cultural Control (2) „

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Provide maximum air circulation in the greenhouse and in plant beds. Maintain the humidity below 85 to 90 percent by (a) forced circulation in each section or the entire greenhouse, or (b) an increased amount of heat To avoid condensation on the foliage, supply heat at night to maintain the indoor temperature higher than the outside. Night heating may be needed from September through mid-June

Botrytis Cultural Control (3) „

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Properly space plants to allow for maximum air circulation. In outdoor plantings, plant in well drained soils. Avoid shady or low spots with poor air movement. Keep down weeds Avoid over-fertilization (especially with nitrogen) and wet mulches

Botrytis Chemical Control „

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Routine fungicide control programs are highly recommended for greenhouse production of all ornamentals, especially crops such as geraniums and chrysanthemums, where cuttings are routinely taken and cutting stubs remain on the plant. There are a number of fungicides that give excellent control of Botrytis when properly applied. Applications are needed at intervals of 5 to 7 days in rainy, overcast weather and every 7 to 10 days in warm, dry weather

Brown Patch of Turf „ „ „

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Turf disease caused by Rhizoctonia solani The fungus survives on decaying organic matters or in soil, but will use living plant tissue if available Rhizoctonia solani is classified in the group of basidiomycetes, club and mushroom fungi. However, the brown patch fungus is known to produce no spores or mushrooms, and is often referred to as being in the group of imperfect fungi known as the mycelia sterilia, fungi with sterile mycelium Sclerotia, compact masses of mycelia, are formed for surviving under unfavorable conditions

Brown Patch Hosts „

Affects many turfgrasses including Kentucky bluegrass but is most severe on„ „ „

Tall fescue Perennial ryegrass Creeping bentgrass

Brown Patch

Brown Patch Disease Cycle „

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The causal fungus overwinters in the form of resting bodies called sclerotia, either within infected grass tissue or in the soil The fungus is capable of surviving in soil for years in the absence of a susceptible grass Disease activity is prevalent when surface moisture and humidity are high, night temperatures are above 68° F and daytime temperatures average 80° F or above

Brown Patch Disease Cycle „

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Rainy weather and a saturated atmosphere (100 percent relative humidity) greatly speed disease development Disease severity is greater on lush, succulent turfgrass maintained with high nitrogen levels than on grass maintained with moderate levels

Brown Patch Cultural Control „ „

Excessive nitrogen fertilizer applications should be avoided, especially in warm and wet weather Keeping foliage dry and avoiding wet soil are the most important practices „ „ „ „

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Irrigation should be reduced If possible, irrigate in the morning Excessive water should be properly drained Dragging or poling in the morning will remove dew and guttation water, and accelerate drying the surface of the plants

Increase light penetration and air circulation to reduce the level of free water and humidity on turfgrass

Brown Patch Chemical Control „

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Preventive fungicide applications are made on bentgrass fairways, greens, and tees when environmental conditions are favorable for brown patch The first application should be made when the night air temperatures do not fall below 67 F, and there are wet conditions

Brown Patch Fungicides „

There are many fungicides labeled for managing brown patch „ „ „ „ „ „ „ „ „ „

chlorothalonil (Daconil Ultrex) iprodione (Chipco 26019 or 26GT) vinclozolin, Thiophanate-methyl (Cleary’s 3336) azoxystrobin (Heritage) flutolanil (ProStar) mancozeb (Fore) PCNB trifloxystrobin (Compass) pyraclostrobin (Insignia) polyoxin D zinc salt (Endorse)

Fungal Cankers „

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Canker disease mostly occurs on ornamental woody plants, forest trees, and some fruit trees such as apple, peach, and pear, etc. It causes dieback of twigs and branches, reduces tree growth, affects lumber quality, and causes significant yield losses on fruit trees Sometimes, it kills the entire tree if the canker girdles the trunk of a tree.

Canker General Symptoms „

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Canker by definition means a definite and localized area that is usually dry and dead, often discolored, sunken or raised, sometimes cracked on a stem, trunk, branch, or even twig Not all cankers have these characteristics at the same time Expression of canker symptoms is very variable depending on the type of host plants, pathogen species, environment and stage of disease development

Canker General Symptoms (2) „

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In the early stage of the infection, abnormal appearance may not be visible or identifiable on the bark surface. However, when the surface tissue is scraped off, significant discoloration may be seen inside the bark tissue As a defensive response, tree plants may exude gum from bark at the site of infection or injury. Bleeding is another sign of infection. In most cases, bacterial infection causes bleeding cankers, however, some fungi such as Phytophothora also cause bleeding symptoms

Canker General Symptoms (3) „

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When a fungus invades and kills a large area of bark tissue, a distinct color change occurs on infected bark Some trees form callus tissue in response to injury or infection, so it is very common to see callus tissue on canker area Bark killed by fungi may be cracked. Some cankered bark may look sooty such as sooty bark canker on trembling aspen trees. As a result of bark canker, the younger branches or twigs may dieback. Sometimes, an entire tree will die if the canker girdles the major stem of a tree

Canker General Symptoms (4) „

In most cases, fruiting bodies of the fungal pathogen are very evident and visible on dead or seriously infected bark. The most common fruiting bodies are stromata, sporodochia, and acervuli

Canker Infection „

Generally speaking, canker disease always occurs on trees that are predisposed by other factors. There are numerous factors that can hurt or stress the tree, for example„

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lightening damage, cold and freezing injury, sun scalds, drought, poor soil, nutrient deficiency, improper pruning, other fungal diseases, wild animal damage, and bark borer insects.

Many fungi cause canker diseases on a variety of trees and shrubs. They are opportunistic pathogens and like to attack those stressed or injured trees

Canker Symptoms

Canker Symptoms

Canker Symptoms

Canker General Disease Cycle „

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Most canker-causing fungi overwinter in dead or infected bark tissue in which fungal fruiting bodies, spores or mycelia are present In the spring, fungal spores are transmitted by wind, rain, water, or pruning tools to other trees or other parts of the same tree If spores reach a stressed or injured tree and find desirable infection sites (usually those injured spots or natural holes on the bark), they germinate immediately and then penetrate into the bark tissue

Canker General Disease Cycle (2) „

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Once the fungus is established in the bark tissue, it kills bark cells and reproduces asexual or sexual fruiting structures there During summer time, the fungus usually produces conidia spores (asexual state) that can be spread to other trees and start another cycle of infection. This cycle may occur many times during the growing season When winter is approaching, the fungus will turn into sexual reproduction and produce ascospores. Ascospores infect trees in the next spring, resulting in primary infection.

Canker Cultural Control „

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Management of canker diseases should be based on integrated pest management (IPM) principles As most of the canker fungi are opportunistic and like to attack those weakened trees, keeping tree’s growth vigor is very critical to lower the chance of infection Avoiding wounding or severe pruning also will reduce opportunities for fungi to attack

Canker Cultural Control (2) „

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Removing cankers and treating with a disinfectant will prevent further expanding of the canker area Burning or burying all cankered or dead branches or twigs will eliminate the infection sources Always spray some protective fungicides after pruning and before rain.

Canker Chemical Control „

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No chemicals are universally registered for treatment of canker diseases Lab- go online and locate a chemical treatment for the following„ „

Nectria canker of apple Cytospora canker

Damping Off „

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Damping off is the sudden unexpected death of seedlings or cuttings Several different fungi can cause damping off Most pathogens that cause damping off also cause disease in maturing plants such as root rots, crown rots, stem lesions, basal rot and stem girdling

Damping Off Pathogens „

The two most common damping off fungi are „ „

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Pythium sp. Rhizoctonia solani (also causes brown patch in turf)

Other species associated with damping off are „

Botrytis cinerea, Sclerotina sclerotiorum, S. minor, Alternaria sp., Phytophthora sp., Fusarium sp., Theilaviopsis basicola

Damping Off General Symptoms „

Damping off injury has two forms „

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Pre-emergent; decay of the germinating seed or seedling before it pushes above the soil. Pythium and Phytophthora cause seed decay Post-emergent; occurs after seedlings have emerged from the soil but while they are still tender. Roots may be affected and plants show a water-logged appearance at the soil line and eventurally fall over. Post-emergent damping off is primarily caused by Rhizoctonia

Damping Off General Symptoms (2) „

Usually occurs in small patches in the seedbed or field. „

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These patches often spread daily until seedlings “harden” Once stems harden damping off doesn’t occur but other problems such as stem lesions or root rots can still damage plants

Stems may show light brown rings at soil line Stems may have a “wirestem” appearance

Damping Off General Symptoms (3) „

Roots may be girdled or rot „

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Sometimes plants with damaged roots do not die immediately but remain stunted or die later when the plant is stressed

Infected roots are usually dark brown, sunken or irregular and spongy Occasionally a white to brown surface mold may appear on roots

Damping Off Symptoms Damping off of seedlings caused by Rhizoctonia. Note the dark color of stems at soil line, also note the thin dark “wirestem” appearance of the seedling second from the left.

Damping Off Symptoms (2) Damping off of pine seedlings in a container nursery.

Damping Off Symptoms (3) Pythium damping off of seedlings. These carrot seedlings were not killed pre-emergent by the fungus. Note the discoloration of the roots as well as malformation of roots. These also display dark rings at the soil line.

Damping Off Disease Cycle „

Infection by Pythium spp. and Rhizoctonia spp. is favored by: „ „ „ „ „ „

Heavy soils Low pH (contradictory evidence for this) Heavy seeding resulting in dense planting Careless handling Excessive soil moisture Low light and presence of weeds

Damping Off Disease Cycle (2) „

Rhizoctonia overwinters as sclerotia in soil „

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Rhizoctonia then attacks stems of emerging seedlings

Stems take on a brown color and water-logged appearance at the soil line. Seedlings the topple over and die Since it produces no spores Rhizoctonia spreads plant-to-plant or mechanically

Damping Off Disease Cycle (3) „

Pythium overwinters as oospores in the soil „

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Pythium then attacks root hairs and root tips often killing the seedling before emerging from soil

Infected plants may not emerge from soil or may emerge only slightly Pythium produces spores and can be spread by wind, water or mechanically (tools, containers, etc.)

Damping Off Cultural Controls „

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As with most fungal diseases cultural control of damping off is the first course of action Reduce watering so soil is not water-logged and water doesn’t sit on stems Properly space plants to allow airflow Use a light soil mix or amended soil to improve drainage

Damping Off Cultural Controls (2) „ „

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Use proper tool hygiene Take care not to drop water or soil from infected plants onto healthy plants Avoid excess nitrogen Use clean treated seeds For greenhouses sterilize soil mix, containers and benches

Damping Off Cultural Controls (3) „

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Low pH in field-grown crops has been shown to increase infection rates, however low pH in container nursery stock seems to inhibit infection rates There are presently no species available that are resistant to Pythium however experiments are underway using antagonistic fungi and bacteria

Damping Off Chemical Controls „

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Several fungicides have proven effective against Pythium and Rhizoctonia A combination of a systemic fungicide and a broad-spectrum protectant have provided excellent control Using seeds treated with fungicide is key for many crops

Dollar Spot on Turf „ „ „

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Caused by Sclerotinia homeocarpa Most prevalent in low-mowed grasses In golf courses it usually causes numerous small, circular, bleached-out spots from ½ inch to 1 ¼ inches in diamter In home lawns it can appear as 4 to 6 inch patches of blighted turf

Dollar Spot Symptoms „

Many circular spots scattered throughout the turf „ „

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Spots have a bleached out appearance After a long period of dew or moisture mycelia will appear on stems

On longer-mowed turf the spots may be larger, up to 6” and irregular in outline

Dollar Spot Symptoms (2)

Dollar spot on golf course. Note the very light, bleached out appearance of the spots.

Dollar Spot Symptoms (3) Closer view of dollar spot showing typical size and appearance of the spots.

Dollar Spot Symptoms (4) Close-up of dollar spot showing mycelia on turf leaves. The mycelia appear after a long period of dew or other moisture (irrigation) The fungi is active over a broad range of temperatures from 55 degrees to 80 degrees F.

Dollar Spot Symptoms (5) Dollar spot on a home lawn. On turf that is maintained at a longer length the spots can be larger and irregular. On home turf treatment with a fungicide is rarely required.

Dollar Spot Cultural Controls „

Use more resistant varieties of turfgrass. „

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All modern varieties of bent grass and Kentucky bluegrass are susceptible to some degree but some are more resistant.

Unlike some other fungal diseases dollar spot occurs most heavily on nitrogen deficient turf so a proper fertilization program is essential

Dollar Spot Cultural Controls (2) „

Properly time irrigation „

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Irrigation should be done early in the day to allow turf to dry before night

Reduce standing water „ „ „

Reduce amount of irrigation if possible Improve soil drainage Drag turf to speed evaporation of water from leaves

Dollar Spot Chemical Controls „

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Several fungicides are labeled for use against dollar spot Applications must typically be made regularly throughout the growing season Cultural controls must also be used to reduce disease pressure in order for chemical controls to be effective

Fungicides for Dollar Spot Selected fungicides registered for use on creeping bentgrass against dollar spot. Fungicide/Trade Name

Application Rate Interval (days)

Type

propiconazole/Banner Maxx 1.24ME® 1-2 fl. oz.

14-28

systemic

triadimeforn/Bayleton 50 W®

0.5-1 oz

14-28

systemic

myclobutanil/Eagle 40WSP®

0.5-1.2 oz

14-28

systemic

thiophanate-methyl/Cleary's 3336F® Fungo Flo 4.5F®

2-4 fl oz 1-2 fl oz 14-21 10-14

systemic

systemiciprodione/Chipco 26GT®

3-4 fl oz

14-21

local systemic

vinclozolin/Curalan 50EG®

1 oz

14-28

local systemic

mancozeb/Fore Rainshield 80WDG® 6-8 oz

7-14

contact

chlorothaloni/Daconil Ultrex 82.5 WDG®1.8-3.3 oz

7-14

contact

Dutch Elm Disease „

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Ophiostoma ulmi is the fungal pathogen responsible It is probably native to Asia but was first identified by a Dutch biologist, hence the name It was introduced to the U.S. on the east coast in the 1920’s and rapidly spread across the country

Dutch Elm Disease Symptoms „ „

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Flagging is usually the first symptom noticed Vascular tissue shows brown streaking when infected branches are cut Emergence holes of the adult elm bark beetles Peeling back sections of bark reveals “galleries” where eggs are laid Since vascular system is clogged decay may cause internal pressure resulting in bleeding

Dutch Elm Disease Symptoms (2) An elm tree flagging. Note the dead leaves on branches. This is often the first sign of infection and at this point the tree is usually beyond help.

Dutch Elm Disease Symptoms (3) Vascular streaking from Dutch elm disease. The twig on the left shows the current year’s vascular tissue streaked dark brown. Vascular streaking is usually present in current year’s tissue but since some trees survive up to 2 years with the disease it may also show up in older tissue. (Middle twig shows streaking in previous year’s vascular tissue.) The twig on the far right is uninfected.

Dutch Elm Disease Symptoms (4) Elm bark beetle emergence holes.

Dutch Elm Disease Symptoms (5) Elm bark beetle “galleries”. These are under the bark and only visible when bark is removed.

Dutch Elm Disease Symptoms (6)

Elm bark beetles. The top beetle is the native elm bark beetle. The lower beetle is the Smaller European elm bark beetle. The Smaller European is actually larger than the native.

Dutch Elm Disease Cycle „

Dutch Elm Disease is spread in several ways „

Elm bark beetles both native and Smaller European elm bark beetle „

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The Smaller European elm bark beetle is actually larger than the native elm bark beetle

By grafted roots By mechanical means such as pruning with infected tools

Dutch Elm Disease Cycle (2) „

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Elm bark beetles are attracted to trees that are stressed or injured Adult beetles feed on the tree and inoculate it with fungi from diseased trees „

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Native beetles feed under the bark on older stems and trunks Smaller European beetles feed on young twigs near the crown

Dutch Elm Disease Cycle (3) „

The fungi may spread between trees by grafted roots „

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Any other elm with 50 feet of an infected elm should be assumed to have grafted roots

Pruning tools also spread the pathogen „

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Tools should ideally be sterilized between every cut, even on the same tree A 70% isopropyl alcohol solution (rubbing alcohol) is an effective disinfectant

Dutch Elm Disease Cycle (4) „

Once infected the fungus spreads rapidly through the vascular system of the tree „

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The vascular system is physically clogged with fungus resulting in wilting and death

Infected trees often die within the season, some may live 2 years „

In very rare instances a tree may actually survive infection and recover. These trees are the subject of breeding programs to develop a resistant tree

Dutch Elm Disease Cultural Control „

Remove dead or diseased trees „

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Burn or bury wood from infected trees

Remove root grafts between trees Prune weakened or stressed branches Prune out branches showing flagging and streaking Maintain vigorous, healthy trees as beetles are attracted to stressed plants

Dutch Elm Disease Chemical Control „

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Many communities require removal of infected trees regardless of other treatments Insecticides can be used to reduce the beetle population „ „

This is less common than it used to be Insecticide usually applied to lower trunks in late summer at the first sign of fall color to kill beetles as they prepare to overwinter in the bark

Dutch Elm Disease Chemical Control (2) „

Theraputic injection (after infection) is only effective when less than 5% of the crown shows symptoms „

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Even in ideal conditions 30% or more of treated trees die

The infected branch should also be removed 10 feet below the point where streaking ceases Theraputic treatment of trees infected through root grafts has never been effective and should not be done

Dutch Elm Disease Chemical Control (3) „

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Protective Injection requires treatment every one to three years Injection damages the tree directly and may lead to other problems such as wetwood The most effective treatment available is Arbotect, it provides three seasons of protection when used at the “high rate” of 12 fluid ounces per 5 inches of trunk diameter

Dutch Elm Disease Treatment Injecting an elm at the root collar. The blue tubing carries the fungicide from a pressurized tank to holes drilled into the tree. The pressurized chemical is forced into the tree’s vascular system.

Phomopsis Twig Blight „

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Phomopsis juniperivora is the pathogen. The disease is twig blight or Phomopsis blight of cedars, junipers, arborvitae, etc. Phomopsis blight is a canker disease which in forest trees kills young growing tips In nurseries Phomopsis can kill all susceptible plants in the nursery

Phomopsis Blight Symptoms „

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In our area Phomopsis is most severe on junipers New growth becomes discolored, browns and dies, older growth is not susceptible In susceptible varieties entire plantings can appear devastated In nurseries, because so much of the stock in young death of the entire plant is common

Phomopsis Blight Symptoms (2)

A planting of susceptible junipers infected with Phomopsis blight

Phomopsis Blight Symptoms (3) Juniper twig with Phomopsis Pycnidia on infected juniper

Phomopsis Blight Symptoms (4)

Nursery planting of junipers infected with Phomopsis

Phomopsis Disease Cycle „

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Spores from Pycnidia produced on twigs infected the previous year are the most significant source of pathogens Pycnidia can develop within three weeks of infection but aren’t usually well developed until after the twig has dried significantly Spores are dispersed primarily by splashing rain

Phomopsis Disease Cycle (2) „

High humidity is required for germination but is only required for a short time „

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Plants subjected to 100% humidity for as little as 7 hours can become infected

Spore germination is optimum at about 75 degrees F. Disease development is enhanced by higher temperatures up to 90 degrees F

Phomopsis Disease Cycle (3) „

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Infected twigs can display symptoms within days Infected twigs develop a gray-brown color and pycnidia are produced „

Infected twigs which don’t die during the first season produce many pycnidia the next year

Phomopsis Cultural Control „ „

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Use resistant varieties Do not use susceptible plants as windbreaks in nurseries Do not sow juniper seedlings near beds containing junipers Since high humidity is required for spore germination the usual techniques of properly timed watering and providing air movement help reduce infection rates

Phomopsis Cultural Control (2) „

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Quickly pruning infected twigs helps prevent the spread of the disease Quickly and completely removing entire infected plants in nurseries reduces infection rates

Phomopsis Chemical Control „

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The only fungicide currently labeled for the treatment of Phomopsis blight is benomyl Since conditions for infection exist during much of the growing season applications must be made at 7 to 10 day intervals Chemical control must be combined with cultural control in order to be really effective