Abiotic disease

Unfavourable soil properties, fertility imbalances, moisture extremes, temperature extremes, chemical toxicity, physical injuries, and other problems. Reduce plant health and can kill plants, and can predispose them to diseases caused by pathogens. Very common: about half of plant samples in diagnostic clinics suffer from abiotic disorders. When all plants in an area are affected, it is likely to be caused by an abiotic disorder.

A form of mechanical injury. May predispose plants to diseases by weakening the plant and providing entry points for pathogens. Includes feeding by insects. Feeding by voles and rabbits results in girdling and death. Porcupines and squirrels remove bark and may leave small twigs on the ground, and can cause branch dieback. Deer may feed on buds and young stems of trees, as well as crops. Male deer may cause limb damage when they rub antlers on trees. Sapsuckers, inluding yellow-bellied sapsucker, drill holes in a straight line, oriented vertically or horizontally, on trees, causing reduced vigour and susceptibility to environmental stress, disease, and insects. May be corrected with protective barriers, live-trapping, repellants, or scare tactics.

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On the top-ten list of plant pathogenic nematodes. An important widespread pathogen. Causes white tip disease in rice. Seed-borne, and infected plants have reduced size. Formation of chlorotic tips on new leaves, which may then have necrosis. The flag leaf may be distorted, leading to a reduction in number and size of seeds produced. Can feed on other plants.

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Infections occur in mid-spring. Symptoms include blackish-purple blotches which become scabs in late summer. There is chlorosis, defoliation, and dieback. Mulch the leaves. Choose resistant cultivars such as Sutyzam. Use fungicides at budbreak.

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Xanthomonas vesicatora

X. euvesicatoria

X. perforans

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Symptoms may be similar to cucumber mosaic virus. Symptoms include leaf necrosis.

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Neonectria ditissima

N. faginata

A complex of fungi and beech scale insect

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Symptoms include root proliferation.

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HCO₃^-

Increases the pH of soil. Causes root dieback and disease, and excess P.

Apiosporina morbosa

Manage by pruning branches.

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Phytophthora capsici

P. citrophthora

P. megakarya

P. palmivora

Losses are as high as 100%. An oomycetes. Quarantines are in different countries. Infected beans have a bad odour.

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Teilaviopsis brasicola

Can become collar rot. Reproduces only asexually. Common in greenhouses. Reduce soil pH, and improve drainage.

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Phytophthora citricola

Affects hops as well as other hosts.

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A symptom of high temperature damage. Leaves become white in colour. Occurs in geraniums when exposed to temperatures above 35ºC.

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A symptom of calcium deficiency. Can often lead to secondary colonization by fungi.

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Grosmannia clavigera

An ascomycetes fungus that evolved in a relationship with mountain pine beetles. lives in dead and dying wood of pines. Produces cobalt-blue discolouration that is prized for its interesting designs. Pine wilt nematode feeds on it. Transmitted by bark beetles. It blocks a tree's vascualr system and can lead to plant death. The tree may be asymptomatic for over a year, especially in colder climates.

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A symptom of phytotoxicity from copper-containing fungicides or insecticides, or ozone.

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An odd growth that can be small, or grow to a large size. Bark covers it, and remains intact, not cracked or sunken.

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A symptom of de-icing salts. A chlorotic scorch symptom of leaf blades, with or without a well-defined lesion margin.

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Radopholus simils

On the top-ten list of plant pathogenic nematodes. A migratory, endoparasitic nematode. Affects banana, citrus, and pepper, causing toppling disease. Causes economic problems in warmer regions, and has been introduced to temperate regions where it causes problems in greenhouses. Infection causes damage to roots, which have dark lesions caused as the nematode migrates through tissue. Tissue rots occur from secondary bacterial and/or fungal infections, weakening root systems, leaving plants susceptible to topping, especially in wind.

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Occurs in fruiting vegetables. A problem in acidic soils. A result of inadequate Ca levels in soil, poor transpiration, or fluctuations in soil moisture. Symptoms include blossom end rot, stunting, localized tissue necrosis, leaf marginal chlorosis, death of terminal buds and root tips, and inhibited root growth. Symptoms start on new leaves. May be corrected by increasing soil pH and applying Ca fertilizer. Increases susceptibility to certain plant diseases due to weakened cell walls. Increases susceptibility to Sclerotirum rolfsii, because calsium is a component of host response to oxalic acid, a toxin of this pathogen. May be caused by over-applicaiton of Mg, causing competition for cation exchange sites.

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Redbud

A variety of apple with bright red, 1 cm fruits. Fruiting is persistent. Very resistant to apple scab. White flowers, with densely branched habit.

Caulimovirus

A pararetrovirus. Affects Brassicaceae and Solanaceae species. Vectored by 27 species of aphid. Symptoms include mosaic and mottle. Its genome has been mapped. Has 35S promoter which can be used to transform dicots.

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Leaves look hollowed out.

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Sugar floatation method

A method of detecting nematodes. After sieving, soil or plant tissues are placed into centrifuge tubes and spun at 3000 RPM for 4 minutes. Nematodes and debris sink to the bottom. Supernatant is discarded and the tube is filled with 1/2 sugar solution and shaken. The tube is centrifuged again at 3000 RPM for 1/2 to 2 minutes, and the clean nematodes are flushed into a dish or tube.

Heterodera avenae

H. filipjevi

Loss can be up to 90% in some environments.

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Low temperature damage that occurs above 0ºC. Plants native to tropical regiosn are susceptible. Damages newly expanded plant parts, causing purplish colouration of foliage, and possible necrosis.

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A PGR, a gibberellin inhibitor. Can cause temporary chlorosis in ornamentals.

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Loss of chlorophyll. Yellowing. Occurs in older growth, or the whole plant.

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A disease that affects onions. Caused by Fusarium oxysporum and Botrytis allii. May be detected with profiling of 25 VOCs identified by Prithiviraj et al, 2004.

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Aphelenchoides

A plant parasitic nematode. Causes angular leaf spots on coral bells.

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A disease which can be detected using hyperspectral imaging. Economic impact of missing a cankerous fruit is higher than that of misclassifying a fruit without a canker. Minimize false negative errors by properly selecting the threshold value with a cost of reducing the overall classification accuracy.

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Symptoms include bark scaling in sweet orange.

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Hemileia vastatrisx

Originated in Sri Lanka. A macrocyclic rust. Resistant varieties produce lower quality coffee.

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A symptom of cucumber mosaic virus in yellow squash lacking the precocious gene. Also a symptom of watermelon mosaic potyvirus. Green blotchy patterns.

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Symptoms vary depending on variety. May be confused with bean common mosaic virus. Leaf curl, green mottle, and blistering, with zupperlike roughness along main veins. When infection occurs before bloom, there may be no yield due to flower abortion and abnormal development. When infection occurs after bloom, plants may recover and have normal growth with limited yield loss.

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Southern mosaic virus

Symptoms can be transient, and may be muted in cool environments. Leaves have vein clearing mosaic, with yellowing and veinal chlorosis. Petioles have long, sunken, beige lesions, and are unmarketable.

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Severe epinasty common in summer squash. Early infections cause severe stunting, malformed leaves, and rough texture on fruit surface, making fruits unmarketable. Vines have stunted growing tips. Colour breaking may occur on some yellow squash. Pumpkins have mosaic pattern on the fruit and are unmarketable.

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Leaf molting, severe roughness of leaf, occasional necrosis. With early infections, the plant is stunted.

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Symptoms vary depending on plant age, and time of infection. Initial symptoms include chlorosis of young leaves. Oak leaf and ringspot patterns develop as the plant ages. New leaves have a chlorotic mosaic pattern on the entire leaf, and later new leaves may have deformations including sunken interveinal lamina with protruding primary veins, with a dull light green appearance. The plant may be stunted. Fruits may have ringspot and roughness, and are unmarketable.

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Spinach blight

Symptoms vary depending on variety, age of plant, temperature, and virus strain. Leaf chlorosis can progress and cause severe blighting of the growing point and plant death. Leaves are narrow, wrinkled, with vein distortion and inward roll.

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Symptoms may be transient, and may appear on new and old leaves only, with normal middle leaves. Leaves are yellow, with mottle similar to tomato mosaic virus, but with shoestring-like blades. The plant is bushy and stunted. Fruits are small, often mottled or necrotic, with delayed maturity. In a greenhouse, symptoms are transient and new leaves are small with varying deformation, with reduced internode and bushy growth habit. In the field, there may be upward cupping of leaves, and mosaic is more obvious in late infections.

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Seiridium cardinale

A disease found in many areas around the world. Kills up to 95% of native cypress trees including junipers and cedars.

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Globodera

Heterodera

On the top-ten list of plant pathogenic nematodes. An obligate biotroph. A sedenray, endoparasitic nematode. Includes a complex feeding structure in the roots of hosts that supplies the nematode with a long-lasting food source. The female's body becomes swollen into a cyst to protect eggs. Includes SCN, PCN, and CCN.

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Xiphinema

A migratory, ectoparasitic nematode. Affects raspberry and rose. Transmits grapevine fanleaf virus.

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Dacthal

An herbicide that can be used to control doder. Applied to the soil in the spring prior to seed germination.

Measures the accumulation of heat and average daily temperature.

Σ(((max temp + min temp) / 2) - 10ºC)

Stenocarpella maydis

Looks like white mould, and can cover an entire ear. Can't spray for it.

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Dispersal curve

The amount of inoculum is greater near the source, and decreases with increasing distance from the source.

Cuscata

Grammica

Devil's guts

Devil's hair

Devil's ringlet

Goldthread

Hailweed

Hairweed

Hellbine

Lone vine

Pull-down

Strangleweed

In the family Cuscutaceae. A twining, yellow or orange parasitic plant, sometimes tinged with purple or red, sometimes almost white. Stems are thin and thread-like, or relatively stout. Have haustoria which are modified roots that press up against host stem and penetrate tissue. Flowers are white, pink, or yellowish, small (2 - 4 mm). Fruit is 3 mm in diameter, containing 1 - 4 brown-black seeds. Rarely kills its host, but stunts its growth. Its vascular system becomes continuous with its host's, and it can transmit viruses between plants that are not closely related.

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Sclerotinia homoeocarpa

The most common turf disease in the Great Lakes region. Affects Agrostis stolonifera, Poa pratensis, and Lolium perenne.

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A symptom of water excess. Corky, blister-like swellings on the underside of leaves. May be worse during cloudy, overcast periods.

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Enzyme-linked immunosorbent assay

A way of diagnosing plant viruses, based on specificity of animal-produced antibodies to protein in virus protein coats. The screening test used for HIV. High sensitivity. An antibody is attached to a solid surface, with affinity for the substance of interest, such as hormone, bacteria, or virus. Tubes are filled with antigen solution to be assayed. Any antigen molecules present bind to immobilized antibody molecules. Substrate solution is added after washing away unbound conjugate. The reaction is stopped after a set interval, and concentration of coloured product is measured by a spectrophotometer. Intensity of colour is proportional to concentration of bound antigen. Similar to bacterial ID assay. More reliable than biological assay, and widely used.

A symptom of cucumber mosaic virus in cucurbits. Downward bending of the petiole and leaf surface, with leaf reduction.

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May cause air pollution phytotoxicity. Can build up in closed production areas such as greenhouses. A gaseous plant hormone that promotes ripening and senescence. May be a byproduct of incomplete combustion in heating systems. Colourless and odourless. Symptoms vary depending on plant species, age, and ethylene concentration and duration of exposure. Symptoms include curled leaves, flower abortion, distorted and twisted stems, leaf and petal abscission, and stunting. May be mistaken for viral infection or herbicide damage. Tomatoes, peppers, and vinca are susceptible. Can occur at concentrations as low as 0.01 - 0.1 ppm, and 1 - 10 ppm causes major damage or plant death.

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Geometric

Logarithmic

Malthusian

A mathematical model for disease epidemics.

Nacobbus aberrans

On the top-ten list of plant pathogenic nematodes. Found in South America and USA. Migratory with veniform juveniles which move through the root and feed on cells, causing cavities and lesions in root tissues. Juveniles can exit and re-enter the root, causing additional damage. Mature females are sedentary and induce partial dissolution of cell walls and fusion of protoplasts, resulting in specialized syncytia that can be up to 8 mm in size, disrupting the stele. Root galls form around feeding sites. Most eggs are laid in an egg sac.

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Sanitation is essential. Equipment for shearing and grafting should be cleaned with alcohol between each use. Wounds are entry points for a disease. Can be detected using an EOS; olfactory fingerprints are determined, and different patterns are found for healthy and sick plants.

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Low temperature damage that occurs below 0ºC. Sustained sub-zero temperatures can kill plants native to tropical regions. Bark can crack, exposing underlying wood, making a tree susceptible to other pathogens including Rhizobacterium radiobacter and insects. Temperatures below -30ºC can kill plants. When water freezes it expands tissues and can kill distal portions of the plant. Can cause wilt in July at the first dry period of the year, because there is not enough phloem to support leaves.

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Can cause phytotoxicity. Designed to protect plants from diseases. Inappropriate rates and tank-mix causes problems. Some may have negative-growth regulating effects, stronger in particular species or cultivars, or more severe in hot weather. Fungicides are toxic to animals only in very high doses, but there is concern about long-term effects, and effects when in mixtures. Suppresses, limits, kills, or inhibits growth and/or developemt of fungi. Increases crop yields, lowers food cost, inexpensive for farmers (we pay the real cost), rapid action, predictable level of control, and reduce mycotoxins. Control when there are no effective alternatives. May also kill non-targets, there may be residues and drift, food contamination, environmental contamination, habitat alteration, and biomagnification. May be toxic to humans, livestock, and wildlife. Repeated use kills off most sensitive fungi, and the remaining resistant types reproduce to form the next generation. Creates pest problems including resistance, resurgence, and secondary pests. Includes the active ingredient, and formulants. Classified based on structure, use (preventative, curative), activity (protectant, systemic), mode of action, and site of action. In Canada it is difficult to register new fungicides, and there are only about 15 available, including DMIs.

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-virus

A group of virus species sharing certain common characters.

A form of mechanical injury. Guy wires, string, trunk wraps, vines, or roots. Pressure or constriction of the bark may collapse phloem tissue, and sometimes xylem tissue. Fewer photosynthates can travel to the root system, leading to development of a smaller root system with less water and nutrient uptake potential. Trees are smaller, have poor leaf emergence, and are less vigorous. Recovery is difficult.

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Geographic information system

A new tool for epidemiology. A computer system capable of assembling, storing, manipulating, and displaying data referenced by geographic coordinates. Relates data collected by GPS to other sources of geo-referenced information. Can integrate spatial information and uncover possible relationships. May make vector and raster maps.

Global positioning system

A new tool for epidemiology. Determines location data using satellites.

A nepovirus that is transmitted by dagger nematode. One of the most important viruses of grape. Particles attach to the cuticular lining and lumen of the odontophore and pharynx of the nematode. It can be retained on a nematode for four yeras, but is not retained when it moults, and is not passed to offspring.

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Doublet

Magnifier

Pocket lens

Can be 10x to 16x magnification. Made by Boreal Labs, Efston Science, and BioQuip. Used to look at tiny insects and symptoms.

Harvest Gold

A variety of apple with bright yellow, 1 cm fruits. Fruits into early winter. Some resistance to apple scab. White flowers.

Can cause phytotoxicity. Used to control weeds. May be non-selective or selective, and have varying modes of action including growth hormone regulation, amino acid biosynthesis inhibitor, lipid biosynthesis inhibitor, membrane disruptor, and respiration inhibitor. May affect photosynthesis and growth, and cause root stunting or swelling, which could be confused with nematodes. May cause necrotic or chlorotic blotches or spots, mottled colour, and vein distortion or banding that could be confused with fungal or viral disease. May have long residual effect in the soil, causing damage to subsequent crops, depending on weather and soil factors. Herbicides may drift on the wind from neighboring properties during application. Confirmed with soil or plant tissue analysis. Includes 2,4-D and diuron.

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A disease that affects citrus. May be detected using VOC analysis.

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Multispectral imaging

An imaging technique. Gaining interest for its application in precision agriculture. Each pixel is acquired for a range of wavelengths in the electromagnetic spectra. Similar to multispectral imaging, but has a broader range of wavelengths being scanned for each pixel. May be used to detect citrus canker. A hyperspectral camera may be embedded on a drone. Cost of acquiring hyperspectral images is high for specific crops in specific climates. Remote sensing use is increasing. May be used to map varieties in a vineyard and develop early warning systems for disease outbreak.

Can cause phytotoxicity. Designed to protect plants from arthropod pests. Inappropriate rates and tank-mix causes problems. Combining captan or sulphur with certian oils can cause damage, especially in hot weather.

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A symptom of iron deficiency and manganese deficiency. Occurs in high pH soils. Treated with chelated Fe or Mn, or acidifying water.

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Iron chlorosis

A problem in calcareous soils. Prevalent in some areas of the USA. Leaves are a normal size and shape, but have interveinal chlorosis, yellow-green, often with a striped appearance. Symptoms develop in new leaves first. May be corrected by lowering soil pH below 7. May occur when soil oxygen levels are low, such as compacted soil. It can be caused by microbial activity, and may be reduced in low temperature, low light, or moisture extremes. Common in potted plants.

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Lancelot

A variety of apple with gold, 1 cm fruits. Fruits into fall. Good resistance to apple scab. White flowers. Dwarf with upright spreading habit.

Pratylenchus

A migratory, endoparasitic nematode. Affects peanut.

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An odd growth that often has a cluster of buds that sprout in the spring. Gnarled growth, but doesn't impact the health of the tree.

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Symptoms include small cherry fruits.

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Symptoms are caused by ice crystals that form in plant cells, causing damage to cell membranes and organelles. May cause water deficiency. Newly expanded shoots are more susceptible. Combined with freezing rain, can cause ice accumulation on limbs, which may cause mechanical damage. May be mistaken for an infectious root disease, chemical injury, or gas injury. It may be necessary to remove damaged plant parts. Includes chilling injury and freezing.

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A problem in alkaline soils, and in acidic sandy soils where magnesium is leached away. Symptoms include reduced photosynthesis, yellowing of leaf margins, early leaf senescence, and interveinal chlorosis and necrosis with an orange, red, or brownish colour. May be mistaken for a potassium deficiency or viral disease. Symptoms appear in older leaves first. May be caused by over-application of K or Ca, causing competition for cation exchange sites. Common in field plants.

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Symptoms include yellow stripes.

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Siberian

A variety of apple with small, red, orange, or yellow fruit. Fruits into late fall. Very resistant to apple scab. White flowers, with various habit.

Sargent

A variety of apple with small, bright red fruits. Fruits into late fall. Good resistance to apple scab. Red buds open to white flowers. Rounded form.

May be caused by storms, misuse of equipment, or animal activity. Linked to a specific event. Symptoms  include broken limbs, flattened tree tops, and torn bark. Symptoms may be subtle when roots are affected. Open wounds may be entry points for pathogens, which can lead to slow decline and death.

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A root knot nematode. Sweet pepper is less susceptible to it.

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Tourney

A DMI registered for use on dollar spot. Introduced in 2012.

A fungal pathogen which attacks cereals including wheat (Triticum aestevum), and barley (Hordeum vulgare), and cool season grasses including bentgrass (Agrostis sp.) and bluegrass (Poa sp.). Asexual reproduction is rare.

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X = X₀RT

X = Disease intensity

X₀ = Initial inoculum

R = Rate of epidemic once it starts

T = Time or duration of epidemic.

The disease progress curve is linear in early phase, with a slope of R. To reduce disease incidence, reduce initial inoculum, rate of infection, or duration of epidemic. Typical R values  are 0.02/day. There is initial inoculum only, and management focuses on reducing amount or efficacy of initial inoculum. Low reproduction and death rate. Often soil-borne. Includes root diseases and wilt diseases.

Negative exponential model

A mathematical model for disease epidemics.

A symptom of many viruses. Lesions are bordered by veins. Occurs when the virus can travel through plasmodesmata, but cannot get into vasculature.

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Monilinia vaccinii-corymbosi

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Eagle

A DMI registered for use on dollar spot. Introduced in 2000. LD₅₀ is 2100 mg/kg.

A symptom of water deficiency in conifers.

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A migratory, ectoparasitic nematode.

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Eelworm wool

The overwintering structure of nematodes. Forms at the end of a growth period. An anhydrobiotic structure, formed of millions of nematodes in a dormant state. Reactivated with moisture, and is a potential source of infestation for subsequent crops. Can survive for hundreds of years, so crop rotations may be ineffective.

"Thread-like"

The largest plant pathogen, just on the edge of eyesight. In the kingdom Animalia, in the phylum Nematoda. Over 6,500 species. Worm-shaped in at least part of its life cycle, 0.3 - 3.0 mm in length, with a round cross section, smooth and unsegmented, without appendages. Some females may become swollen. There is a thick cuticle and egg wall. No skeleton, respiratory system, or circulatory system. May be differentiated by tail shape, stylet, and mouthparts. May have sexual reproduction or parthenogenesis. Females are larger than males, and are usually parasitic. Almost all plants are attacked by nematodes. There can be up to 50,000 nematodes in one plant. Can cause 10% crop loss. Can migrate up wet stems and leaves. May be an ectoparasite, endoparasite, semi-endoparasite, sedendary, migratory, or various combinations. Inoculume is infested soil, nema wool, plant debris, cloves and bulbs, seeds, or weed hosts. Disseminated by movement of inoculum, irrigation or rainwater, equipment and tools, or human movement. Optimum conditions are 15 - 20ºC, moist environments with oxygen. Live mostly in soil, but move through soil when conditions in plant tissue are unfavourable. Detected with Baermann funnel, sieving, or centrifuge methods. Some are saprophytic, not pathogens.

Symptoms are caused by mechanical injury and cellular and physiological changes in the host. May interact with other pathogens, transmit viruses, and increase susceptibility of the host to environmental stresses. Aboveground symptoms include stunting, decline, chlorosis, reduced yield and quality, wilting, nutrient deficiencies, deformed tissue, and death. May cause angular spots on leaves; damage is in distinct zones. Roots may have galls, enlarged tips, lesions, proliferation of lateral roots, and reduced growth. Symptoms are usually caused by large numbers of nematodes, and the more nematodes the more numerous and larger the galls. A field may have a spotty, irregular patch usually oval shaped, or along a row, due to the way nematodes migrate. Damage is influenced by how the field was initially infected, and is more serious in humid climates. Often damage occurs in a dip in the field. Wilting is seen later in the season when there is water stress. Once you see symptoms, nematodes may have already left the plant.

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A major limitation in non-leguminous plants. Symptoms are a pale yellow colour, plant stunting, and poor vigour. Symptoms are observed in older leaves first. May result from an infection of root pathogens such as root knot nematode. Cause increased susceptibility to Alternaria solani.

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A nutrient toxicity. Typical in hot, dry conditions. Plants are an overly deep shade of green. Lesions occur on stems of annual seedlings, and can be confused with a canker disease. Tomato plants twist and distort, and may appear similar to a viral disease. Can be a problem in greenhouses due to lack of microorganisms that convert ammonium to nitrate. Cause increased susceptibility to Botrytis cinerea and Rhizoctonia solani.

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Exserohilum tucicum

Symptoms occur before tasselling.

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Meloidogyne hapla

Produces galls less than half the size of M. incognita. Cannot reproduce on grasses.

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Nutrient excess

Damage from excessive nutrient levels. May occur from over-application of fertilizers or manures. Common in many production systems, especially greenhouse floriculture. Symptoms often include chlorosis or necrosis on leaf margins or tips. Leaf spotting, flecking, and other symptoms can occur. May be triggered by extreme soil pH. May occur when irrigation water or soil has concentrations of micronutrients.

Ceratocystis fagacearum

Tyloses block pathogen spread through root grafts. Affects red oak.

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May cause air pollution phytotoxicity. Produced when compounds of combustion emissions react with oxygen and sunlight. Forms at the ground level. Symptoms include flecking, bronzing, chlorosis, and necrosis. Can cause needle-banding and tip-burn in conifers. May be mistaken as a disease or mite infection.

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Ditylenchus africanus

Affects peanuts in South Africa.

A plant virus which may be transmitted to humans. Causes fever, abdominal pains, and pruritus.

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Phomopsis longicolla

Affects soybeans in warm, wet conditions. Infects through wounds. Harvest as soon as possible. Reduces seed grade, depending on amount damaged.

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Can be a serious problem in some plants. Plants have weaker stems, which can result in lodging in grain crops. There is poor growth, stunting, blue/green hinge to leaves and/or purple colouration in stems and underside of leaves.

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Bursaphelenchus xylophilus

In the family Parasitaphelenchidae, in Clade 10. On the top-ten list of plant pathogenic nematodes. Native to North America, distributed in the Midwest of the USA. Introduced to Portugal, Spain, Japan, China, Korea, and Taiwan where it causes enormous damage. Causes loss of 2 x 10⁶ cubic metres of timbre in some conditions. A migratory, endoparasitic, insect-vectored nematode, 1 mm in length. Feeds on blue-stain fungi that live in dead wood. It destroys pine resin canals, causing clogged water and resin flow. Can kill a tree in a few weeks or months. All infected trees can die when conditions are right.

Needles turn greyish green, then tan to brown. Resin flow from wood causes decline. Needles remain dead on the tree for a year or more. Infection may start with scattered branches or affect the tree all at once.

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Plum pox potyvirus

Sharka

A regulated and quarantined plant disease. The most serious disease in stone fruits. There are different strains, which affect different hosts and cause different levels of damage. Strains include: D, M, C (cherry), CR (cherry Russian), EA, W, Rec, An (ancestral M), and T (Turkey). Laboratory tests are required to distinguish strains. In 1999, the USDA found PPV in Pennsylvania and in Michigan in 2006, but declared it eradicated in 2009. Canada suspended imports from the USA, but detected it in 2000 in Ontario and Nova Scotia, in trees imported from Pennsylvania. An eradication program was implemented, but was given up in 2011. In New York it was found at sites from 2006 to 2015, probably spreading in from Canada.

Symptoms appear several years after infectioin, and are not evenly distributed in the tree. May disappear during extended periods of temperatures over 30ºC. Leaves have chlorotic rings, mottling, vein clearing, chlorotic blotching, and appear small and deformed. Often symptoms appear on basal leaves of current year's growth. Does not kill the tree, but reduces vigour and fruit yield. Fruits fall prematurely and are unmarketable.

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Deformed, unmarketable fruit with low sugar content, poor taste, and gummy texture. Pock marks on the pit. Premature fruit fall. There can be 80 - 100% yield loss.

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Rings and blotches on fruits.

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Rings, lines, blotches, and spots on fruits.

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Deformed, unmarketable fruit with low sugar content, poor taste, and gummy texture. Premature fruit fall. Can cause 80 - 100% yield loss.

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X = X₀e^rt

X = final amount of disease

X0 = initial inoculum

e = base of the natural logarithm

r = rate of an epidemic once it starts

t = time or duration of epidemic

The disease progress curve is a sigmoid curve. An exponential model during early phase. Rate of increase is proportional to the amount of disease at any one time. Absolute rate of disease increase is proportional to disease intensity. To reduce incidence, reduce initial inoculum, rate of infection, or duration of epidemic. High reproduction and death rate. Wind-borne vectors. Includes leaf rust, leaf blight, powdery mildew, tobacco mosaic virus, and late blight. Control by stopping pathogen reproduction and using resistant varieties. Typical r values are 0.3 - 0.5/day. Several to many generations occur in a growing season. Secondary inoculum is produced and causes additional infections. Management focuses on reduction of primary inoculum (hard due to explosive growth), and reducing the rate of increase.

Multi-year cycle

Amount of inoculum increases from year to year. Pathogen can cause severe outbreaks over several years. Monocyclic or polycyclic within each growing season. Inoculum produced in one season can be carried over to the next, leading to a buildup of inoculum over the years. In the tropics there are no breaks between growing seasons, and can lead to accumulation of inoculum. Includes Dutch elm disease (monocyclic), and apple powdery mildew (polycylic).

Symptoms show first in older leaves. Potassium is important for fruit quality, and is important in fruit and vegetable production. Necrosis on leaf margins, leaf curling and browning, and interveinal chlorosis. Increases susceptibility to frost damage and certain diseases.

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Globodera pallida

G. rostochiensis

Causes 9% of losses in potato production worldwide.

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Symptoms include reduced growth and leaf rolling.

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Ditylenchus destructor

Affects potato tubers mainly in Europe.

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Streptomyces scabies

Has spiral hyphae. Favoured in acidic soil. No food risk. Affects most root crops.

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Banner

A DMI fungicide registered for use on dollar spot. Introduced in 1994. LD₅₀ is 1300 mg/kg. An older fungicide. Its mode of action is disruption of ergosterol synthesis. Its site of action is C14-demethylase. Dozens of genes are associated with resistance. There are no cases of resistance in Microdochium nivale. Found that there were resistant variants in BC, which were also resistant to iprodione: these had reduced fitness cost.

Guide to Nursery and Landscape Plant Production and IPM

Available as a PDF online. Has information on plant phenology.

Recombinant

A strain of plum pox virus discovered in 2010. A combination of strains D and M. Evolved when both strains infected the same plant. Found in a tree growing in a residential site near Grimsby. Found again in 2013.

Rotylenchulus reniformis

On the top-ten list of plant pathogenic nematodes. Sedentary, semi-endoparasitic. Induce a feeding structure within the host in its sedentary stage. Affects a large number of annual and perennial plants. There are two races in India. Race A can reproduce on cowpea, cotton, and castor.

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Ditylenchus angustus

Affects rice by feeding ectoparasitically on meristematic tissues of stems and leaves in deep-water and lowland rice. Occurs in India and southeastern Asia.

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Meloidogyne

"Apple-shaped female"

On the top-ten list of plant pathogenic nematodes. The most common and destructive plant pathogenic nematode. First reported in 1855 by Berkeley, and further described by Chitwood and Goeldi. Worldwide distribution, primarily tropical to sub-tropical. There are about 100 species, including M. arenaria, M. incognita, M. javanica, and M. hapla. Species may be distinguished by perineum and molecular analysis. A sedentary, endoparasitic nematode. Obligate biotroph.

Large galls on the root system. Reduced yields. Size and number of galls depends on nematode population density, species, and race, and plant species and variety. The plant often wilts even in sufficient soil moisture, especially in the afternoon. There may be nutrient deficiency, including nitrogen deficiency, not corrected by fertilization. Stunting is observed, and yield is reduced. Can kill the host if populations are high and occur early. Symptoms appear in clusters of plants because nematodes move slowly in soil. Predispose the host to infection by other pathogens.

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Typically severe forking and galling on lateral roots. Carrot is unmarketable.

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Galls are bead-like. There are resistant and susceptible varieties.

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Galls are usually small and barely noticeable, no more than slight swellings.

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Pratylenchus

On the top-ten list of plant pathogenic nematodes. Over 60 species, including P. penetrans, P. thornei, P. neglectus, P. zeae, P. vulnus, and P. coffeae. Worldwide distribution. Pholyphagous, migratory intercellular root endoparasites. Life cycle lasts 3 - 8 weeks, depending on species and conditions. Adults and juveniles can enter and leave roots. Females lay eggs inside or adjacent to roots. Males are common in some species and absent in others due to parthenogenesis. Eggs can survive for long periods in adverse conditions. Can survive for more than a year in the soil.

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RNA 5

An ssRNA molecule that is dependent on cucumber mosaic virus for replication. Provides no essential function, but may intensify or attenuate symptoms, depending on the strain of the virus.

Monochamus sartor

Longhorned beetle

A beetle 2 - 4 cm in length, with long antennae. Attracted to healthy trees for feeding, and dying trees for egg-laying. Transmits pine wilt nematode to both. The nematode is attracted to its pupae, and up to tens of thousands can leave on one beetle when it develops into an adult. It can fly for thousands of miles. Produces feeding wounds on healthy trees that are the entry point of the nematode. Lays eggs under the bark, transmitting nematodes with the eggs. It is transported as a grub in wood used for crates. It lives on spruce Picea species.

A symptom of water deficiency in deciduous trees, especially with high temperature. Marginal leaf necrosis.

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Pinus sylvestris

A tree which was popular in the Midwest, but is no longer recommended due to pine wilt nematode. More than 90% of trees killed by this nematode are Scots pine.

Anguina

A plant parasitic nematode. Affects wheat, causing seed galls.

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May be confused with a disease. A tree that naturally loses bark every year, such as sycamore trees. Sometimes bark falls off gradually, or it can appear to blow off in a few days.

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Bipolaris maydis

Also known by its teleomorph, Cochliobolus heterostrophus. An epidemic in 1970 caused 15% loss of corn in the USA, costing $1 billion. This could have been used to make 30 billion hamburgers.

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Meloidogyne incognita

Produces galls over twice the size of M. hapla. Affects cotton and sweet pepper. Peanut is less susceptible.

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Heterodera glycines

A plant parasitic nematode. Worldwide distribution. The most damaging soybean pest, causing 30% yield loss. Identified in Canada in 1987. Annual losses are estimated at $1.5 million US. Affects soybeans, beans, clover, peas, vetch, and kudzu. The first moult occurs in the egg, forming stage J2, which emerges from the egg and cyst, and lives free in the soil, attacking young roots, causing formation of syncytia. They then moult two more times to form adult nematodes. Males leave the root. Females become an egg-filled sac that may resemble a root nodule, then lays eggs in a brown gelatinous cyst on the root surface. Eggs can survive up to 10 years. Its life cycle is as short as 21 - 24 days. The plant does not produce above-ground symptoms unless there is drought, but may still have yield loss. Integrated disease management includes scouting for soil samples, growing non-host crops, and resistant soybean varieties. Older resistant varieties produce 5 - 10% less yield in absence of the nematode. Populations decline after continued planting of corn.

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Heterodera

A plant parasitic nematode. Affects soybean and sugar beet.

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Ditylenchus dipsaci

On the top-ten list of plant pathogenic nematodes. A migratory, endoparasitic nematode. Worldwide distribution. A rising problem. Can increase more than 1000 times in an infected plant during one season. Can survive severe desiccation. Survives in plant debris, soil, and weed hosts. Causes significant yield loss, feeding on leaves, stems, and bulbs. Can swim through water on the plant surface and enter stomata. Leave a plant once it is no longer suitable for feeding.

Infections cause slight hypertrophy and hyperplasia. Spicules may develop on leaves, which remain short and thick at the base. Nematodes migrate downwards intercellularly on the plant surface, to the scales of the bulb, which appear as mealy or discoloured rings. Juveniles may cling to the bulb surface as nema wool. Foliage may fall over and juveniles leave heavily infected bulbs.

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Yellow leaves, wilt, stunted plants, and collapse. Infected plants are in patches. Bulbs are brown, lightweight, and shriveled, with easily cracked and detachable wrapper layers. Secondary infections may cause rot, and damage can progress in storage. Healthy looking bulbs may be infested with small numbers, but are still marketable.

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A nematode that causes deformed tissue in knapweed.

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Belonolaimus

A migratory, ectoparasitic nematode. Affects bean.

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A form of mechanical injury. Caused by high winds, heavy snow, or ice. Ice storms may deposit an ice coating on trees, leading to breakage of limbs. High winds can lock down trees predisposed by root and butt rots or wood decay. Hail damage is common, producing tattered leaves. Lightning strikes can cause long, narrow bands of dead tissue running tree length, shattered wood, bark blown off the trunk, or tree death. Tornadoes can flatten trees, blow them over, rip off major limbs, or blow off th ebark. Removal of torn limbs and good care after the storm helps plants recover. Significantly damage trees should be removed.

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Puccinia striiformis f.sp. tritici

Yellow rust

Affects barberry and other grasses. A macrocyclic rust. Spores travel on the Puccinia Pathway.

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Paratrichodorus

A plant parasitic nematode. Affects corn.

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Spear

A part of a nematode, 10 - 12 μm long. Functions in mechanical penetration of host walls to deposit eggs, secretion, and ingestion of food. Size and shape may be used to classify nematodes. All plant pathogenic nematodes have a stylet.

Sugar Tyme

A variety of apple with bright red, 1.3 cm fruits. Fruits into spring. Moderate to high resistance to apple scab. White flowers. Oval form.

Giant-cell

A plant cell that a root knot nematode or cyst nematode has stimulated to become large and multinucleate. Produces proteins that the nematode ingests. Acts as a nutrient sink for the plant, feeding the nematode. The nematode's stylet is inserted into the cytoplasm, and filters cytosol that it ingests. Has increased production of plant growth regulators, causing gall formation. If the nematode dies, so does the syncytium.

Rhytisma acerinum

Affects sycamore and maple. Visually unappealing but does not harm the plant. Can indicate low levels of pollution in the environment.

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May be caused by insects, maggots, winter dieback, or disease.

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A virus that is vectored by the nematode Xiphinema americanum.

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The first virus to be discovered. In 1883 it was discovered to be smaller than bacteria. In 1898 Beijerinck discovered it caused disease. In 1935 it was demonstrated that it was not a cell. Symptoms may be similar to cucumber mosaic virus. Symptoms include fern-leaf, where the blade leaflet is not as completely suppressed as in shoestring leaflet. May be used to induce SAR for cucumber mosaic virus.

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A virus vectored by tobacco and western flower thrips. Affects various hosts.

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Triton

A DMI registered for use on dollar spot. Introduced in 2010.

Symptoms include breaking of flower colour in tulips. During tulip mania, in 1637, infected bulbs sold for more than 10 times the annual income of a skilled craftsman. The multicolour effects of intricate lines and flame-like streaks on petals are very beautiful.

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May be confused with a disease. Plants with areas of leaves white, lacking chlorophyll. Grown for horticulture. Caused by a genetic mutation, often not stable through sexual reproduction. Plants tend to be smaller because they produce less chlorophyll.

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