ICAR-DFR

Know Your Enemies

GENERAL SYMPTOMS OF DISEASES IN PLANTS

Spot

Well defined, self limiting lesion on arial plant parts are called spot. They are often named after the plant part on which they are present, for instance on the leaves are called Leaf spot. These maybe of various shapes such as round , circular ,angular, etc. and are often light to dark brown or black in colour. It is worthy to note that in angular leaf spots, veins and vein lets normally restrict the spread of infection.

Blotch

Large areas of discoloration on leaves, fruits etc. are called blotches. There spread on the leaves is not restricted by veins.

Anthracnose

Black or charcoal like, slightly sunken lesion on leaves, stems or fruits result in a disease.

Canker

A necrotic, often sunken lesion, on a stem, branch or twigs of plants is called a canker.

Scab

A rough, crust like lesion on a plant part, showing surface layer thickening ; or the disease condition in which such areas form is termed scab.

Rot

Softening, discoloration and decay of succulent plant tissue as a result of infection is called rotting. Root rot, foot rot, crown rot, bulb rot, collar rot, soft rot, rhizome rot, sett rot, stem rot etc. are some common types of rots.

Damping off

Death and collapse of seedling at or near the soil line is normally referred to as damping off. However, in the strict sense of the term, decay of seeds in the soil or of seedlings before or after their emergence from the soil is called damping off. It is very common in the nursery and they often result in heavy seedlings mortality. If the seedlings are vary mildly infected they may withstand attack but carry infection to the field and at a later stage succumb if weather turns favourable.

Gummosis

External or internal production of an exudates or gum by the plants tissue is referred to as gummosis.

Dieback

Death, decay or drying of twigs or branches from tip downwards is called dieback. Discolouration or darkening of the bark is a very common features in such diseases.

Wilt

A diseased condition that result in dropping of plant parts generally caused by insufficient transport of water in the plants is called wilting. It may occurs due to pathological or a physiological cause.

Shot hole

A disease symptoms in which leaf lesion becomes cicatrized and fall away drop off and leave small holes in their place, is called shot hole.

Mould

A disease in which the mycelium or spores of the fungus are seen as a blackish, brownish, bluish or grayish growth on the host surface. The term also refers to fungal growth, which may be present on the non living substrate, too. Sooty mould is common disease affecting plants and is caused by saprophytic fungi . It is appears as a sooty or black coating on plants and is commonly associated with honeydew secreted by insect such as aphids, mealy bugs, scales and white flies.

Mildews

A disease in which mycelium and spores of the fungus are seen as a whitish or grayish growth on the host surface is called mildew. The leaves are most commonly infected, whereas the other arial plant parts are not exception. If growth develops mainly on the lower surface of the leaves named downy mildew. On the contrary, growth develop on upper surface named powdery mildew.

Rust

A disease representing a “rusty “look to a plants is called rust. It is caused by fungi belonging to the order Uredinales.

Smut

A disease characterized by masses of dark, powdery and sometimes odorous spores and caused by one of the members of fungi belonging to the order ustilaginales.

Gall

A swelling or overgrowth produced on plant due to infection by certain pathogen to called a gall. The galls are commonly noticed on leaves and roots.

Tumor

An uncontrolled overgrowth of tissue due to infection by a pathogen is called tumor.

Mosaic

Presence of dark and light – green or yellow areas on leaves of virus – affected plants, is known by the name mosaic. Associated with them may be thickening, puckering or distortion as well as ring, line and streak patterns may also be encountered in mosaic – types f disease. Vein clearing or vein – banding is also a common symptoms of infection with mosaic diseases.

Colour - break

Narrow elongated streaks r stripes of indefinite or restricted length on flower petals often result in variegation in flower colour and the symptoms are known as colour – break.

Witches Broom

Broom- like growth or massed proliferation is caused by dens clustering of branches of woody plants. In such diseases the internodes gate shortened and the numbers of stems is greatly increased.

Chlorosis

Yellowing of normal green tissue due to destruction or failure of chlorophyll to form is called chlorosis. It is called general chlorosis when uniformly present white interveinal when present between the veins.

Necrosis

Death and discoloration of tissue is called necrosis.

Scorching

Appears as burning of margin or nearly whole leaves as a result of infection or unfavourable environmental conditions.

Stunting or dwarfing

It is reduction in the size of plant. It generally result from fungal, bacterial viral or nematode infections.

DISEASES OF ROSE

Black leaf spot

Circular black spots ranging from 1/16 inch to 1/2 inch in diameter appear generally on upper sides of leaves. The spots are frequently surrounded by a yellow halo. Infected leaves characteristically turn yellow. They fall prematurely. This leaf spot can be distinguished from others by the fringed margin and consistently black color. Cane infection produces a reddish-purple spot. It produces a weakened bush on which cane dieback, stem canker, and winter injury can become severe.

Powdery Mildew

Leaves, buds, and stems are covered with a white powdery coating. This disease can cause young leaves to curl and turn purple. Young canes may be distorted and dwarfed. Badly infected buds do not open.

Botrytis Blight

A smooth, slightly sunken, grayish-black lesion may develop just below the flower head. The bud is destroyed and frequently hangs over at or near the lesion. The disease causes flower buds to droop and remain closed. Buds turn brown and decay. Sometimes partially opened buds are attacked and an entire flower may be covered by gray fungus.

Downy mildew

Downey mildew is characterized by purple-red to dark-brown spots on the leaves with irregular margins, however, often angular. Stems, petioles and flower stalks can split and spotted with purple marks. Buds, sepals, petals and calyces can be affected and will present purple spots. New growth affected will be deformed.

Crown gall

This disease is characterized by large lumps at the base of the plant stem or on roots. Galls may appear higher on stems as the disease progresses. Galls are soft compared to surrounding plant tissues. If the disease affects the plant whilst it is young the plant may be affected to the degree where it will not produce blooms.

Virus Diseases

Rose rosette

Symptoms caused by Rose rosette virus may vary according to climatic conditions and type of roses but they can include the development of witches’ brooms, excessive thorn production, excessive lateral shoot growth, rapid stem elongation, thickened, succulent stems, leaf proliferation and malformation, mosaic, bright red pigmentation, deformed buds and flowers, and lack of winter hardiness. Infected plants lose their aesthetic value and gradually display a general decline leading to plant death. It is reported that infected plants usually die within 1 to 5years.

Rose mosaic

The symptoms caused by Rose mosaic virus are highly variable. The most common symptoms include; chlorotic bands or ring spots, wavy lines, yellow vein banding, oak-leaf pattern, and general mosaic (splotches of yellow and green on leaves). Colour-breaking (mottled flower colour) is also observed. Symptom development on only a portion of a plant is common.

Rose leaf curl

Roses infected by begomovirus show leaf curling, leaf distortion and dwarfing.

DISEASES OF GERBERA

Alternaria leaf spot

Brown specks form on florets and the leaves. Centers become white on the leaf spots

Bacterial leaf spot:

Small to large spots are circular at first, then become irregular and dark brown to black and may have a concentric ring pattern.

Botrytis blight:

Petioles have long brown spots. Leaves yellow and die. Petals have tan spots. Stems at soil level are killed. Infected tissues become covered with gray fungal growth

Phytophthora crown rot:

Plants wilt suddenly. Leaves turn brown. Roots are rotted and a crown rot develops

Pithyum root rot:

Plants wilt and die as roots rot

Rhizoctonia crown rot:

Stems at the soil level have a brown lesion. Plants wilt and die.

Powdery mildew:

Powdery mildew is easy to identify since noticeable white spots or white patches appear on the upper and lower surfaces of the leaves. These spots gradually enlarge to form a white, powder-like mat that can spread to healthy plants.

Virus Diseases

Cucumber mosaic virus causes yellowing and mottling in Gerbera leaves. The CMV infection is characterized by severe chlorotic mosaic, greening of veins on leaves, color breaking in florets accomplished with flower deformations, and poor growth of the bloom. The Common symptoms of Tobacco rattle Virus infection include mottling, cholortic or necrotic local lesion, ringspots or line patterns, and systemic necrosis.

DISEASES OF CARNATION

Virus Diseases

Carnation mottle virus (CarMV) infection is characterized by mild symptoms including split calyces and reduced vigour, lesser lateral shoots, flowers and fresh weight.

Necrotic fleck

The Carnation necrotic fleck virus causes greyish-white or reddish-purple necrotic flecks, streaks or spots on leaves and stems, with yellowing and complete necrosis on older leaves. Symptoms are milder on younger leaves. Flowers generally do not show symptoms, but owing to the severity of symptoms on leaves and stems, flowers from infected plants are of poor quality and mostly unmarketable.

Fusarium Stem Rot/Wilt

Plants wilt, turn yellow, and die. Symptoms on rooted cuttings range from wilted cuttings with a severely reddish-brown crown rot to apparently healthy cuttings with small internal, amber colored crown lesions. Young plants with basal stem rot become ash green, wilt, and die. Upon closer inspection of diseased cuttings, reddish-brown lesions with pink or orange spore masses are found in association with the disease.

Alternaria Blight

Initial leaf symptoms of Alternaria blight of carnation, caused by the fungus Alternaria dianthi, are tiny purple dots (1/ 16 to 1/8 inch).When moist weather prevails, the spots enlarge, developing into large lesions with a purple margin and a yellow-green border surrounding a gray-brown center covered with black spores. Several lesions may expand and coalesce to form large, irregular necrotic areas that eventually kill the entire leaf. The branches are most frequently infected at the nodes and branch base. These infection centers enlarge to form cankers, which eventually girdle the stem, causing the branch to wilt and the girdled portion to turn yellow and die.

Septoria Leaf Spot

Septoria leaf spot is caused by the fungus Septoria dianthi. Symptoms on leaves and stems appear as light brown spots with purple margins. Small black specks are present at the center of the spots. These are the spore producing structures of the fungus. Individual lesions may enlarge and coalesce with adjacent lesions to cause death of the leaf.

Diseases of Tuberose

Foot and tuber rot

The disease appears on patches and causes wilt and stem rot. Fan shaped mycelia strand of the fungus appear at the base of infected plants. The fungus initially attack on roots and later spread to the tubers and petioles, which induce rotting.

Blossom blight

With the infection of fungus light brown lesions develop on petals, which soon darken and result in the drying of the tissue. The blightened blossoms drops off from the plants.

Bacterial- flower bud rot

The young flower buds are affected initially by the fungus causing dry rotting buds with brown scorched necrotic discoloration of peduncles.

Alternaria leaf spot

It is characterized by faint concentric ring on midrib and rarely on the margin of leaves. It is prevalent in the rainy season. Affected peduncle and leaves show circular to oval spots. The leaves and peduncles become necrotic and dry up with the infection.

Virus Diseases

Tuberose mild mottle virus infection causes symptoms of mosaic, mottling and in severe cases reduced tillering and stunted growth

DISEASES OF GLADIOLUS

Fusarium wilt, Yellow or corm rot

The characteristic symptoms is interveinal leaf tip yellowing, which extend down the leaf and whole leaf gradually turns brown and become narrow. The other common symptoms include stunting, curving, arching and bending of leaves. On advancement of infection of plant suddenly wilt or turn yellow and die prematurely. The leaf infection is usually basal and associated with corm rot. Roots arising from corm show brown lesions. The centers of bulb turn black and rot completely. Lesions on corms are reddish-brown with well defined margins, round to oval, somewhat depressed leading to hard shrunken mummified corms.

Storage rots

The disease mostly appears in the form of black, brown, greenish or yellowish mould growth on the corms during storage. Under poor air circulation the corms may rot or emit foul smell.

Dry or neck rot

It is also known as root rot. The disease is seen on the stored corms as small dark more or less superficial spot or lesion on which can also produce collar rot, killing the plants or its delay attack may only harm the new corms for carrying the disease to the next season. Dry rot is wide spread disease attacking gladioli plants in the field . It is more severe during humid condition. The leaves turn brown from the tips downward . Diseased corms show round black and small lesions.

Botrytis blight and flower rot

It is destructive to leaves and flower . Disease epidemic erupt during the cool , wet weather condition. The little brown black spot observed on the top of corms. The symptoms on the leaves consist initially of light afterward dark brown spot . Later in the season large and dead gray brown patches appear on the tissue. Germinating spores may colorless watery spot on the flower.

Virus disease

Cucumber mosaic virus and Bean Yellow Mosaic Virus are most prevalent in gladiolus and their infection results in mosaic, leaf stripe, pale-yellow mottling of the leaves, flower distortion colour-breaking, overall stunting, reduced flower and cormel production.

Phytoplasma Diseases

  • Phytoplasmas are bacteria that are devoid of cell wall, having non-helical shape.
  • They cause Yellows disease in a number of crops.
  • They live in phloem tissue.

sr no Crops Manifestations
1 Dianthus Yellowing, Virescence and Phyllody
2 Hydrangea Virescence and Phyllody
3 Petunia Yellows
4 Rose Multiple bud formation
5 Gerbera Leaf yellowing, Virescence and Phyllody
6 Saponeria Leaf malformations, yellowing and bunching of leaves, Little leaf appearance
7 Jasmine Stem Proliferation and Fassciation
8 Chrysanthemum, China Aster Stunting, Yellowing, Reddening of leaf, leaf margin disappears, Virescence and Phyllody
8 Marigold Stunting, Bunching of flowers, reduction of size of flowers, Fassciation.
9 Periwinkle sp. Reduction of plant height, Little leaf appearance

The typical symptoms found in phytoplasma infected plants are stunting, yellowing, little leaf, witches broom, purple top, stem proliferation, virescence and phyllody. In phyllody the flower turns to leaf like structures. Weeds like parthenium, crops like brinjal, sesamum are alternate hosts of this pathogen. They are transmitted from plant to plant thorugh insect vectors like leaf and plant hoppers and the total parasite cuscuta by establishing vascular connections. Use of phytoplasma free planting materials, use of cultural methods to repel and avoid leaf hoppers and other management strategies of insect vectors are the best possible solution to evade phytoplasma infections.


Viral Diseases

Viruses are submicroscopic entities viewed only under electron microscope, living as parasite in plant cells. The infection of viruses can be envisaged through the symptoms like mosaic, molting, leaf streak, ring spot, flower color breaking, vein and bud necrosis. The viruses can be spread from infected plant to other through insect vectors like aphid, whitefly, leaf hopper, thirps etc. Viral infection can be managed through the use of certified viruses’ free planting material, timely management of the insect vectors and clean cultivation.


Nematodes

Nematodes are multicellular, unsegmented, bilaterally symmetrical roundworms belonging to pseudocoelomates animals. Many of them are parasites of plants and insects. Flower and ornamental crops are susceptible to several species of plant parasitic nematodes. Root-knot nematodes (Meloidogyne spp.), foliar nematodes (Aphelenchoides spp.), root-lesion nematodes (Pratylenchus spp.) reniform nematodes (Rotylenchulus spp.) and other ectoparasitic nematodes can limit quality and quantity of floricultural crops. Cut flower crops (Carnations, Gerbera, Chrysanthemum, etc) grown under protected conditions are highly damaged by root-knot (Meloidogyne spp.) and reniform nematodes (Rotylenchulus reniformis). Flower crops cultivated (Tuberose, Gladiolus, Crassandra, Chrysantamum, China aster, Dahila) in open field conditions are also highly susceptible to root-knot nematodes and exhibit considerable yield loss. These nematodes live in the soil and feed on the root system and damage the root system thoroughly. Besides damaging directly, plant parasitic nematodes also can enhance damage caused by other soil borne fungal and bacterial pathogens. Foliar nematode,Aphelenchoides besseyi , a causal agent of tuberose floral malady is wide spread in tuberose growing areas of West Bengal and Orissa and a potential threat for cultivation of tuberose in West Bengal.

i) Nature of damage

Above ground symptoms of nematode infected plant exhibits various degree of stunting, chlorosis (yellowing) and tend to wilt under dry conditions. Nematodes are usually first detected in localized areas within a field. Gradually, the area of infected plants expands in size and the entire planting can eventually affected. Infection can reduce flower size, no. of flowers/plant, and the productive life of the plant. Infected rows or area appear thinner compared to healthy one and give patchy appearance. Flower yield can be drastically reduce under severe root-knot infestation.

Below ground symptoms of root-knot nematodes include formation of distinctive swelling called root galls (root knots) on the roots of affected plants. Root-knot galls may vary in size and shape. On heavy infected plants, galls tend to fuse together so that large areas or entire root may be swollen. Root injuries from other nematodes include root necrosis resulting in severe root pruning and subsequent dwarfing of plants. Fibrous or feeder roots are mostly attacked which may reduce the absorption ability of plants and other physiological functions of the plant. Root growth slows and secondary root development is limited.

Some nematode parasites on young foliage and flower stalk (Foliar nematode, Aphelenchoides spp. in tuberose). The infected flower stack initially appears rough, stalk become crinkled, stunted and finally distorted and in severe cases flower buds failed to bloom. Brown streaks appear on the leaf bracts and petals and subsequently develop rusty brown spots. The severely infected flower stalk becomes rotten and brittle over drying. The number of flower stalk is also reduced and small crinkled and distorted flowers are produced which are not acceptable in the market.

How to diagnose the nematode infested field?

Due to lack of distinct symptoms on crop plants due to nematodes, the damage often been confused with nutrition problem and occasionally has been attributed to fungi or bacteria. Characteristic foliage symptoms such as yellowing of leaves, stunted growth, wilting and patches of poor crop growth in field are clues that plants are diseased with nematodes. If such plants are uprooted, they show characteristic below ground symptoms like galling and/ or necrotic on roots and reduced root length. Diagnosing the damage on flower crops can best be done by periodic field observations and examinations of roots in conjunction with testing the soil and plant sample for nematode extraction. Testing helps in implementation of nematode management strategies and to avoid future contamination of nematodes in the field.


Insect Pests

Floricultural crops are often attacked by a number of insect pests at various growth stages, some of the important insect pasts are.

Whiteflies

Whiteflies are oval shaped, tiny flies with mealy white wax covering their wing and yellow body. Eggs are laid on the undersurface of the leaves, in circular or semicircular fashion depending on the species. The early stages of nymphs resembles scale insects and there are four nymphal instars. Most whiteflies are confined to undersurface of the leaf and continuously suck the sap from leaves. High population causes yellowing and shriveling of leaves, affects plant health and flower quality. Whiteflies are most common and perhaps most difficult pests to control under polyhouse. Common species found under polyhouse are greenhouse whitefly, Trialeurodes vaporariorum and cotton whitefly, Bemisia tabaci.

Aphids

Aphids are small, 1.5 – 3.2 mm long, soft bodied insects. They range in color from green to brown, red, black or purple. Aphids excrete sugary liquid called honeydew. This honeydew drop into plant foliage and provide suitable place for development of back mold.

Leafhopper

Leafhopper are minute insects which are plant feeders that suck plant sap from grass, shrubs, or trees. Their hind legs are modified for jumping, and are covered with hairs that facilitate the spreading of a secretion over their bodies. Leafhoppers have various host associations, varying from very generalized to very specific, some species have a cosmopolitan distribution. Some species are pests and some are vectors of plant viruses and phytoplasmas.

Thrips

Thrips are tiny insects which feed on mainly new growing points of the plant. Both nymphs and adults suck cell sap resulting in curled or bronzed leaves, deformed buds with burnt margins and some species can also from galls on plant parts. Some specific species may transmit plant viruses as vectors.

Scales insects

Scales insects are flat, circular and reddish in colour and measures about 2 mm in diameter. They appear in severe form before and after the monsoon season. Both adults and young ones suck the sap from mature shoots and deplete vigor of the plant. The infested plant bears a few small flowers.

Leaf miner

Small, black and yellow colored flies. Adult Leaf miner lay eggs on upper surface of leaves by making a small puncture. Eggs can be seen as small white specks on the leaves. After hatching, larva mines into the leaf and form a characteristic serpentine tunnel in the leaf.

Tobacco caterpillar( Spodoptera litura)

The adult moth is brown with complex pattern of cream streaks criss-crossing the fore wing and hind wings are silvery white. Female lays around 100 eggs in groups and covers with tuft of hairs. The early instars are gregarious and feed on the leaves by skeletonizing the leaf. The later instars spread to different parts of the field. The larvae hide in the cracks and crevices in the field during day time and become active during night hours and feed voraciously on different plant parts. The larvae are brown with three thin yellow lines down the lack, one in the middle and one each on either side. A bright yellow stripe along the length of the dorsal surface is a characteristic marking on fully grown larva.

Tomato fruit borer (Helicoverpa armigera)

Adults are medium sized stoutly built moths. Forewings are light yellow in males and brown in female. Female moth lay eggs singly on leaves, buds and flowers. The younger larvae feed on leaves and the older larvae bore into flower buds.

Two spotted red spider mite (Tetranychus spp.)

Adult female is about 0.5 mm long and male is about 0.3 mm long. Females are yellowish-green, with two pronounced dark spots on the body, in males these spots are less conspicuous. During winter, males will die and females stop feeding, change their color to orange-red, migrate to shelters for overwintering. When temperature starts raising, females move from the shelters, begin to feed and the color will be changed to yellowish-green. Females lay upto six eggs a day and each female lays >70 eggs. Eggs will hatch from three to 10 days depending on the temperature, young mites mature in four to 12 days. During summer months, total life cycle may be completed in two weeks and overlapping generations may be seen.

Broad mite (Polyphagotarsonemus latus)

These mites are very tiny, elliptical in shape and cannot be seen without the help of microscope. These mites tend to hide deep within tender buds or deep in the flowers. Older leaves are curled up, younger leaves are deformed and become leathery. Deformed flowers devoid of petals, discoloration and inward curling of petals are some of the symptoms due to broad mite infestation.

Typical Symptoms due to Insect Pest Attack

Pest Damage
Aphids Aphids damage the plants by sucking the leaf sap in young stage, cotyledonary leaves crinkle and in severe cases the plants withers off.
Cutworms The tender plants are found damped at ground level during the night Young larvae feed gregariously on foliage but later segregate and enter into soil.
Jassids/ leafhoppers Both nymphs and adults suck the sap from the lower surface of the leaves. The infested leaf curl upward along the margins, which may turn yellowish and show, burnt up patches.
Defoliator/ Leaf eating caterpillar Larvae feed on lower surface of leaves by scraping while greenish-brown mature larvae feed voraciously during nights on these leaves.
Leaf Roller Caterpillars roll leaves and feed on chlorophyll while remaining inside the folds. The folded leaves wither and dry up.
Mealybug Nymphs and adults of mealy bugs suck sap from the leaves, tender shoots and the fruits. A heavy black sooty mould may develop on the honeydew like droplets secreted by mealy bugs.
Red pumpkin beetle They make holes in cotyledonary leaves of cucurbits. As a result the seedlings die in the younger stage
Red spider mite/ two spotted spider mite Different stages of mites are found in colonies covered by white-silky webs on lower surface of leaves. Nymphs and adults suck cell sap and white patches appear on leaves. Affected leaves become mottled, turn brown and fall.
Thrips Nymphs and black adults feed on tender leaves causing silvering, mottling and distortion of leaves.
Whitefly The damage by whitefly also leads to yellowing of leaves and stunted growth, in severe cases leading to shedding of leaves.

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ICAR-Directorate of Floricultural Research,
College of Agriculture Campus Shivajinagar,
Pune 411 005,
Maharashtra,
India.
Phone: (020)25537024
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Email: aodfr@yahoo.com, ao.dfr@icar.gov.in

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