Zucchini Diseases A

Lecture To ToT trainees ( FFS) By

Mr. Allah Dad Khan Provincial Coordinator

IPM KPK MINFAL Pakistan

Powdery Mildew (Sphaerotheca fuliginea) 

 first appear as white powdery residue primarily on the upper leaf surface. On the lower surface of the leaves circular patches or spots appear. In severe cases, these spread, coalesce and cover both the surfaces of the leaves and spread also to the petioles, stem, etc. Severely attacked leaves become brown and shrivelled and defoliation may occur. Fruits of the affected plants do not develop fully and remain small.

Control: Carbendazim (1ml/litre of water) or Karathane (0.5 ml/litre of water) is sprayed immediately after the appearance of the disease. 2-3 sprays are taken at an interval of 15 days

Symptoms:

Powdery mildew

Fusarium Wilt (Fusarium oxysporum f. sp. niveum)

 Eventually, the plant dies. The roots are not affected. In older plants, leaves wilt suddenly and vascular bundles in the collar region become yellow or brown.

Control: Three sprays of Karathane (6 g in 10 litres of water) or Bavistin (1 g /litre of water) immediately on appearance of initial symptoms at 5-6 days interval controls the disease. Leaves of fully grown vines should be thoroughly drenched during spraying.

Symptoms:

Downey Mildew (Pseudoperonospora cubensis) 

 The disease is first seen as yellow angular spots on the upper surface of the leaves. Under conditions of high humidity, whitish powdery growth appears on the lower surface of the leaves. The disease spreads rapidly killing the plant quickly through rapid defoliation.

Control: Excellent control of this disease can be achieved with Ridomil (1.5 g/litre of water) which must always be used simultaneously with a protectant fungicide such as Mancozeb (0.2%) to prevent the development of resistant strains.

Symptoms.:

Downy Mildew

Downy Mildew

Squash Gourd Mosaic

 appearing on the leaves in the secondary branches produced at the apical end of the plant. Small irregular yellowish patches are seen on the leaves. Some leaves show vein clearing in one or two lobes of the leaf and severely infected plants show reduction in leaf size and elongation and/or suppression of one or two lobes. Young developing leaves are completely distorted and malformed with considerable reduction in their size. Some of the leaves show marked reduction in the development of lamina resulting in a shoestring effect. The virus is transmitted by five species of aphids.

Control: Spraying the crop just after germination with Monocrotophos (0.05%) or Phosphamidon (0.05%) at 10-day intervals prevents aphid vectors.

Symptoms:

Witches' Broom Disease

 of this disease are malformation and proliferation of axillary buds. Diseased plants show many abnormally little leaves, which fail to attain full size. The diseased plants bear many flowers and blossom earlier than healthy plants. Flowers on infected plants show characteristic green, phyllody symptoms. Fruit formation is noticed from the flowers partially infected with the disease. Fruits from these flowers are very small, cylindrical and deformed. The outer surface of the fruits is smooth and fruits are completely seedless. Plants showing severe witches' broom do not bear any fruit.

Control: Application of Carbofuran (1.5 kg a.i./ha) at the time of sowing seeds followed by 5-6 foliar sprays of either Phosphamidon (0.05%) or Monocrotophos (0.05%) or Oxydematon Methyl (0.05%) at 10 days interval, to control the vector population. Spraying of Oxytetracycline hydrochloride solution (500 ppm) at weekly intervals suppress the disease symptoms.

Symptoms:

Angular leaf spotPseudomonas syringae

Small water-soaked lesions on leaves which expand between leaf veins and become angular in shape; in humid conditions, lesions exude a milky substance which dries to form a white crust on or beside lesions; as the disease progresses, lesions turn tan and may have yellow/green edges; the centers of the lesions dry and may drop out leaving a hole in the leaf

Symptoms

Angular Leaf Spot

Angular Leaf Spot

Bacterial leaf spot Xanthomonas campestris

Dark, angular lesions on leaves; leaf lesions may coalesce and cause severely blighted foliage; water-soaked lesions which enlarge and develop into tan scabs, or blisters, on the fruit; blisters eventually flatten as they reach their full size

Symptoms

Bacterial leaf spot

Bacterial wilt

Bacterial wilt

Bacterial Wilt

Bacterial Wilt

Bacterial Wilt

Alternaria leaf blight Alternaria cucumerina

Small, yellow-brown spots with a yellow or green halo which first appear on the oldest leaves; as the disease progresses, lesions expand and becone large necrotic patches, often with concentric patternation; lesions coalesce, leaves begin to curl and eventually die

Symptoms

Anthracnose Colletotrichum orbiculare

Tan to brown lesions with dark spots inside on leaves and petioles, main stem and fruit

Cause Fungus Comments Disease favors warm weather Management Plant resistant varieties; use only

certified seed; apply appropriate protective fungicides; rotate crops every year

Symptoms

Anthracnose

Anthracnose

Gummy stem blight Plectosporium tabacinum

V-shaped yellow to brown areas on stem; cracked dry areas on stem; lesions leaking a sappy material

Cause Fungus Comments Disease may be seed-borne Management Use disease free seed; treat seeds

prior to planting; rotate crops every 2 years

Symptoms

Phytophthora fruit and crown rot Phytophthora capsici

Sudden wilting of plants; brown lesions on stems and roots; rotting fruit; stunted plant growth; downy growth may be present on lesions during periods of high humidity

Cause Oomycete Comments Disease emergence favored by heavy

rainfall and poorly draining, waterlogged soils

Management Do not plant in poorly draining soils;

avoid over-watering plants; rotate cucurbits with non-susceptible plants for a period of at least 3 years

Symptoms

Scab Cladosporium cucumerinum

Angular brown lesions on leaves confined by small veins; pale green and water soaked lesions; holes in leaves from dried out lesions; lesions may also be present on petioles, stems and fruit

Cause Fungus Comments Fungus survives in soil on crop debris; may

be seedborne; disease emergence favored by wet weather and temperatures below 21°C (69.8°F)

Management Rotate cucurbits with non-susceptible crops

for a period of at least 2 years; plant only in well-draining soils; spray plants with appropriate protective fungicides

Symptoms

Scab

Verticillium wilt Verticillium dahliae

Symptoms generally appear after fruit set; chlorotic leaves which develop necrotic areas; leaves collapsing; symptoms only on one side of vine; discoloration of vascular tissue in roots

Cause Fungus Comments Fungus can survive in soil for many years;

disease emergence favored by cool or mild weather in Spring

Management Do not plant in areas where other susceptible

crops have been grown previously; delay planting until temperatures are warmer

Symptoms

Cercospora leaf spot Cercospora citrullina

Initial symptoms of disease occur on older leaves as small spots with light to tan brown centers; as the disease progresses, the lesions enlarge to cover large areas of the leaf surface; lesions may have a dark border and be surrounded by a chlorotic area; the centers of the lesions may become brittle and crack

Cause Fungus Comments Fungus survives on plant debris; spread by

wind and water splash; occurs mainly in tropical and subtropical growing regions

Management Any diseased plants should be removed and

destroyed to prevent further spread; crop debris should be removed after harvest or plowed deeply into the soil to reduce inoculum

Symptoms

Septoria leaf spot Septoria cucurbitacearum

Initial symptoms of disease are small dark water-soaked spots on the leaves which turn beige to white in dry conditions; lesions develop thin brown borders and the centers may become brittle and crack; small white spots may erupt on the surface of infected butternut and acorn squash and pumpkin fruit

Cause Fungus

Symptoms

Septoria Leaf Spot

Cucumber mosaic Cucumber mosaic virus (CMV)

Plants are severely stunted; foliage is covered in distinctive yellow mosaic; leaves of plant curl downwards and leaf size is smaller than normal; flowers on infected plants may be deformed with green petals; fruits become distorted and are small in size; fruit is often discolored

Cause Virus

Symptoms

Cucumber Mosaic

Cucumber Mosaic

Squash mosaic Squash mosaic virus (SqMV)

Symptoms vary with variety being grown but plants can show symptoms which include include green veinbanding, mottled leaves, blisters, ring spots or potruding veins at leaf margins; some squash varieties may develop leaf enations; infected plants are often stunted and fruits may be malformed with mottled skin

Cause Virus

Symptoms

Watermelon mosaic Watermelon mosaic virus (WMV)

Symptoms vary widely depending on species, cultivar, virus strain and environmental conditions; symptoms on leaves may include green mosaic patternation, green vein-banding, chlorotic rings and disfigured leaves

Cause Virus

Symptoms

Blossom-End Rot

Blossom-end rot appears as a dark-colored dry rot on the end of the fruit where the flower was. The problem is caused by a lack of calcium in the developing fruit. It is an indication that calcium is lacking in the soil or that the plant does not have the ability to take up enough calcium. When growth is rapid, not enough calcium may be delivered to the blossom end of the developing fruit.

Target leaf spotCorynespora cassiicolaCorynespora. melonis

Angular yellow spots appear on older leaves; as the disease progresses, the spots enlarge and become circular with light brown centers and dark margins; as lesions mature, they turn gray and drop out leaving holes in the leaves; if fruits become infected early in their growth then the blossom end may darken and become shrivelled

Cause Fungus

Symptoms

Target Leaf Spot

Belly rot (Fruit rot, Damping-off)Rhizoctonia solani

Yellow/brown discoloration on fruit; water soaked spots on side of fruit in contact with soil; brown mold growing on rotting areas; collapse of seedlings

Cause Fungus

Symptoms

White mold

White mold is caused by the fungus Sclerotinia sclerotiorum. This pathogen infects a wide variety of vegetable crops including beans, carrots, tomato, cabbage, and lettuce. In the cucurbit family pumpkins and some varieties of winter squash are most severely affected by the disease. This disease does not cause leaf spots but infects both stems and fruit.

Symptoms

Belly rot

Southern blight Sclerotium rolfsii

Sudden wilting of leaves; yellowing foliage; browning stem above and below soil; browning branches; stem may be covered with fan-like mycelial mat; rot on fruit that begins on side in contact with soil

Cause Fungus

Symptoms