Everything you need to know about controlling diseases of pumpkin.
1. Anthracnose [Colletotrichum Lagenarium (Pass.) Ellis and Halsted]:
Anthracnose is usually a minor disease of pumpkins. The fungus affects all aerial parts of the plant. The symptoms on foliage begin as small, yellowish or water soaked areas that enlarge rapidly and turn brown later on, however, the symptoms that are most noticeable on fruits are roughly circular water soaked sunken spots with dark border.
Red gummy exudates may appear on these lesions. Severity of infection depends almost entirely on environmental conditions. A combination of high temperature and high humidity is very conducive for the spread of this disease.
i. Adopt field sanitation by burning crop debris.
ii. Treat the seed with carbendazim or Captan @ 2.5 g/kg seed.
iii. Two foliar sprays of carbendazim (0.1%) or chlorothalonil (0.2%) are effective to ward off disease.
2. Powdery Mildew (Sphaerotheca Fuliginea):
Pumpkin is comparatively less susceptible to this disease. Fungus inoculums are present in fields almost round the year to some extent. In fields, fungus over-winters in debris or on wild hosts and is windblown for long distances. It has a fairly wide range of hosts but wild and cultivated cucurbit hosts seem to be the primary sources of inoculums.
Hot weather with high humidity and heavy dew at night favours the development of spores. Disease is characterized by the appearance of tiny white to dirty gray spots primarily on upper surface of leaf. The superficial powdery mass may ultimately cover the entire green surface of leaves. These spots later on turn brown and dry. Leaves die down early and collapse before the fruit reaches maximum size or maturity.
i. Collect and burn the disease debris.
ii. Follow at least 3 years crop rotation with crops other than cucurbits
iii. Regular spray of fungicides like penconazol (0.05%) or carbendazim (0.1%) at 10-15 days intervals give satisfactory control.
3. Downy Mildew [Pseudoperonospora Cubensis (Berk. & Curt.) Rosto.]:
Pumpkin is relatively less susceptible to downy mildew disease but this is very common in northern India during later part of rainy season and can be very damaging during prolonged foggy or humid periods. Fungus first grows on underside of the leaves as pale green areas separated by darker green boundary. Very old lesions become necrotic, and they are clearly demarcated with slight yellow areas. Fuzzy growth (gray to purple) appears on underside of the leaves, particularly in moist weather.
i. Grow crop at wider spacing in well-drained soil.
ii. Burning of disease debris is advocated to reduce the inoculums.
iii. Protective spray of mancozeb @ 0.25% at 7 days intervals gives good control.
iv. In severe cases, one spray of metalaxyl + mancozeb @ 0.25% may be done.
4. Fusarium Root Rot or Wilt (Fusarium Solani F. Sp. Cucurbitae Synder & Hansen):
Fungus produces wilt symptoms similar to those caused by Fusarium oxysporum, but wilting is sudden during mild season with extensive brown cortical decay along with mushy tissue maceration. It causes damping off if attack the crop in early stages. The affected leaves show tip burning and later on, whole plant wilt and die. Profuse sporulation occurs on the infected tissues during humid weather. The pathogen is both seed and soil borne.
i. Adopt clean cultivation by burning disease debris.
ii. Follow at least 3 years crop rotation as preventive measures to reduce the inoculums.
iii. Use disease free healthy seed for sowing.
iv. Treat the seed with carbendazim or Captan or bavistin @ 2.5 g/kg of seed.
v. Drench the soil with systemic fungicides such as Benomyl or Bavistin or Thoiphanate M 0.1-0.2%.
This disease causes damage in pumpkin, summer squash, snake gourd, and bitter gourd. The yield losses reported due to the attack of this disease are about 80% in pumpkin and 77% in bitter gourd. The initial infection is noticed as small spots on leaves, which rapidly increase in number and size.
In advance-stage, the burning effects and blight symptoms are seen after coalescing of adjoining spots. The pathogen perpetuates on plant refuse in soil. A temperature of 25-30°C coupled with 92-100% relative humidity is the most ideal condition for the growth and spread of fungus.
i. Collect and burn the disease debris to reduce the inoculums.
ii. Follow a crop rotation of at least 3 years to reduce inoculums.
iii. Ensure proper drainage to reduce the scope of its incidence.
iv. Borax wash (2.5%) at 45°C for 30 seconds before packaging of fruits reduces incidence in storage.
v. Two sprays of Indofil M-45 (0.25%) at 15 days interval are effective for the control of disease.
6. Black Rot or Gummy Stem Blight (Didymella Bryoniae and Phoma Cucurbitacearvm):
The fruit rot (black rot) becomes very serious on pumpkins during rainy season, and losses increased with the severity of other foliage diseases. Seedling death, leaf spots, cankers on stem, petiole and fruit stalk, stem decay, wilt and fruit rot are some common symptoms appear during infection. Watery exudates release from the nodal portion of stem and form a yellowish brown gum.
Striped cucumber beetle is the main vector that spreads the disease. Wet weather favors the development of gummy stem blight, and failure to control foliar diseases leads to the fruits, being more susceptible to black rot, which can be a significant factor affecting the shelf life of pumpkins.
i. Use disease free healthy seeds.
ii. Follow long crop rotation with cereal crops.
iii. Follow deep ploughing in hot summer months.
iv. Destroy the disease debris by decomposing them quickly.
v. Use only the resistant or tolerant varieties to reduce the risk.
vi. Spray the crop with mancozeb (0.25%) or carbendazim (0.1%) to control the secondary infection.
vii. Careful handling of fruits to avoid injury reduces the risk of post-harvest rot.
7. Angular Leaf Spot (Pseudomonas Lachrymans Carsner):
The disease appears on leaves, stems and fruits as small water soaked spots. On leaves, they enlarge up to a diameter of about 3 mm, becoming tan on the upper surface and gummy or shiny on the lower surface. Lesions attain an angular shape as they are delimited by veins. The necrotic centers of leaf spots may drop out.
On stems, petioles and fruits the water soaked spots are covered with white crusty bacterial exudates. As the fruits begin to mature, brown lesions in fleshy tissues beneath the rind develop and the discoloration continues along the vascular system, which extends to the seeds.
i. Follow field sanitation and long crop rotation as the preventive measures to reduce the inoculums.
ii. Grow resistant/tolerant cultivars to reduce the risk.
iii. Destroy the disease debris after harvesting the crop.
iv. Treat the seed with hot water at 54°C for 30 minute or mercuric chloride solution (1 : 1000) for 5-10 minute.
v. Two sprays of Streptomycin at 400 ppm or Bordeaux mixture at 1% are advantageous.
8. Bacterial Wilt (Erwinia Traclieiphila Holland):
Bacterial wilt is a common and often destructive disease of pumpkins and squashes. The first signs of wilt appear usually on individual leaves as drooping, which become flaccid in sunny weather. As the disease progresses, more leaves wilt and eventually the entire plant is wilted. The wilting then becomes permanent and the leaves and vine die.
The viscous and sticky bacterial matrix exudates release from the vascular bundles when wilted stems are cross-sectioned. This feature is used as a means of diagnosis. Occasionally the exudates are visible on fruits too. The bacteria over-winter on the bodies of adult cucumber beetles, particularly red striped and spotted beetle. Primary infection is produced when beetles feed upon young leaves or cotyledons.
i. Since the bacterium is entirely dependent upon the beetle for its perpetuation and dissemination, control of wilt involves the control of cucumber beetles.
ii. Spray insecticides like dimethoate @ 1.5 ml/litre of water or endosulfan @ 2 ml/litre of water.
A number of mosaic viruses infect pumpkins, and it is often hard to differentiate one virus from another visually. Cucumber mosaic, squash mosaic, watermelon mosaic viruses, and papaya ring- spot viruses (PRSV-W) are the most common. The incidence of mosaic in pumpkin ranges from 30-70%, depending upon variety, stage of infection and environmental conditions.
Under field conditions, the plants develop mottling, mosaic, discontinuous vein banding, blistering and reduction in leaf size. The plant shows excessive sprouting, shortening of internodes, and thickening of stems and veins. Diseased plants produce fewer branches, flowers, and fruits. These viruses are transported mainly by infected seed or insect vectors such as aphids, cucumber beetles, and white fly.
1. Yellow Vein Mosaic of Pumpkin:
Mechanically, sap and white fly (Bemisia tabaci) transmits the virus in persistent manner. Most peculiar symptoms are yellowing of veins, veins clearing on young leaves, and later, light green or yellow coloured patches develops. Leaves become smaller than the normal ones. Infected plants show stunted growth and rarely bear fruits. Fruits are small and deformed.
2. Cucumber Mosaic Virus (CMV):
Cucumber mosaic virus known to cause mosaic disease in pumpkin is transmitted in a non-persistent manner by several species of aphids. The most common of them are Aphis craccivora, A. gossypii and Myzus persicae. In pumpkin and summer squash, this virus is also transmitted through seeds.
Young leaves develop small greenish yellow areas restricted by smaller veins of leaf. Yellow mottled leaves, leaf-distortion, and stunting of plants are commonly observed. The stem internodes become shortened. Ultimately, entire fruits become mottled with yellowish green colour.
3. Gemini Virus:
Gemini virus, which is sap transmissible efficiently by whitefly in a persistence manner, is also found associated with pumpkin.
i. Always collect seeds from healthy plants and use only disease free seed.
ii. Collect and destroy the disease debris from the pumkin field.
iii. Spray the crop with Dimethoate (1.0-1.5 ml/litre of water) to reduce the whitefly population.
4. Cucurbit Phyllody:
The growth of infected plant is stunted, which gives a bushy look. Floral parts are transformed into green leafy structures and become leathery. Infected plants rarely bear fruits. This disease is easily transmitted through graft.
i. Avoid grafting since it is sap transmitted.
ii. Spray the crop with Oxytetracycline hydrochloride at 500 ppm for controlling the disease.
Management of Viral Diseases:
Rouging and destroying of virus-infected plants are the successful preventive measures to restrict the spread of viral diseases, however, an effective management of viral diseases demands integration of management practices such as avoidance of sources of infection, use of virus free seeds, avoidance of collateral hosts, avoidance and control of virus vectors, use resistant host plant, and modification of cultural practices.
Infected planting materials or seeds, adjoining crops and volunteer plants are the main sources of infection so always avoid those sources that cause viral infection and take special precautions while selecting the variety and procuring the seeds to be sown.
Certified seeds should be used to avoid primary inoculums. To eliminate CMV infection, the virus can be inactivated by treating seeds with hot air at 70°C for 2 days or hot water at 55°C for 1 hour. Seed can also be treated with 10% solution of tri-sodium phosphate for 30 minute.
Allied crops and weeds are the important hosts for perpetuation of viruses so removal of allied crops and weeds in and around main fields is of course essential to reduce the incidence of viral diseases.
In northern parts of India, early sowing of cucurbits in spring-summer reduces the incidence of viral diseases due to low vectors population. Chemical control of vectors is most commonly useful approach for vectors born viruses. However, for the control of vectors chemically the timely application of chemical is very important.
i. Foliar spray of neem oil is found to be the most effective in controlling whitefly and yellow vein mosaic virus.
ii. Sprays of Dimethoate or Metasystox or monocrotophos @ 1.5 ml/litre of water at an interval of 10 days are very effective for the control of vectors.
iii. Application of oil such as castor, groundnut, and paraffin at 1-2% also prevents virus transmission by Myzus persicae since plants sprayed with castor or paraffin oil are less susceptible to WMV- 2 even by sap inoculation.