dIseases of cucurbits vegetables by MD. RAMJAN

MD.RAMJAN
CHF, CAU, Pasighat

1. Diseases of Cucurbits

2. Anthracnose ( Colletotrichum lagenarium ) Disease sumptoms are found on all plants parts above ground started from cotylodonary leaf to true leaves, stem, fruits and tendril in ash gourd ( Prakash et al., 1974). Light brown circular spots, which later deep to turn brown, appear on the leaves. Later on infected fruit rot and all the seed, which is source of further primary infection. It is seed borne disease ( Sohi and Maholy , 1974).

3. Control measure Collect the seed only from disease-free plants. Avoid growing ash gourd in field repeatedly used for the cultivation of cucurbits. Treat the seed with Capton or Thiram @ 2.5 g/kg of seed before sowing. Spray the systemic fungicide such as 0.1% carbendazim ( Prakash et al., 1974). Spray the hexaconazole @ 0.025-0.05% also give good result.

4. Fruit rots fusarium solani , F. monoliformi , Verticillium dahliae Decaying of fruits is a major problem during storage. Some time rotting start from the lower fruit portion that had been contact from the soil. White fungal growth, which later on turn into brown circular scelerotia , is observed on fruit surface. The infected fruits contain completely rotten seed, which turn white, become hollow, and fail to germinate ( Pandey et al., 2003). Brown dull spots, which lead to softening, and rotting, are developed on fruits ( Upadhayay and Roy, 1987).

5. Control measure Expose the soil following repeated deep summer ploughing . Adopt long crop rotation with cearals and clean cultivation. Use only healthy seed. Train the crop on bower system to minimize the infection. Treat the seed with Trichoderma viridae along with neem cake application. Collect the infected fruit and brunt.

6. Leaf spot ( P homa cucurbitacearum ) Black small dot like structures are developed on older leaves. White fungal growth is clearly visible on outer margins of the spots in morning on under side of leaves. Severely infected leaves give burning appearance. The disease is more common during winter season.

7. Control measure Treat the seed with cardendazim @ 0.25 % to minimize the infection in the crop. Spray mancozeb at 0.25% alterd with one spray of hexaconalzol at 0.05%.

8. Fusarium wilt ( Fusarium oxysporum f. sp. benincasae ) The disease more common in sandy soil. Yellowing of lower leaves, which gradually progress on upper leaves. The plant soon after infection starts drooping followed by wilting, later on, wilting become permanent.

9. Control measure Apply Trichoderma @ 5-8 kg/ha, depending up on the soil structure, to minimize disease. Tret the seed with carbendazim @ 2.5 g/kg of seed.

10. Downy mildew Pseudopernospora cubensis Generally, at initial stage, small irregular yellowish lesion appear on leaves. Old lesion become necrotic, and they are clearly demarcated with light yellow areas. Downy mildew attacks occasionally on ash gourd ( Uppal et al ,. 1935). At Solan , downy mildew was recorded on ash gourd without oospores ( Uppal et al ., 1935).

11. Control measure Grow the crop at wider spacing on well-drained soils. Collect the seed from disease free healthy fruits to avoid further infection. Spray mancozeb @ 0.25% at seven days interval. In severe conditions, follow one spray of metalaxyl + mancozeb 2 0.2%. Spray copper oxychloride 0.2% at 10 days interval ( Munshi and Cohan, 1973). Field sanitation by burning crop debris reduce the inoculums.

12. Powdery mildew Erysiphe cicoracearum It is more severe under dry and rain free weather conditions although it is favored by hot and humid weather, moderate temperature and reduced light intensity and succulent plant growth (Khan et al., 1972). White long patches or powdery coating appears first on the under surface of the leaves, which later spread to the upper surface, stem, petiole and other succulent plan parts. Severe infection cause stunted growth and browning of leaves followed by premature defoliation.

13. Control measure Collect and burn all the infected leaves. Carbendazim at 0.1% at different interval as per need

14. Alternaria blight and leaf spot ( Alternaria cucumeriana ) Bitter gourd/Squash/Pumpkin/ Snake gourd The yield losses reported are about 77% in bitter gourd and 80% in pumpkin. The initial infection is noticed as small spots on leaves, which rapidly increase in number and size. in advance-stages, the burning effect and blight symptoms are also seen.

15. Control measure Collecting and burning of plant debris are effective for reducing inoculums. Following crop rotation for at least 3 year. Providing proper drainage reduce the incidence of this disease. Borax wash @ 2.5% at 45˚c for 30 second before packaging of fruits reduces incidence in storage.

16. Rhizoctonia root rot Rhizoctonia solani Mostly occur in Bottle gourd. The fungus cause pre- and post emergence mortality of seedlings. However, older plants are less susceptible to this disease.

17. Control measure Follow long crop rotation fo non host crops. Treat the seed with vitavex or Brassicol 3-4 g/kg of seed. Drench the soil with Brassicol @ 0.2%.

18. Mosaic disease A large number of viruses attack the bottle gourd crop and cause serious damage. The leaves shows the symptoms like, mosaic mottling, crinkling, and twisting. Internodes are shortened and flowering is affected adversely. In rainy season white fly spread the virus rapidly. Infection during early stages of growth (5-30 days) caused up to 100% loss in yield (Singh, 1989).

19. Control measure Collect the seed from virus fee plants. Spray the crop with systemic insecticides like, Malathion @ 0.05% at 5-7 days interval to control the virus vector.

20. Seed rot and damping off ( Pythium and Fusarium spp.) Mostly in cucumber. This pathogen frequently causes seed rot, damping off, seedling blight and root rot in tropical and subtropical zones. All pathogens are affected by soil temperature and particular by moisture as well as rainfall during seedling stage (Goldberg and Stanghellini , 1990).

21. Control measure Expose the soil to sun by repeated vdeep ploughing . Follow soil solarization practice. Treat the seed with Thiram or Captan @ 2.0 g/kg of seed. Spray Mycostop powder formulation prepared from Pseudomonas fluorescence or Streptomyces sp. Prior and after planting.

22. Bacterial leaf spot ( Xanthomonas cucurbitae ) Bacterial leaf spot is quite common disease of cucumber and gherkin. The disease produced symptoms as spots (water soaked areas enlarge and turn brown with age surrunded by a yellow halo) only on leaf rarely on stems and petioles. Optimum temperature for pathogen survival is around 25-30˚c

23. Control measure Soak seeds for 60 minutes in1: 20 dilution of commercial HCL containing 1% surfactant. Treat the seed with hot water (54-56˚c) for 30 minutes or 1% sodium hypochloride + 1% surfactant for 40 minutes. Grow resistant cultivar like, Japanease Long Green.

24. Scab ( Cladosporium cucumerianum ) The disease appears as dark brown sunken spots on stems and fruits. In moist weather, these spots are covered with a greenish mould. Sometimes, a gum like substances oozes from the affected leaves and fruits.

25. Control measure Adopt clean cultivation and long crop rotation. Spray Streptomycin at 400 ppm in standing crop.

26. Cucumber mosaic/white pickle mosaic (CMV) It causes the 10-20% yield loss in cucumber. This mosaic cucumo -virus described as ‘’narrow leaf of tomato in New Zealand’’, cucumber green mottle mosaic Tobamovirus (CGMMT) In England and cucumber necrosis, cucumber mosaic, cucumber vein yellowing and cucumber wild mosaic and squirting cucumber mosaic in other parts of the world. If the plants are infected with CMV at cotyledonary stage, the yield is reduced by 89 % in summer and 96 % in rainy season.

27. It is characterized by stunting of plants, mottling, yellowing, and wrinkling of leaves and warting and mottling of fruits. In cucumber, its transmission through seed was reported 37 % . The symptoms produced by CMV are dry, brittle, and necrotic lesions along the leaf veins, malformation and internodes shortening, vein clearing, wilting, and drying, particularly in cool weather.

28. Control measure Use disease free seed. Collect and destroy the disease debris. Eradicate the wild host plants. Spray Malathion @ 2 ml/l of water at 5-7 days interval.

29. Gummy stem blight ( Didymella bryoniae ) It is serious problem in ivy gourd. Canker on stem, petiole, and fruit stalk, stem decay and wilt are some common symptoms appear during infection. Watery scoop exudates from the nodal portion of the stems, which turn yellowish brown gum, are other major symptoms.

30. Control measure Follow deep ploughing during summer. Use disease free healthy planting material. Collect and burn the disease debris. Harvest the fruit carefully to avoid injury. Spray carbedazim 0.1% to reduce the infection.

31. Watermelon mosaic virus (WMV) It is transfer through sucking insect like, Aphis gossypii , (Pearson and Liyanage , 1997). The symptoms appear on leaves in the form of curling mosaic or mottling accompained by green vein banding and reduction in leaf size. Sometimes, the petiole and internodes length also shortened.

32. Control measure Use disease free healthy planting material. Follow wider spacing and clean cultivation in well-drained soil. Collect and destroy the infected debris from the field as soon as possible. Spray the crop with Diamethoate @ 0.1% (I ml/liter of water) to reduce the population of whitefly. Spray Emidacloprid @ 3 ml/liter of water at regular interval to check the vector .

33. Cucumber green mottle mosaic virus CGMMV The major symptoms of CGMMV are slight clearing of veins and crumpling of the younger leaves followed by a light and dark green mottle to gather with blistering and distortion of leaves. The CGMMV was first time reported from India in bottle gourd ( Capoor and Verma , 1948., Vasudeva et al., 1950). This virus is naturally infected in musk melon ( Sanker and Nariani , 1974). The cucurbit beetle is able to transmit the virus to extent 27 % ( Rao and Verma , 1984).

34. Control measure Early sowing of crops may reduce the disease due to low vector population. Avoid contamination by worker and implements. Spray Dimethoate or metasystocs (1 ml/l) at 10 days interval to manage the vector.

35. Angular leaf spot Pseudomonas lachrymans The disease appear on leaves, stem and fruits as small water soaked spots. On leaves, they enlarge up to a diameter of about 3 mm, becoming tan on upper surface and gummy or shiny on the lower surface. Lesion attain an angular shape as they are delimited by veins. The necrotic centers of leaf spots may drop out. On the stems, petioles and fruits the water soaked spots are covered with crusty bacterial exudates.

36. Control measure Follow field sanitation and long crop rotation as the preventative measures to reduce the inoculums. Destroy the disease debris after harvesting the crops. Treat the seed with hot water at 54C for 30 minutes. Two sprays of Streptomycin at 400 ppm or Bordeaux mixture at 1%.

37. Water melon bud necrosis WMBNV The virus generally transmitted by sap of already infected plant and thrips . The first symptoms appear on apical bud, which turn brown to black and die. In certain cases, broken or complete concentric rings are also developed on fruit .

38. Control measure Use seed free from virus disease. Spray systemic insecticides Dmethoate or metasysytox @ 1 ml/liter periodically up to flowering to check the vector activity.