Everything you need to know about controlling diseases of ash gourd.
1. Anthracnose (Colletotriclium Lagenarium):
Disease symptoms are found on all plants parts above ground started from cotyledonary leaf to true leaves, stem, fruits and tendril ins ash gourd. Light brown circular spots, which later turn to deep brown, appear on the leaves. Elongated lesions are observed on stem and circular to oval sunken lesions on fruit, which subsequently shrivels, darkens and finally dries up.
Later on infected fruit rot and infect all the seed, which is source of further primary infection. It is a serious disease of ash gourd, and it was first time reported at Bangalore by Prakash et al. (1974). It is seed born disease and seed from infected fruits also carry the primary inoculum for further infection.
i. Collect seeds only from disease-free plants.
ii. Avoid growing ash gourd in fields repeatedly used for the cultivation of cucurbits.
iii. Treat the seed with Captan or Thiram @ 2.5 g/kg of seed before sowing.
iv. Spray systemic fungicide such as 0.1% carbendazim.
v. Spray of hexaconazole @ 0.025-0.05% also gives good control.
2. Fruit Rots (Fusarium Solani, Fusarium Moniliforme, Verticillium Dahliae, Sclerotium Rolfsii and Phomopsis Cucurbitacearum):
Decaying of fruits is a major problem during storage. Sometime rotting starts from the lower fruit portion that had been in contact of soil. White fungal growth, which later on turned into brown circular scelerotia, is observed on fruit surface. This is more common in fields having high moisture during September-October. The infected fruits contain completely rotten seeds, which turn white, become hollow, and fail to germinate.
Phomopsis cucurbitacearum mostly affects the mature fruits. Main symptom appears on upper surface of fruits as black dry rotting, which is localized, and does not affect entire fruit. The bark of fruit, which remains covered by white wax, becomes black and rough. Close observation reveal small circular black numerous pycnidia over infected fruits, which later on arrange very close in circular lings, and finally, the pathogen infects the seed and becomes seed born.
Infected seeds look like healthy ones and germinate easily but contain seed born inoculums. The disease is caused by Fusarium solani and Fusarium moniliforme in the field as well as during storage in ash gourd. Gubler and Burnhardt (1992) isolated Verticillium dahliae during storage as a causal agent of fruit rot. Brown dull spots, which lead to softening and rotting, are developed on fruits. The flesh of rotten fruit contains pockets of dry brown rot and masses of white mycelium.
Sclerotium rolfsii causes wet rotting of fruits in which entire flesh of fruit is rotted followed by collapsing of fruit. Ash gourd fruit is also infected by Sclerotium rolfsii and Phomopsis cucurbitacearum that also cause rotting of fruits. The pathogen Phomopsis cucurbitacearum was first reported from India in the world and disease was first seen in India during cropping season of 2002.
i. Expose the soil following repeated deep summer ploughing.
ii. Adopt long crop rotation with cereals and clean cultivation.
iii. Use only healthy seeds and grow tolerant/resistant varieties.
iv. Train the crop on bower system to minimize the infection.
v. Treat the seed with Trichoderma viridae along with neem cake application.
vi. Collect the infected fruit and burnt.
3. Leaf Spot [Didymella Bryoniae (Teleomorph), and Phoma Cucurbitacearum (Anamorph)]:
Initial symptom is observed as small irregular wet lesions on outer leaf margins. Sometime circular, concentric rings are also observed on the lesions. Papery with rhythmic large spots followed by shot hole are observed if infected by Didemella. Black small dot like structures are developed on old spots. White fungal growth is clearly visible on outer margin of the spots in morning on underside of leaves.
Severely infected leaves give burning appearance. The disease is more common during winter season. Didymella leaf blight was observed first time in ash gourd during 1998-99 and reported from India by Pandey et al., (2003), and since then the severity of this disease is increasing every year, causing more loss. Teleomorphic stage is observed in later phase, causing leaf drying.
i. Treat the seed with carbendazim @ 0.25% to minimize the infection in the crop.
ii. Spray mancozeb at 0.25% altered with one spray of hexaconazole at 0.05%.
4. Fusarium Wilt (Fusarium Oxysporum F. Sp. Benincasae):
This disease is more common in sandy soil. The symptom is characterized by yellowing of lower leaves, which gradually progresses on upper leaves. The plant soon after infection starts drooping followed by wilting, and later on, wilting becomes permanent. Characteristic symptom was observed after splitting of roots and lower portion of stem as vascular browning.
Severity of disease is more if soil is infected with root knot nematode. The pathogen determined for wilt in ash gourd is Fusarium oxysporum f. sp. benincasae and severity of Fusarium oxysporum f. sp. lagenariae is tested by grafting and also caused wilting.
i. Apply Trichoderma @ 5-8 kg/ha, depending upon the soil structure, to minimize disease.
ii. Treat the seed with carbendazim @ 2.5 g/kg of seed.
5. Downy Mildew (Pseudopernospora Cubensis):
Generally, at initial stage, small irregular yellowish lesions appear on ash gourd leaves. Old lesions become necrotic, and they are clearly demarcated with light yellow areas. In high humid weather, faint white downy fungus growth is observed on lower surface of the leaves. Downy mildew attacks occasionally on ash gourd. In South India, because of the continuous cropping and the prevailing climate suitable for mildew, it perpetuates on various cucurbitaceous host without any difficulty. At Solan, downy mildew was recorded on ash gourd without oospores.
i. Grow the crop at wider spacing on well-drained soils.
ii. Collect seed from disease free healthy fruits to avoid further infection.
iii. Spray mancozeb @ 0.25% at seven days interval.
iv. In severe conditions, follow one spray of metalaxyl + mancozeb @ 0.2%.
v. Spray copper oxycloride 0.2% at 10 days interval
vi. Air movement and sunlight exposure helps in checking the disease initiation and development.
vii. Field sanitation by burning crop debris reduces the inoculums.
6. Powdery Mildew (Erysiphe Dehoracearum):
The disease caused by Erysiphe cichoracearum DC. 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. White long patches or powdery coating appear(s) first on the under surface of the leaves, which later spread to the upper surface, stem, petiole and other succulent plant parts.
Severe infection causes stunted growth and browning of leaves followed by premature defoliation. Usually the fruits of affected plants do not develop to maturity. Good conidial germination is observed within a temperature range of 22-31°C with optimum at 28°C and low relative humidity of 20% for less than 2 hours.
i. Collect and burn all the infected leaves.
ii. Spray the crop with fungicides like penconazole (0.025-0.05%), tridemorph (0.05-0.1%), or carbendazim (0.1 %) at different intervals as per need commencing from first appearance of disease.
7. Watermelon Virus (WMV):
Most of the cucurbits and cowpea plants act as host for the virus. Initially, the symptoms appear on leaves. The leaves of diseased plants develop mosaic or mottling accompanied by green vein banding and reduction in leaf size. The petiole and internodes also shortened. The mosaic in ash gourd was reported from Gorakhpur and the virus was identified as WMV. It is sap transmitted by vectors M. persicae and A. gossypii in a non-persistent manner.
i. Avoid the overlapping of vines maintaining proper sowing distance.
ii. Spray insecticide Emidacloprid @ 3 ml/10 liter of water at regular interval for controlling vectors.
iii. As far as possible, keep the field weed free.