“Guarding Your Cucumbers: A Guide to Detect and Prevent Common Cucumber Diseases”


The older leaves have small, water-soaked or yellowish areas that grow quickly and become tan to reddish brown, often round or angular. Eventually, the spots may merge and affect large portions of the leaf, causing blight. The petioles and stems turn tan to black and form elongated streaks known as cankers. The immature fruit becomes black, shriveled, and dies. The older fruit develops round, water-soaked spots, which turn dark green to brown over time and may sink. When it’s wet, pinkish spore masses can be seen oozing from the sunken spots.

Management practices 

Spray Propineb 70% WP @ 1.2-1.5 gm/ltr Water or Azoxystrobin 18.2% + Difenoconazole 11.4% SC @ 1 ml/ltr Water.

Downy Mildew

Small, yellowish areas appear on the upper leaf surface of cucurbits other than watermelons. These areas later develop into more vibrant yellow spots, with the center of the lesion turning brown. The yellow leaf spots can have angular or non-angular shapes and eventually turn brown or black. When there is more soil moisture & leaves are wet, a downy growth of fungus can be observed on the underside of the leaves. The spores produced on the lower leaf surface are easily spread by the wind. Rainy and humid weather conditions promote the growth of downy mildew.

Management practices 

Spray Iprovalicarb 5.5% + Propineb 61.25% w/w WP @ 2 ml/ltr Water or Metalaxyl-M 3.3% + Chlorothalonil 33.1% SC @ 1.5-2 ml/ltr Water.

Powdery Mildew 

Powdery mildew is noticeable as a powdery, grayish-white growth on the upper parts of leaves, petioles, and even the main stems of infected plants. The affected areas change from yellow to brown and eventually die. During dry seasons, powdery mildew can cause leaves to fall prematurely and fruits to ripen too soon. Some early instances of the disease come from spores produced on remaining cucurbit debris, but the main source of the disease is wind-carried spores from crops in the southern regions. The development of powdery mildew is favored by warm and dry weather conditions.

Management practices

Spray Azoxystrobin 23%SC @ 1-1.25 ml/ltr Water or  Fluopyram 17.7%+ Tebuconazole 17.7% w/w SC @ 1 ml/ltr Water.

Gummy stem blight and Black spot

Gummy stem blight and black spot cause water-soaked lesions with necrotic scorching between the veins on the leaves. These lesions are surrounded by a yellow halo, and when they dry up, they often crack. On the stems, there are water-soaked lesions that later turn tan. Stem lesions can also cause gummy, reddish-brown, or black beads to exude. Black rot affects the fruit, making the affected area brownish and water-soaked. In advanced stages, the fruit’s rind becomes black and deeply wrinkled. There are large irregular areas on the fruit that turn bronzed with distinct concentric rings.

Management practices 

Spray Copper Oxychloride 45% + Kasugamycin 5% @ 1.5-2 gm/ltr Water or Thiophanate Methyl 70% WP @ 2 gm/ltr Water.

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