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Yellow Leaves on Zucchini

Updated July 19, 2017

Diseased zucchini plants may display similar symptoms to pumpkin or squash plants. They all belong to the gourd section of the cucumber family. Yellow leaves are just one of the outward warning signs to suggest a plant has a problem.

Cucumber Mosaic Virus

Zucchini and marrows are most susceptible to cucumber mosaic virus. The leaves are a mottled yellow with green patches. The leaf surface become puckered and distorted. There is no effective treatment for the virus and infected plants should be removed and destroyed. Hands should be thoroughly washed before touching other plants. Ideally a resistant variety should be grown.

Verticillium Wilt

The lower leaves turn yellow and the discolouration moves upwards when a zucchini is effected by verticillium wilt. Eventually all leaves become dry and wilted. Young plants in cold, wet conditions are most susceptible. Verticillium wilt can be verified by cutting the stem. Brown streaks will be found inside the stem tissue. It is a soil-borne fungus and infects the plant via the roots. Crops should be rotated to prevent infection.

Iron Deficiency

The yellowing of leaves doesn't always indicate disease. If a soil is lacking in nutrients, it can cause leaves to turn yellow and can stunt growth. Iron deficiency does not always mean the soil is lacking in iron. It could mean that other nutrients are stopping the plant from absorbing iron. Using a well-balanced fertiliser can help.

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About the Author

Emma Hall has been writing articles since 2008. She grew up within the market gardening community and spent 10 years in horticulture. She has begun researching more ecological ways of gardening and has work published on websites relating to gardening and travel. She has A-Levels in English and film studies.