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A fungal attack on plants can be recognized by a white coating on the leaves, called powdery mildew. Vegetable plants such as zucchini are particularly often affected. Luckily, there are effective ways to biologically combat white spots.

In a nutshell

  • fungus as the cause
  • No chemicals needed to combat it
  • Make your own home remedies
  • or use predators
  • multiple applications required
  • if left untreated, the plant will die

Powdery mildew in the portrait

Powdery mildew or downy mildew is a plant disease caused by the fungal species Erysiphe cichoracearum or Sphaerotheca fuliginea. Dry summers with high temperatures favor their occurrence. Especially in the second half of the year from July, powdery mildew develops its spores on leaves. Since this date overlaps with the ripening time of the zucchini, the pumpkin plant is considered to be particularly endangered.
Erysiphe cichoracearum and Sphaerotheca fuliginea leave the following marks on the leaves of zucchini:

Powdery mildew on zucchini leaves
  • initially white spots
  • initially washable
  • condense into a gray coating
  • Leaf edges curl
  • Leaves curl up
  • browning of the leaves

root cause

Vital plants are usually able to develop their own defenses against fungi. However, if the health is weakened by unfavorable site conditions or care errors, the powdery mildew pathogen has an easy time spreading to the leaves. Zucchinis need a lot of heat. A shady bed can be fatal to the vegetables. Frost also damages the health of the plant. Another reason for a weakened defense system could be wrong fertilizer. Erysiphe cichoracearum and Sphaerotheca fuliginea thrive in a nitrogen-rich environment. In general, an infestation of powdery mildew can be prevented with sufficient air circulation, since this develops primarily in stuffy environments. Zucchinis in greenhouses are particularly vulnerable due to the greenhouse effect.


It is often not even necessary to use chemical fungicides. Simple home remedies are enough to get rid of the fungus inexpensively.

Production of a biological spray from milk and water:

  • Mix 900 ml of low-lime water with 100 ml of fresh milk
  • put in a spray bottle
  • spray on the leaves every other day
  • refresh after every downpour

Notice: Whey is just as suitable as fresh milk, but must be mixed with water in a 1:1 ratio.

mode of action

Milk contains the active ingredient lecithin and numerous microorganisms that naturally break down the fungus.

Preparation of a decoction from field horsetail:

  • Optionally soak 1000 g fresh or 150 g dried field horsetail in 10 l water
  • leave for a day
  • let simmer at more than 75°C water temperature for 1 hour
  • let steep again under the closed lid
  • pass through a sieve
  • dilute with water
  • Spray on the plant every 2 to 3 days

mode of action

The silicic acid contained in field horsetail strengthens the vitality of the plant and also fights fungal spores.

Notice: Field horsetail grows along roadsides and in meadows from May to July.

baking powder

  • Dissolve 3 packets of baking soda in 5 liters of water
  • add some rapeseed oil
  • Add dish soap to bind
  • stir well
  • pour into a spray bottle
  • spray on the plant every 8 to 10 days

mode of action

Like milk, baking powder contains fermenting acids that the fungus does not like. However, the addition of washing-up liquid and oil is urgently required.


If the zucchini thrives in a greenhouse, predators will find optimal living conditions here to colonize the vegetable plant as well. After all, there is an abundance of food, since the fungus is at the top of the beneficial insects’ menu. Recommended types are

Source: AfroBrazilian, Psyllobora vigintiduopunctata 04, edited by Plantopedia, CC BY-SA 4.0
  • the mushroom ladybird (Psyllobora vigintiduopunctata)
  • the sixteen-spotted ladybird (Halyzia sedecimguttata)
  • and the squirrel hover fly (Myathropa florea)

Notice: Beneficial insects are probably the most environmentally friendly way to combat white spots on zucchini. Unfortunately, they are only used for acute combat. Since the fungus grows again after they disappear, they are not suitable for prevention.


The fungus can not only be treated with the self-made sprays, the solutions are also suitable for counteracting the development or spread. For this, gardeners should not only spray the affected leaves, but the whole plant.
If you do not want to give Erysiphe cichoracearum and Sphaerotheca fuliginea a chance, it is best to use resistant varieties such as:

  • dundoo
  • Excalibur
  • Mirza F1
  • Anissa F1
  • Leila F1
  • Diamond F1
  • solar
  • Mastil F1
  • or radians F1

frequently asked Questions

Does the fungal attack cause the plant to die?

By sucking the juice from the leaves, Erysiphe cichoracearum and Sphaerotheca fuliginea deprive the zucchini of important nutrients. Without countermeasures, the plant does not survive a severe infestation.

Are there other leaf diseases with similar symptoms?

Botany differentiates between powdery mildew and downy mildew. The latter causes yellowish-green leaf spots on the undersides, which later turn into a bluish-grey shimmering coating. Means that show success in powdery mildew are partially ineffective in this disease.

Can I still harvest the fruits?

After thorough cleaning, gardeners can safely eat the harvest. There is no risk of poisoning.

Does powdery mildew also occur in the greenhouse?

Sphaerotheca fuliginea and Erysiphe cichoracearum not only settle on open field zucchini. The pest feels particularly at home in greenhouses with high humidity.

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