Powdery mildew on cucurbits in zucchini

Zucchini

by admin
March 25, 2024

Powdery mildew on cucurbits in zucchini

The scientific name : Powdery mildew of cucurbits
The causative fungus : Sphaerotheca fuliginea Pollacci
Symptoms of powdery mildew on cucurbits in zucchini:

The infection begins on the lower surface of old leaves around the base of the plant, then spreads to new leaves. Symptoms appear in the form of small, round, white, powdery spots. Then these spots expand and connect with each other to cover most parts of the plant, which leads to the leaves turning pale, then yellowing, drooping, and drying out.

Similar symptoms may appear on petioles and stems.

The fruits do not suffer from the disease, but they are few in number and small in size, and may become deformed, and the percentage of solid matter decreases, thus having a poor taste, and becoming more susceptible to post-harvest diseases.

A picture showing you the beginning of powdery mildew infection on cucurbits in zucchini

An image showing the symptoms of an infection

An image showing the symptoms of a leg injury

Causes of powdery mildew on cucurbits in zucchini:
Cultivation of sensitive varieties
Powdery mildew infection prefers humid conditions with temperatures between 68-81 degrees Fahrenheit.
Spores produced in leaf spots are blown away by wind to infect other leaves
Powdery mildew affects heavily planted plants, plants crowded with weeds, plants in shady locations, and plants that have been overfertilized.
Suitable conditions for the spread of powdery mildew on cucurbits in zucchini:
The disease prefers moderate temperatures of 68-80°F, medium to high humidity (50-90%), dense foliage, and low light. Infection can occur under dry conditions and relative humidity as high as 50
Powdery mildew development cycle on cucurbits in zucchini:
Given the rarity of the ascomycete stage of the fungus, infection most likely occurs at the beginning of the season through airborne conidial spores from other cultivated cucurbit plants, or from wild plants and weeds that the fungus harbors during the period of absence of cucurbits.
Conidial spores form within 3-7 days of infection, depending on the prevailing weather conditions. These spores are responsible for spreading the disease during the season by wind and some insects.

An image shows you the progression of symptoms

Losses of powdery mildew spread on cucurbits in zucchini

– Reduced yield by decreased number and/or size of fruits. Fruit quality can also be negatively affected by sunburn (due to leaf drop), incomplete ripening, reduced storability (winter squash), poor peel quality or discolouration of the handles ( Pumpkins). In addition, infection with powdery mildew exposes plants to other diseases (gum stem blight

Infected plants reach senescence early, which leads to a shortened production period

A picture showing a severe injury

Control strategy
Preventive measures to prevent powdery mildew on cucurbits in zucchini
Cultivation of varieties or hybrids that are resistant or tolerant to the disease.
Provide good air movement around plants through proper spacing, plant stacking, and weed control.
Proper spacing when planting is important
Chemical and organic control recommendations against cucurbit powdery mildew in zucchini
Organic control: Explore fields regularly (especially the lower surfaces of leaves) and apply fungicides early in the development of the disease
Chemical control: This disease can be controlled by using a surface pesticide, or by spraying or fumigating with sulfur as soon as symptoms appear, and spraying is repeated whenever necessary. Its harmful effect can be reduced by diluting it with a carrier substance such as furnace ash (10_15% sulfur). It is preferable not to use sulfur when the temperature is high and the weather is dry.
Because powdery mildew appears on the lower leaves first, especially on the lower surface of the leaves, it is difficult for the surfactant to reach it. Therefore, it is preferable to use a systemic pesticide, such as thiophanate methyl and mancozeb.
References
McGrath, Margaret T. “Powdery mildew of cucurbits.” (1997).
Lina Quesada-Ocampo
Professor, Plant Pathology (Cucurbits and Sweetpotato)
Entomology & Plant Pathology
PÉREZ‐GARCÍA, ALEJANDRO, Romero, D., FERNÁNDEZ‐ORTUÑO, DOLORES, LÓPEZ‐RUIZ, FRANCISCO, De Vicente, A., & Torres, J. A. (2009). The powdery mildew fungus Podosphaera fusca (synonym Podosphaera xanthii), a constant threat to cucurbits. Molecular plant pathology, 10(2), 153-160