Oidium  spp.

Eggplant external powdery mildew

General

• Leaf fungi reported more or less in several countries of the world.
• Disease observed both in the open field and under shelter.
• Species reported on eggplant : Erysiphe sp., E. cichoracearum , E. orontii , E. Polyphaga ,, Oidium sp. O. longipes, O.erysiphoides, Sphaerotheca fuliginea,  S. fusca . In fact, it seems that at least two species are rife on eggplant: Euoidium longipes, and  Podosphaera xanthii, characterized in China more recently. Note that in Japan, O. neolycopersici grows abundantly on the foliage of all the tomato cultivars tested and of tobacco; it produces weak colonies accompanied by necrosis on potato, red pepper, petunia and eggplant leaves.
• Organs attacked : mostly leaves, stem.
• Symptoms :
  • Powdery and white spots rather localized on the upper surface of tomato leaflets (figure).
  • Affected tissues become chlorotic, locally brown and eventually necrosis.
  • The entire leaf blade may be covered by the mycelial network of the fungus, and some leaflets turn yellow and completely necrotize.
  • Comparable spots can be observed very locally on the stem, even the peduncles.
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• Signs : felting made up of a mycelial network surmounted by numerous conidiophores producing isolated hyaline conidia or sometimes in pseudo-chains of a few spores when the relative humidity is high.
• Possible confusion  :

Biology

• Conservation  : numerous alternative hosts, cultivated or not (several Solanaceae and Cucurbitaceae, etc.), perhaps its globular cleistothecia which do not seem to have been observed in the field.
• Infection : Conidia germinate in a few hours and enter directly into the epidermal cells.
• Sporulation : production on the spots of a very large number of conidiophores and conidia within a few hours.
• Dissemination : by wind, drafts in shelters, incidentally by splashing water, workers' clothing.
• Favorable  conditions: prefers humid and hot environments, in particular humidity equal to or less than 80% humidity; above, its development is gradually reduced. Excessive nitrogen fertilization would sensitize leaf tissue.

Protection  

• Carry out crop rotations of two to three years.
• Provide balanced manure to the plants.
• Use healthy plants.
• Carefully choose the location of the future plot so that it is located in a fairly ventilated and sunny place. Avoid proximity to plots already affected.
• Eliminate the weeds from the plot and its surroundings, which can serve as relay plants for the parasitic fungus.
• Create a crawl space under shelters as well as washing or even disinfection of surfaces.
• Avoid too high planting densities in order to promote aeration and sunlight of the foliage.
• Eliminate plant residues fairly quickly, during cultivation following the various cultivation operations, and at the end of cultivation after uprooting the plants. They will have to be destroyed or buried deep.
• If necessary, spray fungicides taking into account the authorized uses.