Pseudoidium neolycopersici (L. Kiss)

Tomato powdery mildew

General

• Leaf fungus of rather recent worldwide extension in many countries of the world (for more than two decades): Europe, Africa, North and South of the American continent, Asia.
• Disease observed both in the open field and under shelter.

• Susceptible botanical family(s)

• Production areas affected :

• Organs attacked

Symptoms  and signs

• Symptoms :
  • Powdery and white spots rather localized on the upper surface of tomato leaflets (figures 1 to 4).
  • The affected tissues become chlorotic, brown locally and eventually become necrotic.
  • The entire leaf blade may be covered by the mycelial network of the fungus and some leaflets turn yellow and completely become necrotic (figures 5 and 6). Sometimes the fungus develops only on the veins (figure 7).
  • Comparable spots can be observed on the stem, peduncles. The fruits do not seem affected, on the other hand we observe its sporulation on the sepals.

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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 4 to 6 spores when the relative humidity is high.
• Possible confusion :

Biology

• Conservation  : many alternative hosts, cultivated or not (several Solanaceae and Cucurbitaceae, etc.), perhaps its globose cleistothecia which do not seem to have been observed in the field.
• Infection : the conidia germinate in a few hours and penetrate directly into the epidermal cells.
• Sporulation : production on the spots of a very large number of conidiophores and conidia (figures 8 and 9) in a few hours.
• Dissemination : by the wind, air currents in the shelters, incidentally by splashing water, workers' clothing.
• Favorable conditions: likes humid and warm environments, in particular hygrometry equal to or less than 80% humidity; above, its development is gradually reduced. Excessive hygrometry would lead to a reduction in the severity of the disease. Excessive nitrogen fertilizers would sensitize the leaf tissues.

Protection  

• Use resistant varieties .
• Carry out crop rotations of two to three years.
• Provide balanced fertilizer to plants.
• Use healthy plants.
• Carefully choose the location of the future plot so that it is located in a fairly airy and sunny place. Avoid proximity to plots already affected.
• Eliminate weeds from the plot and its surroundings, as these can serve as relay plants for the parasitic fungus.
• Carry out a crawl space under shelter as well as a washing, or even a disinfection of the surfaces.
• Avoid too high planting densities in order to promote ventilation and sunshine 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 authorized uses.