Yellowish spots of different sizes appear on the surface of young developing leaves. The spots later enlarge and become angular and delimited by veins. Their center becomes necrotic with different shades of brown. A dense white to grayish cottony layer develops beneath the spots after a series of warm humid nights, and they disappear as soon as it becomes sunny. Young shoots defoliate or experience stunted growth. The disease also affects the fruits and other plant parts.


The symptoms are caused by fungi of the group of the Peronosporales and can be very destructive in shaded areas with frequent rainfalls and warm temperatures (15-23°C). These fungi have adapted pretty well to their hosts, meaning that each major crops harbor its own species of fungus. The fungus overwinters in infected plant debris or shoots, in the soil or on alternative hosts (crops and weeds). Wind and rain spread the spores during favorable conditions. The spores germinate and produce structures that enter the leaf through natural pores on the underside of leaves. There it starts to spread through tissues, eventually outgrowing the internal tissues and forming the characteristic mildew coating outside.



Preventive Measures

  • Choose resistant varieties, if available.
  • Keep plant dry, for example through proper ventilation.
  • Make sure soils are well-drained.
  • Ensure a balanced fertilization for plant vigor.
  • Provide good spacing between plants.
  • Plant in sites well exposed to the sun and choose right orientation.
  • Control weeds in and around the field.
  • Remove plant residues from the field.
  • Keep tools and equipment clean.
  • Fortifiers can be applied to strengthen the health of the plant.


Control Dose/Litre Trade Names
3-4 gram Ridomil MZ, Apron, Amistar, Moximate, Fond