Alternaria late blight of pistachios

Image of a plant suffering from Alternaria late blight of pistachios

Alternaria late blight of pistachios - Plant World

Symptoms of the disease appear in the form of widespread, fine, dark brown spots on the leaves with black centers.

This is then followed by leaf wilting and premature defoliation.

Then brown circular necrotic spots appear on the fruits surrounded by a red halo.

As these spots grow, mold begins to grow on them.


Symptoms generally appear in summer and are characterized by angular or circular spots 3 to 7 mm in diameter on the leaves.

In some severe cases or in particularly susceptible varieties the spots become spots up to 3 cm in diameter.

Black spots are also present on petioles and main veins of leaf blades.

Severe infection can also cause leaves to wilt and fall.

On immature fruits, fine brown or black spots appear.

On mature fruits, the spots are somewhat larger (1 to 5 mm in diameter) and surrounded by a red halo.

Mold begins to grow on the fruit, causing it to rot.

In severe cases, the disease greatly reduces the quality of the product.

Organic control

Spray the Bordeaux mixture on trees and cuttings after pruning the affected parts. Alternatively, you can apply a mixture of garlic or plantain on the leaves and fruits. You can also use solutions based on the bacteria Bacillus subtilis, which is a predator of fungi.

Chemical control

Always consider integrated pest management with preventive measures and biological treatments if available. Treatment against this disease should begin in early summer, before the fruits ripen. Products based on the active ingredients methyl thiophonate, manip, and copper products work well.

At least two treatments are needed to reduce the incidence. The effectiveness of treatment depends on the timing of spraying, proportionality to the age of the tree, and application of the recommended dose.

Cause of disease

The symptoms are caused by a group of three fungi of the genus Alternaria, among others the genus Alternaria alternata.

As it hibernates in the soil or plant waste. When conditions are favourable, they produce spores that are transported by wind and rain to susceptible trees.

High temperatures associated with high humidity, including dew formation, alternating wet and sunny periods, and nutrient deficiencies are major factors in disease development on pistachios. The symptoms of this disease can be confused with those of inflorescence bud blight caused by Pietrosphaeria dunedia.

To differentiate between them, rub the affected leaves when wet conditions prevail: if your fingers become black, it is late blight caused by Alternaria.

Preventative measurements

  • Use varieties that are less susceptible to disease and use healthy seeds from certified sources.
  • Avoid tight planting to promote ventilation within the canopy.
  • Inspect the orchard regularly to detect the first signs of the disease.
  • And control weeds on the orchard land.
  • Cut and burn the affected parts as soon as the first symptoms appear.
  • . Also prune trees during dormant times to obtain well-ventilated canopies.
  • Avoid irrigation by spraying, especially during the ripening of fruits.
  • Remove crop residues after harvest and burn them.
  • Above all, do not compost these plant parts because they will carry the disease to another season.

There are three types of this disease that affect pistachios. This disease appeared in 2008 in America, and it leads to a decrease in yield. It also prefers high humidity, so the dry climate contributes to reducing it. Below are some points that explain the causes, symptoms, and methods. disease treatment:

Pathogens: This disease is caused by a black lesion called Alternaria.

Symptoms of the diseaseBlack spots appear with a red edge, then the spores infect in humid weather, and may lead to leaf fall in an advanced period of the disease.

Methods of TreatmentIt is recommended to spray appropriate insecticides, irrigate the tree well, and remove weeds around it.

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