Verticillium wilt. It is a soil borne fungal disease that enters the pistachio tree through the root system and can finally kill the tree. After some years, it actually blocks the water and nutrients that are supposed to be transferred from the roots to the upper parts of the trees, resulting in the collapse of whole branches. It is created from the pathogen Verticillium dahliae. Verticillium wilt has created huge economic loss in the pistachio orchards of California Valley. Unfortunately, the pathogen can live in the soil for many years, without any plant host. As stated in Pistachio Soil Preparation article, the first precaution against Verticillium wilt would be to keep a field fallow for 4 years, if cotton or Solanaceae species (Tomato, Potato, Tobacco) were cultivated in this field. Alternatively, a farmer can sow a variety of grasses for a couple of years (ask a licensed agronomist). The second precaution against Verticilium is to select a rootstock that is resistant to this disease (for instance UCB 1). Over irrigation and the presence of certain weeds favor the rapid spread of the disease.
Phytopthora root rot. Phytopthora root rot is a soil borne fungal disease. The pathogen initially attacks the roots and makes them weak. This will finally block the water and nutrients that are supposed to be transferred from the root systems to the upper part of the tree. As a result, pistachio trees will suffer from slow growth, defoliation and reduced fruit set and production. The pathogen can live several years in the soil, without depending on a plant host. Heavy and waterlogged soils favor the spread of the disease.
Armillaria root rot, Pistachio dieback (Xanthomonas translucens) and Septoria leaf spot are also famous pistachio tree diseases.
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12.) Pistachio Tree Diseases & Pests
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