Walnut trees are a valuable crop, but are susceptible to various diseases that can reduce yields and compromise the quality of the nuts. In this article, we will discuss some of the main walnut diseases, how to recognize them, and how to manage them effectively.

Alternaria leaf spot and kernel mold are fungal diseases caused by the Alternaria species, attacking leaves, fruits, and young shoots of walnut trees. It thrives in high humidity and warm temperatures.

• Dark brown-black spots on leaves and green walnuts
• Spots often have a yellowish halo around them
• Leaves begin to yellow, dry out, and fall off
• Walnuts rot and fall prematurely
• Advanced stages lead to significant yield losses

• Conventional farming: Spraying with fungicides such as mancozeb, chlorothalonil, azoxystrobin, or captan.
• Organic farming: Use of biodegradable fungicides such as Bacillus subtilis and copper-based products.

Insects can cause severe damage to walnuts by attacking both leaves and fruits. Common pests include the codling moth (Cydia pomonella), walnut weevil (Curculio nucum), and various leaf-chewing caterpillars.

• Holes in nuts and fruits
• Larvae inside the nuts
• Premature fruit drop
• Drying of young shoots

• Conventional farming: Use of insecticides such as deltamethrin, lambda-cyhalothrin, or thiamethoxam.
• Organic farming: Biological control through attracting natural enemies like parasitic wasps, using pheromone traps, and spraying with natural insecticides such as neem oil.

A fungal disease caused by the Penicillium species, affecting stored nuts and leading to the formation of green mold colonies.

• Mold growth during storage due to high humidity and poor ventilation
• Fungal infections such as Penicillium spp. that cause nut decay
• Mycotoxins produced by Penicillium spp. can reduce nut quality. 
• Aflatoxins — which are especially dangerous to human health — are typically produced by Aspergillus flavus.

• • Green coating on the nut surface
  • Rotting and unpleasant odor
  • Reduced quality and edibility of the nuts
  • Possible production of mycotoxins, which are harmful to human health

• Conventional farming: Fungicides like thiabendazole have been used postharvest in other crops, but their use on walnuts may be restricted. Check local regulations before applying postharvest fungicides.
• Organic farming: Use of biological preservatives such as Pseudomonas fluorescens and proper storage of walnuts in dry and well-ventilated areas.

Combating walnut diseases requires a comprehensive approach, including regular monitoring, preventive measures, and timely treatments. Maintaining good agricultural practices, using appropriate treatments (both conventional and organic), and implementing sanitation measures can significantly reduce the risk of diseases and ensure high-quality yields.