The Top 5 Diseases Affecting Almonds in California

California is a major producer of almonds, accounting for around 80% of the world's almond supply. However, the almond industry in the state faces several challenges from various soilborne diseases that can threaten productivity and yield.

In 2023, BeCrop technology identified various diseases for major crops within the soil in the United States. This article serves as a guide and tool for California almond growers, providing them with microbial insights to identify and combat top soilborne diseases affecting their crops.

The top 5 diseases detected by BeCrop Tests affecting almonds include Green Fruit Rot/Jacket Rot, Hull Rot, Alternaria Leaf Spot, Stone Fruit Rust, and Phytophthora Crown and Root Rot. 

Top 5 Soil Borne Bacterial and Fungal Diseases For Almonds in California

• Green Fruit Rot/Jacket Rot: Caused by the microbial species Monilinia fructicola, Botrytis cinerea, and several other fungal pathogens, this disease affects almonds, leading to the rotting of developing fruits.
• Hull Rot: Caused by Rhizopus stolonifer and other fungi, this disease affects almond hulls, leading to rot and reduced nut quality.
• Alternaria Leaf Spot: Caused by Alternaria spp., this disease leads to the development of dark spots on almond leaves, potentially impacting photosynthesis.
• Stone Fruit Rust: This disease is caused by the fungus Tranzschelia discolor, leading to rust-like symptoms on almond leaves.
• Phytophthora Crown and Root Rot: Caused by Phytophthora spp., this disease affects the roots and crown of almond trees, leading to rot and potential tree death.
  
  

Ways to Control Bacterial and Fungal Diseases in Almonds

To control the top 5 diseases affecting almond crops, the following strategies can be employed:

Green Fruit Rot/Jacket Rot

This fungal infection attacks the developing fruit of almonds, so the best preventative measures are always more effective when detected and treated during the early stages of growth. Preventative biocontrols applied during bloom shield young fruits from infection.

Remember to adhere to responsible use and consult experts for specific recommendations to avoid fungicide resistance. Second, microclimate management is crucial. Improving air circulation and reducing humidity around trees through strategic irrigation practices creates a less favorable environment for fungal growth.

Hull Rot

This is another fungal disease that greatly impacts the almond quality, which can impact farmers’ profits. Preventative measures include irrigation management. If detected, farmers should avoid over-irrigation, especially during hull development, as it creates a moist haven for Rhizopus.

Adjust irrigation practices based on weather and soil moisture. Second, nutrient management is necessary, and farmers must balance fertilization to prevent excessive vegetative growth. This makes hulls more susceptible.   

Alternaria Leaf Spot

Alternaria leaf spot can be managed by utilizing management practices and biocontrols.

Orchards with high humidity, heavy dew, and stagnant air often have severe problems, so selective pruning of the canopy can help increase ventilation, and improving water infiltration can reduce orchard humidity. 

Stone Fruit Rust

For controlling stone fruit rust, specifically referring to fungal diseases like brown rot and scab, a comprehensive fungicide program is advised in orchards where these diseases are prevalent and environmental factors promote their growth. 

Phytophthora Crown and Root Rot

A combination of soil management and biocontrol application strategies is recommended to effectively control Phytophthora crown and root rot in almonds. Ensuring proper drainage to prevent waterlogged conditions that favor Phytophthora is crucial, as saturated soils provide an environment for the pathogen to thrive. 

BeCrop Biological Soil Analysis For Disease Prevention in Almonds

Analyzing the soil microbiome through methods like the BeCrop Test can greatly enhance soil disease management in almond orchards. This approach, rooted in regenerative agriculture, focuses on boosting soil health and microbial diversity. Such examination reveals beneficial microbes that protect against disease and promote plant health. Additionally, it guides targeted management strategies to improve soil quality and combat disease, making it a critical step for effective almond orchard management.

See below a sample report that detected several diseases early from a single soil sample.

These soil tests will also indicate the best management practices, like drainage, to help prevent and treat diseases that thrive in moist conditions.

In addition to soil health, insights into the current and desired microbial community in orchids can pinpoint the best products to use to help combat certain diseases. This is especially important during the early stages of almond production, given that many prominent diseases attack young almonds. 

Note: Biome Makers agronomists have identified some of the top soilborne bacterial and fungal diseases affecting crops in the US. These diseases are found in the soil. While not all soilborne diseases are included, the selected ones are among some of the most impactful, with variability by region. It's important to note that the diseases are not listed in order of impact, and they do not include viruses. The detection of these diseases is made possible by BeCrop technology and soil database, offering valuable insights for crop management and disease prevention.