Fungal Diseases

There’s a fungus among us!


Actually, there are millions of fungal species and more individual fungi than anyone could possibly imagine. Fungi are the most common cause of plant disease and a major player when it comes to the loss of fruit and other produce.


You may be surprised to learn that fungi are more closely related to animals than plants. How is this possible? Let’s find out!

Mycologists, scientists who study fungi, are still debating where, exactly, fungi fall in the world of taxonomy, because fungi have characteristics of both plants and animals. Like plant cells, fungal cells contain mitochondria, ribosomes, vacuoles, and a cell wall. But they lack chloroplasts, the same as animal cells. Most fungi lack a vascular bundle, so they use tiny structures in the base, similar to roots, to suck nutrients out of whatever is beneath them. Fungi can reproduce sexually or asexually, depending on the species, but they all use spores, or similar structures, and this is where problems in the garden start happening.

Strawberry fruit with fungal growth (Kate Russell)

Spores in spring
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As weather starts warming and rains start to fall, a common weather pattern in California in March, fungal spores take to the skies on every breeze that passes. A single citrus mummy can hold billions of fungal spores that can infect nearby fruit, trees and other plants. If you see a mummy in the garden, get rid of it. Also, don’t count on the drier weather of June and July to clear out fungal diseases - powdery mildew LOVES dry weather!


Common fungal diseases

Fungal plant diseases can be very difficult to combat. Here is a list of common fungal diseases:

• anthracnose
• black root rot
• black spot
• crown rot
• damping off
• Eutypa dieback
• Fusarium wilt
• powdery mildew
• root rot
• peach leaf curl
• shot hole disease
• sooty mold
• stem blight
• Verticillium wilt

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How to control fungal diseases

The most common response to fungal infestations is the use of fungicides. As quickly as fungi evolve, however, applying fungicide frequently creates resistant varieties that are even more difficult to control. Good cultural practices can help your garden plants protect themselves without the use of chemicals.

• Regular, proper pruning can remove infected or damaged areas, increase air flow, and improve overall plant health.
• Early morning irrigation should be allowed to saturate the soil, not touching tree trunks. Potatoes will rot in the ground if the soil stays wet too long. Apricot, avocado, citrus, and most other trees are prone to infection when the trunk is wet repeatedly. Think sprinkler placement.
• Improve soil structure with compost for better porosity and drainage.
• Keep plants healthy with regular, appropriate feeding. Stimulating too much tender new growth can be an invitation to disaster when fungal spores are abundant.
• Plant resistant varieties. Plant labels that carry “VF” after the plant name are resistant.
• Control pests, such as soft scale and aphids, that support and spread fungal disease.
• If you must use fungicides, follow the directions exactly, completely, and without fail.

When it comes to fungal diseases, prevention is far more effective than trying to get rid of them.