How to Monitor
Look for conditions that favor pathogen infection and disease development, such as inadequate cultural practices and mechanical injury to plants. Especially look for, and remedy, inappropriate irrigation.
Look for signs and symptoms of disease, and record the date and location of problem trees or sites.
- Signs (visible pathogen structures) include Armillaria mushrooms, and Ganoderma fruiting bodies, and white fungal mycelium growing beneath bark, and rhizomorphs (not common in CA) (i.e., Armillaria mellea).
- Symptoms of diseased plants include:
- Leaves that are downward-hanging, necrotic-tipped, pale or yellow, or wilted.
- Premature leaf drop or a sparse canopy of drooping older leaves,
- New shoots of small pale leaves.
- Abundant small fruit.
- Fruit that are blotched, discolored, spotted, streaked, or rotted.
- Cankered, cracked, discolored, or oozing bark.
- Black, brittle, or dead roots and relatively few small roots (rootlets).
- Variegated stems, leaves or fruit indicative of sunblotch
- White crusty exudates on the main trunk or major branches indicative of bacterial, crown rot, Dothiorella blight or black streak
Inspecting Trees
If a tree looks unhealthy, examine as many of plant parts as possible (see Monitoring for Root and Crown Diseases in Avocado Orchards for more information).
- Brush away mulch to examine the appearance of small roots for root rot and the main stem where it enters the soil for crown rot.
- Remove soil from around the root crown and cut beneath unhealthy looking bark to expose cankers or small patches of white fungal mycelium.
- Look for discolored or oozing bark on main limbs and trunks and examine beneath damaged bark to discern cankers.
- Use appropriate tools, such as a chisel or knife, to cut away bark and view deeper cankers. Keep monitoring tools, including a chisel, hatchet, hand lens, pocket-knife, and shovel, close at hand.
Diagnosing the Cause
Inspect several nearby trees, which may show earlier, more characteristic or subtle symptoms. Patterns in symptoms among trees can provide clues to the cause. Do not rely on a single symptom. Compare your observations to photos of common root and crown diseases . If cankers are present, distinguish among the causes of cankers, which include:
- Abiotic disorders
- Various pathogens
- Certain vertebrates
Send samples to a diagnostic laboratory or consult an expert to help diagnose the cause. Keep records of testing results.
Recording the Location of Diseased Trees
Record the date and location of problem trees or sites.
- Mark problem spots on a map of the grove or using a hand-held GPS (global positioning system).
- Use florescent spray paint and colored plastic flagging to mark trees.
- Mark maps and trees or both with symbols or color codes keyed to symptoms or the suspected or confirmed cause of disease.
- Repeat monitoring at intervals to document the progression or seasonality of symptoms and to assess whether management practices are effective.
Managing Disease
Improve growing conditions, use good sanitation, and provide appropriate cultural care as the primary means of managing:
- Anthracnose fruit rot
- Armillaria root rot
- Avocado black streak
- Bacterial canker
- Branch canker and dieback
- Phytophthora root rot
- Phytophthora trunk canker and crown rot
- Sunblotch
Fruit should be picked by clipping rather than snapping the pedicles. Clippers should be frequently sterilized using a dilution (e.g., 1:10) of household bleach.