How to Manage Pests
UC Pest Management Guidelines
Diseases and Disease-Promoting Conditions
In this Guideline:
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
- Signs (visible pathogen
structures) include Armillaria mushrooms, Ganoderma fruiting
bodies, and white fungal mycelium growing beneath bark.
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
- New shoots of small pale leaves.
- Abundant small fruit.
- Fruit that are blotched, discolored, spotted, streaked,
- Cankered, cracked, discolored, or oozing bark.
- Black, brittle,
or dead roots and relatively few small roots (rootlets).
If a tree looks unhealthy, examine as many of
plant parts as possible.
away mulch to examine the appearance of small roots.
- 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
- 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
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 trunk
and root 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
problem spots on a map of the grove or using a hand-held GPS (global positioning system).
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.
Improve growing conditions, use good
sanitation, and provide appropriate cultural care as the primary means of
UC IPM Pest Management Guidelines: Avocado
UC ANR Publication 3436
Acknowledgment for contributions to General Horticultural Information:
M. L. Arpaia, Botany and Plant Sciences, UC Riverside
M. L. Bianchi, UC Cooperative Extension, San Luis Obispo County
C. J. Lovatt, Botany and Plant Sciences, UC Riverside
P. Mauk, UC Cooperative Extension, Riverside County
G. W. Witney, California Avocado Commission, Irvine, CA
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