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How to Manage Pests
UC Pest Management Guidelines
Floriculture and Ornamental Nurseries
Begonia (Begonia spp.)
Disease Control Outlines
(Reviewed 1/02,
updated 1/02)
In this Guideline:
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| Disease (causal agent) |
Symptoms |
Survival of pathogen and effect
of environment |
Comments on control |
Bacterial leaf spot
(Xanthomonas campestris pv. begoniae) |
Circular, necrotic spots start as small, watersoaked,
blisterlike spots. Premature abscission occurs when spots are numerous. |
Systemic as well as in dead begonia leaves. Favored by
splashing water or overhead irrigation and high temperatures (80° to
90°F). |
Keep humidity low. Avoid wetting foliage. Do not crowd plants.
Remove and destroy infected plants. |
Gray mold
(Botrytis cinerea) |
Soft, brown rot of leaves, stem, and flowers occurs. Woolly
gray fungal spores form on decayed tissues. Fungus is common on weakened
plants. Botrytis may also start in powdery mildew spots, sunburned tissues,
tissues injured by other means, or in ligules. |
In plant debris; common on any dead plant material on soil if
moist. Resting sclerotia favored by high moisture conditions and low
temperatures. |
Control root rot and powdery mildew. Pick up dead flowers and
leaves. Keep humidity low. Protect plants with fungicide such as fenhexamide.
Avoid overhead irrigation. more info. |
Powdery mildew
(Erysiphe cichoracearum, Odium begoniae) |
White, powdery spots develop on upper and lower leaf surfaces
and small, greasy spots occur on undersides of leaves. Also may appear on
flowers of some fibrous begonias. |
On living begonia leaves; rarely as resistant fungal structures
(cleistothecia). Spores are airborne as well as spread in water, but do not
survive in free water. Favored by moderate temperatures and shade. Common on
plants as they senesce in fall. |
Increase air movement; some resistant cultivars available. Spray
at the first sign of mildew and at 2- to 3-week intervals thereafter.
Use fenarimol, myclobutanil, or triadimefon. Triadimefon is very effective
but expect stunting of some plants. more
info. |
Root and stem rot
(Pythium spp.) |
Plants are stunted, unthrifty, and may die. Root system is
small and discolored. Also invades tubers of tuberous begonias. Stem rot phase:
stems become water soaked and discolored, and collapse. Disease also causes
damping-off of seedlings. Plants are predisposed to sunburning. |
In soil. Spores spread in water and when infested soil is moved
to uninfested areas. Favored by excess water. |
Steam or chemically treat soil. Observe strict sanitary measures.
Drench plants with mefenoxam. Do not drench very young seedlings.
more info. |
| |
| Virus or viruslike diseases |
Symptoms |
Host range and natural spread |
Comments on control |
Spotted wilt
(Tomato spotted wilt virus) |
Rings or zoned spots develop on leaves. Plants are stunted;
flowers are of poor quality. |
In living begonias, nasturtiums, callas, dahlias, and
some weeds. Transmitted by thrips. |
Eliminate nearby weeds and susceptible ornamental plants.
Control thrips. |
Begonias are also susceptible to Armillaria root rot (Armillaria
mellea), anthracnose (Gloeosporium sp.), black root rot (Chalara
elegans), cottony rot (Sclerotinia
sclerotiorum), crown gall (Agrobacterium
tumefaciens), leaf nematode (Aphelenchoides olesistis), leaf
spot (Phyllosticta sp.), Rhizoctonia stem rot (Rhizoctonia solani),
root knot nematode (Meloidogyne
spp.), Sclerotinia rot (Sclerotinia sclerotiorum), soft rot (Erwinia
carotovora), and Verticillium wilt (Verticillium
dahliae).
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UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Diseases
R. D. Raabe (emeritus), Environmental Science, Policy, and Management (ESPM),
UC Berkeley
M. E. Grebus, Plant Pathology, UC Riverside
C. A. Wilen, UC IPM Program, UC Cooperative Extension, San Diego Co.
A. H. McCain (emeritus), Environmental Science, Policy, and Management (ESPM),
UC Berkeley
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