| HOST PLANT |
DISEASE |
SYMPTOMS |
MANAGEMENT |
Crabapple,
Ornamental
Malus spp. |
Black rot canker, Botryosphaeria obtusa |
Cankers develop on limbs esp. at wounds, enlarge during the
growing season, and may grow for one or more seasons. Dead bark remains
attached for 1 year or more then slowly falls apart. |
Plant only fully hardy trees and prevent stress, esp. from
drought. Remove dead and cankered branches.
CHEMICAL: None. |
| Cedar-apple rust, Gymnosporangium sp. |
Yellow/orange spots on leaves, petioles, fruits. Tiny white
tubes or cups form on under surface of other plant parts. Spores produced
in these tubes infect the alternate host, juniper species. |
Where feasible, remove alternate host (junipers) within 1
mile or remove brown galls from nearby junipers. Use resistant
varieties.
CHEMICAL: Chlorothalonil, fenarimol, mancozeb, maneb,
myclobutanil, propiconazole, or triadimefon beginning when orange masses
are present on juniper. |
| Fireblight, Erwinia amylovora |
Succulent tissue and flowers turn dark brown to black.
Yellow/tan droplets of bacterial ooze may be present. Can spread into
woody tissues causing cankers and branch dieback. Common following warm
rainy weather. |
Plant resistant varieties. Avoid excessive use of nitrogen.
Remove and destroy all diseased branches in early spring (before March 15)
or late fall.
CHEMICAL: Copper. |
| Frog-eye leaf spot, Botryosphaeria obtusa |
Leaves have circular spots with indefinite purple margins
becoming brown spots with abrupt margins. Some may enlarge giving the
lesion a “frog-eye” appearance. Severe infection may cause yellowing and
defoliation. (See black rot canker above.) |
Rake up infected leaves. Remove black rot cankers. Grow
fully hardy tree species and manage to minimize stress.
CHEMICAL:
Seldom necessary. |
| Powdery mildew, Podosphaera leucotricha |
White powdery patches on leaves, esp. underside. Twigs,
blossoms, and fruits may also become infected. Terminal growth stunted.
Infected fruits exhibit light brown russeting. |
Remove and destroy infected shoots as they appear early in
the season. Prune to allow for good air circulation. Not
common.
CHEMICAL: Fungicides are seldom necessary. Triforine, wettable
sulfur (can russet fruit), fenarimol, myclobutanil, propiconazole or
triadimefon. |
| Scab, Venturia inaequalis |
Initially watersoaked lesions, esp. along the veins which
turn olive-brown to black and may appear fibrous. Foliage yellows and
drops. Fruits develop scabby lesions which may appear corky. |
Use varieties with resistance. Apply nitrogen (urea) to
fallen leaves in the fall to enchance decomposition or remove fallen
leaves to reduce disease pressure. Prune for good air
movement.
CHEMICAL: Captan, triforine, lime sulfur (fruit injury on
some varieties), dodine, maneb, benomyl (do not use alone),
thiophanate-methyl (do not use alone),wettable sulfur (may cause
russeting), myclobutanil, propiconazole, fenarimol plus captan, ferbam,
mancozeb, chlorothalonil, zyban and propiconazole. |
