|
|
Bromine
toxicity
Pathogen - Excess bromine from foliar applications of Agribrom
Symptoms - Distortion and burning of new leaves especially.
Failure to root out and develop good shoot growth are also common.
The plants on the lower row in the figure were rooted with Agribrom
at 55 ppm while those on the upper row were rooted with water alone.
Control - Rates of Agribrom delivered in an overhead misting
system should stay be approximately 25 ppm bromine to insure benefits
of disease and algae control without causing bromine toxicity. Using
as little as 55 ppm bromine caused these symptoms. |
|
|
Cercospora
leaf spot
Pathogen - Cercospora spp.
Symptoms - Leaf spots appear very similar to those caused
by the bacterial pathogens. Laboratory culturing is required to
obtain an accurate diagnosis and design the appropriate control
program.
Control - Thiophanate methyl compounds (Cleary's 3336, Domain
and Topsin M 4.5F) are effective for control of Cercospora leaf
spot on many ornamentals. Be sure to direct the sprays to the lower
leaf surfaces in order to make contact with the spores and reduce
disease spread. Avoid using stock plants with a history of Cercospora
leaf spot. |
|
|
Choanephora
blight
Pathogen - Choanephora cucurbitarum or C. infundibulifera
Symptoms - Symptoms occur very rapidly on spent flowers.
The black spores of the pathogen form in the dead flowers and leaves
within a day of first symptom expression. Choanephora blight is
most common when conditions are very hot and light levels are high.
Control - There are no fungicides which are available for
this pathogen on hibiscus. When weather conditions are optimum,
plants should be examined daily and old flowers removed and discarded
to reduce spread of spores to adjacent plants. |
|
|
Root
rot
Pathogen - Fusarium, Phytophthora, Pythium or Rhizoctonia
spp.
Symptoms - This condition is usually not a problem once plants
are established in the landscape. In containers, plants are small,
unthrifty and can give the appearance of lacking fertilizer. Roots
should be examined to determine their health. Rotted roots are mushy,
wet and disintegrate when handled. They are also usually brown to
black. Since these symptoms can be caused by nematodes as well as
pathogenic fungi a laboratory diagnosis is required for best course
of treatment.
Control - Diagnosis of the causal organism is the most important
step toward control of root diseases. The combination product of
etridiazol and thiophanate methyl (Banrot 40WP and 8G) and iprodione
(Chipco 26019 50WP) are effective in controlling Fusarium and Rhizoctonia.
Metalaxyl (Subdue formulations), Banrot, fosetyl aluminum (Aliette
80WP) and etridiazol (Terrazole and Truban formulations) are all
effective in controlling Pythium and Phytophthora. |
|
|
Rust
Pathogen - Puccinia heterospora
Symptoms - This disease occurs only on Hibiscus syriacus
(rose of sharon, althea). Rust disease is easily recognized because
of the yellowish-tan pustules which occur on leaf undersides. The
spots first appear white or light yellow when viewed from the upper
surface. Most rust pustules form on the undersides of leaves but
some can be found on leaf upper sides.
Control - Rust diseases are inhibited by frequent rainfall
or irrigation and high temperatures. Fungicides for rust control
include chlorothalonil (Daconil 2787), ferbam (Carbamate), triadimefon
(Bayleton) and mancozeb (Dithane M-45 and Fore). |
|
|
Sunburn
Pathogen - Bright sunlight after long periods of cloudy days
or sudden exposure to direct sunlight following pruning.
Symptoms -Large areas of leaves become brown and dead. It
is common to find only a few leaves in the highest light affected
with surrounding leaves apparently undamaged. Sunburn usually appears
within a week of the damaging incident.
Control - Be careful to protect plants from sudden exposure
to bright light following pruning. Avoid drastic changes in the
plant canopy and those surrounding it by regular pruning. Since
the damage will not continue it can usually be tolerated or carefully
removed to improve plant appearance. |
|
|
Xanthomonas
leaf spot
Pathogen - Xanthomonas campestris pv. malvacearum
Symptoms - Foliar infections on hibiscus start as tiny pinpoint
water-soaked areas which can rapidly enlarge. They tend to remain
confined to the areas between leaf veins and sometimes have a bright
yellow border. In severe infections leaf drop is common. All hibiscus
species tested have been found susceptible to the pathogen, although
some cultivars are more resistant than others. Two other bacterial
pathogens can cause similar symptoms on hibiscus; Pseudomonas cichorii
and Pseudomonas syringae pv. hibisci.
Control - Minimize foliar wetting through irrigation or rainfall
to reduce spread of the bacterium and its ability to infect. Preventative
applications with copper containing compounds are sometimes helpful
but cannot control the disease under severe conditions. This disease
is more of a problem during the warm wet periods of the year. Never
use infected plants for cuttings even when the cuttings appear healthy
since latent infections will simply continue to develop as the cuttings
root. |
