is a Plant Pathologist and President of Chase Research Gardens, Inc.
C.R.G. is a private research and consulting corporation specializing in
Both hourly and contract services are available.
You can reach C.R.G. at P.O. Box 168, Mt. Aukum, CA 95656 Phone and Fax:
916-620-1624 - E-mail: MTAUKUM@AOL.COM
Pathogen - High heat and/or light and lack of water
Symptoms - The bases of the flower buds appear dry and turn
tan to dark brown. Buds rapidly drop from plants without signs of
Control - Maintain adequate water especially when temperatures
rise dramatically or when light level suddenly increases. Plants
may be especially sensitive to dessication when conditions change
from cool and dark to hot and bright as can occur during the spring
Pathogen - High medium pH and/or low levels of iron available
Symptoms - High medium pH can induce deficiencies of manganese,
magnesium and most commonly, iron. This can result in interveinal
chlorosis of young foliage. As deficiencies become more severe,
necrotic spots will appear within the chlorotic tissue.
Control - Maintaining soil pH below 7 will improve the availability
of iron and manganese and slow the leaching of magnesium. Application
of the appropriate nutrient to the soil or potting medium will correct
this problem, but plant response tends to be slow. Foliar sprays
will hasten color improvement compared to soil application, but
use low rates of application rates to avoid phytotoxicity from the
leaf spot and petiole rot
Pathogen - Myrothecium roridum
Symptoms - Myrothecium leaf spot most frequently appears
on wounded areas of leaves such as tips and breaks in the main vein
which occur during handling. The leaf spots are watery and nearly
always contain the black and white fungal fruiting bodies in concentric
rings near the outer edge of the spot. They are seen on the leaf
undersides. The presence of these bodies is good evidence that the
cause is Myrothecium. Newly planted cuttings are especially susceptible
to this disease since they are frequently rooted under mist conditions.
Control - Iprodione (Chipco 26019 50WP) provides some disease
control. Preventive treatments to newly rooted cuttings may be required.
In addition, mancozeb (Dithane M-45) provides good control of the
leaf spot on some plants. Avoid wounding leaves and keep the foliage
as dry as possible.
stem rot and leaf spot
Pathogen - Phytophthora parasitica
Symptoms - This disease occurs primarily on plants grown
in or on the ground. Leaf spots are initially small and water-soaked,
with irregular margins. They may become tan and papery if conditions
are dry or their centers may fall out if conditions are wet. Stem
rot usually begins at the soil line where the stem becomes soft
and watery and lower leaves turn yellow. Eventually, the area becomes
sunken and a cavity may form and result in lodging of the stem.
Control - The combination product of thiophanate methyl and
etridiazole (Banrot), etridiazole (Terrazole and Truban), and metalaxyl
(Subdue 2E) provide disease control. Growing plants on raised benches,
away from the natural source of infection (the soil), is the best
way to avoid this disease. Due to similarities between this and
several other diseases, diagnosis must be confirmed by a diagnostic
laboratory before optimum control strategies can be chosen.
aerial blight or leaf spot
Pathogen - Rhizoctonia solani
Symptoms - Rhizoctonia aerial blight occurs primarily during
the summer months. Disease development can occur in less than a
week, so plants should be checked carefully and frequently. Brown
irregularly shaped spots form anywhere in the foliage, but most
commonly within the crown of the plant which is often wet. Sometimes
the first spots form near the top of plant confusing the source
of the disease (the soil). The spots spread rapidly and cover the
entire plant with the brown weblike mycelium of the pathogen.
Control - Since this pathogen inhabits the soil both the
roots and the foliage of the plants must be treated to provide optimal
disease control. A combination drench-spray will best accomplish
this. Thiophanate metyl compounds (Cleary's 3336 or Topsin M) and
chlorothalonil (Daconil 2787) are effective in controlling this