Container Gardening Complete

Job:06-700309 Title: CPS - Container Gardening Complete

700309 - ContainerGardens_001-272_FINAL.indd 206 5/24/17 12:20 PM
Job:06-700309 Title: CPS - Container Gardening Complete
Job:06-700309 Title: CPS - Container Gardening Complete

700309 - ContainerGardens_001-272_FINAL.indd 207 5/24/17 12:20 PM

206 chapter 4

Cercospora Leaf Spot

(Cercospora spp.)

Description: The first sign of this fungal disease

is small circular, yellow lesions on the lower

foliage. Eventually the lesions develop a soft gray

fuzz at the center with a dark brown ring around

the exterior. Sometimes concentric rings appear.

The disease is sometimes also called “frog eyes”

because of this. In severe infestations, defoliation

may occur and fruit size and production may

be reduced.

Plants affected: There are many different species

of this fungal pathogen, and each species affects

a different species or group of plants. Common

hosts include hydrangeas, beets, eggplants, okra,

carrots, roses, beans, peppers, and figs.

Solution: Cercospora leaf spot survives the

winter in plant debris, and when spring arrives

the spores are spread by wind, rain, people, and

animals. To keep spores off plants, clean up

and dispose of infected leaves and fruits at the

end of the season and wash all pots with a 10%

bleach solution. Cercospora leaf spot is mostly an

aesthetic issue for home gardeners and fungicide

use often isn’t necessary.

Fusarium Wilt

(Fusarium oxysporum)

Description: Fusarium wilt symptoms often begin

with drooping leaf petioles. Sometimes a single

branch may wilt before the rest of the plant.

Wilting often starts with the lower leaves, quickly

progressing up the plant until the whole thing

collapses. The entire plant may be killed, often

before the plant reaches maturity. If you cut the

main stem of an infected plant, there will be dark

streaks running lengthwise through the stem.

Dark brown, sunken, cankers may be seen at the

base of the plant.

Plants affected: A broad range of plants can

succumb to fusarium wilt, including tomatoes,

eggplants, potatoes, daffodils, legumes, cucumbers,

melons, as well as certain ornamental plants.

Solution: The fusarium fungus survives in the

soil for several years and is spread by equipment,

water, and plant debris. Like many other diseases,

it favors warm soil and high moisture. Fusarium

wilt is typically not problematic in container

gardens, as long as the containers are disinfected

with a 10% bleach solution at the start of the

growing season and a fresh potting soil/compost

blend is used to fill the container each year.

Verticillium Wilt (Verticillium spp.)

Description: Verticillium wilt is caused by a group

of soilborne pathogens that block the vascular

system of the plant, causing it to wilt. Symptoms

progress slowly; often the foliage on one branch

wilts suddenly. As the disease progresses, the

plant turns yellow and withers, one branch at a

time. Eventually, the entire plant dies. Cutting

through the main stem of the plant will reveal

dark brown discoloration inside. Symptoms are

most likely to appear in July and August.

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Troubleshooting 207

Plants affected: Verticillium wilt affects hundreds

of species of vegetables, herbs, flowers, and woody

trees and shrubs.

Solution: Verticillium fungi can survive for

many years in the soil and on plants. They prefer

slightly cooler summer temperatures (between

70 and 80°F). Because this organism resides in

the soil, changing the potting soil/compost blend

in your containers every year will suppress it.

Also, clean containers with a 10% bleach solution

before filling and planting them. Plant resistant

varieties whenever possible, as there are no

effective fungicides.

Basil Downy Mildew

(Peronospora belbahrii)

Description: Basil downy mildew is a recently

introduced disease that’s incredibly destructive

to its namesake herb. First found in Florida in

2007, basil downy mildew has since spread across

much of North America. The fungus is air-borne,

seed-borne, and tissue-borne, making it extremely

easy for the disease to spread via contaminated

seed, plants, or air currents. Because this disease

looks at first like a nutritional deficiency or a

spider mite infestation, it’s difficult to diagnose.

Basil downy mildew first appears as pale yellow

mottling between the veins on the upper leaf

surface and miniscule purplish-gray spores

splattered on the lower leaf surface. The disease

eventually progresses to dark brown to black

irregular splotches and mottling on the leaves.

You’ll also see the powdery, dark gray spore

clusters on the leaf undersides. The disease does

not live in the soil.

Plants affected: Basil.

Solution: Start battling this disease by planting

only basil varieties with some resistance. Studies

have shown that all sweet basil varieties are

highly susceptible. Lemon, Thai, ‘Red Rubin’,

‘Spice’, and ‘Red Leaf’ basils were noted as being

the least susceptible. Breeders are currently trying

to breed resistance into new basil varieties. Be

sure to properly space the plants, and remove

and throw out any plants with a suspected

infestation immediately. Organic fungicides are

also an option, though they must be applied early

and often, and as soon as symptoms are noticed.

Potassium bicarbonate–based fungicides have

been shown to be effective against the fungus.

The first signs of a basil downy mildew infection look

a lot like a spider mite infestation. Pale yellow mottling

between leaf veins and tiny purplish-gray spores on

the leaf undersides are identifying features.

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