FAQ: Plant Diseases

I want to grow beautiful tomatoes every year, but they always rot. What can I do?

Begin spraying the plants soon after first bloom with a good fungicide such as Bravo, Maneb, Mancozeb, or Zineb. Spray in the morning. When irrigating, never wet the entire plant. For complete pest control, mix Sevin and Cygon at the recommended rates with the fungicide and spray every seven days until you're tired of tomatoes.

What is the most common disease of turnips in the fall - early winter and how can it be controlled?

Cercospora or Cercospora-related leaf spot which is controlled by (1) removing damaged leaves (if possible) and application of protective sprays of Benlate or copper fungicide sprays.

What causes camellias to develop yellow ring spots on the foliage? Is it a serious problem and how can it be controlled?

A virus infection causes the problem. It is usually not a serious problem. It may cause some reduced growth. Virus infections are systemic and the only way to control the problem is to remove the infected plant(s).

Will Entomosporium leaf spot on photinia continue to spread during fall and winter?

Yes, especially if temperatures remain between 55-65 F and conditions are wet.

What is a common disease of sweet potaotes that causes brown or black superficial spots or blotches? Does this disease affect the edibility of the roots?

The disease is called scurf and it is caused by the fungus, Monilochaetes infuscans. The damage is only skin deep and it does not affect edibility of the roots.

What is an 'anthracnose' disease?

Anthracnose is usually a disease caused by a related group of fungi that all produce similar types of reproductive structures in the form of a pustule of spores (called an acervulus). Symptoms are typically leaf spots and blotches. Blotches often occur along the side of leaf veins.

What fungus is a common problem in greenhuses in the winter and causes a foliage blight?

Botrytis cinerea.

When house plants (or any plants) grow poorly and develop yellowed lower leaves, what is the usual problem?

Often the problem involves root damage.

What are some non-chemical methods that will help control the fungus disease in the previous question?

(1) Remove the damaged plant material. (2) Increase plant spacing and/or increase ventilation to decrease the relative humidity around the plants (3) Increase the temperature to 70 or above.

When green leaves develop brown leaf tips and/or leaf edges, what is often (but, not necessarily always) the cause?

The leaves are not receiving enough water to maintain a normal, healthy condition.

In the winter, geraniums may develop yellow spots on upper leaf surfaces with small brown corky, slightly raised spots on corresponding lower leaf surface areas. What causes this condition?

The condition is called oedema. It is caused usually after several cloudy days when roots absorb water normal for sunny days. On cloudy days, stomates are closed somewhat and transpiration (normal water loss through open stomates) is reduced. Leaf cells become too turgid and burst with resulting corky spots developing on lower surfaces. Irrigation should be reduced on cloudy days, if this is possible.