Respuesta :
black spot is a plant disease caused by the fungus Diplocarpon rosae. It is the primary
cause of rose defoliation in the Midwest. Over time, repeated defoliations can weaken the
plant, reducing flowering. Severe defoliations that result in a loss of most of the leaves, and
repeatedly occur, predisposes the plant to insect attack, other diseases, winter injury, and
even death.
Symptoms
Roses infected with black spot primarily develop dark spots on the upper leaf surface in
the late spring (Figure 1). Some of these spots occasionally develop feathery edges and can
expand up to 1/2-inch in diameter. The leaf spots may also have yellow halos surrounding
them. With severely infected plants, the leaves may turn yellow prior to leaf drop. In severe
cases, the canes may have small purplish spots on the current year’s growth.
Disease Cycle
The disease cycle typically begins on fallen
leaves or canes that were infected the previous
season. Rain or sprinkler irrigation splashes
fungal spores from infected leaves that were shed
the previous year to the plant’s lower leaves. The
spores must remain wet for several hours for
infection to occur. Symptoms can become visible
within 72 hours after infection during warm,
wet weather, and a secondary infection cycle can
develop within 10 days after the initial infection.
The fungus that causes this disease tolerates a
wide range of temperatures, and symptoms can
continue to develop all season long if moisture
is adequate. The fungus overwinters in infected
canes and fallen leaves