Black Rot
Jim Kamas and Ed Hellman
Texas Cooperative Extension
Black rot of grape is an important fungal disease of American origin
that was probably spread to the Old World through the importation of phylloxera
resistant rootstock. Primary infection usually arises from infected fruit
from the previous season and all green tissue of the grapevine is susceptible
to infection. Brown circular lesions appear on infected leaves and within
a few days, black fruiting bodies are formed within the lesions. These
leaf lesions then become the primary source of infection to developing
fruit clusters. An infected berry first appears light brown, soon the
entire berry turns dark brown, and black pycnidia develop on its surface.
Infected berries shrivel, turn hard and black and are called mummies. The
black rot organism overwinters in mummified fruit on the vine and on the
ground. Spring rains trigger the release of airborne ascospores from mummies
and subsequent infection of susceptible tissue takes place if temperature
and duration of leaf wetness are conducive.
Pycnidia form within lesions and produce pycnidiospores that are spread
by rainfall. Leaf lesions are capable of producing spores and causing secondary
infection approximately five to seven days after they first appear. Control
of black rot is based on properly timed applications of fungicides.
Black Rot Infection Chart
Temperature
'C |
Temperature
'F |
Hours of leaf wetness required for infection* |
| 7.0 |
45 |
No Infection |
| 10.0 |
50 |
24 |
| 13.0 |
55 |
12 |
| 15.5 |
60 |
9 |
| 18.5 |
65 |
8 |
| 21.0 |
70 |
7 |
| 24.0 |
75 |
7 |
| 6.5 |
80 |
6 |
| 29.0 |
85 |
9 |
| 32.0 |
90 |
12 |
*R.A. Spotts, Ohio State University
*Note that at 55'F, it takes 12 hours of leaf wetness
for infection to occur, but only 6 hours at 80'F. Most fungicides are protectants
and must be applied before an infection period to provide effective control.
Fungicides that provide "reach-back" properties must be applied within
a specific time period after the infection period starts. Site selection,
row orientation and canopy management techniques that increase airflow
and decrease canopy-drying time can be beneficial in a black rot management
program.
Symptoms
Leaf spot with ring of black spore-producing bodies
|
Fruit infections at varying stages
 |
Chemical control
See the Fungicide Efficacy Table for comparisons of various labelled fungicides.
