Botrytis Symptoms on Citrus

The fungal pathogen, Botrytis cinerea can infect citrus trees through flowers, fruits or shoots and can cause die-back on shoots as well as post-harvest fruit decay. Infection usually occurs through injuries or wounds on leaves or shoots or it first occurs on fruit or flowers and then moves into the shoots. Infected tissues wilt and die, which is followed by gray spores that serve as inoculum to infect other plant tissues.

Infected flowers wilt and die, causing drops in fruit yield. Immature fruit can also be damaged. Sometimes symptoms become more recognizable post harvest, during storage. Botrytis cinerea related diseases are often referred to as “gray mold” on and are easily recognizable for the velvety gray spores that form on infected areas. These spores are not always present early on after infection. Botrytis infected areas on fruit may also appear soft and brown with brown or gray bumps and irregular scars. Fruit injury on more mature fruit can result in ridges on the fruit surface.

Conditions for Infection

The optimum conditions for growth and development of Botrytis cinerea are cooler, wet conditions. Usually prolonged wetness is needed for infection to occur. The Pest Prophet can help to monitor weather conditions to assess risk for Botrytis cinerea infection, based on localized weather data. This can be helpful in determining risk of Botrytis epidemics occur and may be used to optimize preventative fungicide sprays, if necessary.

Post-harvest storage conditions can also affect severity of disease symptoms. Moderate temperatures and higher humidity storage conditions are optimum for growth of this disease on infected fruit.

Botrytis Disease Management

Botrytis related disease are not usually very common or economically damaging to citrus orchards, but if optimum weather conditions are met and sufficient inoculum is present, it can cause fruit yield loss, or reduced fruit quality. Lemon tends to be more susceptible than other citrus crops.

Avoiding mechanical injuries or frost damage can help reduce the numbers of infections that can occur. During periods of prolonged wetness during cooler times, preventative fungicides (such as copper) may be needed to prevent infection on blossoms or fruit. Infected fruit should be culled and removed from field and infected shoots should be pruned and removed from the field. These steps will reduce the amount of inoculum present in the field and help prevent infection on other trees.

To avoid post-harvest infection or disease spread, fruit should be stored in dry a place, or post-harvest fungicides can be used in cases where infection may be widespread.

Learn More: Complete Guide to Botrytis (Gray Mold)

Sources:

Post-harvest diseases of citrus fruits. Eckert J W. Outlook on Agriculture. 1978.