Deterioration of Stone Fruits Due to Brown Fungus

Deterioration of Stone Fruits Due to Brown Fungus

In the world of stone fruit cultivation, one of the most destructive diseases is brown rot, caused by the fungus Monilinia fructicola. This disease poses a significant threat to peaches, plums, nectarines, apricots, and cherries, especially just before ripening, during and after harvest.

The brown rot fungus survives the winter in mummified fruits and in twig and branch cankers produced the preceding year. During moist periods in May and June, masses of conidia are produced on the newly cankered twig surface. These spores are carried by wind to open or unopened blossoms and young shoots, infecting fruit and causing soft brown spots that rapidly expand and produce a tan powdery mass of conidia.

Any type of injury to the fruit provides entry points for brown rot spores. Infected blossoms soon wilt and tan-gray tufts, composed of masses of another type of spore (conidia), develop on the outside of the flower shuck. The entire fruit rots rapidly, then dries and shrinks into a wrinkled "mummy."

Under favorable conditions, the entire crop can be rotted on the tree. Insect and hail wounds, fruit cracking, limb rubs, twig punctures, and a variety of picking and packing injuries greatly increase the losses due to brown rot.

Effective control methods for brown rot disease in stone fruits involve a combination of cultural practices, sanitation, fungicide applications, and resistant varieties.

Key strategies include:

1. Sanitation: Regularly remove and destroy mummified fruits and infected plant material (such as dead branches and cankerous twigs) from trees and orchard floors. This reduces overwintering inoculum of the fungus, which helps control the spread of the disease.
2. Pruning: Prune during the dormant season to remove infected wood and improve airflow within the canopy, which reduces humidity favorable to fungal infection.
3. Fungicide applications: Apply fungicides at critical growth stages such as petal fall, fruit set, and preharvest (7 to 0 days before harvest). Effective fungicides for conventional orchards include Merivon, Topsin-M, and OSO; organic options with evidence of efficacy include Cueva, AVIV, Serenade OPTI, and Cinnerate.
4. Orchard management: Maintain orchard hygiene by flail-mowing floors to remove debris, scout regularly for cankers and twig dieback, and monitor for fungicide resistance to ensure effective chemical control.
5. Varietal selection and growing conditions: Plant recommended peach and nectarine varieties suitable to your region and provide optimal growing conditions to reduce disease susceptibility.
6. Integrated approaches: Combine cultural methods with biological controls and targeted pesticide applications for sustainable management, including pruning to improve airflow and applying fungicides based on weather conditions conducive to disease.

Peaches not kept in cool storage may be rotted in two to three days by the fungus. Brown rot conidia can germinate and infect at temperatures of 32 to 90 degrees F. Wet weather and temperatures ranging from 60 to 70 degrees F are most favorable for disease development. These summer spores are easily detached and are mainly wind-borne, also splashed by rain or carried by insects to the growing fruit. If a film of water is present for 5 hours or longer, the spores can germinate and penetrate the plant.

Together, these integrated practices reduce the likelihood of infection during the growing season and postharvest, thereby minimizing losses due to brown rot in stone fruits. It's essential for growers to implement these strategies to protect their crops and ensure a successful harvest.

Scientific advancements in pest management have led to the development of integrated strategies to combat brown rot in stone fruits. These include sanitation measures such as removing mummified fruits and infected plant material, pruning during the dormant season, and applying fungicides at critical growth stages. Nutrition plays a role in maintaining producing healthy stone fruits, as optimal growing conditions reduce disease susceptibility. Fitness and exercise are also important for growers, as regular scouting and maintenance are essential components of brown rot management. Medical-conditions, such as fungicide resistance, need to be monitored to ensure effective chemical control. Health and wellness of the orchard can be improved through integrated approaches combining cultural methods, biological controls, and targeted pesticide applications for sustainable management.

Read also: