Peach trees and other crops have been exposed to a variety of factors this season that cause stress in trees. This stress often results in reduced yield, reduced growth, or even plant death. The following are some of the stresses that peach crops have experienced this season.
Peach growers and fruit crop specialists have noticed peach trees with sparse fruit load and considerable dieback of shoots and branches, including entire scaffold branches in many cases. Trees have also exhibited sparse leaf coverage for this time of year and leaves have been small. Shoot and branch dieback is a hallmark symptom of Armillaria root rot (ARR) (Figure 1).
The pattern in which the condition has occurred, however, indicates that conditions are not just related to ARR. Shoot dieback is also a symptom of another fungal disease known as phomopsis. This disease causes a canker that girdles the shoot and causes death to tissue beyond the point of infection. Disease Alert: Phomopsis Twig Blight Common on Peaches this Spring provides more information about phomopsis.
This season, peach trees on rootstocks are succumbing to diseases for which they have resistance or tolerance, such as peach tree short life (PTSL). Peach tree short life is caused by a combination of factors, one of which is ring nematode infestation of roots. This root feeding causes susceptible trees to be less tolerant of cold weather, which leaves the trees vulnerable to the development of bacterial canker. Bacterial canker is caused by the bacterium Pseudomonas syringae pv. syringae. A canker forms at the infection causing plant dieback beyond this point. Bacterial canker is lethal when it occurs on the trunk (Figures 2a and 2b). Learn more about bacterial canker in Bacterial Canker in Peach.
Another fungus known as Monilinia fructicola can also cause fruit dieback. This fungus causes brown rot in fruit that are nearly ripe or ones that are ripe on the tree or in storage. When conditions are more challenging, it can affect green fruit in a condition known as green rot. Monilinia fructicola can also affect the bloom stage similar to Pseudomonas by forming a canker at the base of a bloom. This is known as blossom blight. In response, an amber-colored gel will ooze from the base of the bloom (Figures 3a and 3b).
Rainfall occurred in excessive amounts in late 2019 and continued into the spring of 2020, which left standing water in orchards. Generally, peach roots are sensitive to standing water. It causes an increase in root diseases and death of root tissue because of the lack of oxygen in the soil. Excessive rains can spread spores of the Monilinia fungus creating a broader area of infection.
For dormant buds to become resistant to low temperatures, they must acclimate to the cold. This is accomplished by exposure of dormant buds to cool but not damaging temperatures. Late last year, high, summer-like temperatures stretched into the fall followed by an abrupt drop in temperature. The abrupt change did not allow buds to become sufficiently acclimated to cold temperatures. As a result, buds were likely damaged. Low temperatures occurring in February likely affected early blooming varieties. If buds were not destroyed, the effects of low temperatures can still be seen on some surviving fruit (Figure 4). Damage to fruit or shoots created by low temperatures can serve as infection routes for disease.
The less-than-optimal chill accumulation was not a significant factor when the chill portion accumulation is considered. However, when combined with other factors, a lack of chill can stress trees and further exacerbate other stresses. Additionally, lack of chill results in a protracted bloom period allowing blooms to be exposed to potential infection with brown rot. For more information on chill accumulation, see Fruit Culture in Alabama: Winter Chilling Requirements and Chill Hour and Chill Portion Comparison in Peaches.
When trees are stressed, they emit ethylene, which can be detected by insect pests, such as ambrosia beetles. Ethylene is a signal to these beetles that the tree is in a weakened state and is ideal to colonize. Growers can determine if they have ambrosia beetles if they see a protrusion of “matchsticks,” which are a combination of sawdust and beetle feces (Figure 5). This mixture is pushed out from holes created by the female beetle as she excavates a tree trunk or branch to create a place to lay eggs and raise young.
Peach tree borers also track stressed or declining trees, which provide an ideal location to lay eggs. For more information about ambrosia beetles, see First Ambrosia Beetles Discovered in Monitoring Traps in Chilton County in 2020.
Plan and Prepare
The most efficient way to reduce these factors is to have an orchard management plan before and after it is planted. Even the most careful planning cannot prevent all of the environmental pressures on crops. However, proper planning and adherence to established protocols can reduce the damage that results from these conditions.
- Site selection is important to the production and longevity of a peach orchard. Select land that is not prone to standing water. Placing an orchard on a sloped area that allows proper water drainage and cold air is important.
- Select the best trees for the area. For example, planting trees that have high chill hour requirements well beyond those the area is known for will result in trees that are in a continual stage of stress. Likewise, trees that have a chilling requirement that is too low will likely result in early blooms that become damaged by a late-season frost. For management and production of peaches, consult the most recent version of the Southeastern Peach, Nectarine and Plum Pest Management and Culture Guide.
- Apply insecticides and fungicides at the appropriate time to reduce or prevent the occurrence of these pests. Well-timed fertilizer applications will promote growth and better health of the trees.