The success of a cherry harvest relies heavily on the precise timing of protective sprays, a concept known as phenology, which links application windows to the tree’s biological growth stages. Cherry trees are susceptible to various insects and diseases throughout the growing season, making timely treatment crucial. Applying treatments when they will be most effective against the target pest or disease life cycle is more important than product selection. This guide outlines the different stages of cherry tree development, from the dormant season to the final pre-harvest period.
Dormant Season Treatments
The earliest preventative treatments occur during the dormant season, typically in late winter or very early spring before any bud swell is visible. The goal of this application is to target pests and diseases that overwinter on the bark or in the buds. Dormant oil is applied during this time to smother overwintering scale insects, mite eggs, and aphid eggs before they hatch and begin feeding on new growth.
Horticultural oil must be applied when the tree is completely leafless and temperatures are above 45°F, with no risk of freezing overnight. Oil can damage tender green tissue and is less effective in extreme cold. Copper fungicides are often included in a dormant spray to reduce fungal spores and bacteria, such as those causing Bacterial Canker or Coryneum blight (shothole). Applying copper before bud break helps prevent these pathogens from establishing themselves in the spring.
Protecting Early Growth: Pre-Bloom Timing
The period from the first sign of green tissue until the flowers open is a high-risk time for disease development. This phase begins at the “green tip” stage, when the first quarter-inch of a developing bud shows green. It progresses through the “tight cluster” and “popcorn stage,” where flower buds are visible but have not yet opened.
Fungicide applications are crucial during this pre-bloom window, particularly to manage Brown Rot blossom blight and Cherry Leaf Spot. Prevention is necessary before the flowers open, as the Brown Rot fungus enters through the bloom. Initial controls for overwintered insects, such as aphids and leafrollers, are also timed for the delayed dormant or pre-bloom stage. These insecticide applications must stop completely once flowers begin to open to protect pollinators.
Fruit Protection: Post-Bloom to Harvest
The post-bloom stage, beginning at “petal fall” when 90% of the flower petals have dropped, signals the start of the primary insect control period. This is the first safe window to apply insecticides, as the risk to pollinating bees has passed. Key insect pests during this time include the Plum Curculio, which damages the developing fruit, and the Cherry Fruit Fly, whose larvae infest the cherry flesh.
The initial post-bloom spray often coincides with the shuck-split stage, when the dried flower parts fall off the tiny developing fruit. Subsequent applications, known as cover sprays, are needed every seven to fourteen days to maintain a protective residue as the fruit expands. Fungicide re-applications may be necessary if the weather remains wet, favoring the development of Cherry Leaf Spot and late-season Brown Rot. A key consideration for all sprays in this period is the Pre-Harvest Interval (PHI), the minimum number of days that must pass between the final application and picking the fruit.
Understanding Spray Safety and Pollinator Protection
Protecting beneficial insects, especially pollinators, is a primary concern when spraying cherry trees. The rule is to never apply insecticides during the active bloom period when flowers are open and bees are foraging. Even certain fungicides are noted to be toxic to bee larvae when fed tainted pollen, requiring careful product selection if a bloom-time fungicide is unavoidable.
Reading the product label is mandatory for any application, as it specifies the correct mixing ratios, required personal protective equipment (PPE), and environmental limitations. Spraying should be avoided when wind speeds are high to prevent drift onto non-target plants or pollinator foraging areas. It is advised to apply sprays in the early morning or late evening when temperatures are cooler and bees are not actively flying.