Recommendations for applying pesticides are usually listed by the stage of bud, floral, and fruit development. The reason for this is because certain pests and diseases are often prevalent at specific stages of plant development. Also, some pests are only problematic at specific range of temperatures or after a number of hours in a range of temperatures have accumulated. For example, streptomycin is only applied during bloom and petal fall for fire blight control on apple trees because this is when bees transfer the pathogen to the flowers during pollination and environmental conditions (temperature and moisture) are favorable for infection. Insecticide applications are often targeted to the insect stage when they are most susceptible. For instance, Lorsban insecticide is recommended to control the American plum borer on apple trees at petal fall which is generally the time of peak egg laying of the first brood. It is also important to know the bud stages because certain pesticides, such as dormant oil can cause foliar damage if applied at the wrong time. Lastly, as flower buds develop, they are more susceptible to spring frost injury. Thus, charts have been developed to predict the temperatures at which a range of injury will occur at each floral development stage and are listed in the 2015 Midwest Tree Fruit Spray Guide.
The table below summarizes the floral and fruit developmental stages used for applying pesticides for apple.Peach fruit bud stages for chemical applications include dormant, pink, full bloom, petal fall, shuck split, and fruit set, and are similar to those described for apple. Shuck split is when the dried floral remnant splits away from the developing fruit and is sloughed off after petal fall.
REVISED: April 27, 2015