Ready or not, spring is here!
Despite the recent cool weather, apple bud development has progressed rapidly over the course of the past two weeks. In Henderson County, most varieties are at pink to full bloom. Treatments to increase lateral branching on young apple trees are effective at this time. Below are recommendations for stimulating lateral branching on one and two-year-old wood.
Stimulating lateral branching on young trees: one-year-old wood
In recent trials in North Carolina, application of 6-benzyladenine based compounds (MaxCel®; Exilis® Plus; Exilis® 9.5 SC, etc.) to one-year-old wood has increased branching in young apple trees when applied after bud-break. The goal of this application is to minimize development of blind wood, particularly in high-density orchard systems. Methods of application can range widely, including spray application or more directed applications with a brush, roller, sponge, etc. A rate of 500 ppm (3.2 fluid ounces per gallon of water) has been effective in promoting branching on one-year-old wood.
Stimulating lateral branching on young trees: two-year-old wood
Inducing lateral bud break on two-year-old blind wood requires a combination of cultural and chemical practices. Research by Dr. Steve McArtney and J.D. Obermiller demonstrated that notching followed by a spray application of MaxCel® at 500 ppm was very effective in increasing lateral bud break on 2-year-old-wood of young apple trees.
Notching is imposed with a double-bladed hacksaw and a narrow strip of bark is removed (~4 mm) just above latent buds located on blind wood of the trunk (Figure 1). Immediately after notching, 500 ppm 6-BA is sprayed directly into the notch with a squirt bottle or backpack sprayer.
After shoots have developed from treated areas, a targeted application of 6-BA + GA4+7 (Promalin®, Perlan®, etc.) can increase shoot length and potentially increase bearing surface. This application occurs when shoots are ~ 1-2 inches long at a rate of 250 to 500 ppm.
**CAUTION** Do not impose notching/scoring treatments when conditions are conducive to fire blight infection. Notching may create sites for infection.
Early Thoughts on Thinning in 2017:
While there are some exceptions, most varieties appear to have a moderate to heavy bloom density in western NC. Considering this high blossom density and the favorable pollination conditions from 4/9 to 4/11, this may be a great year to thin early. If not already part of your thinning plans for 2017, I would consider adding a petal fall application of carbaryl to your thinning program.
A petal fall application of carbaryl has been recommended widely as a safe and effective early thinning strategy. Early thinning can confer significant benefits to apple growers including increased fruit size and improved return bloom. There is very little risk of over-thinning at this timing. When using a liquid formulation, use a rate of 1 pint per 100 gallons (4 lb a.i. per gallon product; equivalent to half a pound of active ingredient in 100 gallons).
Some growers may have concerns regarding carbaryl’s potential negative impacts on fruit finish with sensitive varieties, such as Golden Delicious. If this is a concern, you can: 1) keep the carbaryl in the shed, or 2) test carbaryl at petal fall on a small scale, until you gain confidence with this product/timing. Wait to apply carbaryl at 80% petal fall or later, since this product is toxic to bees. Do not apply carbaryl until bee hives are removed from the orchard. Also, consider making the application at the end of the day, when wild bees are not actively foraging.
As discussed by Dr. Mike Parker during the winter meetings, twelve weather stations are part of the Network for Environment and Weather Applications (NEWA) system in western North Carolina. Several decision making-aids are available with this system, including the Apple Carbohydrate Balance Model. This model was developed by researchers at Cornell University, uses temperature and light data to predict the daily carbohydrate balance of a model apple tree, and has been used to help inform thinning decisions. To use the model on NEWA, the user needs to enter dates for two stages of bud development: green tip and full bloom. As the season progresses, I plan to provide comments regarding model output and factors that are not accounted for in the model.