Terminal Bud Set in Apples: Time to Sample for Plant Tissue Analysis and Apply Calcium

by: Amanda Green, Tree Fruit Specialist, OMAFRA                                             Christoph Kessel, Nutrition (Horticulture) Program Lead, OMAFRA

 Terminal buds have started to set in mature trees and will be starting to set in younger trees now until the end of July. Terminal bud set is when the current season’s vegetative growth stops and a bud is formed at the end of the branch. There are two things to think about at this stage and that is to collect leaf samples for tissue sample nutrient analysis and foliar calcium applications.

Tissue Sample Nutrient Analysis

It is best to do plant tissue analysis at terminal bud set because some nutrient levels are very variable throughout the growing season but at terminal bud set, the nutrient concentrations are the most stable and it is the standard time for sampling.

• Sample 10 leaves from 10 representative trees.
• Sample from the same trees each year.
• Sample trees separately from areas that you would sample your soil or manage your fertilizer separately.
• Avoid collecting damaged or abnormal leaves.
• Collect tissue samples into labelled paper bags and deliver right away.
• If you can’t deliver right away, dry the leaves in the sun or in an oven at 65°C or less.

Remember, plant tissue sampling does not replace soil testing, the results are the most useful with a visual assessment of the crop and soil conditions and a recent soil test.

Foliar Calcium Application

If you are planning on applying calcium, now is the time to start foliar applications (Table 1). Calcium is a nutrient that moves with the xylem which transports water to fully developed leaves. It is not mobile in the phloem, which transports sugars from photosynthesis to new growth and fruit. Because xylem transport is limited to the fruit, there is difficulty obtaining sufficient calcium in the fruit. Most calcium flows into the fruit 4-6 weeks after bloom and starts to decline after that. Calcium deficiency is associated with bitter pit and cork spot (Figure 1).

Figure 1. Bitter pit symptoms. (Source: OMAFRA Factsheet 00-009, Bitter Pit Control in Apples)

Table 1. Calcium Foliar Sprays (Source: OMAFRA Publication 360)

Timing	Product	Rate	Notes
Four sprays spaced two weeks apart beginning in mid-July. Additional sprays can be applied up to harvest.	Calcium chloride* (77% flakes)	5 kg/1,000 L water	Not recommended on McIntosh or Idared. Wet tree to point of runoff. Pesticides may not be compatible – check label.
	Calcium nitrate	9 kg/1,000 L water	Use only if leaf nitrogen is low. Do not apply later than the end of July. For pesticide compatibility consult labels.
	Other formulations including chelates	Consult label

* When using calcium chloride, mix required calcium in a pail of water first to be sure all product is dissolved before adding slurry to spray tank.

For further information please consult the OMAFRA Publication 360 Guide to Fruit Production.

See factsheet http://www.omafra.gov.on.ca/english/crops/facts/00-009.htm for more information on controlling bitter pit in apples with calcium.