Precision Crop Load Management - A New Concept

The crop load on each tree will be a key factor in the success of your apple crop. The crop load affects fruit size, fruit colour, spray penetration, evenness of maturity, ease of harvest as well as return bloom next year. Each year, we try to reduce crop load through chemical thinning and follow-up hand thinning. However, sometimes the results are disappointing, and at times, disastrous.

Recently Dr. Terence Robinson and the Cornell Fruit Team hosted an Apple Summit on Precision Orchard Management. One of the 8 sessions focused on Precision Crop Load Management, and growers were keenly interested to learn how to better manage their crop loads. A 6-step process was proposed to achieve the proper crop load and maximize profits. It is most suitable for use in high density Tall Spindle orchards, but these principles apply to all orchards.

Since 2000, Dr. Terence Robinson and Dr. Alan Lakso have been working on developing a model to explain how trees respond to thinning. The Carbohydrate (CHO) Model (which is renamed Malusim) uses weather data to calculate the CHO balance of the tree, which helps predict how susceptible the tree is to thinners. Sunlight and warm temperatures increase the tree's CHO balance, and make it resistant to thinners. On the other hand, cloudy, cool weather decreases the tree's CHO balance, and makes it more susceptible to thinners. This helps decide which day is best to apply thinners and what rate to use. We are working to get this model in Ontario.

Dr. Duane Green from Massachusetts has also been studying thinning response for many years and has proposed a Fruitlet Growth Model. By comparing fruitlet size at 3- and 7-days after thinning, you will know the results of chemical thinning within 7 days of application. Fruitlets that keep growing will stay, and fruitlets that stop growing will drop. The results are known days before fruitlets start to change in colour or appearance. We have a spreadsheet to enter your data after measuring fruitlets.

Both of these models are used to make decisions in Steps 2-5 of the Precision Crop Load process. Here are the proposed 6 steps:

Step 1: Precision Pruning (leave 2x the number of buds needed)

  • use Malusim to determine rate for Step 2

Step 2: Bloom thinning spray (60-80% full bloom)

  • use Malusim to determine rate and timing for Step 3

Step 3: Petal fall thinning spray (5-6 mm)

  • check results with Fruitlet Growth Model
  • use Malusim to determine rate and timing for Step 4

Step 4: 10-13 mm thinning spray (if needed)

  • check results with Fruitlet Growth Model
  • use Malusim to determine rate and timing for Step 5

Step 5: 16-20 mm thinning spray (if needed)

  • check results with Fruitlet Growth Model

Step 6: Precision hand thinning

There are many benefits to Precision Crop Load Management including:

  • Energy directed to fewer buds - early removal at dormant, bloom and petal fall
  • Low risk of over-thinning at bloom and petal fall
  • Prediction of optimum rates of chemical thinners using Malusim
  • Information to correctly time sprays to avoid over-thinning or under-thinning
  • Early assessment of thinning results using the Fruitlet Growth Model
  • Reduced costs for hand thinning
  • Less risk of biennial bearing due to enhanced return bloom
  • Increased profits due to matching fruit size to your markets.
  • Larger fruit, since energy is focused on remaining buds
    ? Reduced harvest costs due to reduced sorting of undersized fruit

Many of the Summit participants plan to try these techniques this year. Further testing and research is needed to assess these steps under Ontario conditions, so it is best to test new techniques on a small acreage. Always, always: leave untreated trees, take many observations, and write it all down for future years.

Using Precision Crop Load Management takes us closer to managing our trees at the level required to maximize yields and profits. We know that each year, thinning is a learning process, and no doubt this year will be as well, but we have new tools to help us achieve the results we want.


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca