Pollen Tube Growth Model For Apple Blossom Thinning

Sherif M. Sherif, PhD

Alson H. Smith Jr. Agricultural Research and Extension Center

Email: ssherif@vt.edu

Tel. 540-232-6035

3-25-2019

The PTGM is now available on NEWA website : http://newa.cornell.edu/

You need to create a block for each

Variety or location The model is available for the

seven listed varieties only.

Only weather stations connected to NEWA are listed here. Choose the

nearest one to your location

After creating the block, style length and

start data should be entered.

Style length (mm) can be inserted as an average length (based on 15-20 flowers), or as individual value for

each flower. The model will calculate the average.

Measuring Style LengthA) Collect 15-20 open

king blossoms for measuring style length

B) Anthers and petals should be removed as

shown above

C) For measuring styles without removing from tree, measure the longest style as

shown.

D) For detached flowers, cut at the location shown above,

and measure only the longest style for each flower

sampled.

A) The start date is determined based on the

percentage of flowers needed to keep a crop.

A) Both day and time should be determined.

When to start the model?A) When you have open blossoms, and good bee activity.

B) Assess the frost damage, if any. Don’t apply blossom thinners if

you have more than 20% damage (2 out of 10 flowers with signs of

frost/freeze injury).

C) Depending on the desired crop load, and how heavy is the

bloom, you should start the model when you have 30-80% of kings

open. In other words, 3 out of 10 clusters with kings open (30%)

or 8 out of 10 clusters with kings open (80%).

D) Is some doubles are desired, or post-bloom thinners will be

applied, you can start the model at 40% full bloom.

Brown or dark brown center of the flower is the typical sign of frost/freeze damage

https://www.canr.msu.edu/news/assessing_frost_and_freeze_damage_to_flowers_and_buds_of_fruit_trees

The start Date

The date of the first thinning spray is when

pollen tubes reach 100% growth

The first thinning spray

If more thinning sprays are required, you can set 2nd or 3rd

spray

The second and third thinning sprays are applied when pollen tubes reach less than 100% growth (e.g. 60-70%)

The second thinning spray

Blossom Thinning Products for Virginia

• Lime Sulfur Solutions• Rex Lime Sulfur Solution

• 28% Calcium Polysulfide

• Registered in VA

• NovaSoure Lime-Sulfur Solution• 29% Calcium Polysulfide

• Registered in VA & NC

• Spray Oils• Can be combined with LSS

• Increase thinning efficacy

• Dormant & summer spray oils

• Biocover, Damoil, etc.

• Fish oil (organic)

What Rates Should be Used?

• Lime Sulfur Solution Rates (Rex & NovaSource)

• Easy to thin Varieties

• Without oil = 4% - 10%

• With oil = 1% - 2%

• Hard to thin Varieties

• Without oil = 6% - 12%

• With oil = 1% - 3%

• Spray Oils

• 0.5% - 2%

• Depends on oil type