2.4 Flowering & Fruit Set

Question 1

When is Flowering and Fruit Set in the Northern Hemisphere?

Answer 1

May–June

Question 2

When is Flowering and Fruit Set in the Southern Hemisphere?

Answer 2

November–Decemeber

Question 3

What happens to buds during Flowering and Fruit Set?

Answer 3

• New buds develop at the base of the leaf stalks (petioles) on the new growing shoots
• Prompt buds will burst within the growing season producing new shoots called lateral shoots
• Compound buds will remain dormant until the following spring and provide the shoots for next year.

Question 4

What buds form and when do they burst?

Answer 4

• Prompt buds will burst within the growing season producing new shoots called lateral shoots
• Compound buds will remain dormant until the following spring and provide the shoots for next year

Question 5

What 4 factors can limit bud fruitfulness (the number of inflorescences that will develop from a bud) in the next growing season?

Answer 5

1. Shading of compound buds
2. Temperatures that are too low (under 25°C / 77°F)
3. Water stress
4. Nutrient deficiency

Question 6

Why is the flowering and fruit set period important for the next year’s yield?

Answer 6

• Shading of compound buds, temperatures that are too low (under 25°C / 77°F), water stress and nutrient deficiency can all limit bud fruitfulness (the number of inflorescences that will develop from a bud) in the next growing
• Each inflorescence will become a bunch of grapes next year

Question 7

Define Flowering.

Answer 7

Flowering describes the opening of the individual flowers within an inflorescence.

Question 8

Define Fruit Set.

Answer 8

Fruit set is the term used to describe this transition from flower to grape.

Question 9

How does a flower become a grape?

Answer 9

1. The pollen-laden stamens (consisting of an anther and filament) are exposed.
2. The pollen grains are shed and land on the moistened stigma surface, a process called pollination. Here, they germinate, with each pollen grain producing a pollen tube.
3. These pollen tubes penetrate the stigma and then the ovule (the female reproductive cells) in the ovary.
4. The pollen tube delivers the sperm cells, which fertilise the eggs in the ovule. This leads to the formation of a grape berry.
5. The fertilised ovules form seeds, with up to four per grape.
6. The wall of the ovary enlarges to form the skin and pulp of the grape.

Question 10

How are vines typically pollinated?

Answer 10

Cultivated varieties of vines are normally self-pollinating (the pollen from the stamens of one flower is transferred to the stigma of the same flower, or a different flower in the same plant)

Question 11

What conditions are needed for successful flowering?

Answer 11

Warm conditions (minimum temperature of 17°C / 63°F)

Question 12

What condition is not ideal for successful flowering? Why?

Answer 12

• Low temperatures
• Can lengthen the duration of flowering, with weeks passing between the earliest and latest flowering
• Uneven ripening

Question 13

How long after budburst does flowering typically occur?

Answer 13

Flowering typically takes place within eight weeks of budburst.

Question 14

What conditions are needed for successful fruit set?

Answer 14

Pollen germination requires warm temperatures (optimal at 26–32°C / 79–90°F).

Question 15

What percentage of flowers become grapes?

Answer 15

• Typically, 30%

- Can range from 0-60%

Question 16

What conditions are not ideal for successful fruit set? Why?

Answer 16

Cold, rainy and/or windy conditions

• Pollen tube growth negatively affected
• Irregular fruit set
• Key cause of poor yields in cool climates

Hot, dry, windy conditions

• Water stress
• Reduced yields

Question 17

What are the two common forms of irregular fruit set?

Answer 17

• Coulure

- Millerandage

Question 18

What is Coulure? Is it normal?

Answer 18

• A condition of the grape bunch in which fruit set has failed for a high proportion of flowers.
• Some coulure is normal; however, excessive coulure can reduce yield dramatically.

Question 19

What 4 grape varieties are more susceptive to coulure?

Answer 19

• Grenache
• Cabernet Sauvignon
• Merlot
• Malbec

Question 20

What causes Coulure?

Answer 20

Coulure is caused by an imbalance in carbohydrate levels.

• • Cold, cloudy conditions
• • Hot, arid conditions with high water stress

Vigorous shoot growth diverting carbohydrates from the inflorescence.

• • Very fertile soils
• • Heavy application of fertilisers
• • Vigorous rootstocks

Question 21

What is Millerandage?

Answer 21

• A condition of the grape bunch in which there is a high proportion of seedless grapes.
• The seedless grapes can still ripen normally, but are smaller than grapes with seeds.
• Millerandage may therefore reduce the volume of wine that can be produced.
• Some seedless grapes stay small, green and unripe, which can be negative for wine quality.

Question 22

What causes Millerandage?

Answer 22

Millerandage can result from cold, wet, windy weather at pollination and fruit set

Question 23

What grape varieties are more susceptible to Millerandage?

Answer 23

• Chardonnay

- Merlot