Flowering and Fruit Set

Question 1

When is flowering and Fruit set in the Northern hemisphere?

Answer 1

May-June (5-6)

Question 2

When is flowering and Fruit set in the Southern hemisphere?

Answer 2

November-December (11-12)

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 next year’s yield?

Answer 6

• shading of compound buds, temps that are too low, water stress, and nutrient deficiency can all limit bud fruitfulness in the next growing season
• each inflorescence will become a bunch of grapes next year

Question 7

Define flowering

Answer 7

the opening of the individual flowers within the inflorescence

Question 8

Define fruit set

Answer 8

the transition from flower to grape

Question 9

How does a flower become a grape?

Answer 9

1. the pollen-laden stamens (consisting of a filament and anther) 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, which leads to the formation of the grape berry
5. the feritilised 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 are 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, with a 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

within eight weeks of budburst

Question 14

What conditions are needed for successful fruit set?

Answer 14

Pollen germination requires warm temperatures

• optimate 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?

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

Which four grape varieties are more susceptible to coulure?

Answer 19

• Grenache
• Cab Sauv
• Merlot
• Malbec

Question 20

What causes Coulure?

Answer 20

An imbalance in carbohydrate levels

• cold, cloudy conditions
• hot, arid conditions with high water stress

Vigorous shoot growth diverting carbohydrates from the inflorescences

• very fertile soils
• heavy application of fertilizers
• 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 negatively impact quality

Question 22

What causes Millerandage?

Answer 22

Cold, wet, windy weather at pollination and fruit set

Question 23

Which grape varieties are more susceptible to Millerandage?

Answer 23

• Chardonnay
• Merlot