WHY DOES APPLE FRUIT DROP BEFORE HARVEST?
Apple fruit drop is relatively common in apple trees. However premature apple fruit drop is a serious threat to all the commercial growers. Normally apple trees naturally thin itself by dropping excess fruit prior to harvest. There are two drop periods normally which occurs on apple. The first drop period occurs after petal fall and continues for 3 to 4 weeks. The second drop period occurs when fruits are 1.5 to 2 inch in diameter. This drop is due to the competition among developing fruits for carbohydrates and water. It is a natural process referred to as June Drop occurring in mid may till late June in the areas of Himachal Pradesh.
- Natural Drop due to over crop,
- Insufficient or poor pollination,
- High ethylene levels,
- Moisture stress,
- Pests injury,
- Poor tree nutrition,
- Young trees,
- Weather conditions.
The main reason of apple fruit drop is overbearing of apple fruits, if there are too many fruits on the tree, tree drops fruit. Trees drop these fruits to protect their branches, if fruit remains on tree till harvest the branches will break. Fruit drop is often due to the competition of the developing fruits for nutrients and water, excessive fruits drops down and allows the remaining fruit to develop properly. It is recommended to do early thinning in order to avoid biennial bearing.
It is also a major cause resulting in fruit drop. Insufficient pollination means lesser pollen grains traveling to destination flower. It is caused when there are few pollination helpers like bees, or the pollinators are planted too far apart. It is recommended to place bee hives in orchard during bloom and pollinators should be planted more in number and near to main apple cultivars.
HIGH ETHYLENE LEVELS
Ethylene is a ripening hormone of apple plants. Ethylene promotes ripening process and is responsible for the formation of abscission layer in fruit stem. This abscission layer loosens the fruit stem from its node. So it is advised to spray NAA @ 15 ppm before 20-25 days prior to harvest to control premature fruit drop.
Apple drop due to moisture stress is more common in lower altitudes and areas with no irrigation. It is recommended to irrigate dry areas and to maintain moisture in the soil by doing mulching.
Insects and mites chew the leaf tissue and reduce the capability of the leaves to make food for the fruit. Pest’s injury reduces the carbohydrates availability causing premature fruit drop. It is recommend to control mites population and manage other leaf chewing insects in time.
POOR TREE NUTRITION
Improper nutrition is yet another reason responsible for premature fruit drop. Incorrect nutrition levels like low magnesium and high potassium levels in the soil can result in apple fruit drop. It is recommended to analyze the soil first and correct the nutrient deficiency accordingly.
Apple fruit dropping is more common in young trees. It is due to the reason that the fruits in young trees compete for carbohydrates from the shoots and roots. The problem gets itself solved when trees gets mature.
Unfavorable weather conditions can also result in apple fruit drop. Wind storm and hail storm can cause fruit drop and other types of damages to the fruit. It is recommended to put hail nets to the orchards prone to hail storm.