Why plums fall off and what to do

Plum

Plum is a fruit tree that requires attention from gardeners. When plums drop unripe fruit, deciding what to do, what to feed them, and whether fertilizing is necessary is a decision made only after identifying the exact cause of the plant's condition. Plums only drop fruit when proper agricultural practices are violated, pollination is insufficient, or the tree is affected by disease or pests. This problem is common; almost every gardener has observed it.

Common causes

When plum trees are covered in blossoms in spring, gardeners hope for a good harvest, but the plant can drop ovaries and fruits before they're fully ripe. There are many factors that can cause plum fruit drop, ranging from gardener-inappropriate practices to those that are largely unrelated. The most common causes are as follows:

lack of watering or overwatering;
deficiency or excess of nutrients in the soil;
attack of harmful insects;
disease affection;
lack of pollination.

Attention!

It is difficult to determine the exact cause "by eye", but it is possible to narrow down the possible range of provoking factors if you pay attention to the period when the plum fruits fall.

The plum tree froze over

Plum trees bloom around the end of April or the first days of May. Often, only a few flowers develop into ovaries, or they fall off completely before the fruit tree's flowering phase is complete. This is often due to frost damage caused by late spring frosts. This situation is common in temperate climates, where sudden cold snaps can occur even at the end of the spring season. Plums are heat-loving plants and are sensitive to adverse conditions. You can tell that the tree has been frost-damaged as early as the beginning of flowering—when the stamens and pistils of the flowers turn brownish, indicating frost damage.

Plum trees can freeze during the winter season, which happens when gardeners plant varieties that aren't zoned for the season. These varieties, with frost resistance below average winter temperatures, freeze, causing damage to the bark, fruit buds, and the inner wood. After such a winter, the tree is unable to produce a bountiful harvest, and the plums fall almost immediately; sometimes, the tree fails to even set fruit.

Localized plum tree varieties can also freeze during the winter due to improper planting. This occurs when seedlings are placed in windy northeastern, northwestern, or northern areas. When there's no other suitable location for fruit trees in the garden, installing a frost protection screen for the winter solves the freezing problem. Without one, young specimens planted in the fall may not survive the winter, freezing to death.

Incorrect irrigation scheme

The plum tree has a fibrous root system. Its rhizomes are located in the surface layers of the soil. Because of their shallow root system, the tree is unable to obtain water from the soil itself. When watering is insufficient, the tree cannot support its full load of fruit and sheds it to survive. To prevent this, apply approximately 10 liters of water around mature fruit trees at least once every 7 days.

Attention!

When the soil moisture is sufficient, ripening plums should be harvested immediately, as too much water can cause the fruit's skin to crack.

Over- or under-fertilization

Fertilizing is essential when growing plums. This is also due to the fact that plums have fibrous rhizomes that are unable to penetrate the soil and obtain the necessary nutrients. When a plum tree lacks these nutrients, it begins to drop its fruit. You can determine which nutrient a fruit tree is lacking based on its condition:

Nitrogen deficiency is first indicated by the tree's leaf blades turning pale. When this element is lacking, green fruit ovaries fall off. Nitrogen deficiency is addressed by fertilizing the tree with a solution of mullein or urea.
Phosphorus deficiency – the plum tree is dropping large, but not fully ripe, fruits. The garden plant requires fertilizing with double superphosphate according to the manufacturer's instructions.
Potassium deficiency is indicated by the dropping of large, but not yet green, fruits. Fertilizing the plant with potassium salts is recommended.

Poor pollination

Non-self-pollinating plum tree varieties are often chosen for garden planting. These plants require insect pollinators. They also need nearby plants whose flowering period coincides with the plum tree's. To increase the number of pollinating insects, honey plants are planted near the plum tree.

Note!

Honey plants include basil, hyssop, mint and clover.

Diseases and pests

Often, a fruit tree shedding its blossoms, fruit ovaries, or already formed, green, or nearly ripe plums is due to disease or insect attack. The solution to this problem lies in timely preventative treatment of the plum tree, as it is difficult to save the crop after a disease or pest attack. Plums are often attacked by the following insects:

Sawfly – when the tree is in bloom, the butterfly lays eggs. First, the caterpillars eat the pit out of the green fruit, then emerge and pupate. The process then repeats itself. If the tree isn't treated for pests, several generations of these harmful insects can infest a single tree over the course of a season.
Thick-legged - only specimens that have finished flowering suffer; the butterfly lays eggs, and the caterpillar that emerges from them eats the seeds, which are still green, and the fruits fall off.
The plum codling moth has similar effects to the sawfly, but it attacks the fruit ovaries and plum flesh. The fruit fails to ripen and falls off.

Fruit-bearing crops are susceptible to many diseases, but the main ones that can cause fruit drop are scab and other fungal infections. When a garden crop becomes diseased, its strength is insufficient to support the fruit ripening process, and it sheds its fruit. Fruits already damaged by disease are the first to drop.

Which varieties are susceptible?

Virtually all plum tree varieties and hybrids are susceptible to the problem of fruit drop, flower drop, and shedding of already formed fruits. However, cultivar selection can alleviate this problem somewhat. Some relatively recently developed varieties already have increased disease resistance and are less susceptible to attacks by harmful insects.

How to solve the problem

When plums drop before they're ripe, it's important to take action to address the problem. There are also some steps that can help gardeners prevent a decline in the tree's yield. First, identify the underlying cause of the plums dropping ovaries or nearly ripe fruits. Based on this, the following can help:

When a plum tree sheds fruit due to damage from spring frosts or winter freezes, prevention is the only solution. To do this, select zoned and frost-resistant varieties, and line the area around the trunk with spruce branches before winter. After the snow falls, compact it and form a snowdrift directly under the trunk, protecting the fruit buds from freezing.
When fruit buds drop after flowering, it's advisable to replant neighboring plum trees closer to the affected tree. It's also a good idea to check whether the flowering phase of these self-sterile plants coincides.
When fruit buds drop due to excess or insufficient moisture, revise the watering schedule. Moisten the soil around the tree's trunk as it dries—when rainfall is regular, no more than once a month. If there hasn't been any in a while, pour a bucket of water under the tree every 7-10 days. When the trunk area is moist, watering is not necessary. It's also important to consider nearby trees, which can draw moisture away from the plum tree.
If a plum tree is dropping fruit due to a long period of neglect and a nutrient deficiency, expecting a good harvest this year is pointless. However, in June, the tree should be given a boost with potassium-containing fertilizers. A light application of nitrogen fertilizer, such as urea or similar, should be applied around the trunk in the fall. If fruit drop is due to an overabundance of nutrients, the soil composition should be assessed for possible excessive lime content.

When a fruit tree's future harvest fails before ripening due to pest attacks, the easiest solution is preventative treatment. In the spring, during the flowering phase, the tree is sprayed with specialized products such as Dantop, Fitoverm, Confidor, or Lepidocit. Regular loosening of the soil around the tree trunk and timely removal of fallen leaves and fruit also reduce the risk of pest attacks.

Attention!

When a plum tree develops twisted or dried branches or yellowed foliage, all damaged areas are cut off and then treated with copper sulfate. The tree also requires regular sanitary pruning.

Prevention of diseases and insect attacks

To prevent plum trees from being infested by harmful insects that attack all fruit crops, preventative measures should be taken rather than addressing the problem after it occurs. To prevent crop losses, spray the fruit tree with pesticides. It is not recommended to treat the tree during the flowering stage. Once the petals have fallen, a general preventative spray can be used to help prevent attacks by common pests. These pesticides also prevent most plum diseases. For this treatment, prepare the following mixture of solutions in equal proportions:

Cuprozan 0.4%;
Copper oxychloride 0.5%;
Chlorophos 0.2%.

This preventative treatment addresses the problem of aphids and other small pests, as well as diseases. However, plum sawflies and plum codling moths are also dangerous to plum trees. The latter can destroy about half the crop. Even after preventative insecticide spraying, there's no guarantee that it won't damage the fruit. Since the insect can produce up to three generations per season, damage to fruit ovaries can occur at any time.

The plum sawfly is also dangerous because it lays its larvae directly into young ovaries, which fall off as they grow—they are eaten from the inside. The beetle poses no threat to the fruit as adults, but plum worms are a consequence of its activity and reproduction. Gardeners control these pests with a solution of Sumition, 20 ml of which is diluted in 10 liters of water.

The product is toxic, so the final treatment should be performed no less than 20 days before harvest. If there are no pest infestations, using this product is not recommended. Regularly inspecting the tree is sufficient; if pests do occur, only then should the product be applied. The need for Sumiton treatment is determined by periodically picking unripe fruit and cutting it open to check for pests inside.

Attention!

If a sawfly was present on a plum tree last year and was not destroyed, then it is highly likely that it will parasitize the garden crop this year as well.

If gardeners don't want to use chemicals, they can kill plum sawflies manually. To do this, shake the tree during bud swelling. Adult insects will fall to the ground, where a blanket is spread. The harmful beetles are collected and then either burned or sprayed. For this, they are treated with 3% Bordeaux mixture directly on the blanket.