If your apple tree’s leaves are turning yellow, it could have apple chlorosis. Chlorosis occurs when the soil in which the tree is planted lacks iron. This nutrient deficiency will cause the leaves to turn yellow, starting from the leaf veins and spreading outward, until the entire leaf is yellow except for its bright green veins.
Other causes of yellowing apple tree leaves are weather changes, watering issues, lack of nutrients, and disease.
In this article, we will discuss the causes of yellowing apple tree leaves and how to remedy each one.
Why are my apple tree leaves turning yellow?
Apple chlorosis
Chlorosis in apple trees is caused by a lack of iron. This causes the leaves to turn yellow and eventually die off. You will notice that the yellowing starts just outside the leaf’s veins, and will then spread out to the entire leaf. If the chlorosis is left unmanaged, the leaves can become pale with scorched edges.
Chlorosis affects the younger leaves first, and these are far more damaged by the condition than the older leaves. It is possible that only one side of the leaf may be affected, but it is also possible that the entire tree is compromised. Because the leaves are damaged, photosynthesis cannot take place, and less plant sugar means no fruit production.
Apple chlorosis can be caused by a lack of iron in the soil, or because the tree itself cannot absorb any iron. If the pH of the soil around the tree is above 7.0, the iron will solidify and the plant cannot absorb it. Cool soil temperatures, mulch or any covering over the soil, and overwatering can worsen the problem.
Prevent apple chlorosis by regularly checking your soil’s pH levels. If the plant is not native to where you live, it may prefer a lower pH to effectively absorb iron. You can also apply chelated iron in the form of a foliar spray, or simply mix it into the soil.
Foliar sprays need to be reapplied every two weeks. If the application is successful, the apple tree should become green after 10 days.
Soil application of chelated iron works well in calcareous or clay soils and it will also last longer, for about one or two seasons.
Changes in weather
When the cold season starts, an apple tree’s leaves will turn yellow and fall off. This is completely normal and is the tree’s way of withholding water and nutrients from its leaves so that it can prepare itself for dormancy during the winter.
The leaves will turn yellow and drop off because photosynthesis cannot occur if they are cut off from both water and nutrients.
This type of yellowing will look familiar, because normal apple trees do it every year. After the fruits have matured, the leaves will turn yellow and then brown. The tree will lose all of its leaves just as winter is about to start.
This is part of a tree’s natural life cycle so there is nothing wrong with your tree.
Underwatering
When your apple tree does not get the amount of water that it needs, it can develop drought stress. Drought stress causes the leaves on the tree to turn yellow and fall off. It also causes increased fruit drop. Dwarf varieties and young apple trees are more susceptible to drought stress because of their shallow roots.
You can tell a tree has drought stress because their leaves yellow out of season. If your tree is yellow but all other trees are green, you may need to water it more. Apple trees need an inch of water a week. If there has not been much rain, be sure to water it.
Overwatering
Overwatering your apple tree is more damaging than underwatering it. When the soil around the tree’s roots are waterlogged, they are less effective at absorbing nutrients. Eventually, the leaves will turn yellow as more and more of its roots start to die.
You might be wondering how you can tell the difference between yellowing leaves due to overwatering and yellowing leaves due to underwatering. In an overwatered tree, the yellowing of the leaves will start at the bottom foliage and work its way up.
To avoid overwatering, make sure you plant the tree in well-draining soil so that it does not get boggy, even during heavy rains.
Disease or pests
It is also possible that the yellow leaves on your apple tree are caused by disease or pests.
It could be due to necrotic leaf blotch, which starts as brown blotches in the leaves followed by yellowing and dropping off. You can use a fungicide with zinc ions to get rid of this problem.
The tree could also have apple scab, which is caused by a fungus. This will initially appear as pale spots on the top side of the leaves and dark spots on the bottom side. You can get rid of the fungus by applying liquid copper fungicide once a week until the yellowing has stopped.
Pests such as aphids can also cause the leaves to turn yellow. You can use insecticides to rid your tree of these pests.
Conclusion
Apple tree leaves turning yellow are most probably due to apple chlorosis, in which the soil lacks iron which ultimately affects photosynthesis and fruit production. This can be resolved by foliar sprays or applying chelated iron directly to the soil.
Other causes of yellowing apple tree leaves are weather changes, overwatering, underwatering, disease and pests.
Image: istockphoto.com / Mikola249