Four reasons for yellow leaves on fruit trees

Welcome to autumn! Though we’re having quite a warm summery week here in central Vic, we’ve had the first few cool, crisp mornings, and there’s a definite shift in the air.

Leaves on Angelina plum trees (on the LHS) starting to turn yellow in autumn
Leaves on Angelina plum trees (on the LHS) starting to turn yellow in autumn

Even if it still feels quite summery at your place, you can expect to start seeing some typical autumn features in your fruit trees soon.

For example you might start to see the leaves on your fruit trees start to turn yellow (if they haven’t already), especially if you’ve already picked the crop. The typical pattern is that the leaves will stay green and continue doing their job as long as the tree is bearing fruit, but once the fruit is off, it will quickly start go into senescence, or winter dormancy.

Close-up of yellowing leaves on plum tree
Close-up of yellowing leaves on plum tree

At that time, the tree starts to withdraw all the useful nutrients from the leaves back into the buds and bark — the first sign of this happening is the leaves changing colour. This type of yellowing is completely normal, and you see it every year.

Another reason for yellowing leaves that is of more concern is caused by lack of water, as you can see on this cherry tree.

A cherry tree that has turned yellow from lack of water
A cherry tree that has turned yellow from lack of water

It’s all too easy for this to happen when you have an automatic irrigation system, because drippers can easily block up, and unless you’re checking them regularly (which is a really good idea), you might not realise you have a problem until the tree starts telling you loud and clear by the leaves turning unseasonally yellow (you can see all the other trees nearby are still green).

Another common reason for leaves to turn yellow is from nutritional deficiencies.

Iron deficiency (chlorosis) on peach leaves
Iron deficiency (chlorosis) on peach leaves

A number of nutritional deficiencies can cause yellow leaves as one of their symptoms, including iron (as you can see above), manganese and zinc.

The fourth reason for yellow leaves is because of a virus disease, such as apple mosaic virus as you can see in this leaf.

Apple mosaic virus on leaf
Apple mosaic virus on leaf

Viral diseases are not good news, but unfortunately are not really treatable, so the best bet is to look after the tree as well as you can, and try to avoid the virus spreading by not planting other trees of the same type nearby.

So if the leaves on your fruit tree are turning yellow it’s probably a perfectly normal seasonal response, but your tree might also be trying to tell you something! If you feel like you need more detailed help diagnosing what your fruit tree is trying to tell you, please download a copy of Keep Your Fruit Trees Free From Disease short course.

Apricot leaves showing beautiful autumn yellow and orange colours
Apricot leaves showing beautiful autumn yellow and orange colours

Sunburn strikes again

If you live in a hot climate (like we do) sunburn is an inevitable part of fruit growing, but it can also happen in temperate fruit growing areas during heat waves, which unfortunately are becoming more common due to climate change.

There are three types of sunburn damage you may see:

1. Sunburn necrosis

sunburn-necrosis

2. Sunburn browning

sunburn-spots

3. Photo-oxidative sunburn

sunburn-cooked

This week Ant (who leases our orchard) had his first experience of sunburn, when the Pizzaz plums were not quite ripe enough to pick last week, then the heatwave hit—a blistering day of 44C!

You can see the spots and shrivelling on the skin – that’s a version of sunburn browning. Most of the plums are still perfectly usable for jam, or cooking, or even for eating, but it definitely downgrades them.

Is it preventable? It can be incredibly difficult in cases like this, where there was probably only a very brief window of a day or two when the plums were ripe enough to pick (with the confidence that they would continue to ripen off the tree) before the heat wave hit.

In a home garden, if you were paying careful attention to both your trees and the weather forecast, it may be possible to harvest the fruit (or at least some of it) in time. In Ant’s situation, where he’s managing the competing needs of 5,000 trees it’s much harder.

If you live in an area that experiences heatwaves there’s a number of other things you can do to prevent sunburn damage, including irrigation practices, pruning practices, and careful monitoring—we list 10 different ways to minimise sunburn in “What’s that spot? Common diseases of deciduous fruit trees” (even though sunburn is not actually a disease, but an environmental impact).

The main thing to do when a heat wave is predicted is to make sure your trees are getting enough water, which may mean watering every day. The best time to water is either overnight or in the morning, to reduce evaporation.