Advice on Leaf Quality

Frank P Matthews is a ‘Plant Healthy’ certified British tree nursery. ‘Plant Healthy’ is the officially recognised industry standard for using best practice methods to produce the healthiest crop of plants.

At Frank P Matthews we work very closely with our independent Agronomists and Technical Advisors to ensure that the trees we produce are healthy. Regular inspections and reviews of all growing methods are an important part of our business. We always strive to produce trees that meet the highest standards whilst using the most environmentally friendly methods possible.

Sometimes the leaf quality of trees is not perfect and in this article we will explain the reasons that can cause this and why it is not something that should cause concern. On deciduous trees and, to a certain extent on evergreens, leaf imperfections are very minor in terms of their impact on the tree growth and establishment.

There are three groups of causes we may come across:

Biotic. This group of causes relates to pests and diseases. They are almost certain to occur in commercial production of young trees due to crop densities, the lush fresh growth, and the artificial environment, e.g. being container grown. Most commonly these are leaf spots, shot hole, leaf blight, mildews and scab which tend to develop on the newest leaves and therefore the trees can cope with these infections as they rely on older leaves for the generation of carbohydrates. Infections such as these are only cosmetic, the pathogens are latent most of the time and will only surface when the trees are under stress. Once the trees are planted out and develop a good root system, they become far more robust and unaffected.

Physiological. The second group is related to physiological problems caused by abiotic factors such as humidity, rain, ground water, light levels, high or low temperatures etc. Symptoms which may arise include oedema, sap ooze, splitting of stem and bark, leaf scorch from sunshine or winds etc . These are much less in our control but we grow the relevant species and cultivars in specific growing conditions for their requirements (e.g. in tunnels, glasshouses or outside, in different pot sizes, different production cycles etc.) which we know from experience are most suitable to produce healthy trees. However, as we rely on natural seasonal environmental conditions, if weather conditions are poor during the growing season the trees can suffer and the incidence of minor leaf imperfections becomes higher. Due to our stringent cultural and husbandry protocols we can sometimes anticipate these problems and slightly influence the growing conditions where possible. Again, these issues are not a concern and the trees will continue to grow as expected.

Image: Pear leaves displaying some weather related scorch and Prunus leaves with shot hole.

Nutrition. The last group of problems is those of nutritional issues, such as an imbalance of nutrients in the soil. This group is influenced by a number of factors so their control is slightly more difficult to spot in the early onset, however, impact on the tree is minimal and the tree will revive itself when conditions in substrate/soil improve. As trees mature they develop a lot of beneficial flora and fauna in the root zone and their root systems become far more efficient and tolerant. Trees transferred from a small container to being planted in the ground will almost always see an improvement in growth and health.

Treatment

The best treatment for these issues is good planting and aftercare so that the trees can grow well and are not put under any stress. This includes being planted in good soil, being well watered (especially in the first summer), adding fertiliser if necessary and applying a light mulch around the base to retain moisture and inhibit competition from weeds. Good garden hygiene such as removing affected leaves can also be beneficial.

If necessary, the next level would be to utilise biostimulants and biopesticides where relevant from the garden centres to help boost the trees defence mechanisms. Regular applications of some of the biostimulants from the garden centres can be a very effective way to control and eliminate leaf infections.

Only biotic causes could spread in a garden and even this is more often than not generally limited to species or even varieties. For example, if you had Prunus caucasica and you introduced Prunus laurocerasus ‘Rotundifolia’ the shot hole will most likely remain on the Rotundifolia and over time completely disappear as the trees build up resistance. Pests are slightly more challenging but even with those we rarely see too many issues and they are usually seasonal.

Conclusion

In summary, we grow trees in the natural environment and they are therefore exposed to all sorts of factors that can cause leaf imperfections at various time of the year, particularly in late summer and autumn. In the case of deciduous trees, leaves will naturally deteriorate when abscisic acid builds up in the leaf petioles prior to leaf fall. The factors that cause leaf imperfections are all part of the natural cycle of life and can be seen in nature throughout the year.

If we want to produce a tree with no imperfections than we would have to grow them in sterile laboratories, but as we see with trees grown in vertical farms now, they do not possess natural defence mechanisms so as soon as they are planted out in the natural environment they often quickly deteriorate, unlike our hardy stock.

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