Why Are There Yellow Or Brown Leaves On Boxwood Shrubs?

The reason why there are yellow or brown leaves on boxwood shrub is because they have been infected with fungus called rust fungi. Rust fungus attacks boxwoods during spring and summer time. When rust fungus infects the tree it causes the leaf surface to turn yellowish-brown color. This disease is very dangerous because it kills the tree. If you see yellowish-brown leaves on your boxwood shrub, then please do not touch them! You can safely remove them from the tree.

What Causes Rust Fungus To Attack Boxwoods?

Rust fungus is caused by two types of fungi: rust spores and rust bacteria. Both kinds of fungi produce their own kind of spores which are carried inside the soil particles (soil microorganisms). These spores are released when rust fungus spores germinate in the soil. The rust fungus spores germinate and grow into small white mushrooms called rust molds. They can live up to three years but usually only live one year before dying out.

Rust Molds Cause Rust Fungus To Spread On Boxwoods

When these moldy mushrooms mature, they release their spores which cause rust fungus infection on boxwoods. In the spring, during wet and humid conditions, if you do not treat your boxwoods they will soon start to show yellow and brown leaves on the edges of the leaves. The yellowing will then spread throughout the whole leaf until it turns completely brown and dies off.

If you want to preserve your boxwood shrubs, then you must start treating them with a good fungicide. It is important to remove all the yellow leaves as soon as you see them, because the rust fungus will continue to spread if you don’t treat your boxwoods.

In many countries, the spores of rust fungus are native and live in the soil. Boxwoods are very susceptible to rust fungus, but it is not the only plant that can catch this disease. Many people do not realize their boxwoods are infected by rust fungus until it is too late to save them.

There are no real signs to look out for, but it is a good idea to inspect your boxwoods during the late winter months before the spring growth starts. If you see small white mushrooms with red spots around the base then you should immediately contact a local plant clinic. They will be able to tell you what to do next.

Always keep an eye on your plants and inspect them on a regular basis.

What Is The Best Way To Treat Boxwoods For Fungus?

The best way to treat your boxwood for rust fungus is to use a fungicide specifically designed for treating rust fungus. You can also try and use an organic spray made from milk as an alternative, but it isn’t as effective. It is very important to apply the treatment before the yellowing starts to spread. If the leaves are yellow or brown, then you should get rid of them as soon as possible and stop using that particular shrub.

In some cases, you may have to dig up the whole shrub out of the ground and dispose of it. This is a very drastic solution, but if the fungus has infected your entire garden then it is sometimes necessary to do so.

Which Fungicides Are Effective At Treating Fungus On Boxwoods?

Fungi-Flex 600 FT (Fungicide) – This is the best fungicide for treating rust fungus on your boxwoods. It is a clear liquid that you can easily apply with a watering can or sprayer. The boxwoods will need to be thoroughly watered before applying the fungicide.

How To Apply Fungicide To Your Boxwoods

To make it easier to treat your shrubs, you should dig a trench around the base of the plant and about 8-10 inches deep. This is so the fungicide can flow around the whole shrub and get to the roots. You should only use this method on shrubs that are in large boxes or raised beds.

After digging the trench, apply the fungicide around and over the top of the shrub. You should try and apply at least 1oz of fungicide per year of the shrubs age (in gallons of water). So for a 3 year old shrub you would need to apply 3oz of fungicide.

Water in the fungicide after application and keep doing this every week for 3 weeks. This will ensure that the roots and leaves of the shrub are both drenched in the fungicide.

For smaller shrubs that can sit on the ground, you will need to water them daily for a week before applying the fungicide. This will get the soil nice and wet so the shrub can easily take up the liquid. Next you need to add a couple of inches of water on top of the soil.

After letting the water soak in, apply the fungicide and make sure the shrub hasn’t lost more than 10% of its volume in water.

Why Are There Yellow Or Brown Leaves On Boxwood Shrubs - igrowplants.net

You should keep applying the fungicide every week for 2-3 months after the leaf loss starts.

Sources & references used in this article:

Shrubs and trees of the southwest uplands by FH Elmore – 1976 – books.google.com

Insects on trees and shrubs around the home by PH Schwartz – 1980 – books.google.com

Insect pests of nursery and ornamental trees and shrubs in Oregon by J Schuh, DC Mote – 1948 – ir.library.oregonstate.edu

Broadleaved Shrubs and Shade Trees: Problems, Picture Clues, and Management Options (NRAES 183) by MK Malinoski, DL Clement – 2009 – ecommons.cornell.edu

The shrubs and woody vines of Florida: a reference and field guide by G Nelson – 1996 – books.google.com

Insects on Trees and Shrubs Around the Home by H Garden – naldc.nal.usda.gov

Boxwood blight: Threat to ornamentals by ML Daughtrey – Annual review of phytopathology, 2019 – annualreviews.org

Box tree moth Cydalima perspectalis as a threat to the native populations of Buxus colchica in Republic of Georgia by I Matsiakh, V Kramarets, G Mamadashvili – Journal of the Entomological …, 2018 – entomol.org

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