A number of factors can contribute to the leaves of a shrub or bush turning yellow, from disease and insect problems to problems with the plant's growing environment. Identify the cause of the discoloured leaves so you can fix the problem and restore the shrub to health.
Serious insect infestations cause health problems for bushes and shrubs, including yellow and discoloured leaves. Aphids, spider mites, Japanese beetles and other kinds of insects feed on the leaves of shrubs; their grubs or larvae may also feed on the roots of the plant. Insects feeding on the leaves or roots of the plant are a major contributor to yellowing and unhealthy leaves on a shrub. Pesticides help control serious insect problems on garden bushes.
A lack of the appropriate resources in a bush's soil leads to an unhealthy plant. One sign of this is the production of small, weak leaves that are yellow or light green in colour. Nitrogen, potassium and phosphorus are three of the primary nutrients necessary for landscaping plants like bushes and shrubs to remain healthy. Fertilisers, compost and organic matter in the soil all help provide the bush with the appropriate nutrients for its growth.
Fungal and bacterial diseases such as anthracnose or root rot cause the leaves of a bush to become yellow. These diseases affect the tree's ability to process sunlight and nutrients, diverting the plant's energy to feeding the fungus or bacteria instead, which leads to discoloured yellow leaves. Keep the ground free of standing water and apply fungicides to a bush or shrub to help combat problems with yellow leaves and fungal diseases during the growing season.
Some shrubs grow best in full sunlight, while others prefer indirect light or shady conditions. Plant the bush where it will receive the right amount of light. Too much and too little light are damaging and cause the plant to produce unhealthy, yellow leaves. Additionally, a lack of water causes the leaves of the shrub to become yellow because the bush is dehydrated. Give the bush the right growing conditions to keep its leaves green.