Common Yarrow Plant Diseases:
How to Identify and Treat

Yarrow is a beautiful and versatile perennial plant that is commonly found in gardens. With its delicate fern-like foliage and clusters of small, colorful flowers, yarrow adds a touch of elegance to any landscape. However, like any other plant, yarrow is susceptible to diseases that can hinder its growth and overall health. In this article, we will explore some common yarrow plant diseases, how to identify them, and the best ways to treat and prevent them.

Powdery Mildew (Erysiphe cichoracearum)

Powdery mildew is a fungal disease that affects a wide range of plants, including yarrow. It is characterized by the presence of a white powdery substance on the leaves, stems, and flowers of the plant. This powdery substance consists of fungal spores that are easily spread by wind or water.

To identify powdery mildew in yarrow, look for white patches or spots on the leaves and stems. These spots may gradually expand and cover larger areas of the plant. Infected leaves may also become distorted or curl up.

To treat powdery mildew in yarrow, remove any infected parts of the plant immediately. Prune away affected leaves and stems, making sure to sterilize your pruning tools between cuts to prevent further spread of the disease. Additionally, you can apply a fungicide specifically formulated for powdery mildew according to the manufacturer’s instructions.

Preventing powdery mildew in yarrow can be achieved by providing adequate air circulation around the plants. Avoid overcrowding by spacing your yarrow plants properly and thinning them out if necessary. Watering at the base of the plants rather than from above can also help prevent the spread of fungal spores.

Root Rot (Pythium spp.)

Root rot is a common problem in yarrow plants, especially when they are grown in poorly-drained soil or overwatered. It is caused by various species of the Pythium fungus and can lead to the decay of the plant’s roots, resulting in stunted growth, wilting, and eventually death.

To identify root rot in yarrow, look for yellowing or browning leaves that may appear wilted or droopy. The roots may also appear dark, mushy, and have a foul odor. In severe cases, the entire plant may start to decline and die.

Treating root rot in yarrow requires improving drainage and reducing excess moisture around the roots. If possible, transplant the affected plant to a well-draining soil mix. Avoid overwatering and make sure the soil is allowed to dry out slightly between waterings. Applying a fungicide labeled for controlling root rot can also help eliminate the fungal infection.

Preventing root rot in yarrow starts with choosing a planting location with good drainage. If your soil tends to be heavy and retains too much moisture, consider amending it with organic matter such as compost or sand to improve drainage. Proper watering practices, such as watering deeply but infrequently, can also help prevent the development of root rot.

Aster Yellows (Phytoplasma)

Aster yellows is a bacterial disease that affects a wide range of plants, including yarrow. It is transmitted by leafhoppers and can cause severe damage to infected plants. Symptoms of aster yellows include stunted growth, yellowing or purpling of leaves, distorted flowers, and abnormal shoot development.

To identify aster yellows in yarrow, look for yellowing or purpling of leaves that may be accompanied by twisted or deformed growth. Infected plants may also produce malformed flowers or develop witch’s broom-like clusters of shoots.

Unfortunately, there is no effective treatment for aster yellows once a plant is infected. The best course of action is to remove and destroy the infected plant to prevent the disease from spreading to other plants in the vicinity. It is also important to control leafhoppers by using insecticides or physical barriers such as row covers.

Preventing aster yellows in yarrow can be challenging due to the nature of its transmission. However, keeping your garden clean and free from weeds can help reduce the presence of leafhoppers, which are known carriers of the disease. Regularly inspect your yarrow plants for any signs of infection and promptly remove and destroy any affected plants.

In conclusion, yarrow plants may encounter various diseases that can affect their health and vigor. By learning to identify common yarrow plant diseases early on, you can take prompt action to treat and prevent further spread. Remember to practice good cultural practices such as proper watering, adequate air circulation, and regular inspection to keep your yarrow plants healthy and thriving.