Common Hop Plant Diseases:
How to Identify and Treat

Hop plants, also known as Humulus lupulus, are essential for brewing beer and are prized for their unique flavor and aroma. However, like any plant, hop plants are susceptible to various diseases that can significantly affect their growth and yield. In this article, we will discuss some of the most common hop plant diseases, how to identify them, and the appropriate treatment methods.

1. Downy Mildew (Pseudoperonospora humuli)

Downy mildew is one of the most destructive diseases for hop plants. It is caused by a fungus-like organism called Pseudoperonospora humuli. The disease mainly affects the leaves, but it can also infect cones and shoots. Infected leaves develop yellowish-green spots on the upper surface with a grayish-white fuzz on the lower surface.

To treat downy mildew, it is important to ensure proper air circulation and reduce humidity around the plants. Fungicides containing active ingredients such as copper or phosphorous acid can be used to control the disease. Regular pruning of infected leaves and shoots should also be done to prevent further spread.

2. Powdery Mildew (Podosphaera macularis)

Powdery mildew is another common disease that affects hop plants. It is caused by the fungus Podosphaera macularis. The disease appears as a whitish-gray powdery growth on the leaves, cones, and shoots of the plant. If left untreated, powdery mildew can hinder photosynthesis and reduce yield.

To control powdery mildew, it is crucial to maintain proper air circulation and reduce humidity in the hop yard. Fungicides containing active ingredients like sulfur or potassium bicarbonate can be used to treat the disease. Regularly removing infected plant parts and avoiding overhead watering can help prevent its spread.

3. Verticillium Wilt (Verticillium albo-atrum)

Verticillium wilt is a soil-borne fungal disease that affects a wide range of plants, including hop plants. It is caused by the fungus Verticillium albo-atrum. Symptoms of verticillium wilt include wilting, yellowing, and browning of leaves. The disease progresses from the lower parts of the plant to the upper sections.

Once infected, it is challenging to treat verticillium wilt directly. The best approach is to prevent its occurrence by planting disease-resistant hop varieties and maintaining proper soil health. Crop rotation with non-host plants for at least three years can also help reduce the disease’s impact.

4. Hop Stunt Viroid (HSVd)

Hop stunt viroid (HSVd) is a small infectious RNA molecule that affects hop plants and can cause significant damage. Symptoms of HSVd include stunted growth, reduced yield, and abnormal leaf development. Infected plants often show a bushy appearance with shortened internodes.

Unfortunately, there are no effective chemical treatments for HSVd. The best method to control the spread of the viroid is through the use of clean planting material and strict sanitation practices. Infected plants should be promptly removed and destroyed to prevent further transmission.

5. Ringspot Virus (Hop Latent Viroid)

Ringspot virus, also known as Hop Latent Viroid, is another devastating disease that affects hop plants. It causes yellow or light green ringspots on the leaves, which can lead to reduced photosynthesis and stunted growth. Infected plants may also exhibit chlorotic mottling or necrotic streaks on the leaves.

There is no cure for ringspot virus once a plant becomes infected. The best course of action is prevention through the use of disease-free planting material and strict sanitation practices. Infected plants should be removed and destroyed to prevent further spread.

6. Fungal Diseases (Alternaria, Cercospora, Fusarium)

Various fungal diseases can affect hop plants, including Alternaria leaf spot, Cercospora leaf spot, and Fusarium wilt. These diseases cause characteristic leaf spots, browning, and wilting of the foliage. Fungicides containing appropriate active ingredients can be used to treat these diseases. Additionally, maintaining good sanitation practices and removing infected plant parts can help prevent their spread.

In conclusion, hop plants can be vulnerable to several diseases that can affect their growth and yield. Early identification and proper treatment are crucial in mitigating the impact of these diseases. Regular monitoring of the plants, implementing preventive measures, and using appropriate fungicides can help protect hop plants from common diseases. By taking proactive measures, hop growers can ensure healthy plants and a successful harvest of hops for brewing flavorful beer.