Thrips, including the Onion Thrip and the Western Red Flower Thrip can cause reduced yields. They pierce plant tissue and remove sap while their wingless cream coloured larvae feed on the younger leaves of the plant. Leaves are marked, often with silvery streaks.

Rain or overhead watering can reduce numbers, but crop should be monitored using yellow sticky traps. If there is more than 5 adults per plant, numbers are reaching epidemic and you could spray with an insecticide. Onion thrips are yelow and brown at 1.3 mm long and Western Red Flower are a bit longer at 1.5mm long. You will need a microscope to clearly determine between them. Thrips can also carry a virus (see below)

Wheat Curl Mite – These mites can also be on corn or wheat crops also. They cause leaf stunting and curling and cloves infested wit them become twisted and have brown spotted areas on them. Bulbs can completely dry out in storage. Avoid growing these crops successively in the same area.(also see virus below)


Downy mildew is a fungal disease often present during cool wet weather. You get pale oval spots on leaves that can eventually turn grey as the leaf yellows and dies. Dead leaf tips can also be seen, especially on young plants. Some solutions to minimise downy mildews include watering before midday and spacing subsequent crops further apart to allow for improved air flow. Fungicides can be used.

Rust (Puccinia allii) is a fungal disease that can also affect onion and leek. Symptoms are orangey rust coloured spots on leaves of plant. It is caused by planting garlic close together, thus reducing airflow. It is also wind borne and often occurs when conditions are conducive to its development. This includes cool wet, cloudy and humid weather. Water early in the day and keep leaves dry. There is no real cure, but you can prune off affected leaves, but expect reduced bulb size, especially if it has occurred early in the growing season. Wash hand and tools after handling. Do not plant in the same area for at least 2 years. You can harvest the bulbs for replanting next year. For more information:

White Rot is a fungal disease assisted by cold and wet conditions. It’s white fluffy growth can be seen at the base of the plant around the roots and bulb. Other symptoms include leaves yellowing, wilting, decaying and toppling over. Tops can be pulled away from the base of the plant. This disease may survive for 20 years in the soil and one outbreak can infect 20 – 30 plants around it. It’s potential for damaging a particular garlic growing region can be devastating. Even lightly infected bulbs can carry this disease through storage. Because of this it is very important to select planting material from crops free of this disease.

Virus – There are at least 3 well know viruses but they can combine and show varying symptoms and be hard to identify specifically. Leek yellow stripe virus, shallot virus and onion yellow dwarfing virus can all affect garlic and reduce its yield. Plants can appear stunted, yellowed or mottled on the yonger leaves. Bulbs can deteriorate quicker in storage. As well as being spread by an infected bulb, insects like aphids and thrips can also transmit the disease. There is no real solution to this problem other than only selecting planting material that is free of a virus – another reason to buy garlic for planting from a reputable source.