Virus Problems Found in Garlic

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

Garlic growers may be noticing symptoms of virus infection in their plants that show yellowing tips on many leaves with some that are completely yellow (Fig 1). If you look closely at the yellow leaves you will see mottling or striping on the leaves (Fig 2). These symptoms are usually more pronounced on young leaves. Infected plants are stunted and bulb size can be reduced. Garlic crops infected with viruses are usually more susceptible to weather conditions like extreme heat, and do not keep well post-harvest.

What is usually called a ‘garlic virus’ is caused by several different viruses that can be grouped under the name “Potyvirus”; all symptomatic garlic that was tested was positive for Potyvirus. Some people lump these viruses under the name “garlic mosaic”. In this case garlic mosaic is thought of as a disease caused by one or more viruses that include onion yellow dwarf virus, leek yellow stripe virus, and others. These viruses can be transmitted through the planting stock or by aphids and it is thought because garlic is clonally propagated much of the planting stock could be infected with some type of virus. These viruses are usually mild and do not seriously affect yield. The problem comes in when the plants are infected with several different Potyviruses, and then there can be moderate to severe yield reductions. We may have had more aphid movement earlier this year, which may have increased additional virus infections in garlic plantings. You cannot reduce virus transmission by spraying pesticides. Any garlic with symptoms should be watched and possibly harvested early or rouged out if yellowing and decline increase in the coming weeks.