Bean Common Mosaic

Bean common mosaic is a viral disease caused by several different virus strains. A close cousin to bean yellow mosaic and clover yellow vein virus, bean plants can be unfortunate enough to be infected with all three simultaneously.

​What’s fascinating about this disease is that two different sets of symptoms may occur.

Bean common mosaic necrosis virus (USDA) Public Domain

Symptoms of bean common mosaic

Bean plants infected with these viruses may come down with bean common mosaic or bean common mosaic necrosis:

• Bean common mosaic is very common. It appears as mosaic patterns of light and dark green on the leaves. Puckering, blistering, rolling, and downward cupping are also common symptoms. Plants that become infected while young will exhibit stunting.
• Bean common mosaic necrosis is rare, but you’ll want to be on the lookout, just in case. Symptoms include small, reddish-brown spots on the leaves. Nearby leaf veins become brown or black. This necrosis (death) then spreads to the phloem and throughout the plant, ultimately killing it. If you take a cross-section of an infected stem or pod, you will see reddish streaking in vascular tissue. These symptoms look very similar to black root rot and Fusarium wilt, but those conditions also cause pod streaking.

In both cases, leaves may be smaller, and blossoms and pods may be deformed. The symptoms your plants will exhibit depend on the virus involved, whether or not your plants have dominant or recessive genes, or if a particular gene is present. Symptoms of bean common mosaic are most likely to appear when temperatures are between 68 and 77°F.

Bean common mosaic transmission

The bean common mosaic virus overwinters in infected seeds and weeds. It is most often transmitted by aphids or spread on infected pollen. It can also move from plant to plant on clothing, tools, and vegetative material.

Use these tips to avoid introducing this virus into your garden:

• Use certified disease-free seeds and plants [not grocery store beans].
• Select disease-resistant varieties.
• Employ crop rotation.
• Keep weeds away from bean crops.
• Control aphids.
• Toss infected plants in the trash.

Aphids (OllieMartin) CC-BY-SA 3.0

Resistant bean varieties

These bean varieties are resistant to one or more strains of this virus:

• Black beans: Black Turtle T-39; Midnight
• Cranberry beans: Etna, Hooter
• Dark red kidney beans: CA Dark Red Kidney; UC Nichols
• Large white beans: Cyrrus
• Light red kidney beans: CA Early Light Red, Red Kidney M, Sacramento
• Pink beans: Yolano
• Yellow beans: Canario 707

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Once these viruses are in your soil, it is hard to get rid of them. It is far better to start with clean seeds and do what you can about those pesky aphids.