Mottles

Mottles are symptoms of viral disease.

Mottles are irregularly colored, spotted, or blotched areas. These discolored areas are usually yellow, but not always. Mottles often indicate viral mosaic disease.

Tobacco vein mottling virus (RJ Reynolds) CC BY-SA 3.0

Viral families

Several families of viruses cause mottling in plants. And each of these families causes dozens, maybe hundreds, of diseases. There are even sub-viral agents that lack the genetic instructions needed for replication. Because of this, they use helper viruses to set up households in plant victims. The more we learn, the stranger the world gets.

Diseases that present as mottling

When plants are struggling, many normal behaviors are interrupted. The discoloration associated with mottling can indicate any of the following diseases:

• Bean pod mottle (Secoviridae) - spread by bean leaf beetles to legumes
• Blueberry leaf mottle virus (S.) - infected seeds carry this disease to blueberries and grapes
• Broad bean mottle virus (Bromoviridae) - spread by infected sap to legumes
• Cowpea mottle virus (Tombusviridae) - beetles and infected seed carry this disease to cowpeas and other legumes and many members of the nightshade family
• Cucumber green mottle mosaic virus (Tobamovirus) - spread by infected sap to cucurbits
• Pepper mild mottle virus (Tobamovirus) - transmitted mechanically and by infected seeds to bell peppers and chili peppers
• Soybean yellow mottle mosaic virus (Tombusviridae) - spread by infected sap to  soybean
• Strawberry mottle virus (S.) - aphids infect strawberries
• Tobacco vein mottle virus (Potyviridae) - aphids infect tobacco, groundcherries, and other nightshade family plants

Mottling can also occur in response to cold temperatures. Or it may indicate a zinc deficiency. Air pollution can also cause mottling. In the case of mottle-leaf in citrus, it gets confusing. The jury is still out on whether this condition is from too much nitrogen, insufficient nitrogen or organic matter (SOM), or mineral deficiencies or toxicities.

Yes, assessing poor plant health can be challenging. But the more you know, the better you can help them grow.

Mottle or mosaic?

Mottling is a symptom. Mosaics are diseases. And mottling can be a symptom of a mosaic disease.

Bottom line, if you see uncharacteristic coloration on leaves or fruit, take a closer look and consider what might be causing it before a full-blown infection wipes out your crop.