What Is Cherry Rusty Mottle: Treating Cherries With Rusty Mottle Disease

What Is Cherry Rusty Mottle: Treating Cherries With Rusty Mottle Disease

By: Teo Spengler

If your cherry trees are producing sickly fruit late in the season, it may be time to read up on rusty mottle cherry disease. What is cherry rusty mottle? The term includes several viral diseases of cherry trees, including rusty mottle of cherry and necrotic rusty mottle.

What is Cherry Rusty Mottle?

Several viral diseases attack cherry trees, and two of these diseases are called rusty mottle of cherry and necrotic rusty mottle.

While experts have determined that rusty mottle diseases are caused by viruses, they do not have much other information. For example, scientists agree that your tree will get a rusty mottle cherry disease if you plant infected stock, but they don’t know how else the viruses are spread.

The exact symptoms of a viral cherry tree disease differ among trees. In general, rusty mottle cherry disease reduces fruit harvest and fruit quality. It also slows down fruit ripening.

Treating Cherries with Rusty Mottle

How can you tell if you have cherries with rusty mottle? Don’t look for your trees to die suddenly, because generally they won’t. They just lose energy.

Rusty mottle of cherry causes the cherry tree leaves to turn yellow or red. Many will drop before the fruit harvest. Those leaves that don’t drop turn rust colored, and are mottled with yellow and brown.

What about the fruit? Cherries with rusty mottle will be smaller than normal cherries of the same cultivar. They will ripen late and lack flavor. Some are totally tasteless.

If your tree has necrotic rusty mottle, you’ll see both flowers and leaves appear late in spring. The leaves will develop brown necrotic or rusty chlorotic spots. These may fall from the leaf leaving holes. The entire tree can lose its leaves.

Sadly, if your cherry tree has rusty mottle of cherry or necrotic rusty mottle, the best thing you can do is to remove it from your garden and dispose of it, as there is no effective treatment. You can buy virus-free trees to reduce your chances of having to deal with these viruses in the future.

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Cherry rusty mottle-associated virus (CRMaV), which belongs the genus Robigovirus of the family Betaflexiviridae, is strongly associated with cherry rusty mottle disease of sweet cherry, Prunus avium. Here, we report on the successful development of an Agrobacterium-based inoculation system for a cloned CRMaV cDNA construct. Agro-inoculation of virus-free cherry rootstock ‘Krymsk6’ [P. cerasus x (P. cerasus x P. maackii)] resulted in the development of chlorotic yellow mottle symptoms on systemic leaves beginning at 50 days post inoculation. The presence of CRMaV in ‘Krymsk6’ agro-inoculated plants was confirmed by RT-PCR and ELISA. Subsequently, CRMaV from agro-inoculated ‘Krymsk6’ was graft-transmissible onto virus-free sweet cherry rootstock P. avium ‘Mazzard’ as evidenced by the production of typical cherry rusty mottle symptoms beginning at 35 days post grafting, and further confirmed by western blotting and RT-PCR. These results showed conclusively that CRMaV is the causal agent of cherry rusty mottle disease in sweet cherry. The reverse genetic system presented in this study can be used as a tool to investigate the molecular biology of CRMaV and also a template for infectious clone development for other viruses in the genus Robigovirus.

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">Chemical Causes of Curling Leaves

Some cherry tree leaf symptoms may look like the result of a disease when they’re actually caused by nonpathogenic responses to certain chemicals. Salt (from seaside spray or roadside deicing products), excessive application of nitrogen fertilizer (or from the application of a quick-release nitrogen fertilizer) and chemical drift can cause cherry tree leaves to curl and twist before they turn yellow and brown and fall off. Even excessive amounts of chlorine in municipal water supplies may cause cherry tree leaf damage, including curling of the foliage.

Use a slow-release fertilizer if indicated by soil-test results. Plant cherry trees away from streets, driveways and sidewalks that may have salt runoff from deicing products and spray pesticides and herbicides on nonwindy days so that the chemicals will not drift and settle on your cherry trees.

Victoria Lee Blackstone is a horticulturist and a professional writer who has authored research-based scientific/technical papers, horticultural articles, and magazine and newspaper columns. After studying botany and microbiology at Clemson University, Blackstone was a University of Georgia Master Gardener Coordinator. She is also a former mortgage acquisition specialist for Freddie Mac in Atlanta, GA.

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