Friday, July 16, 2010

Mosaic Virus in Cucurbits

Mosaic Virus in a Marina di Chioggia Squash

Mosaic is a major problem in the summer months in Kihei. It's caused by aphids that feed on infected weeds. They fly around and spread the virus to other plants. If that's not bad enough,  the ever present Kihei ants, who eat the aphid honeydew, spread the virus even further.

In the summer, the surrounding areas become drier due to the higher temps, intense sun and little or no rainfall. As the weeds and wild plants dry out, aphids look for greener areas. That's why some sources on mosaic virus will recommend cutting back on the nitrogen in the summer months as a preventative.

Mosaic virus is another reason why February and March are good months to plant cucurbits. I've had the most problems with this virus during the summer months. It can spread rapidly throughout the garden and can infect tomatoes, peppers and beans.  

The classic symptoms in winter squash are the large areas of lighter green pigmentation in the leaves and leaves and fruit that are misshaped. The leaves and fruit develop normally on one side and appear stunted on the other side. If I were to let this squash grow, the right side will become twice the size of the left.

Emperuer Alexandre Cucumbers
The Fruit on the Right has Mosaic Virus

Cucumbers with mosaic virus have misshaped leaves, similar to winter squash, but the fruit develop abnormal pigmentation and dark green blisters.

It's best to pull the plants as soon as these characteristics appear. Dispose of the plants in the trash, don't put them in a compost bin. Make sure to clean any tools and wash your hands before working in your garden again. I watch the plants closely until I feel certain it's mosaic. I try not to over react, especially with the non-cucurbits, as discoloration in the leaves is normal here due to the heat.
In some cases, the main portion of the plant and the developing fruit are not infected, just a lateral vine. Lateral vines can usually be removed without damaging the plant. The bees can spread flower pollen from an infected vine to a female flower on a normal vine resulting in a deformed fruit. 

I leave little containers throughout my garden of sugar mixed with borate. This helps to cut back the ant population. The mixture can be left dry or mixed with water. Ants are smart so I do both as well as vary the ratio of water in the mixture.

A Pepper Plant Infested with Aphids and Mosaic Virus

The aphid population escalates during the summer months. I've found them to be difficult to control. The best beneficial insect for aphids is the lady bug but I rarely find them in my garden. I've tried many different OMRI garden sprays and so far none have made any significant difference.


  1. How frustrating to have to pull the vines up just as they are forming fruit Jane. Is it too hot for nasturtiums? i grow a patch as a trap crop for the white cabbage moths but i read they are a good aphid trap too.

  2. Hi Julie! Funny you should mention nasturtiums...I had to pull them out 2 weeks ago as they were covered in and essentially destroyed by black aphids. Summer is a very difficult time to garden in Kihei as the bugs are at exponential levels!

  3. Hi Jane,

    I am a newcomer to gardening on Maui; I have gardened on the east coast but this is so much more complicated. Thank goodness I have found your blog. I also live in Kihei and have been dealing with what I believe is blight or some other fungus that has been attacking my tomatoes and recently my parsley. I used a whole bottle of Garden Safe Organic Fungicide in one week and have also tried a mixture of H2O2 and H2O but I still see early signs of disease. Do you currently deal with blight on any of your tomatoes and if so, do you have any suggestions? Thank you!!


  4. Hi Skye! Occassionally I get symptoms of what looks like blight but it hasn't been that much of a problem. At around 3 months, my tomato plants usually have severe mite infestation. The white flies and powdery mildew are also a problem and sometimes what looks like mosaic virus. Mosaic in my tomato plants is not as easy to pinpoint after there is a lot of sucking insect damage done to the leaves.

    I haven't found an OMRI spray that really knocks out mites, aphids and white flies. For blight you might ask at Kula Hardware.

    On the right side bar of my blog is a section for Maui Garden blogs. Check out the blog called Ocean Gardener - he had problems with blight. I'm not sure if he found a remedy but you might ask him.

  5. thanks for the descriptive and useful information you have provided about mosaic plant virus.. just keep up the good work!

    1. Hi Vibhuti! Mosaic is a miserable disease. I'll have to check your product. I didn't know there was anything that could be used for to prevent it.