Squash Mosaic

Beetles among your squashes and melons is never a good thing, especially when they carry the squash mosaic virus.

Squash infected with squash mosaic (Alton N. Sparks, UG)

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Squash mosaic is second only to cucumber mosaic in damage to cucurbits caused by disease. There are two strains of squash mosaic, strain 1 affects melons most often, while strain 2 prefers squash. In either case, your crop will be lumpy, discolored, and significantly reduced, but still edible.


Crops vulnerable to squash mosaic

All cucurbits are susceptible to squash mosaic. This includes your zucchini and other summer squashes, melons, gourds, cucumbers, and pumpkins. Watermelons, however, are not susceptible to squash mosaic. Some legumes and umbellifers can also become infected with squash mosaic.


Squash mosaic symptoms

Squash mosaic causes a dark green mottling or mosaic pattern on leaves, as well as blistering, yellowing (chlorosis), leaf hardening and distortion, and vein clearing. Vein clearing is a common symptom of viral disease and it refers to the way leaf veins become almost translucent while the rest of the leaf remains green.

Effect of squash mosaic virus on squash leaves (OllieMartin) CC BY-SA 3.0

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Squash mosaic carriers

​Unlike other mosaic diseases, squash mosaic is not spread by aphids. Instead, striped and spotted cucumber beetles, leaf beetles, and 28-spotted ladybird beetles are the most common vectors of squash mosaic. Many other beetles are also capable of hosting the virus. As these insects feed, their saliva transfers the virus to the plant. This is why it is so important to remove infected plants right away.


Squash mosaic controls

In addition to removing infected plants, beetle control is important in the prevention of squash mosaic. And beetles can be tough to control. The virus can stay viable inside a beetle for up to 20 days, so it is worth the effort. A single beetle can infect dozens of plants in that time frame. To control beetles, handpicking is always an option, if you are quick enough. You can also use neem oil to kill beetle eggs. Encouraging beneficial predators, such as ladybugs, mantids, and solider bugs, in the garden with fresh water, insectary plants, and little or no chemical use is probably the easiest method of keeping beetle populations within reasonable limits.


Squash mosaic can also be carried on melon seeds, so be sure to get clean, disease-resistant seeds from a reputable supplier (and not that melon from the grocery store).


Certain chenopod weeds, including lambsquarters, goosefoot, Russian thistle, and kochia, provide overwintering sites, so keep these weeds away from your cucurbits.


As with many other viruses, tools, clothing, and other surfaces can also become carriers. To prevent the spread of this disease, sanitize tools regularly and avoid working around plants while they are wet.