Squash Mosaic

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

​​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 both cases, your crop will be lumpy, discolored, and significantly reduced, though still edible.

Yellow squash infected with squash mosaic virus (Alton N. Sparks, Jr., UGA, Bugwood.org) CC BY 3.0

Crops vulnerable to squash mosaic

All cucurbits are susceptible to squash mosaic, including cucumbers, melons, pumpkins, and zucchini. Except for watermelons, they do not get 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, blistering, yellowing (chlorosis), leaf hardening and distortion, and vein clearing. Vein clearing is a common symptom of viral disease. It refers to how leaf veins become almost translucent while the leaf blades remain green.

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

Squash mosaic carriers

Unlike other mosaic diseases, aphids are not responsible for squash mosaic. Instead, striped cucumber beetles, leaf beetles, spotted cucumber 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, so remove any infected plants.

Squash mosaic controls

In addition to removing infected plants, beetle control helps prevent 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. Handpicking is one way to control beetles, but only if you are quick enough. You can also use neem oil to kill beetle eggs. Encourage beneficial predators, such as ladybugs, mantids, and soldier bugs, in the garden with fresh water, insectary plants, and little or no chemical use. Supporting beneficial insects is the easiest method of keeping beetle populations within reasonable limits.

Squash mosaic can infect seeds, so get clean, disease-resistant seeds and seedlings from a reputable supplier (not that melon from the grocery store).

Certain chenopod weeds, including lambsquarters, goosefoot, and Russian thistle, 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 leaves are wet.