Squash mosaic

About

Squash mosaic infects squash, pumpkins and melons. Unlike most squash viruses, it is carried by cucumber beetles, not aphids, and it often arrives in infected seed. There's no cure, so virus-free seed is the most important defense.

Also called squash mosaic virus, SqMV

How to recognize it

Symptoms

The first true leaves of seedlings show a yellow-green mottle, dark green bands along the veins, and twisting; later leaves may look normal. Older melon leaves can have a dark green mosaic and blisters and feel stiff. Fruit is mottled with green blotches and often misshapen, and melons may lack their normal netting. Plants that look fine may still grow weakly and branch poorly.

Often confused with

On older melon plants, the stiff, blistered leaves can look like herbicide injury. Other squash mosaic viruses look similar too, so a lab test is needed to be sure.

Worse when

Infected seed, lots of striped or spotted cucumber beetles, and nearby weeds that host the virus, such as lambsquarters and kochia.

How it spreads

Seed brings it into the garden, especially melon seed. Striped and spotted cucumber beetles then spread it as they feed from plant to plant, and grasshoppers may too; aphids do not. Sap on hands and tools can also move it.

When

Often shows on seedlings' first true leaves, then spreads through summer while cucumber beetles are active.

What to do, gentlest first

Prevention works best; most sprays only protect healthy leaves and can't cure infected ones. Always read and follow the product label.

1. Plant virus-free seed Prevent

   Buy fresh seed from a trusted source and never save seed from mottled plants or fruit. Cornell notes that hot-water and other seed treatments do not remove this virus.

2. Keep host weeds down Prevent

   Clear weeds in and around the garden, especially lambsquarters, kochia and Russian thistle, which can host the virus.

3. Pull infected plants By hand

   Pull and bag infected plants as soon as you spot them, since they won't recover. Wash your hands and tools with soap and water afterward.

4. Row cover on young plants Barrier

   Floating row cover keeps cucumber beetles off seedlings and young vines.

   Remove row cover when flowers open so bees can pollinate.

5. Beetle control can slow spread Organic spray

   Keeping cucumber beetle numbers low helps limit spread to healthy plants.

   No spray cures an infected plant. Follow the label and don't spray open flowers while bees are active.

Plants it affects

Cantaloupe (muskmelon), Winter squash and pumpkin, Zucchini and summer squash