Spinach is prone to pests such as cutworms and wireworms, flea beetles, slugs and snails, aphids, and leaf miners. Spinach diseases include damping-off, downy mildew, and viruses.
Pests:
- Cutworms and wireworms – Cutworms cut young seedlings off at ground level, and wireworms feed on the foliage and roots. Older transplants are less appealing to these insects than tender seedlings.
 
- Flea beetles – Flea beetles feed on young foliage. The damage consists of several small holes, leaving the leaf looking as though it’s been hit by a blast from a shotgun. The leaves sometimes have bleached and pitted areas as well. The insects are so tiny that may never be seen.
 
- Slugs and snails – Slugs and snails also leave holes in spinach leaves. Can tell the difference by the size of the hole—slug and snail holes are much larger—and by the slime trail slugs and snails leave behind.
 
- Aphids – Aphids are probably the most common of spinach pests.
 
Diseases:
- Damping-off – Damping-off disease causes seedlings to fall over and die soon after it emerge. Plant quality seeds and avoid overwatering to help prevent the disease.
 
- Downy mildew – Downy mildew causes yellow or light green spots on the upper surface of leaves with white fungus on the lower surface.
 
- Viruses – Viruses that infect spinach are often spread by insects, so control insect infestations as much as possible.