In the field, garden, or planter box, seedlings often fail to come up, or die soon after they have emerged from the soil. Seeds may rot before they germinate, shoots may be decayed before they emerge, or stems of seedlings may be attacked near the soil line, causing young plants to collapse. These diseases often are collectively referred to as “damping-off,” and may be caused by a number of soil-inhabiting pathogens.

Species of the soil organism Pythium are most often responsible for damping-off, but several other pathogens, including species of Rhizoctonia, Fusarium, and Phytophthora, can also cause decay. Decay is most likely to occur when old seeds or seed pieces are planted in cold wet soil, and is further increased by poor soil drainage, the use of green compost, and planting too deeply.

SYMPTOMS

The first evidence of damping-off or seed piece decay (as in potatoes) is the failure of some plants to emerge. If seeds are attacked before they germinate, they become soft and mushy, turn dark brown, and decay. They may have a layer of soil clinging to them when they are dug up because the soil is interwoven with fine, threadlike fungus growth. Germinating seedlings shrivel and may darken. If seedlings are attacked after they emerge, stem tissue near the soil line is decayed and weakened, usually causing plants to topple and die. When only roots are decayed, plants may continue standing but remain stunted, wilt and eventually die. As seedlings get older, they become less susceptible to damping-off pathogens.

SIMILAR INJURY

Garden pests such as cutworms, earwigs, flea beetles, snails and slugs, and root maggots may also damage seedlings in the garden. It’s important to distinguish the damage done by pests from damping-off injury.

• Cutworms are dull-brownish, smooth-skinned caterpillars that emerge from the soil at night to feed on newly emerged seedlings and newly set transplants. They are called “cutworms” because they frequently snip plants off at or just below the soil surface. Look for cutoff plants, and dig around the base of injured plants to look for cutworms.
• Earwigs feed most actively at night, and can cause substantial damage to seedling plants. Damaged seedlings may be missing all or parts of their leaves and stem.
• Flea beetles are small, shiny beetles with large hind legs used for jumping. They are common in newly planted vegetable gardens, and may seriously damage seedlings by chewing dozens of holes in leaves or removing leaves completely. Feeding by large numbers of beetles gives leaves a shot-hole appearance and slows plant growth.
• Snails and slugs are most active at night and on cloudy or foggy days. Snails and slugs chew irregular holes with smooth edges in leaves, and can clip succulent plant parts and seedlings. Look for the silvery mucous trails to confirm damage was caused by slugs or snails and not damping-off pathogens or other causes.
• Root maggots are small, legless, and white. Look for their brown pupal cases in or around damaged seeds or seedlings. Seedcorn maggots infest newly sprouted seed before plants can emerge. Cabbage maggots attack older plants, riddling roots with tunnels.

Thanks and regards,

Jessey
Managing Editor
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