It was only a few weeks ago that your newly planted garden seemed to be doing great, perhaps even picture perfect. But now the season of mysteries has begun, with leaves showing spots, holes, and missing parts, usually with no insect in sight. Good thing we live in age of easy digital photography, which makes it possible to get a closeup view of holes in leaves, making the clues easier to see. Here are some seasonal problems you are likely to discover when you snap closeups of distressed leaves, or make use of a simple magnifying glass.
Slugs and Earwigs
Slugs are the most common cause of holes in leaves, but they often remain unseen because they feed at night. Sometimes larger slugs eat leaves from the edge inward, but small slugs make irregular holes inside leaves, as shown in the chard leaf on the right in the above photo. Slug holes always have smooth green edges.
The pepper leaf on the left has been sampled by slugs, but most of the damage was done by earwigs, which make ragged, irregular chomping patterns. The bane of container gardeners and those with framed raised beds, earwigs hide under pots or in bed frame crevices during the day and feed on tender plant leaves at night. They love basil and the new growth of peppers, artichokes and even milkweed.
What to Do: Use homemade traps to manage slugs and earwigs, and be ready to move containers to interrupt infestations. Delay mulching when slugs and earwigs are present in the garden, because mulches provide daytime cover for these nighttime feeders.
Cucumber Family Foes
The coarse, hairy leaves of cucumbers and squash repel feeding by many pests, including furry four-legged ones. Despite their prickly defenses, squash and cucumbers are often damaged by striped and spotted cucumber beetles (see damaged seedling on left, above), squash bugs, and squash vine borers.
What to Do: With so many able enemies on the wing, cucumber family crops benefit greatly from insect-excluding row-covers, which can be left on until pollinators are needed to work the flowers. Inexpensive wedding net (tulle) is perfect for this use.
Tomato Tribe Troubles
Flea beetles make tiny round pinprick holes in tomato, eggplant, pepper and potato leaves, but while eggplant needs the protection of a fabric barrier, tomatoes, peppers and potatoes usually outgrow flea beetle damage. Leaf spots caused by fungi are a much bigger threat to tomatoes. Tomatoes have juicy leaf hairs that retain moisture in wet weather, making them easy targets for fungal diseases like early blight, which causes spots to develop on lower leaves in early summer. Spots on leaves caused by early blight have a bulls-eye pattern, with rings of dead tissue surrounding a sporulating center. Leaf tissues between the spots turn yellow, and then the whole leaf withers to brown.
What to Do: Grow plants at proper spacing to promote good air circulation. When lower leaves show spots, use sharp pruning shears to remove all leaves up to at least 12 inches (30 cm) from the ground. This basal pruning removes inoculum and helps the plants dry faster after rain or heavy dew.
Frog-Eye Spots on Chard
Warm summer rains often give rise to cercospora fungi, which cause spots and holes in leaves of chard, beets, carrots, celery and a few other crops. Different cercospora strains infect the two plant families, but in both cases blister-like spots form that often crack open in the center. With cercospora-related carrot leaf blight, infected foliage becomes weak and brown, though the carrots may continue to produce new growth.
What to Do: You can’t stop the rain that contributes to cercospora outbreaks, but you can keep plants thinned and weeded to help them dry out between showers. Problems often begin on the oldest leaves, which can be cut out and composted to slow the spread of this widespread disease. Harvest aggressively to remove inoculum and encourage new growth.
We like to think of a garden as a natural ecosystem created by a human for the benefit of plants, but it’s actually a very wild place where the fate of a crop is up to very tiny life forms. The more you understand about them, the more fascinating your garden’s secret world becomes.