CORVALLIS, Ore. — Although it’s common to find strawberries that have turned brown, soft or fuzzy with gray mold, proper watering and yearly renovation can help stem the problem.

Strawberries can suffer gray mold, also known as Botrytis fruit rot. Symptoms may begin during flowering as petals and stems turn brown and entire blossoms die. More often, the rot shows up on fruit, typically starting at the stem end. Tissue turns light to medium brown, and lesions on green or white berries develop slowly, sometimes making the fruit misshapen.

Fruit rot expands rapidly near harvest, as berries redden. In advanced stages, the fungus produces a gray mold across the fruit surface. Sometimes rot doesn’t develop until after berries are picked.

To keep gray mold in check — or prevent it from worsening — Oregon State University Extension plant pathologist Jay Pscheidt recommends several strategies.

Space plants so they dry quickly after rain or irrigation, and avoid overhead watering. Drip irrigation works best. During the growing season, strawberries need about one inch of water a week, more in sandy soil or very hot weather.

Wet the soil to a depth of 6–8 inches with each irrigation, but avoid saturating soil for long periods. Even a day or two of standing water can be harmful.

Harvest and storage tips

Pick berries every few days, especially during warm, wet periods. Refrigerate ripe berries as soon as possible, removing and composting diseased fruit.

Fertilizing and renovation

Fertilize established strawberries in late summer to keep plants vigorous and encourage fall growth. Spring fertilization leads to excessive leaf and runner growth and does not increase yield.

After harvest, apply 2–3 pounds of 10-10-10 (or equivalent balanced fertilizer) per 100 square feet of row. Apply when foliage is dry.

You can maintain June-bearing strawberries for several seasons with proper management and renovation. To avoid spreading gray mold, renovate two to four weeks after the final harvest. Ever-bearing and day-neutral plants do not require renovation.

To renovate June-bearers, remove old leaves with a hedge clipper or mower after fruiting, taking care not to damage the crown. Do not remove leaves from day-neutrals or ever-bearers.

At season’s end, remove plantings that lack vigor or are no longer productive. When starting a new bed, use a different location. Gray mold overwinters in old leaves, petioles and mummified fruit.

For more information, consult the publication Growing strawberries in your home garden.

Previously titled Keep those gray fuzzy strawberries in check