Late Blight Is Spreading Through Kitsap County Gardens Now

It's mid-August 2026, and if you've been watching your tomato or potato plants closely, you may have already noticed something alarming: dark, greasy-looking patches spreading across the leaves, stems turning black at the base, and fruit developing firm brown rot that seems to appear almost overnight. This is late blight — Phytophthora infestans — and it is moving through Kitsap County gardens right now.

Late blight is not a typical fungal disease. It's caused by an oomycete, a water mold that behaves differently from the powdery mildew and botrytis that Kitsap gardeners more commonly deal with. It spreads aggressively in exactly the conditions our county produces in late summer: cool nights, warm days, persistent morning fog off the Sound, and humidity that rarely fully breaks. The spores travel on wind and water, and a single infected plant in a neighborhood can seed multiple gardens within days.

How to Identify Late Blight Right Now

The symptoms appear first on older, lower leaves. Look for:

• Water-soaked, pale green or dark olive lesions on the upper leaf surface, often with a greasy or translucent appearance
• White, downy sporulation on the underside of leaves, particularly visible in morning humidity — this is the most diagnostic sign
• Brown-black lesions on stems that spread rapidly upward and girdle the plant
• Firm, brown, corky rot on tomato fruit, usually starting at the shoulder or top of the fruit
• Dark, sunken lesions on potato tubers that extend into the flesh and smell faintly of decay

Late blight moves fast. A plant that looks mildly affected on Monday can be dead by Friday. Do not wait for confirmation — act the moment you see suspicious lesions combined with that characteristic white fuzz on leaf undersides.

Note that late blight is distinct from early blight (Alternaria solani), which produces concentric ring patterns and yellowing that progresses more slowly. If you're seeing yellowing with brown rings, that's early blight — serious, but manageable differently. If you're seeing dark water-soaked spreading with white undersides, that is late blight and requires immediate action.

Why Kitsap County Is Particularly Vulnerable

Late blight thrives when temperatures sit between 60°F and 70°F at night with high relative humidity, combined with daytime temperatures below 85°F. Kitsap's marine climate delivers exactly this pattern during August. The fog that rolls in from Hood Canal and Puget Sound in the early morning hours keeps leaf surfaces wet well into mid-morning, and our heavy dew means spores have extended wet periods to germinate even when it hasn't technically rained.

Our regional proximity to commercial potato and tomato growing regions in the Willamette Valley and eastern Washington also means airborne spore loads can be significant during outbreak years. Late blight can spread via infected transplants purchased from garden centers, and in high-spore years it rides weather systems across significant distances.

Dense planting, overhead irrigation, and beds with poor airflow all amplify risk. The summer garden threat profile in Kitsap County is real — this is not a disease that rewards a wait-and-see approach.

Immediate Steps If You See Late Blight

1. Stop overhead watering immediately. Switch entirely to drip irrigation or hand-water at the soil line only. Wet foliage is the single fastest way to spread this disease through your remaining plants.

2. Remove and bag infected material — do not compost it. This is critical. Late blight spores survive and continue to sporulate on plant tissue. Every infected leaf, stem, and fruit must go into sealed plastic bags and into your garbage — not your compost pile, not your yard waste bin if you're using a shared composting service. The heat of a home compost pile is not sufficient to kill Phytophthora infestans.

3. Work in infected beds last. If you have multiple growing areas, always handle your healthy plants first, then move to affected beds. Wash your hands and change gloves between beds. The spores transfer easily on tools and clothing.

4. Remove lower leaves on all remaining Solanaceae plants. Even on plants that don't yet show symptoms, removing the bottom 12 inches of foliage improves airflow dramatically and removes the most likely entry points for splash-borne spores.

5. Apply a copper-based fungicide immediately. Copper fungicides (copper hydroxide or copper sulfate formulations) are the most effective organic-approved tools for suppressing late blight. They work as a protective barrier — they cannot cure infected tissue, but they significantly slow spread to healthy tissue. Apply to all remaining Solanaceae plants, including those showing no symptoms yet. Reapply every 5–7 days, or after any rain or heavy dew event.

Important note: copper applications are suppressive, not curative. If a plant is more than 50% affected, removal is almost always more effective than treatment.

Should You Pull the Whole Plant?

This is the question most Kitsap gardeners struggle with in August, when tomatoes are just beginning to ripen and the season feels too short to give up any ground. The honest answer: if late blight is confirmed and a plant is significantly affected, pulling it protects your other plants more than saving that plant will benefit you.

A heavily blighted tomato plant will not recover. It will continue producing spores that infect neighbors. The fruit already on the plant is unlikely to ripen normally — it will often develop blight rot before maturity. If you pull the plant now and remove all infected material, you have a much better chance of preserving your remaining plants through to first frost.

For potatoes, the calculus is similar but with one additional consideration: late blight spreads into the tubers. If you're seeing heavy foliar blight on potatoes, cut the tops off at soil level — do not pull the whole plant immediately. Leave the tubers in the ground for two to three weeks after top removal. This allows the skin to set and reduces the risk of blight entering through harvest wounds. When you do dig, cure and inspect every tuber carefully, and consume or store only those with completely clean skins.

The Botanical Family Factor: Why This Affects More Than Your Tomatoes

At Roots and Wings Gardening, we think in botanical families rather than individual plants — and late blight makes this approach essential. Phytophthora infestans infects the entire Solanaceae family: tomatoes, potatoes, peppers, eggplant, and tomatillos are all susceptible to varying degrees. Tomatoes and potatoes are highest-risk, but during a heavy outbreak year, it's wise to monitor all your Solanaceae plants.

This is also why crop rotation matters so much. If you've grown tomatoes and potatoes in the same bed year after year, any infected tuber material left in the soil becomes a reservoir for next season's outbreak. This disease can overwinter in infected tuber debris — a potato left in the ground after harvest, a piece of root system not fully removed. Understanding how potatoes grow and overwinter in Kitsap County soil is part of understanding how to break the blight cycle.

Our rotation protocol is to never plant the same botanical family in the same bed within three to four years. After Solanaceae, follow with nitrogen-building Fabaceae (beans, peas, favas), then soil-restoring Apiaceae or Amaranthaceae. This rotation doesn't prevent all blight risk from airborne spores, but it eliminates the soil reservoir risk entirely, which is a significant portion of the problem.

Resistant Varieties Worth Knowing for Next Season

You can't change your variety selection now, but you can make very different choices for next season. Late blight resistant tomato varieties have improved dramatically in recent years, and several perform well in Kitsap's climate:

• Defiant PhR — excellent late blight resistance, good flavor, determinate habit that suits our shorter season
• Iron Lady — resistant to both early and late blight, solid flavor for a disease-resistant variety
• Jasper — cherry type with strong resistance, very productive in Kitsap conditions
• Mountain Magic — grape-type with outstanding resistance and reliable flavor
• Legend — developed at Oregon State specifically for the Pacific Northwest, good resistance and excellent flavor

For potatoes, varieties with late blight resistance include Elba, Jacqueline Lee, and Sarpo Mira, though Sarpo Mira is harder to source in the US. Elba is a good mid-season option with reasonable resistance that suits Kitsap's season length.

Resistant does not mean immune. In a high-pressure year, resistant varieties will still show blight — just more slowly and less catastrophically. They give you time to intervene rather than watching a plant collapse in a week.

Cultural Practices That Reduce Risk Going Forward

For the remainder of this season and planning ahead to next year, these practices meaningfully reduce late blight pressure in Kitsap County gardens:

Increase spacing. Dense plantings restrict airflow and keep foliage wet longer. Tomatoes in Kitsap should be spaced at minimum 24 inches apart, with 30–36 inches preferred for indeterminate varieties. More space means leaves dry faster after morning fog and dew.

Use a high trellis or stake system. Getting tomato plants off the ground and training them vertically improves airflow around the entire plant. This is not just about productivity — it's about disease suppression. Vertical growing systems are particularly valuable in Kitsap because of exactly this humid-summer dynamic.

Mulch heavily at the base. A 3–4 inch layer of straw or wood chip mulch around the base of Solanaceae plants significantly reduces splash dispersal of soil-borne spores onto lower leaves. This is one of the most underused tools in Kitsap tomato growing.

Monitor weather windows. Late blight pressure surges when you have five or more consecutive days with nighttime temps below 68°F and humidity above 90%. In Kitsap, that's essentially every week in August. This means preventive copper applications during those windows are almost always worth applying — even if you see no symptoms.

Source clean transplants. Many late blight outbreaks in home gardens begin with infected transplants purchased from garden centers. Inspect transplants carefully before purchase — look for any suspicious stem discoloration or leaf lesions. If you start from seed, you eliminate this risk entirely. Starting your own tomato seeds at home is one of the most effective long-term disease management strategies available to Kitsap gardeners.

What to Do With Tomatoes Still on Blighted Plants

If your plant is coming out but you have green or partially ripe tomatoes on it, all is not lost. Green tomatoes without visible blight lesions on the fruit itself can be ripened indoors at room temperature away from direct sunlight. Do not store them in plastic bags and do not refrigerate them — cold temperatures stop the ripening process entirely and degrade flavor.

Inspect every tomato before bringing it inside. Any fruit with dark, firm, slightly sunken patches on the skin is blighted and should be discarded, not ripened. The blight rot within blighted fruit spreads to neighboring fruit, so don't let a blighted tomato sit next to healthy ones.

Green tomato chutney, fried green tomatoes, and green tomato salsa are all genuinely excellent uses for the harvest you pull early. This is where a blight outbreak, handled early and decisively, can still produce a meaningful yield.

The Bigger Picture: Disease Management as Garden Health

Late blight is a dramatic and fast-moving disease, but it is also a useful reminder of why regenerative garden management matters. Healthy soil, diverse plantings, proper rotation, and strong airflow don't just make plants more productive — they make gardens genuinely more resilient when disease pressure spikes.

Monoculture beds of tomatoes with poor airflow, grown in the same location year after year, are maximally vulnerable. Diverse gardens with good structure, managed rotation, and healthy soil biology recover faster and sustain less total loss when blight does arrive. The principles that guide everything we do at Roots and Wings — back-to-basics tradition, holistic ecosystem thinking, regenerative stewardship — are the exact same principles that make late blight manageable rather than catastrophic.

If you're uncertain about what you're seeing in your beds right now, the WSU Extension office for Kitsap County can help with disease identification. A confirmed diagnosis is worth the effort before you strip a bed that might actually have early blight or another, more manageable problem.

Act fast, remove thoroughly, protect what remains, and let this season be the one that changes how you set up your Solanaceae beds for next year.