Early blight and late blight are both tomato leaf diseases, but they do not behave the same way. Early blight usually starts low on the plant with dark, ringed spots on older leaves. Late blight is faster and more destructive: water-soaked patches can spread through leaves, stems and fruit in cool, wet weather.
The practical difference is urgency. Early blight is often managed by slowing its spread and keeping enough healthy leaf on the plant to ripen fruit. Suspected late blight is a stop-and-contain problem, especially where potatoes are growing nearby.
Quick Diagnosis
Start with where the damage appears and how fast it moves.
| Symptom | More likely problem | What to do first |
|---|---|---|
| Dark spots with target-like rings on older lower leaves | Early blight | Remove the worst leaves and improve airflow |
| Lower leaves yellowing, then browning and dropping | Early blight | Keep foliage dry and mulch soil splash |
| Dark, water-soaked patches on leaves or stems | Late blight | Remove affected material and check nearby potatoes |
| Brown, greasy-looking patches on green fruit | Late blight | Do not compost affected fruit or vines |
| Small spots on many leaves after wet weather | Could be Septoria or bacterial speck | Compare the pattern before treating it as blight |
Do not diagnose from one damaged leaf. A tomato plant can carry sunscald, wind damage, nutrient stress, psyllid damage and ordinary old-leaf decline at the same time. Blight is a pattern across the plant, not a single mark.
Early Blight: The Slow Burner
Early blight is usually associated with Alternaria fungi. It often shows first on the older leaves near the base of the plant, where foliage is shaded, humid and close to soil splash. The classic mark is a brown spot with concentric rings, sometimes surrounded by yellowing tissue.
Despite the name, early blight is not only an early-season problem. In home gardens it often becomes obvious once tomato plants are large, crowded and carrying a lot of lower foliage. Warmth, leaf wetness and stressed plants all make it easier for the disease to build.
Early blight can reduce yield by stripping leaves before fruit has finished, but a mild late infection does not automatically mean the crop is lost. The question is how much healthy leaf remains. A plant with a few marked lower leaves and a clean upper canopy can often keep ripening. A plant losing leaves up the whole stem needs firmer action.
What to Do About Early Blight
Remove the worst affected lower leaves first. Use clean secateurs or pinch carefully, and take the leaves out of the garden rather than dropping them under the plant. Do not strip a tomato bare; fruit still needs leaf cover and the plant still needs leaf area to feed the crop.
Then change the conditions that let the disease spread.
- Water at soil level, not over the leaves.
- Mulch under plants to reduce soil splash.
- Stake, tie or prune enough to keep airflow through the canopy.
- Remove yellowing lower leaves before they sit wet against the soil.
- Avoid working through wet tomato foliage if disease is active.
- Rotate tomatoes and potatoes away from the same bed where possible.
Sprays are prevention-and-slowdown tools, not a reset button. If you use copper or another fungicide, follow the current NZ label for tomato, disease, rate and withholding period. Food-crop labels matter more than generic garden advice.
Late Blight: The Fast One
Late blight is caused by Phytophthora infestans, the same pathogen family gardeners associate with potato blight. On tomatoes it can move quickly when conditions suit it: cool to mild temperatures, high humidity, rain, heavy dew and leaves that stay wet.
The symptoms look wetter and more aggressive than early blight. Leaves can develop dark, water-soaked patches that enlarge rapidly. Stems may show dark lesions. Fruit can develop firm brown patches, often with a greasy or bruised look rather than the dry ringed spots of early blight.
In humid conditions, whitish growth may appear around the edge of lesions, especially on the underside of leaves. You may not always see that in a home garden, so do not wait for a textbook sign if the plant is collapsing fast after wet weather.
What to Do About Suspected Late Blight
Treat suspected late blight as a containment problem. Remove badly affected plants or heavily infected sections and dispose of them away from the compost. Bagging the material before carrying it through the garden is better than shaking spores across the path.
Check potatoes at the same time. Tomatoes and potatoes are close enough hosts that a late blight problem should be managed as a solanaceous patch problem, not just a tomato problem. Volunteer potatoes are especially unhelpful because they can carry disease pressure quietly into the next season.
Do not save seed potatoes from a suspect crop. Do not compost infected tomato or potato foliage. If fruit is visibly infected, discard it. Healthy-looking fruit from a lightly affected plant is a judgement call for fresh eating, but do not store or preserve damaged fruit.
Do Not Confuse Blight With Psyllid or Leaf Roll
Tomato-potato psyllid can also cause curling, yellowing and stunted plants. The check is different: turn leaves over and look for tiny insects, nymphs or white sugary specks. If those are present, read Tomato-Potato Psyllid in NZ before assuming a fungal disease.
Physiological leaf roll is milder again. Older leaves roll upward but stay mostly green, and the plant keeps growing and fruiting. That is common after stress and is not the same as blight moving through the canopy. For a fuller comparison, see Why Are My Tomato Leaves Curling in NZ Temperate? and Why Are My Tomato Leaves Curling in NZ Cool/Mountain?.
NZ Timing and Risk
Blight risk rises when tomato foliage stays wet. That can happen in different ways across NZ: humid northern summers, still sheltered gardens, close-planted glasshouse tomatoes, wet late-season spells, or cooler districts where evening dew sits on leaves for hours.
In warmer gardens, the canopy can get dense early, so lower-leaf hygiene and spacing matter before disease is obvious. In cooler or mountain gardens, the growing season is shorter and late-season rain can arrive while fruit is still trying to ripen. There, keeping plants open and picking mature fruit before a wet spell can matter as much as squeezing out one more week on the vine.
The planting calendar matters because strong, well-timed plants cope better. Use the NZ Temperate Planting Calendar or NZ Cool/Mountain Planting Calendar to keep tomatoes inside the realistic local season instead of nursing stressed plants through the wrong end of the year.
Prevention Checklist for Next Season
Most blight prevention happens before the first spot appears.
Give tomatoes space. Dense planting looks efficient in spring, then turns into a damp wall of foliage in summer. Stake or cage plants early so you are not trying to untangle diseased stems later.
Mulch once the soil has warmed. A clean mulch layer reduces soil splash onto lower leaves and helps moisture stay even. Water deeply at the base, preferably in the morning, so the plant is not sitting wet overnight.
Prune with restraint. Removing the lowest leaves and some crowded laterals helps airflow, but hard stripping can expose fruit to sunscald and stress the plant. The aim is a canopy that dries, not a bare stem with fruit hanging in full sun.
Keep potatoes, old tomato vines and volunteer solanaceous plants under control. Pull out finished crops promptly, especially if they were diseased. Rotate where space allows, and avoid planting tomatoes straight back into a bed that carried heavy disease the previous season.
Finally, inspect regularly. Early blight caught on lower leaves is much easier to slow than disease found after half the plant has browned. Late blight caught early is easier to contain before it jumps through the tomato and potato patch.
The Bottom Line
Early blight is usually the lower-leaf, ringed-spot disease you manage by removing infected foliage, improving airflow and keeping leaves dry. Late blight is the fast, wet-looking disease that can damage leaves, stems and fruit and should be contained quickly.
For both, the best control is a dry, open canopy, clean crop hygiene and realistic tomato timing for your part of NZ. Once blight is established, the goal is not a miracle cure. It is protecting the remaining healthy leaf, saving clean fruit, and preventing the problem from carrying into the next season.
Growing tomatoes this season? Check your timing: NZ Temperate Planting Calendar or NZ Cool/Mountain Planting Calendar.