Tomato and potato: early blight and late blight

Tomato and potato share two major diseases: early blight and late blight. Late blight can wipe out a field within a week of cool, cloudy, humid weather, so prevention is everything.

Doses in this guide are taken from the product labels. Always read the label and leaflet before use, respect the pre-harvest interval, and check with your nearest Biostadt retailer or agronomist for advice specific to your field.

Identify the blight

	Early blight	Late blight
Leaf spots	Brown spots with concentric rings ("target board"), starting on old leaves	Water-soaked, dark patches that spread fast, white growth under the leaf in the morning
Weather	Warm, alternating wet and dry	Cool (15–22 °C), cloudy, foggy or drizzly
Fruit / tuber	Dark, leathery sunken spots near the stalk	Greasy brown patches on fruit; reddish-brown rot inside tubers

Prevention

• Use healthy seed tubers and disease-free seedlings; rotate with non-solanaceous crops for at least 2 seasons.
• Stake tomatoes and remove the lower leaves touching the soil.
• Earth up potatoes well so tubers are covered and protected from spores washing down.
• Remove volunteer plants and cull piles, which are the first source of late blight.

Spray plan

Situation	Tomato	Potato
Preventive, before canopy closes	Captek 2500 ml/ha	Dolby 300 g as per label or Captek 2500 ml/ha
Early blight	Alliance 750 ml/ha or Decimer 500 ml/ha	Bendaco 1750 ml/ha
Late blight risk weather	Duo guard 1500 ml/ha	Sanchar 2500 ml/ha or Duo guard 1500 ml/ha

• In late blight weather, spray every 7 days; otherwise every 12–15 days.
• Rotate products and never apply the same systemic fungicide more than 2–3 times in a season.

Pests to watch

• Tomato fruit borer: Fulstop – D or Tremor at the label dose, starting at the first flower.
• Thrips and whitefly spread leaf curl and bud necrosis viruses: EDAN is labelled for both on tomato. Use yellow and blue sticky traps.
• Aphids in seed potato: EDAN at the label dose.

Nutrition

BioGreen Calcium B+ 2–2.5 ml per litre during fruit development in tomato reduces blossom-end rot and cracking.

Spray safely

• Wear gloves, a mask, full sleeves and eye protection while mixing and spraying.
• Spray in the early morning or late evening, never against the wind or before expected rain.
• Use clean water and the full recommended water volume. Poor coverage is the most common reason a spray "does not work".
• Do not mix products unless the label allows it. If unsure, do a jar test first.
• Keep children and animals away, and never reuse empty containers. Rinse them three times, puncture them and dispose of them safely.