Potato

Potato blight

What you will see

Watery brown, collapsing leaves with a fine white growth on the undersides; tubers rot.

The source says: it is the most serious disease of potatoes.

How to protect

1. Prevention

   • Earth up potatoes well; the tubers are then protected from spores washed into the soil.
   • Early varieties often escape the disease, but they are not immune.
   • Rotate crops (at least 4 years) and do not grow tomatoes in that soil during that time either — they suffer from the same blight.
2. By hand when symptoms appearOnce about 25% of the leaves are affected or the stems show lesions, cut the haulm off 2 in above the ground and lift the tubers two weeks later. Dispose of the debris; do not compost it.

Potato blackleg

What you will see

Yellowing stems, stunted growth and black rot at the base of the stem.

The source says: it is a common bacterial disease of potatoes.

How to protect

1. Prevention

   • Most important: remove and dispose of affected plants immediately.
   • Use certified seed potatoes and store potatoes in dry conditions.
   • Improve drainage in wet parts of the bed; rotate crops.
   • Try more resistant varieties (e.g. 'Charlotte', 'Pixie', 'Saxon', 'Vales Sovereign').
2. By hand as soon as it appearsDig up the diseased plant straight away and dispose of it. There are no chemical products for gardeners.

Potato cyst nematodes

What you will see

Damaged root system, weak growth and low yield.

How to protect

1. Prevention

   • Do not grow potatoes and tomatoes repeatedly in one place: leave a gap of at least 5–6 years on affected soil.
   • Harvest in good time, do not let plants grow for long; weed out volunteer potatoes.
   • Try varieties with resistance to cyst nematodes (e.g. 'Cara', 'Maris Piper').
2. By hand ongoingLong crop rotation and removal of volunteer potatoes.

Wireworms

What you will see

Wiry larvae of click beetles eat holes in roots and tubers.

How to protect

1. Prevention

   • Tolerate a few wireworms; in grass and turf they are usually harmless.
   • The population usually falls within two years after turf is dug up.
2. By hand when digging overCultivating the soil exposes the larvae to birds.
3. Biological April to SeptemberNematodes against wireworms, watered into moist soil at 12–68 °F (April to September).

Colorado potato beetle

What you will see

Larvae (mainly the last two stages) eat the leaves and can strip plants down to the stems; damage is high in warm, dry weather.

How to protect

1. Prevention

   • Regularly check the undersides of leaves; watch for the first beetles and larvae.
   • Act only when the threshold is exceeded (15 young larvae per plant in field growing).
2. Gentle spray at the first larvaeNeem extract (azadirachtin) is weaker, so it is applied earlier, ideally at the first larvae (L1).
3. Chemical — only when nothing else helps when most larvae are at stage L1–L2A product authorized in your country against Colorado beetle; leave out pyrethroids entirely (resistance has been reported in Bavaria) and rotate groups of active substances.