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  • W. H. Perron

Late blight, Phytophtora infestans


For many home gardeners, Phytophtora infestans, or late blight, is known as THE most devastating tomato disease in gardens.

This disease triggers fairly regularly when there is too much moisture in the air and on the plants, it is manifested by rotting stems, leaves and fruits. The rainy summers of recent years have greatly favoured late blight.

Recognize the disease

At the end of summer, black spots can appear on the inferior leaves of the tomato plant.

The spots quickly get bigger and can be accompanied (or not) of white down on the reverse side of the leaves.

The disease rises at the top of the plant. The stems become brown.

Sluggish black spots appear when the fruit is almost at maturity.

Tips for preventing disease

Select only strong, healthy plants. If you made your own seedlings, once your seedlings are ready for transplant, select the strongest seedlings, they will start better and will be more resistant to disease.

Choose a favourable exposure. The tomato loves the sun. An exposure to a moderate wind is also favourable. Mildews are fungi whose spores are carried by the air. By locating your plants in a place where the wind is flowing, mildew spores will have less chance of attaching to your tomato plants. In addition your plants will dry more quickly after a rain or watering which will limit the sporulation of late blight.

Plant in favourable soil. The land must be fertile, light, the soil balanced. An imbalance always favours an illness. So never sow in the same place as the previous year.

When planting, add some nettle leaves to

the bottom of the hole, cover them with a thin layer of soil, then place your tomato plant and top up. The nettle will release nitrogen that will give the tomato vigour to ensure a good start. Watering with nettle manure the weeks following planting will have the same effect.

Water properly. Never water the leaves and stem of the tomato. Water your feet. Ban sprinklers, prefer drip, see no system. Let the soil dry between two watering, it must never remain sodden continuously. Your tomatoes will taste better with less water.

Diversify. Set up several varieties of tomatoes. They do not all react in the same way to mildew. Similarly, diversify between early, mid-season and late varieties.

Plant on the right date. The tomato is a frosty plant, so wait until the end of the frost before planting your tomatoes in the garden.

Distance your tomatoes sufficiently. The best way to lose control of late blight is to plant your tomatoes too tightly together. In many gardening works it is advisable to distance the tomatoes by 50 cm. It is not enough ! Leave 75 cm at 1 m between two plants and put companion plants between two plants (basil, parsley, carnation).

Straw your tomatoes. If it is possible to mulch your plants with nettle or try mulching comphrey or horsetail fields. Any other mulching is also welcome as long as it remains natural, it will limit evaporation and by decomposing will feed the plant.

Prune the plants at favourable times. Because the injury caused by tearing the greedy favours the gateway to mildew. If you cut the greedy ones, make it only on sunny days and as far as possible during the hottest hours of the day. By cutting the greedy at the hottest time and in the sun the wound will dry faster. If you cut the greedy pruner (which is not necessary) regularly disinfect your tool with alcohol at 70 °.

Treatment both preventive and curative.

Use baking soda. Every 10 days (from the beginning of July), spray the plants with this mixture:

1 teaspoon of baking soda.

1/2 teaspoon of dish-washing liquid

1 litre of water

Do this early in the morning instead of in the evening so that the leaves dry quickly.

Baking soda is a 100% natural product that is used in the kitchen.

• In the event of an attack on a plant, burn affected leaves and spray horsetail, comphrey or a garlic decoction on all plants in the garden every 8 days, or more often if it rains.

Grow varieties that are late blight tolerant

Tolerance to late blight means that an outbreak of the disease progression, will be delayed to allow a reasonable harvest.

Varieties that have proven tolerance to late blight.

Hyb. Plum Regal

Our first variety of Italian tomato resistant to mildew and late blight. Plum Regal has a beautiful dark red internal color and a fabulous flavor making it ideal for sauces or salsas. It is also crack resistant and the determinate plant will keep healthy in the garden.

Plant habit: determinate

Maturity (Days): 73

Color: Red

Plant size: Medium

Fruit weight: 120-130 g

Hyb. Mountain Magic

Excellent tasting Campari type cocktail tomato. Tolerant to cracking with a long shelf life. Fruit can also be harvested in clusters. Dark red fruit. A must in your garden!

Plant habit: semi-determinate

Maturity (Days): 65

Color: Dark red

Plant size: Large

Fruit weight: 35 g

Hyb. Mountain Merit

Mountain Merit is considered as a superior tomato by vegetable growers. With a 4-5 week harvest window, the dark red fruits grow on a compact, determinate plant and offer good resistance to multiple diseases common to homegrown tomatoes such as late blight. High adaptability. An all-around flavorful fruit, perfect for sandwiches or as side-dish.

Plant habit: Determinate

Maturity (Days): 69

Color: red

Plant size: Small

Fruit weight: 280-330 g

Hyb. Jasper

URBAN GARDENER. AAS 2013 winner. This small tomato about 10 g, stands out for its distinctive flavor, smooth texture, holding ability, and overall garden performance (high yield). Jasper is tolerant to Mildew and Blight (Early and Late Blight).

Plant habit: indeterminate

Maturity (Days): 60

Color: Red

Plant size: Large

Fruit weight: 10 g


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