Is late blight lurking in your garden?

It is a late, white spring but those that start growing bedding-out-plants already have seeds in the pot.

It is a late, white spring but those that start growing bedding-out-plants already have seeds in the pot.

Alberta Agriculture wishes to remind growers and gardeners to keep a lookout for late blight which is caused by the fungi, phytophthora infestans.

Late blight is most often seen in tomato and potatoes but will also infect eggplants, peppers, petunias and the weeds nightshade and wild tomato.

Last season this disease was reported in many home gardens as well as in market gardens and some commercial operations. The pathogens spread quickly in cool, wet weather, like last summer, and can infect large areas very quickly.

If weather conditions are similar this season the disease will once again be prevalent.

The pathogen does not survive our cold weather unless in is enclosed in live material such as potato tubers. Infected tubers are easy to spot because they will have sunken rotten areas around the eyes. Given the correct conditions they will quickly infect all the tubers that are being stored.

This is not always the case and some bins might have a few infected potatoes that are planted or discarded in the spring.

Even a few infected tubers can cause major problems. Plant only healthy tubers that have either been stored at home or purchased from a reputable source. Discard any diseased material. If diseased material has been purchased return it to the point of purchase and report it to Alberta Agriculture.

Diseased plants that were discarded last fall into compost heaps or refuse piles need to be re-examined and properly disposed off.

If all parts of the infected plants were frozen the pathogens should be dead.

If tubers or fruit are still recognizable the material should be either buried or double bagged and sent to the landfill.

As the disease will overwinter in tubers, dig and properly dispose of all volunteer potatoes. Loosing a hill of early potatoes is much better than an entire crop.

Other precautions can be taken this spring. Plant tomatoes and potatoes further apart. Crowded plants that are competing for water, sunlight and nutrients are more likely to become diseased.

Air circulation between plants cuts down on the spread of diseases.

Spend a little more time this growing season looking for diseased plants. Initially late blight infects older leaves. Look for spots on leaves that look wet or rotten. These spots will spread over veins and become dry and brittle in a couple of days.

The fungi will fall to the ground to infect tubers or move to the fruit of the tomato.

Give the correct conditions, wet and cool, the plant could be dead in a few days. The timeline is extended in warm, dry weather.

Remove all infected plants as soon as they are discovered. Infected plants can be buried, frozen or double bagged and sent to the landfill.

During the growing season the disease spreads through spores which will travel between plants through wind, rain or movement of water.

The best ways to stop the spread of any infestation: insect, disease or fungi is to keep have good cultural practices. Keep the garden area clean. Remove weed piles, old plants and any plant litter. Plant far enough apart to allow the air to circulate between the pants.

For more information on late blight visit or contact Rob Spencer at 403-742-7563. Fax: 403-742-7527, or email

Linda Tomlinson is a horticulturalist and educator living in Rocky Mountain House. You can contact her at