Blight stories and clean garden practices

Last week’s column generated interest on the subject of blight. Many Pontiac home gardeners’ vegetable patches are infested with this fungal disease which results in black patches on tomatoes and related plants.

I discovered that our Pontiac blight appears to be Phytophthora infestans, a “protist” otherwise known as a fungi, or “water mould.” Spores travel up to 20 km in rainy, windy conditions and are particularly successful at infecting potatoes, tomatoes, eggplant and nightshade in wet, humid or cool weather. (For anyone who missed last week’s column, you can find the information on blight at www.agf.gov.bc.ca/croplive/cropprot/lateblighthg.htm). Many Pontiac residents pulled out all of their tomato plants.

Otter Lake area cottagers Doug and Lindy Brandy confirmed by e-mail that they and many of their neighbours experienced blight.

 “We experienced the blight this year as did, it seems, many of the gardeners in the Ladysmith and Otter Lake area. In our case, the effect on the potato plants was even more dramatic; they went from healthy to dead in about three days. Fortunately, the tubers were well developed by then and we dug them up a couple of weeks later. Except for a minority with whitish mould on the outside, they seem fine after drying and storing but we'll need to watch them closely.”

Yes, do watch those spuds... you can’t beat the fresh crispness of home-grown potatoes, and it would be a real shame to lose them.

Has anyone noticed blight on their eggplants? Ours are clean so far, as are our spuds...

It is extremely frustrating to lose one’s crop and my sympathies go out to everyone whose plants are infected.

 Even though most people’s home vegetable gardens are purely for family/home use, (i.e. not a cash crop), the plants nonetheless represent a great deal of energy, time and, frankly, love. Typically we gardening types spend a lot of time prepping the beds, choosing the plants, growing them from seed else choosing healthy-looking vigorous plants from nurseries, weeding the beds, tying up plants -- and so on. Not to mention picking, eating or processing the fruits and vegetables... Frankly, we gardeners love this work and, those of us who practice organic growing methods are particularly thrilled when our gardens do well, chemically-free.

In future, what can home gardeners do to help prevent the spread of blight?

Janice Elmhirst, the BC Ministry of Agriculture and Food plant pathologist who wrote the web page that I quoted last week, “Late Bight Disease on Home Garden Tomatoes” had several suggestions. Here they are in entirety, quoted from the BCMAG website I listed above.

1. Grow tomatoes in a warm, dry, sunny area. If you have had blight previously, move to a different area if possible, or replace the upper soil layer since "oospores" will carryover in soil.
   
2. Water only underneath the plants, not the leaves or fruit. Drip irrigation is preferable to watering with a hose, to reduce water splash. Don’t overfertilize or overwater.
   
3. Grow on a light sandy soil if possible or cover soil with a white plastic mulch to increase soil and air temperatures around the plants and reduce humidity.
   
4. Growing plants under an overhang or a clear plastic shelter will help prevent spores from being deposited on plants by wind and rain. But plants must be covered before infection has occurred. Covering the plants after they are infected may raise humidity and make the disease worse.
   
5. Grow the tomatoes on raised beds with well-spaced trellises or in containers off the ground. Tomatoes grown on balconies or roof-tops rarely develop late blight, probably because the environment is warmer and drier.
   
6. Remove all of last year’s tomato or potato debris to prevent carry over of disease.
   
7. Remove diseased leaves or shoots immediately and all plants that are severely diseased. Bury them, or seal them in a plastic bag and take to a landfill. Do not compost diseased plants. If "oospores" are present, they will survive in compost.
   
8. Destroy any volunteer potato or tomato plants in the garden.
   
9. Destroy any nightshade weeds along fencerows. Nightshade is related to tomato and potato and is also a good host for late blight.
   
10. Apply copper sprays or other home garden fungicides recommended for late blight at least once a week when weather is favourable for disease. READ THE LABEL. Copper, which is accepted by most organic producers, should be applied for prevention more than cure, that is, before the disease has become established.

GARDENERS who are unable or choose not to follow a regular fungicide spray program for late blight are strongly urged to destroy (bag or bury) all infected tomato or potato garden plants or plant parts as soon as the disease is observed. If in doubt whether it is late blight, take a sample to a local garden centre or Master Gardener for identification.

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I cannot emphasize how important keeping a clean garden is. Composters beware: do not put infected garden vines, leaves, fruit or vegetables in the compost. Burn, bag & landfill or create a completely separate compost for your garden waste this year if your garden plants are infected with blight, wilt or bacteria infections. Compost can spread these diseases: keep it clean so it can work for you.

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Katharine Fletcher is a freelance writer based near Quyon. Contact her at fletcher.katharine@gmail.com