Plant Doctor Archive

Tomatoes and blight

I have a question for the Plant Doctor regarding blight and tomatoes. Last year I had quite bad blight on my tomatoes and was wondering if I should not use my old wooden tomato stakes and buy new ones. Can blight remain on the wooden stakes and infect plants the next year? Also, is it worth adding copper to the soil when planting tomatoes to fight against blight or is this an old wives' tale?

I had exactly the same problem as you did last summer — so I asked our head of Horticulture, Ingrid Ennis (my boss!) what she suggested. Her advice was to try to prevent the pathogen from infecting the plants in the first place. So this year, I've avoided planting other members of the potato family (which tomatoes are in) nearby — so no more potatoes. The neighbour's potato jasmine has also had a good chop back, so it isn't too close to my new tomato plants. Members of the same family can often harbour the same diseases. I've also been growing other different vegetables in the area that was affected, in an attempt to reduce the disease in the soil (like a mini crop rotation). In my case, I planted lettuces, rocket, silverbeet, and spring onions, all of which I could harvest before the tomatoes went in. To replenish the nutrients in the soil I added compost and sheep pellets.

Like you, I was also worried about the stakes possibly harbouring fungi or bacteria, so I am using new stakes this time. I am also putting down a nice layer of pea and lucerne straw around my tomato plants — not only does this cut down on watering needs in summer, but it will stop pathogens being splashed onto your plants when it rains or when you water them. You can buy this straw from most garden centres. The only drawback is that nesting birds tend to rake it up for their nests.

I wouldn't put copper into the soil. Too much copper is toxic to plants and it can build up in the soil. However, a good copper spray on the foliage every now and then is a good preventative for blight, so I will be trying that soon (most garden centres stock several choices of spray).

Different tomato cultivars have different levels of resistance to blight. I personally found last summer that cherry tomatoes, such as 'Sweet 100' seemed to have more resistance than some of the larger cultivars I was growing.

I hope this helps.

Advice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

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