Fusarium wilt a ‘nasty’ fungal disease

We think one of our cucumber plants was stricken with this disease although the leaves only showed wilting, no yellowing...

A sick cucumber plant.

A sick cucumber plant.

Fusarium wilt. Nasty fungal disease that attacks the vascular system of a plant. Symptoms include leaf wilting and yellowing on the leaves. Some reference books call the disease ‘yellows.’ We think one of our cucumber plants was stricken with this disease although the leaves only showed wilting, no yellowing. The name of the pathogen that causes this wilt is Fusarium oxysporum.

There are more than 100 species divisions of this pathogen that attacks specific host plants. For instance, the fusarium wilt fungus that affects cucumbers is called Fusarium oxysporum f. sp. cucumerinum (the f. sp. stand for forma specialis).

Other strains target tomatoes, sweet potatoes, melons, squashes, pumpkins, bananas, cabbage, a host of ornamental plants…the list goes on.

Fusarium oxysporum attacks plants when soil and air temperatures are between 24 and 32 degrees Celsius for a period of time such as what we have been experiencing this summer.

And once this disease is loose in the soil, it is difficult to get rid of…if ever. Needless to say, we are a little concerned.

However, we may be OK since none of the other six cucumber plants are showing any signs of wilting. Our fingers are crossed that we perhaps misdiagnosed the problem. I am fairly certain we would have seen some sign by now if the others were to catch the disease.

Fusarium wilt works fast, killing the plant off in three to five days. Close down the food channels of a plant and it is definitely not long for this world.

So…if our cucumber did not have fusarium wilt why were the leaves wilting? Well…there is a crown and root fusarium wilt disease that also attacks cucumbers but more usually when they are still just seedlings. This form of fusarium wilt is more commonly called damping off.

Our sick plant was at least six feet, so not sure that diagnosis is accurate. But the roots were definitely in very poor condition when we yanked it out. Only had a spread of about four or five inches and they should have been over a foot at this stage of their growth.

Wilting from inadequate water should not have been a factor as we have a soaker hose in the cucumber bed set on a timer. All of the plants have been getting regular water.

My big mistake was I did not look at the cut stem to check the condition of the vascular system. If it was showing signs of discoloration, this would have definitively told us we had fusarium wilt. But I was too busy holding the garbage bag for John and trying to keep the leaves away from neighboring cucumber plants.

So…we will never know for sure what was wrong with our sick cucumber plant. Rather than take chances of losing the whole crop, we jumped on the problem plant quickly. Better to lose just one.

Still on a bit of a sour note…an update on Rudbeckia hirta ‘Cherry Brandy,’ the new burgundy-maroon-red-flowered gloriosa daisy. A new acquisition to John’s garden this year, it has been an absolute stunner, despite the heat. We love it.

But I have recently discovered it is actually a half-hardy annual, not a perennial. If the label had mentioned hirta, I would have clued in as these are typically short-lived while others such as Rudbeckia fulgida ‘Goldsturm’ reliably return every year.

This is highly reminiscent of Coreopsis ‘Limerock Ruby,’ a new introduction from a few years ago. We purchased three plants three years in a row (because John just had to have that fabulous shade of red flower in his garden) before we discovered it was not a perennial. Ouch.

We may still come out on top with ‘Cherry Brandy’ though as the seeds are viable, whereas ‘Limerock Ruby’ was sterile. The plant will self-seed and I will also store some seeds over the winter. Just to be sure.

Leslie Cox co-owns Growing Concern Cottage Garden in Black Creek. Her website is at www.duchessofdirt.ca and her column appears every second Thursday in the Record.

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