Thursday, 30 October 2008

Catastrophic crop failure

The dependence on a monoculturely produced crop can lead to large scale catastrophic crop failures when the single genetic variant or cultivar becomes susceptible to a pathogen or when a change in normal weather patterns occur.

The Great Irish Famine (1845-1849) was caused by susceptibility of the potato to Phytophthora infestans. The wine industry in Europe was devastated by susceptibility to Phylloxera during the late 19th century. Each crop then had to be replaced by a new cultivar imported from another country that had used a different genetic variant that was not susceptible to the pathogen.

When I look at that field of virus contaminated cannas, I think that qualifies as a catastrophic monoculture crop failure as well. The picture originates from Keith Hayward's article on Canna virus. Unfortunately, we don't have anything that is immune to Canna virus at present. However, if that field had been rotated with another crop regularly, is it possible that it would not have occurred?

This brings the topic around to crop rotation. Crop rotation avoids a decrease in soil fertility, as growing the same crop repeatedly in the same place eventually depletes the soil of various nutrients, causing plant stress. Crop rotation is also used to control pests and diseases that can become established in the soil over time. Just adding chemical fertilizer does not avoid catastrophic crop failure.

There is no evidence to suggest that our major problem of viruses is transmitted through the soil, but the general rotation principles apply, and Cannas are a particularly hungry crop, quickly consuming whatever nutrients are present. It is actually an agricultural plant. Should we be thinking about rotating the locations in which we grow our Cannas?


  1. Is this a suggestion that the various mainifestations of the canna virus are soil born?

    I have not observed this in my own gardens, and I haven't the space to rotate ornamentals.

  2. Hello rosie,

    I think the point of this article was drawing on farmers experiences when producing the same crop for many years on the same land, where the plants become susceptible to a pathogen or a change in normal weather patterns. So, was a badly weakened crop susceptible to an aphid carrying the Canna virus, when if the crop had been healthy, as you would expect from a rotated crop, it may not have been susceptible.

    The effect of monoculture is abhorred throughout agriculture and horticulture, but we do not seem to have considered its effect on our greedy, hungry Cannas, which seem to be grown that way, especially amongst large scale growers.

    I do not know the answer to this question, but I wanted to raise our consciousness to take the issue aboard.

    I also agree that there is no evidence that the canna virus is soil born, and my apologies if the article implied such a suggestion.