Saturday, 28 July 2007

Systemic sprays give virus protection

Just read an interesting paper, Studies on the relationship of canna mottle virus and its vector myzus persicae, authored by M. Datta-Gupta & S.P. Raychaudhuri in 1975, published in the Indian Journal of Entomology 37(4): pages 336-343. So, this again proves that Canna virus is not a recent phenomenon, that paper was over 30 years old. Moving on, myzuz persicae is the formal name for the common-a-garden aphid, the culprit that spreads Canna Mottle Virus.

Interestingly, the paper stated that when a contaminated aphid eats at the Canna leaf for 1 minute it is contaminated. Equally, an uncontaminated aphid eats the foliage of a contaminated Canna, then it is also contaminated in one minute.

This started me thinking; once an aphid starts eating the leaf of a Canna protected by a systemic insect spray it dies within seconds. On that basis we can assume that regular spraying with a systemic insect spray can protect our Cannas from the virus.

This leaves us with a dilemma, those of us trying to advocate non-chemical solutions cannot win this particular argument, because it may be an hour before a ladybird ascends on the aphid, and the damage is done.

This brings us to ants. A drop of honey, or something like it, is the connecting bond between the ant and the aphids. It is exuded by the latter through certain tubercles which are situated at the end of the abdomen, and is, of course, the product of the endless quantities of sap, which, so long as it lasts, these insects are for ever pumping up and swallowing from the plant they inhabit. This honey, or honey-dew, to use the more special name bestowed on it, the ants want, but they are not content with drinking it whenever it issues from its manufacturers, in natural course. This is not sufficient, and they have learned to increase the flow of so valued a beverage by their own efforts, in other words, they milk the aphids, which thus become their cows. To do this they tap them with their antennæ, softly and gently, on the sides of the abdomen - a quick little shower of touches. Under the influence of this probably pleasant sensation the aphids becomes willing to part, and, raising the abdomen, "teems her refreshing dew" in a drop from the tip of it. This action of the ants cannot, in Europe, be successfully imitated, at least it has not been, and if an ant is not forthcoming the fluid is contained in the body of the aphids until necessity compels its being ejected. Probably the ants, if delayed in their visits, are missed by the aphids, as a cow misses her milker, and long before they do excrete, as the process is called, they would perhaps have done so had they felt able. The sensation no doubt of the ant's antenne on the abdomen has become, through usage, the almost necessary stimulus to the act produced by it.

So, logically, we also have to destroy ants, as they are the next step in the vector. They farm the aphids and protect them from predators, and if they are also eliminated then that reduces the risk of virus contamination considerably, by reducing aphid activity considerably. However, there is one more aphid fact that I picked up recently. Flying aphids can travel up to 10 miles, using the winds to keep them afloat for considerable periods. So, if anyone within 10 miles has virus on their Cannas and the wind is in the right direction, then we are all vulnerable, no matter how we try to protect our plants. However, if our plants have a systemic protection, then they will kill the aphid before it contaminates the plant.


  1. hi there-what would be a good systemic product to use to protect my cannas? thanks

  2. We have found that the Pravado Ultimate Bug Killer works fine for us. We are trying others, as we don't want to become too dependant on one product, especially the way that the EU keep banning gardeners chemicals.