When we returned recently from holiday we found, as is to be expected at this time of year, a growth explosion in the glasshouses and polytunnel, and a most unwelcome population explosion of aphids. There are often one or two times in the year when aphids can become problematic. The first attack of the year typically occurs on the broad beans. At that early time of the year there can be insufficient numbers of predators to keep them under control, and the gardener may need to intervene to prevent significant loss of crop. Generally a little later in the year, fruit trees and bushes are another popular target for aphids, where they can cause a fair bit of damage to the young leaves and shoots. It was on our fruit trees that we noticed a substantial infestation that was not present when we left.
Fortunately, aphids are fairly easy to deal with. More often than not, they can be squished and rubbed off, perhaps with the aid of a jet of water from a hose. One can also use various sprays to kill them. In our garden, we do not use synthetic bug sprays. I am not keen either on some of those intended for organic use. Even though a given treatment might be based on naturally occurring substances, that does not necessarily make it a good thing to spray around the garden, and I have found in the past some products that the plants clearly do not like. Instead, a spray of soft soap is quite effective and, as far as I can tell, a more gentle way of dealing with soft bodied insects like aphids. Soft soap may be sold as insecticidal soap, or any natural unfragranced soap based on potassium fatty acids should be suitable. Some household soaps might be suitable, but synthetic detergents are best avoided. I use an organic castile soap, which is based on vegetables oils. Diluted to a 1% solution with water, this is a mild spray that is effective only on contact, so must be sprayed thoroughly, lifting affected leaves to ensure that the target pests are covered. Repeated applications might be needed to deal with a particularly heavy infestation.
Treatment was delayed on this occasion, as I had run out of soft soap last season. I placed an order for some more, and a week or so later we mixed up a solution and went to spray the affected fruit trees and bushes. However, in the days between observing the infestation and getting around to actually spraying the plants, nature had intervened. When spraying the only mildly affected apple cordons, we spotted a few ladybird larvae on the more heavily infested parts. Ladybirds are truly one of the gardener’s best friends. In both their adult and larval state, they can consume large numbers of aphids.
We stopped spraying immediately and examined the situation more closely. On the apple trees, we observed a few larvae. Aphids, being sap sucking insects, favour the softer plant tissue around new shoots. On our cordons, the affected parts of the trees are to be pruned out in late summer, so any damage is generally inconsequential. On the more heavily infested plants, notably the cherry trees in the fruit cage, we found that the aphids had been all but wiped out, and there were ladybird larvae everywhere. We did not spray at all in the fruit cage. With so many larvae predating the aphids there was no need for further concern. Indeed, without a good supply of aphids, we would not have our good supply of those insects that feed on them.
This was a good reminder of the principles of organic gardening. It is not simply a case of adopting the same approach but replacing synthetic fertilizers, pesticides, and fungicides with organic alternatives. There is, or should be, a different philosophy. One of the key principles is diversity, as monocultures are not natural and are difficult to maintain. If one can provide a more diverse environment that supports natural predators, then nature will tend to maintain a reasonable balance. On occasion, the gardener must intervene to prevent substantial loss of crop, but in the main, predator and prey can be kept in reasonable balance. Spraying is usually non-specific, affecting equally predator and prey. Had we continued even with our soft soap spray, we may have harmed the ladybird population, and at the least, deprived them of the food source needed for them to proliferate, something we might have regretted next year, when the aphid population might then have fewer natural predators about to keep a check on it. I make few interventions in the garden; partly as I lack the time and inclination, but also because it is, more often than not, unnecessary, and quite possibly counterproductive, except when things have become markedly unbalanced.
It is worth noting that some plants can be susceptible to various viruses. These can cause weak and distorted growth, and poor crops. Aphids can cause the spread of such viruses, so, although there are good reasons not to overreact to an aphid infestation, there may be circumstances in which one might wish to be rather more proactive in dealing with them. An alternative approach with various sap sucking insects is to try to deter them before they become problematic. A popular organic option appears to be a spray made from an infusion of hot chillies. One can imagine how the capsaicin in the chillies – the compound that makes them hot to taste – might be a discouraging irritant to potential pests. Garlic is also commonly used, the scent supposedly being an effective deterrent to many pests. I have used such an infusion in the past, and perhaps I should think about spraying some next season to discourage the pests, particularly early in the year when there are fewer predators about.