One of the products that I often hear gardeners raving about are their fertilizer / pesticide combination spikes which are supposed to not only feed your plants, but also kill all of the insects which attack them. I, personally, have not used these products, but I’m generally the kind of person who says “If it works for you then keep using it”. Still, these spikes bug me a little. Here’s why.
First of all I should point out that I’m not opposed to fertilizer spikes by themselves. I’m a little concerned that fertilizer should be spread out instead of concentrated in one place, but still, I don’t consider them that bad. The insecticides used for these spikes is where I have the problem. Once upon a time these spikes were made with a chemical called disulfoton (aka disyston) which is bad news. It’s a water soluble chemical which is highly toxic to people. If you have an old package of fertilizer / insecticide spikes around there’s a good chance they were made with this chemical. Do yourself a favor and get rid of them. This stuff is really toxic and not to be messed with. On the other hand, if you’ve purchased fertilizer / insecticide spikes recently, then the active insecticide in those spikes is probably imidacloprid. Imidacloprid is a mixed bag when it comes to safety. It’s not nealy as toxic as disulfoton, but it’s not non-toxic. It has been banned in Europe for a variety of reasons, the most important of which seems to be that it was implicated in the collapse of bee hives (imidacloprid is systemic insecticide so it will get into a plants pollen where honey bees could eat it). At this point it hasn’t been ruled out as having something to do with hive collapse here in the states — though if it does have a role it does not seem to act alone. It can also affect other beneficial insects who feed on pollen. Additionally, it has been known to control some pests while allowing mites to go crazy — in fact, it may even increase the rate of mite egg laying.
But imidacloprid is an effective insecticide which works against a wide range of insects which you that you might find on your plants. It is much safer than many of the older systemic insecticides, and it isn’t readily translocated to fruits (a problem that many people are concerned about with systemic insecticides is the movement of these insecticides into the fruit itself where it can’t be washed off — Imidacloprid is translocated to fruits –just not that much — it moves in the xylem and fruit takes up mostly phloem).
So these spikes are one of those things that I’m wary of. Not to say you shouldn’t use them, but be aware of what they are and what they could do before you buy them.