Inch by Inch: When it's time to call in the chemicals

Posted Wednesday, August 29, 2012 in Sustainable Maine

Inch by Inch: When it's time to call in the chemicals

This is cedar-apple rust on leaves. In later stages, the pustules grow into large orange spore cases, which open and spread the spores to other trees.

Once in a while, you may be faced with two heartbreaking options: Let an otherwise sturdy and healthy plant die, or admit that organic techniques aren't going to save it and call in the chemicals.

What you do will depend on many factors. Was the plant very expensive? Is it very productive? Is it one of several that may develop the same disease or fungus?

The more expensive the plant, pr the more likely it is to spread its disease to others, or the more productive it is, the more likely you are to try to save it, regardless of your organic convictions.

We were faced with one of these choices this year. One of our apple trees developed a blight that looked like cedar-apple rust. It can kill a young tree. 

Since the tree in question (a Gravenstein apple) had already been quite productive in its third year, we were unwilling to let the tree die. There was also the consideration that this apple tree was part of a small orchard, and there was a good chance that the sick tree might infect the others.

We had tried the various tools in the organic arsenal, including copper sulfate, to no avail.

Since the Gravenstein had already been harvested, and none of the other young trees were fruiting this year, we went ahead and treated it with Captan, a fungicide which is known to treat cedar-apple rust (if that is what it is) and isn't systemic. That is, it doesn't get into the apples — it's a topical spray.

It wasn't an easy decision. Captan is a known carcinogen, and is toxic to animals that consume large quantities of it, but the apples are not in a location where they are being consumed by cattle and sheep, nor were the chickens affected, as they live in a completely different part of the property. Captan has a short half-life, of only about 13 days on apple trees, which was another factor in the choice. We were late enough in the season that bees and other pollinators were not affected.

And the choice of uprooting an otherwise healthy tree when a possible chemical medicine could help seemed extreme. 

With luck, this treatment will work and the apple tree will recover and not spread the fungus to its fellow trees. 

If you are faced with this choice, do your homework and decide whether the plant is worth saving, whether the chemical will cause more harm than good, and whether the risks to your health, your livestock's health, and the pollinators' health is too great. 

Then select the narrowest possible choice in chemistry, if your organic arsenal doesn't do the trick.

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