I read with interest the article in the October issue of the ARS magazine by Steven Steps about "organic growers". He discussed the differences among "organic" and "environmentally friendly". He cited the main differences as those who use nontoxics, natural "toxics", and natural materials that easily breakdown in the environment. It really comes down to a personal preference, but there is no clear line that makes an individual one type or another. Common household bleach is manmade, yet since it is relatively safe and many "organic" growers I know recommend its use. Personally, I don't care for highly toxic or carcinogenic materials, so I prefer using low toxic materials such as Malathion and Funginex over many of the "natural" materials. To illustrate toxicity, Steve mentioned that baking soda, a natural, organic, fungicide, is much more toxic than Funginex. So is baking soda bad because it is more toxic than other materials?

When I was working on my Master's degree, Toxicology was one of my favorite classes (this was before roses). The bottom line is: everything is toxic. It all depends on the dose or amount of material the individual is exposed to. For example, if you drink 4 gallons of water all at once, you will "drown" in your own tissue, and we are largely made of water. One of my favorite "toxics" is common table salt. The ladies of Victorian times committed suicide by ingesting a pound of salt. So in reality, the amount of the material has a lot to do with toxicity.

To understand toxicology and toxics, there's a few definitions you will need to know first:

• Toxic- poisonous to living organisms.
• Toxicology- the study of chemical substances which exert deleterious effects on living organisms; also called the study of poisons.
• LD50 - the average lethal dose or concentration necessary to kill 50% of the test subjects. This is usually expressed as oral exposure in milligrams (mg) per kilogram (kg) of body weight of the test subject, which is normally rats.
• Dose- the amount of toxicant exposed to the subject.
• Highly Toxic- single dose levels of 50 mg/kg or lower.
• Carcinogen- capable of creating, directly or indirectly, cancer.
• Mutagen- effects DNA in cells.
• Teratogen- effects embryo development.

The first thing I'd like to do is to put the LD50 definition in perspective. Malathion is one of the less toxic pesticides known today. It's LD50 is 1375 mg/kg orally, 4444 dermally (skin). An average person weighs around 70 kg or 154 pounds. So the LD50 orally is 1375 times 70 which equals 96,250 mg or 96.25 grams. This amounts to taking a "swig" directly from the bottle, and that would only kill half of the population who drank it. The actual amount that we would use, let alone breathe, is far less than these amounts. In perspective to other "common" materials, Steve's article lists baking soda as having a LD50 of 3500 mg/kg, aspirin at 1800 mg/kg, and Funginex at 16,000 mg/kg!

To further understand the materials we use, the following definitions are necessary:

• Pesticide- a material used to kill or keep away an pest. This includes insects, mites, and fungus.
• Insecticide- a material used to kill or control insects.
• Fungicide- a material used to kill or control fungus growth.
• Miticide- a material used to kill or control mites, for us, spider mites.

So what about the so called "natural" insecticides. There are three main insecticides that are considered natural: Nicotine, Pyrethrum, and Rotenone. So, are they really "safe" or nontoxic? Nicotine is the main component of tobacco and has a LD50 range of 10-60 mg/kg which places it in the highly toxic range. Pyrethrum, from chrysanthemums, and Rotenone, from tropical plant roots, are both in the 100-300 mg/kg range which is moderately toxic. Both Nicotine and Rotenone persists on the plant, so you have to make sure you don't spray around vegetables. Rodale's Successful Organic Gardening also recommends Sabadilla, which is moderately toxic not only to mammals, but also to honey bees, plus the toxicity increases with age. The organic and environmental people approve of these products because they come from natural products, and breakdown into harmless components in the environment, or do they? In any case, they are toxic to man and animal. So how do these natural materials compare to man-made pesticides?

Before we get to today's pesticides, let's look back on the older pesticides. There are several types of pesticides that were man-made. The organophosphates were among the earliest. The organophosphates work by inhibiting acetylcholine (ACH), a main component of nerve impulse transmittal in the central nervous system. Tetraethyl pyrophate (TEPP) was the first member of this class. It was a good insecticide, but it was highly toxic to mammals. It's LD50 is 1.1 mg/kg orally and 2.4 mg/kg dermally. Several of the older rose references recommend the use of TEPP. Following TEPP was a material that is still in use today, Parathion. Parathion is likewise very toxic with a LD50 of 13 mg/kg orally and 21 mg/kg dermally, and is the insecticide with the greatest number of reported accidental deaths. Another member of this family is still used today, Diazonion. Diazonion is also toxic with a LD50 of 108 mg/kg orally and 200 mg/kg dermally. Have you noticed that these materials are just as toxic as the previously mentioned "naturals"?

Another insecticide class that was created about the same time as the Organophosphates were the Organochlorines. The Organochlorines operate by damaging neuromuscular motor nerves. The first member of this group was the golden cure-all of pesticides, DDT. DDT has a LD50 of 113 mg/kg. The biggest problem, as we found out later, is that it was bioaccumative (builds up in the body) and didn't readily breakdown in the environment. There were other Organochlorines that were just as bad as DDT; Chlordane, Lindane, and Aldrin. Another insecticide group was the Carbamates. Baygon is the most common Carbamate and is still used today. As a class, they have lower dermal toxicity, but are very toxic orally (Baygon's LD50 is 83 mg/kg orally).
Rodale's takes a greater liberty concerning the use of organic fungicides. They recommend copper, but mentions its toxicity to mammals, fish, and aquatic invertebrates, plus the compound "persists indefinitely in soil". They also recommend Bordeaux Mix, sulfur, lime-sulfur, and fungicidal soap. As previously mentioned, most fungicides have a low toxicity, and one, Captan, is a suspect teratogen. Note: several fungicides have a metal cation base, which can be determined by it's name, e.g. Zineb is zinc and Maneb is manganese.

There are two miticides in general use, Avid and Vendex. Believe it or not, Avid is a natural product. Avid is a by-product from a natural occurring soil microorganism. Many "organic" growers don't consider it natural because it is currently manufactured synthetically, since the natural process does not produce enough to meet demands. Both Avid and Vendex are slightly toxic, having LD50s of 650 and 2631 respectively.

The "newer" insecticides and fungicides are far less toxic than their ancestors, and many are less toxic than those from natural sources. Orthene is one of the most common insecticides and comes as a 9.4% solution of the active ingredient. The LD50 for a 100% solution of the active ingredient is 980. So Orthene is 10 times less toxic than the pure material. Sevin, Maverik, and Cygon have similar toxicity, around 250, except Sevin is a 22% solution, so its toxicity is 5 times that number. Actually, Malathion comes as a 50% solution, so its LD50 is double the previously mentioned number.

Most of the fungicides are considered low toxic to relatively nontoxic. Captan has a LD50 of 10,000, but is a teratogen suspect material. Eagle (Rally) comes as a 40% solution, with the pure material having a LD50 of 1600. Pure Triforine has an LD50 of 2000, but Triforine EC is a 18% solution and Funginex is a 6.5% solution, so the LD50s for these compounds are roughly 5 and 15 times that number, respectively. The main problem with some fungicides is the oil they use can cause eye damage, so they are moved up in the hazard category. The hazard categories in decreasing order are: Danger, Warning, and Caution. The problem with the newer insecticides and pesticides continues to be a longer breakdown period in the environment compared to the naturals, but they are far superior to their ancestors.

So you can see that nothing is perfect for either method of pesticide or fungicide control. Hopefully, our "newer" pesticides have a low biological life and will do little harm, except to slaughter those mean, nasty, bugs that ate my potential queen!