by Steve Jones, past ARS President
This article is an ARS Award of Merit Winner, originally published in "Rose Ecstasy," bulletin of Santa Clarita Valley Rose Society, Kitty Belendez, Editor
If you are like most people, you will pull out the old bottle of pesticide when you see something eating or covering your roses. You probably don't give a lot of thought about the material itself, other than it works. In this article we will cover the different types of pesticides and their modes of action.
WHAT IS A PESTICIDE?
The first definition we need to know is that of a pesticide. The Latin root "-cide" means poison or to kill. So a pesticide is a pest poison. A pest is anything that annoys you, like insects, fungus, weeds, dogs, kids, etc. The pesticides most likely used by rosarians would be:
1) insecticide kills insects
2) fungicide kills fungus
3) miticide kills mites (aka aracnacide kills members of the spider family)
4) herbicide kills weeds.
There are other "cides" that a rosarian might use like a rodenticide, which kills rodents.
THREE SIGNAL WORDS
Next would be the three signal words. These are on the label of all toxic materials and will let you know the degree of toxicity. The signal word could be based on the material itself or the carrier.
The three signal words are:
1) Danger Highly toxic. Generally not available to the home gardener.
2) Warning Moderately toxic. Most of the insecticides that we use will fall into this class.
3) Caution Slightly toxic. Most fungicides fall into this class. There are two subclasses, category 3 and 4, where 4 is less toxic than 3.
The insecticides are divided into numerous groups, mostly by their mode of action or type. These range from virtually harmless to very toxic. These groups include:
3) Insecticidal Soaps
9) Sulfur Compounds
12) Growth Regulators
As you can see, there are several classes of pesticides, and their modes of action can vary from one classification to the next. Most of these are unlikely to be used by the rosarian or the general gardener, so there is no need to know them all. Of the ones that we do use, you should have a general knowledge of the material and mode of action, which will be important for the treatment of exposures.
The botanicals are those insecticides that are derived from plant products. Each has a different mode of action, but are commonly grouped together. The ones most likely to be used by rosarians are:
1) Pyrethins and Pyrethrums
There are a host of other botanicals but they are not likely to be used by rosarians, such as anabasine, limonene, nicotine, and quassia. Nicotine is very toxic and not used as much as in the past. Nicotine sulfate was sold as Black Leaf 40 for many years. The effects of both of these compounds is complex, involving disruption of several bodily functions but mostly attacks the skeletal muscle and central nervous system and the insect dies from respiratory paralysis.
Pyrethins and Pyrethrums are obtained largely from dried chrysanthemum flowers. They are effective insecticides and have good knock down power. They are generally safe to humans and thus used for indoor insecticides. Some of the "safe" insecticides use these materials. They have a paralytic effect on insects. Most products contain another pesticide to make sure the insect is killed, usually piperonyl butoxide.
Rotenone is found in many different plants but mostly harvested from the roots of certain tropical plants. It breaks down quickly, thus has a low environmental burden. It affects the central nervous system of the pest, which leads to respiratory paralysis. It is also very toxic to fish and birds, so care needs to be taken with this product. It is mostly safe for mammals. It takes about 2-3 days to kill insects.
Sabadilla is from the seeds of the sabadilla plant (a member of the lily family). It was once used as an ointment. It is a stomach and contact poison that affects the central nervous system causing paralysis. Considered one of the least toxic materials. Not used much in the United States, but still available. It is toxic to bees.
Ryania is extracted from the stems of a South American plant. It is a stomach poison that causes insects to stop feeding soon after ingestion. It is moderately toxic but relatively harmless to humans and animals.
There are a few products that the rosarian might use containing microbiologicals. These are:
1) Bacillus thuringiensis
2) Beauveria bassiana
3) Milky Spore
These are a group of beneficial bacteria and other microbiologicals that attacks the insect. There is one product that is commonly used and that is bacillus thuringiensis (BT). When the bacteria grows, it produces toxic compounds, which disrupt the stomach lining of the insect. Commonly sold as DiPel.
Another product is the fungus beauveria bassiana. This is an effective insecticide for all stages of the insect. It is safe to use around crops as is BT. The fungus spores attach to the shell of the insects and as it germinates, it enters the body of the insect, causing death.
Milky Spore is not used in California. It is an effective pesticide for the control of Japanese Beetle grubs in lawns. It takes several years for the spores to spread before they become effective. Milky Spore is a bacterium, bacillus popillae, and is safe to pets and humans.
For the environmentally concerned rosarian, the insecticidal soaps and oils are largely safe. There are several types used by the rosarian:
1) Insecticidal Soap
2) Horticultural Oil
3) Natural Oils
4) Petroleum Oils
The insecticidal soaps are mostly potassium salts of fatty acids. They are non-toxic to humans and are the main ingredient in Safer products. The soaps impair the waxy layers on the exoskeleton and the insect desiccates. Soaps are also suffocating. Safe to humans and most animals, plus safe to use around food crops. Effective against aphids, grasshoppers, leafhoppers, and somewhat for spider mites and thrips.
Most of the horticultural oils will suffocate the insect. These oils have been around for many years and are effective against scale. Petroleum oil is commonly used for dormant sprays. Natural oils, such as neem oil, have both smothering and paralytic effects on pests. Neem oil comes from a tree and the main active ingredient is azadirachtin. Most of the oils have some fungicidal effects by smothering the spores before they can form. Castor oil has been found effective in the control of moles and other rodents. It doesn't kill the critter but is effective as a repellent. Most are effective against aphids and whiteflies.
Special care needs to be taken with oils when our summer temps exceed 80 degrees, as the oil will burn the foliage.
This is by far the largest group of insecticides, and the ones rosarians are more likely to use. The mode of action is pretty well the same in all of this class. The acetylcholinestarase (ACH) enzyme is phosphorlated rendering it worthless. This enzyme is important for the transmission of nerve impulses. So basically all motor and nerve functions cease and death comes from respiratory and pulmonary edema. They are easily absorbed into the body through the skin and by respiration. Needless to say, all rosarians should take special care when using these products. Typically they are highly toxic to animals, fish and birds.
Here are the more common organophosphate insecticides that rosarians use:
Disulfoton This is by far the most toxic of any insecticide you can buy from the nursery. It is the main ingredient in the dry, granular systemics. We discourage rosarians from using products with this poison. Highly toxic to pets and birds. Newer systemics do not use this compound, so try those instead. Effective against all sucking insects, such as aphids and thrips.
Malathion Anyone in California is very familiar with this insecticide. Used for controlling the Mediterranean fruit fly, massive spraying of neighborhoods occurred via helicopters at night to eradicate this pest. One of the least toxic members of this class, it has a highly odorous scent. The carrier can eat into car paint as we found out from the nighttime spraying. Overall, the best of the chemicals in this class for the home gardener. Effective against aphids, thrips and grasshoppers.
Cygon (dimethoate) This chemical is used as a foliar systemic and soil drench. It is good for controlling mites and sucking insects.
Dursban (chlorpyrifos) This product was commonly used for controlling ants. Now banned; when it leaves the shelves it is gone for good.
Diazinon One of the most widely used of the organophosphates. Used for a wide range of insects and thrips, plus lawn insects. Quite toxic.
Orthene (Acephate) The most common insecticide sold to the general public. Generally low toxicity compared to other members of this group, this chemical remains popular today. Effective against aphids, beetles, midge and thrips.
This is one of the newest groups of insecticides for general use by the home gardener; most are derived naturally or as a by-product. There are two main compounds that are used today by rosarians:
Avid (abamectin) - The main compounds from Avid are natural fermentation by-product of the soil bacteria streptomyces avermitilis. It acts as an insecticide/ miticide/ nematicide by affecting the nervous system and paralyzing the pest. A common miticide, it appears to have some effect on the control of fire ants. Basically non-toxic to humans, but highly toxic to fish.
Conserve (spinosad) Similar to Avid, this product is from the fermentation of the soil actinomycete saccharopolyspora spinosa. It is less toxic to fish and is a good choice for IPM programs as it is relatively non-toxic. Effective for caterpillars, thrips, aphids and spider mites.
These chemicals are compounds of nicotine. The main member of this family is Imidacloprid, which is the main ingredient in Merit. Like organophosphates, these chemicals block nerve impulses from occurring causing paralysis of the central nervous system. Merit itself is moderately toxic, but very effective against many insects. It is not toxic to fish, but toxic to birds and bees. Good for controlling white flies, scale, thrips, aphids and grubs.
Once the most popular insecticide, there are few members of this family still in commerce. The only one the rosarian would use is Sevin (carbaryl). The mode of action is similar to the organophosphates. These highly toxic materials function by carbamation of the ACH enzyme, thus causing skeletal and nerve paralysis. They are very persistent in the environment thus leading to their demise. Sevin is a common insecticide for the homeowner. It is a contact poison rather than a systemic. In other words, the insect has to come into contact either directly or indirectly. Good for controlling sucking insects, ants and grasshoppers.
These are compounds of the pyrethins and are more stable and toxic. They last longer in the environment than their parents. The one material that the rosarian would likely use is Mavrik (fluvalinate). I personally dislike this chemical as I am very allergic to it and have found others that have the same reaction. These compounds will destabilize nerve membranes thus interrupting nerve impulses, and the insect dies from paralysis. It is moderately toxic to humans and birds, and highly toxic to fish. It breaks down rather quickly in the environment. Effective for caterpillars, beetles, aphids and spider mites.
A new product available to rosarians is Talstar (bifenthrin). It is effective for worms and chinch bugs. Another new member of this class is cyfluthrin, which is being used in Bayer Advanced Rose Spray.
Sulfur compounds are still used today, either as elemental sulfur or by their compounds. Sulfur is more effective as a fungicide but has some effect on insects such as thrips and spider mites. Elemental sulfur is most likely the chemical used by rosarians.
The chlorinated pesticides are rarely used today, mostly banned by EPA for their long persistence in the environment and damage to wildlife. DDT is the best known of all these chemicals. DDT was the pesticide of choice in the 50s and was very effective for controlling mosquitoes. Lindane is one of the best of these compounds, which was very effective of controlling the hard to control pests like flatheaded borers. It is also not available today to the rosarian. The only materials that might be found and used today are methoxychlor and Kelthane (dicofol). Kelthane is not easily available and no longer approved for use on roses. It was a good miticide.
The chlorinated chemicals destabilized nerve cell membranes thus stopping nerves impulses, which paralyzes the insect.
Once very popular, especially as Arsenate of Lead, this was an effective pesticide. No longer used due to toxicity and metal poisoning of humans and the environment.
Grow regulators are not short-term pesticides, rather, they affect the skin or exoskeleton of growing insects. The skin is damaged, so when the insect molts as they grow, the skin will be damaged or stunted and the insect will not develop, or will be deformed. We don't use any pure growth regulators, however, several chemicals has this effect, with the most noticeable being azadirachtin, the main ingredient in neem oil.
Rosarians can use fumigants if they have problems in their house or in their soil. We are familiar with the fumigants used for termites, often having to tent your homes. If you have problems with soil pests like fungus, nematodes, etc., you may need to fumigate the soil. The most common is methyl bromide, a common fumigant used on fields before planting strawberries. Most fumigants are controlled substances so the general rosarian would not have access to them.
There is a large host of pesticides that we consider inorganic. The main ones in this class are:
1) Diatomaceous earth
We discussed elemental sulfur before. Diatomaceous earth (DE) is used for the control of sow bugs, slugs and snails. DE is the skeletal remains of algae. DE absorbs moisture and waxes from the skins or surfaces of pests, causing them to dry out. It has a low toxicity to humans. Salt acts the same way as DE, and is very effective against slugs and snails. Remember our childhood torturing of snails with salt? Fun, but can damage plants by salt build-up in soil and not recommended.
There are several other chemicals or methods for control of insects. There are also spreaders/stickers like Indicate 5 that are not actual insecticides, but they make the insecticide more effective. Stirrup M is a sexual attractant for spider mites and will lure them to the miticide, but is not an insecticide itself.
One of the miscellaneous materials used by the rosarian and general gardener are the hexakis compounds. The most common is Vendex, which is the miticide used in Orthenex Formula III products. The active ingredient is fenbutatin oxide. It is toxic to birds, mammals and fish.
A new material to rosarians is Floramite (bifenazate). It is a good miticide but not for continual use as it has a high risk of resistance. Another new miticide is Hexygon (hexythiazox). It is only effective for controlling mite eggs and not the adults.
My favorite insecticide is my fingers or a good pair of sharp pruners. They are very effective for controlling beetles, caterpillars, grasshoppers, etc. The sole of my shoe if also effective for controlling slugs and snails.
Although they are not insecticides per se, there are a lot of beneficial insects and critters that are effective for controlling insects naturally. Ladybugs, birds, lacewings are but a few of the beneficials available to the rosarian.
Fungicides are those materials used to control fungus. The most common fungal diseases for roses are blackspot, downy mildew, powdery mildew, botrytis, anthracnose and rust. Rosarians are more likely to spray to control this pest than insecticides, often combining them together in the sprayer.
Fungicides can also be placed into different categories, but typically they are either eradicants or protectant. They can be further broken down into systemics or protectives. There are few if any eradicants on the market today, most have been banned over the years based on environment persistence or toxicity. There are generally three modes of action by a fungicide: inhibits energy production, interferes with the cell structure or interferes with growth.
Protectant fungicides are those that protect the plant from spores at the point of application. They are not absorbed into the leaf; rather they form a protective coating. With watering, rain, etc., they need constant application to be effective. Most protectant fungicides have a low risk of resistance.
A systemic is absorbed into the leaf and moves around within the plant. Usually they have a specific mode of action. Because fungicides have low toxicity and come in a form not readily absorbed into the body, they are of minor danger to the applicator. Most warnings deal more with the carrier rather than the material itself.
The classifications of fungicides can be broken down into the following:
6. Copper Compounds
As mentioned earlier in this article, several natural products have fungicidal properties such as neem and horticultural oils. By having an oily coating on the foliage, most of the airborne fungal spores will not stick nor survive, especially powdery mildew. Safer fungicide has fatty acids (soaps) and other organic materials in their fungicide, which stops the growth of fungus by contact. A new product for controlling powdery mildew is E-rase, which is jojoba oil and it provides a protective cover for the leaf. It is not considered toxic, and is actually used in cosmetics.
The antibiotics are commonly used for treatment of bacteria and fungal diseases in humans, and have made the transition to the world of plants. Streptomycin is a common antibiotic, but not used on roses. The most common of the antibiotics is Compass, which has the active ingredient trifloxystrobin. It works by interfering with the respiration of the fungus, attacking the mitochondrial pathway, and inhibits spore generation and growth. It breaks down freely in the environment and is unlikely to cause harm to birds, bees or fish, even though aquatic animals may be affected in higher concentrations. Good for controlling blackspot, anthracnose, downy mildew, botrytis, rust and powdery mildew.
The aromatics are generally benzene ring based compounds. The only member of this class that a rosarian would use is chlorothalonil, commonly known as Daconil. A more concentrated form is Bravo. Daconil is one of the most common protectant, broad-spectrum fungicides available to the home gardener. Normally used for lawns, it is the old standby for blackspot control. However, Daconil burns leaves, so it is not used as much on roses. It acts on the enzyme systems within the fungus, thus stopping growth. It is still a good fungicide due to its low risk of resistance and is not toxic to birds or bees, but very toxic to fish.
There are two main azoles for use on roses, the conazoles and benzimidazoles. Both have the same mode of action; they are steroid inhibitors, which stop the growth of fungal cells. They have both protectant and some curative properties.
There are two members of the benzimidazole family that rosarians would use, Benomyl (also sold as Benlate) and Cleary 3336 (thiophanate methyl). Both are very low in toxicity to humans and animals. Cleary is good for control of powdery mildew, anthracnose, botrytis and blackspot to a lesser degree. Benomyl is good for control of powdery mildew, however, it also has a high risk of resistance. Both have modes of action that interfere with cell growth.
The largest class of fungicides used by rosarians is the conazoles. These are steroid inhibitors, which stop the growth of the fungus. All are systemic in action, and have moderate risk for resistance build-up. The main conazoles are:
Cyproconazole (Sentinel) This product has been taken off the market due to toxicity problems. A long-term control for blackspot, it has been replaced by Compass as the main blackspot fungicide.
Myclobutanil (Nova, Eagle, Rally, Systhane) One of the most effective of the conazoles, this product has been in use by rosarians for control of powdery mildew for several years now. Somewhat toxic to fish and bees.
Propiconazole (Banner Maxx, Immunox) This product is commonly found on the shelves of most garden shops and Kmart. A very effective fungicide for blackspot, rust and powdery mildew if used in combination with another fungicide like Compass. Very toxic to fish.
Triadimefon (Bayleton, Fung-Away) Mostly used for turf diseases, the rosarian is not likely to use this material. This systemic is absorbed through the roots of the plant. Effective for rust, anthracnose and powdery mildew. High risk of resistance build-up.
A relatively small class of fungicides, the main member is Oxycarboxin (Plantvax). Excellent for the control of rust. Not to be mixed with other materials when you spray. Not toxic to birds or fish.
Although these could be considered inorganic fungicides, copper compounds are among the oldest protectant fungicide controls and have some bacterial control as well. There are a few available to the general gardener in most nurseries and mail order catalogs. Their mode of action is inhibition of energy by the cell.
Kocide (copper hydroxide) is the most common of the copper compounds found at any nursery. Effective for powdery mildew, anthracnose, botrytis and blackspot.
Phyton 27 (copper sulfate) Another common copper compound found at most nurseries. Effective for powdery mildew, botrytis and blackspot. Also effective as a bactericide.
Bordeaux Mixture One of the oldest fungicides, it contains copper sulfate and slacked lime. First used in 1882, it is still found today in many organic catalogs.
Cheshunt Mixture Another of the old-time remedies, was made from copper sulfate and ammonium carbonate. It was used to stop damping off of seedlings.
The only member of this protectant class that a rosarian would run into is Captan, which is commonly used to stop damping off of seedlings. It could be used for other fungi control, however it is pretty specialized for the rosarian. Low risk of resistance build-up. Captan inhibits energy production by the cell.
This is another large fungicide family and one of the oldest. These are heavy metal based fungicides. Very effective especially when used in combination with other fungicides for controlling blackspot. Most were developed during the 1940s and 50s. Their mode of action is inhibiting energy production by the cell which interferes with enzyme activities. They are still in use today because they have a low risk of resistance. The common Dithiocarbamates are:
Mancozeb (Manzate, Fore, Dithane M-45, Protect) Contains zinc and manganese ions, good for control of botrytis, blackspot, downy mildew and anthracnose. Somewhat effective for powdery mildew.
Maneb Contains manganese ions, good for control of blackspot.
Zineb Contains zinc ions, it readily breaks down to ethylenethiourea (ETU), a known teratogen. Effective for downy mildew, rust and anthracnose. Not used much today by rosarians.
A class of preventative systemics that is not used by rosarians except for Rubigan. Because of our hot sun and high temperatures or cool coastal weather, rosarians out west rarely use Rubigan. It can cause leaf damage known as puckering. Good for the control of powdery mildew, but there are other better, less damaging materials available. Rubigan stops fungus from growing by reducing their ergosterol production. It is also toxic to fish.
There is one member of this class that rosarians will use if they need to and that is mefenoxam (Subdue). This is a systemic that is quickly absorbed into the plant. One of the few fungicides that is effective against downy mildew. Originally the main ingredient in Subdue was metalaxyl, but the product was taken off the shelves voluntarily by Ciba. Mefenoxam is an isomer of metalaxyl and is under scrutiny by EPA. One problem is it has a high risk of resistance, so you have to careful about overuse.
There are several inorganic fungicides available for the general gardener and rosarian. We have already discussed copper compounds. Here are some the more common inorganics fungicides:
Sulfur The oldest known fungicide, it is still widely used today. It is used mostly as a dust with the elemental sulfur, and is a main component of lime sulfur, a common dormant spray for fungal spores. It is a direct contact fungicide and effective against powdery mildew. Sulfur inhibits energy production in the cell. However, it is rarely used out west because high heat will cause burnt foliage. It is still around today because it has a low risk of resistance.
Baking Soda (sodium bicarbonate) Another age-old remedy against powdery mildew and blackspot. The early ARS Annuals published articles about the effectiveness of baking soda back in the early 1920s. Causes damage to the cell walls of the spores.
Potassium bicarbonate (Remedy, Armicarb 100) A relative of baking soda, it has the same effect. Considered environmentally friendly, its use is rising among the populace. More effective than baking soda.
There are a few of the fungicides than don't fit neatly into the above classes. The first is
Aliette (fosetyl aluminum), which is an aluminum based phosphate systemic which is effective for downy mildew.
Other materials that have some fungicidal properties are the antitranspirants, such as Wilt Pruf, which is effective against powdery mildew.
Of the miscellaneous materials, only one is commonly used by the rosarian and general gardener, and as Vanessa Williams would sing, "you've saved the best for last."
Funginex (Triforine) This is the best of all the systemic fungicides on the market today and the most effective. It is the one material that anyone can purchase at their local nursery and even grocery store. It comes in a powdered form, liquid, spray bottle and aerosol. Funginex is very effective against powdery mildew, rust and blackspot to a lesser degree. It has a danger warning on the label due to the carrier, which can cause eye damage.
Rosarians will often use herbicides to control weeds and grasses from around their roses. Special caution needs to be taken as many will also damage or kill a rose bush. Never use the same sprayer for herbicides and pesticides. A common "rose problem" that I see as a Consulting Rosarian is leaf damage largely from overspray by a herbicide. These are the most common of the herbicides that the rosarian and general gardener would see at nurseries:
Round-up The most popular home use herbicide for several decades. The main ingredient is the isopropylamine salt of glyphosate. It is quickly absorbed into the plant and moves to all parts. Once inside, it inhibits the production of an enzyme, called EPSP synthase, which in turn prevents the plant from manufacturing certain amino acids essential for plant growth and life. It also decomposes the plant's underground roots and rhizomes.
Finale Uses the ammonium-based member of the glyphosate family. Same mode of action as Round-up.
Weed B Gone This common broad spectrum herbicide causes damage to the cell walls of the weed.
Grass B Gone This herbicide uses fusilade, which has the same mode of action as Proast.
Proast (sethoxydem) This is a post-emergent herbicide. It is very specific to grasses; therefore, it is considered safe to use around existing rose plants. It is part of the group of herbicides known as lipid biosynthesis inhibitors. It affects the enzyme controlling the formation of lipids. It spreads quickly through the grass.
Another type of weed killer is the pre-emergent. While it does not actually kill weeds that are already growing, a pre-emergent is designed to prevent the weed seeds from germinating.
Preen A popular pre-emergent for home garden use. Its main ingredient is trifluralin. It is said to prevent most weeds from germinating around bulbs, flowers, roses, shrubs, and trees.
When using any of these materials, make sure you read the label, never mix more than the label requires, use on non-windy days, and wear protective clothing.
Reprinted from the September 2001 issue of Rose Ecstasy, bulletin of the Santa Clarita Valley Rose Society, Kitty Belendez, Editor.
© Copyright Steve Jones. All rights reserved.
Updated January 7, 2016