Insect and Mite Control on Woody Ornamentals and Herbaceous Perennials

Bulletin 504

Insect and Mite Management Alternatives

The Control Options

Chemical Controls

Probably our second most useful control option in ornamental plant IPM is chemical control. Unfortunately, we have over used and misused this option so that most citizens are beginning to cast a weary eye to its use. Chemical control to most people means pesticides though other chemicals such as attractants and pheromones are increasing important in our IPM practice. Even if pesticides are our principal weapon, we need to understand that not all pesticides are created equal. In IPM, we want to use the ideal pesticide - a material that only kills the target pest. Unfortunately, we don't have these "silver bullets." Most of the pesticides which are currently used have short residual life spans (this reduces accumulation in the environment), are more selective (this reduces the chance of killing nontarget animals), and are used at lower rates (this reduces the total chemical "load" used). Because of these characteristics, we need to be able to better target our applications in order to achieve satisfactory control.

Another general public misconception about pesticides is that "natural" pesticides are better than "synthetic" pesticides. IPM does not make this distinction. Using pesticides in IPM is evaluated on economic, ecological and sociological impacts together. In other words there are "natural" botanical insecticides (e.g., nicotine sulfate with an LD₅₀=55 and a known carcinogen) which are much more toxic and have more adverse effects than some synthetic organic insecticides (e.g., acephate with an LD₅₀=866). In short, chemical controls used in IPM should be selected on their total attributes.

By knowing that we do not have "ideal" pesticides, whether natural or synthetic, we must use great caution to limit their adverse effects. Generally, this means that we should only target sprays to those individual plants or blocks which need it - not cover sprays. General cover sprays (spraying everything in the landscape or nursery whether needed or not) tend to cause several problems.

Cover sprays often tip the balance of control in favor of the pest. As incredible as this seems, cover sprays usually kill beneficial insects and mites (predators and parasites) better than they kill pests! Since pests usually have good reproductive ability, they rebound faster than their natural controls. This causes what we call pest resurgence and secondary pest outbreak.

Cover sprays tend to cause development of resistance. Pests and potential pests often develop resistance to pesticides when they are under constant pressure from a specific pesticide. In other words, a few insects on a plant may not be causing significant damage, but if we constantly spray these insects we are forcing them to develop resistance. Then, when they reach damaging levels our pesticide is no longer effective.

A more recently identified problem with general cover sprays of pesticides has been identified to be enhanced degradation. Since most of our current pesticides are organic compounds (i.e., containing carbon, hydrogen and oxygen), microbes are able to use the chemicals as foods or nutrients. Generally these microbes are beneficial in aiding in the removal of these pesticides from the environment. However, when constantly "feed" through general cover sprays, these microbes "learn" to "eat" these pesticides more rapidly than normal. In summary, if we are going to use the chemical control option, we need to use target sprays only when needed.

The chemical control option should be considered a limited resource. As with all limited or scarce resources, we need to conserve what we have. Many of the chemical companies are no longer developing traditional pesticides. The cost of discovery, development and registration are simply too costly. Therefore, we must conserve what we have and guard carefully the few new products which become available.

Most people think that chemical control merely means pesticides. The chemical control option also contains repellents, attractants and pheromones, and desiccants. It is easiest to discuss these by their chemistry and activity:

1. Pesticides - are chemicals which directly kill the pest.
   1. Inorganics are pesticides without carbon which can be natural earth minerals or man-made compounds. Examples are:
      1. Boric Acid - used for cockroach control, not registered for landscapes.
      2. Diatomaceous Earth - glass like remains of single celled organisms, diatoms, which scratch insect cuticle or puncture gut cells. Acts mainly as a desiccant and is rarely useful in landscapes unless combined with an insecticide like pyrethrin.
      3. Sulfur - an ancient control for insects and mites.
      4. Sodium Fluoaluminate (=Kryocide, Cryolite) - an earth mineral (or man made) which forms sharp glass-like particles which puncture insect gut cells if ingested. Since it is a stomach poison, it does not adversely affect beneficial predators and parasites. Good only against leaf feeding caterpillars, sawflies and beetles.
      5. Mercury, Lead, Arsinates - metal compounds used in the past for insect control which are now generally considered too dangerous to use.
   2. Oils are petroleum or plant based hydrocarbon chains which have insecticidal activity. Toxicity appears to be caused by suffocation and/or membrane disruption. Examples are:
      1. Summer Oil - a highly refined mineral oil used on green plants at a 0.5-2.0% rate.
      2. Dormant Oil - a slightly less refined mineral oil or summer oil used at a 2.0-4.0% rate when plants are in winter dormancy. When used in winter, has minimal adverse affect on beneficial insects.
      3. Citrus Oil - raw oil or separate constituents (e.g, d-Limonene) which have insecticidal properties at low dosages. Usually combined with other insecticides such as soaps.
   3. Fatty Acid Salts or Soaps are man made hydrocarbons using an ion, usually potassium or sodium, to join together fatty acid chains. Fatty acid chains containing 6 to 10 carbons have insecticidal properties. Insecticidal soaps apparently disrupt cell membranes. Soaps tend to be very good at controlling soft bodied insects such as aphids, mealybugs, soft scales, caterpillars, beetle larvae and spider mites.
   4. Microbial Toxins are molecules produced by bacteria, fungi, protozoa and other microbes which are toxic. Toxins like Bt endotoxin are relatively low in toxicity to mammals while botulism toxin is one of the most toxic molecules known. These toxins are used by extracting the microbe or using whole organisms. Examples are:
      1. Bacillus thuringiensis (Bt) - a bacterial product containing both endotoxins and spores which are active on a variety of insects. See Biological Control below.
      2. Avermectin-B (=Abamectins, Avid) - a powerful toxin (LD₅₀ = 10mg/kg) derived from Streptomyces fermentation.
      3. Chitin (=Clandosan) - is the chemical which makes up the exoskeleton of arthropods (insects, crustaceans, etc) and nematodes. By adding chitin to the soil, microbes produce toxins (ammonia) and/or produce digestive enzymes which destroy the cuticle of insect and nematode pests. Field results in landscapes have not been consistent in efficacy.
      4. Spinosyns (=Conserve) - are a group of chemicals derived from the fermentation of a soil dwelling microbe, Saccharopolyspora spinosa. They have LD₅₀s of greater than 2,000.
   5. Botanicals are plant extracts, usually alkaloids, which have insecticidal properties. Most people believe that since these are "natural" products, they are safer than other pesticides. Many of these chemicals have not been fully tested and many have striking adverse affects on mammals. Many cause severe allergic reactions (e.g., pyrethrin and sabadilla), are very high toxic (e.g., nicotine), or are even suspected carcinogens (e.g., nicotine). Examples are:
      1. Pyrethrin (LD₅₀=200) is derived from a specific species of chrysanthemum originally grown in Iran. The natural product is mainly an irritant to insects and is usually mixed with piperonyl butoxide (PBO) or rotenone to provide better kill of insects. Some people are very allergic to the compounds.
      2. Rotenone (=Cubé, Derris)(LD₅₀=132) is an alkaloid from roots of a tropical plant. Highly toxic to fish, and it was used originally by South American Indians to collect fish from lakes and rivers. Very toxic to pigs.
      3. Sabadilla (LD₅₀=2500-4000) is an alkaloid derived from a lily seed from South America. Though having low dermal toxicity, it is a powerful irritant which if inhaled can cause severe circulatory and respiratory failure. In spite of some magazine articles, this product is only registered for vegetable pests. d. Nicotine (LD₅₀=55) is an alkaloid derived from tobacco which high toxicity and is a suspected carcinogen.
      4. Neem (Azadirachtin, BioNEEM, Azatin) (LD₅₀ >3000) is an interesting botanical derived from an Asian tree grown in India. Neem is used as a general cleaning chemical and is found in tooth paste. It seems to act as a systemic with repellent and growth regulator effects on insects and mites.
      5. Ryania (LD₅₀=750) is an alkaloid from a tropical tree with rather high oral toxicity. The oral LD₅₀ to dogs is 150 mg/kg. It is only registered for some vegetable crops.
   6. Synthetic Organics are man made compounds containing carbon and are usually synthesized from petroleum products. This is the group most people refer to when they mention pesticide. Because of the diversity and number of materials in this group no attempt will be made to cover these compounds.
      1. Organochlorines (=Chlorinated hydrocarbons) are organics which usually have long residual life spans in the environment. This quality has caused most to be banned because they end up in the food chain or cause damage to non-target organisms.
      2. Organophosphates usually have short residual life spans. They are often stated as being related to nerve gas. Compounds in this group range from category 1 to 3 in toxicity and are generally neurotoxins.
      3. Carbamates may have long or short residual life spans and range from category 1 to 3 in toxicity. Carbamates are neurotoxins that affect nerves like organophosphates.
      4. Neonicotinyls (which include Chloronicotinyls) are synthetics that affect the post synaptic receiving nerve and block nervous transmission. They selective affect the nicotinic receptors, which insects have in much greater abundance than other animals. These compounds cause the insects to stop feeding or stop normal behavior.
      5. Pyrethroids are synthetics which look and act like the botanical, pyrethrins. They range from category 1 to 3 in toxicity though most are in categories 2 and 3.
      6. Insect Growth Regulators (IGR) are synthetic chemicals which look and act like insect hormones. They are often metabolism modifying organophosphates and carbamates with very low toxicities to mammals or other non-target animals.

2. Repellents are compounds, both natural and synthetic which cause a pest to stop feeding or move away. Most are used as products applied to skin or clothing to repel mosquitoes and ticks.
3. Attractants and Pheromones are compounds which attract a pest thinking that the compound is food or another of the species (aggregation and sex pheromones). Most of the compounds in this group have not been used effectively to reduce pests but are used in traps to sample pest activity. Examples are:
   1. Geraniol/Eugenol is the attractant "floral scent" used in Japanese beetle traps. These traps do not reduce beetle damage or grub populations. In fact, evidence exists that plants near traps may sustain more damage.
   2. Disparlure is the sex pheromone attractant for gypsy moth males. It is a powerful sampling tool but has not been successful in disrupting mating.
   3. Clearwing Moth Borer Pheromones is a mix of sex pheromones attractive to several borers such as the dogwood, lilac/ash, rhododendron and peach tree borers. These traps allow for precise timing of larval controls.
   4. Pine Tip Moth Pheromones are sex pheromones for various pine tip moths. These traps determine the starting point for degree-day models for predicting larval control windows.

4. Desiccants are materials which cause the insect pests to loose water faster than they can replace it. Since insects are very small, this water loss is rapidly lethal.

   Unfortunately, most desiccants must be kept dry so outside usage is limited. Examples are:

   1. Silica Gel is the same drying agent used in packing or flower drying and can be ground to a powder to dust onto insects.
   2. Diatomaceous Earth acts like a desiccant when dusted on the exterior of insects. The sharp edges of this product abrades away the thin wax waterproofing coat on the exoskeleton of insects.

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