Author Topic: General Tools for Insect Management  (Read 1743 times)

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General Tools for Insect Management
« on: April 29, 2011, 10:12:11 AM »
Endophyte-Enhanced Grasses
Endophytes are seed-borne fungi present in tall fescue, fine-leaf fescue and perennial ryegrass that supply defensive compounds, known as alkaloids. Alkaloids are toxic to many insects and other animals. They kill insects that ingest them, or discourage further feeding. To reduce damage from chinch bugs, bluegrass billbugs and webworms, overseed with endophyte-enhanced grasses (25 to 30 percent of the mix).

A note of caution about endoyphytic grasses: Do not use these grasses in areas that will be grazed by animals you care about, including domestic animals such as sheep, cows, goats and pet rabbits, and also wild animals such as deer, rabbits, geese and ducks. The seeds also contain the toxic alkaloids, so seed eaters such as birds, mice and voles are also strongly affected.

If more than 60 percent of a seed lot contains endophytes, the seed is classified as high-endophyte turfgrass seed. Be certain the seeds you purchase are fresh. The endophytes lying dormant within the seed cannot endure more than 15 months of storage. Each bag should be marked with a date.

Dethatching
Excessive thatch provides good habitat for insect pests. When there is a thatch layer greater than 1/2-inch deep, insect pests that feed aboveground, such as chinch bugs, sod webworms, armyworms, cutworms and billbugs, become a much larger problem.

Remove thatch by raking, vertical mowing or topdressing with compost or compost tea to help soil organisms break down thatch naturally. Excessive thatch points to a problem in fertility management and usually means a lawn is being given an excess of nitrogen. (See the section on cultural practices for more about removing thatch.)

Conservation of Predators
Natural predators are one of your biggest allies in controlling insect pests. Spiders, ants, ground beetles, rove beetles and big-eyed bugs are all carnivorous and eat harmful insects, keeping their populations in check.

Avoid applying broad-spectrum insecticides (organic or conventional), which will wipe out the predators as well as the pests. Wherever possible, choose insecticides that are specifically targeted at the pest of concern. For example, products based on Bacillus thuringiensis are a good choice to control caterpillar pests because they are essentially non-toxic to beneficial insects. Conserve® (spinosad) is also relatively low in toxicity to beneficial insects. Use of pyrethrum is illegal on Massachusetts school grounds and synthetic pyrethroids are not acceptable in organic land care.

To encourage natural predators, mow high; at least three inches. Taller grass offers better habitat for predators than a closely cropped lawn.

Insect Parasitic Nematodes
Insect parasitic nematodes, are microscopic worms that live in the soil and attack insect larvae. They occur naturally in soils around the world, with about 50 known species belonging to the genera Heterorhabditis and Steinernema, and many more awaiting description and isolation. Under the right conditions, nematodes not only infect and kill hosts after an application but will also reproduce in these hosts to produce new generations that can kill additional hosts.

All known insect parasitic nematode species have a similar life cycle. The only stage that can survive outside of an insect is the infective juvenile stage. These free-living, non-feeding infective juveniles seek out a host and penetrate it through natural openings or thin parts of the cuticle. Once inside the host?s body, the juvenile nematodes release the symbiotic bacterium that they carry around in their intestines, and bacteria and nematodes cooperate to overcome the host?s immune response and kill the host, typically in one to four days. The bacteria propagate and protect the cadaver from colonization by other microorganisms. The host cadaver assumes a characteristic coloration (often yellow or red, depending on the species of nematode and symbiotic bacterium). The nematodes develop through one to three stages, feeding on the bacteria and host tissues metabolized by the bacteria. Depletion of food resources in the host cadaver leads to the development of infective juveniles that emerge from the host cadaver in search of a new host.

A few species of insect parasitic nematodes are commercially available as biological control agents. They are exempt from EPA registration because they are unlikely to harm people, pets or wildlife. Because they are living organisms, nematodes require careful handling and storage under cool and dry conditions (or refrigeration), and their effectiveness is considerably improved by selecting the most appropriate species for the target pest.

The commercially available nematode species Steinernema carpocapsae is most effective against aboveground feeders in turf, such as sod webworms, cutworms, armyworms and the early stages of billbugs. Other species, including Heterorhabditis bacteriophora, are more effective against white grubs. More specific information on the use of nematodes against white grubs is given on Page 59. A list of suppliers of insect parasitic nematodes is available online at: www.oardc.ohio-state.edu/nematodes/

Here are general guidelines for applying insect parasitic nematodes. Apply the nematodes on a warm sunny day, either early in the morning or at dusk, at a rate of 1 billion per acre (23 million per 1,000 square feet). Nematodes should not be applied to hot, dry soil. Irrigate before application if needed. If you are applying nematodes as a spray, use two to five gallons of water per 1,000 square feet of area to be treated. Keep the mixture agitated in the spray tank and remove sprayer screens to prevent clogging (and damage to the nematodes). Immediately after spraying, wash the nematodes into the root zone with 1/4- to one inch of irrigation, and keep the soil moderately moist for at least one week, two to three weeks would be better.

Microbial Products
There are several types of microbial insecticides.  
The most widely used are products derived from strains of the bacterium Bacillus thuringiensis (Bt). The active ingredients in these insecticides are proteins produced by the bacteria, and they act by interfering with the insect?s digestion, so the insecticide must be eaten by the target insect to be effective. The strains of Bt that affect caterpillars (Bt kurstaki and Bt aizawai) are very effective against sod webworms, cutworms and armyworms. (There are other strains used against other groups of insect pests.) Bt breaks down very quickly in sunlight and has very little effect on non-target organisms, with the exception of other species of moths and butterflies.

Another microbial product that has been used for many decades is derived from the bacterium Paenibacillus popilliae. This is the bacterium that causes milky disease in white grubs, and is better known by the trade name of Milky Spore® (St. Gabriel Laboratories).

Many different species of white grubs are affected by milky disease; however, each is susceptible to a different strain of the bacterium that is more or less specific to that grub species. The milky disease spores naturalize in the soil, where they remain viable for many years. Milky Spore® (the only strain that is still commercially available) is effective only against Japanese beetle grubs. Unlike commercial formulations of Bt, Milky Spore® contains viable spores of a bacterium that can infect the target host, causing disease and potentially spreading and persisting in the area. (More details about using Milky Spore® against Japanese beetle grubs are given on page 59).

Spinosad, a product containing soil microbes called actinomycetes, is commercially available for lawns and ornamental plants under the name Conserve®. Spinosad is very effective against caterpillar pests, and also has activity against some species of thrips, flies and beetles (but not beetles that damage turf, such as white grubs and billbugs). It acts as a neurotoxin in insects that have eaten the toxin or come into direct contact with the insecticide before it dries. Spinosad is a broader spectrum insecticide than Bt. Direct spraying of beneficial insects should be avoided, but Spinosad has little effect on beneficial insects once the spray has dried. It has low toxicity to most vertebrate wildlife and to humans, but is toxic to aquatic invertebrates.

Other microbial insecticides are based on the fungi Beauveria bassiana (commercially available as Naturalis® or Mycotrol®). These products contain live fungal spores that attach to the insect and infect it. Because these insecticides are living organisms, the specific conditions of storage, handling and application, and the environment at the time of application can have an impact on the effectiveness of the insecticide. Research is needed to firmly establish how effective these materials are on specific insect hosts.

Insecticidal Soaps
Soap that is specially formulated to kill insects can be effective against soft-bodied insects such as aphids and caterpillars. It works by smothering insects and breaking down the protective layer on the outside of their bodies, so it must make physical contact with the target insect in order to be effective.

Insecticidal soap works best when applied in water that is not hard. In hard water, calcium, magnesium and iron precipitate the fatty acids and render them useless against the insects. It is also important to use the purest water possible. Conduct a “jar test” to determine if your water is compatible with the soap. Mix the soap concentrate with water in a glass jar and allow to stand 15 minutes. If the mix remains uniform and milky, then your water quality is adequate. If a scum develops on the surface of the water, then conditioning of the water will be necessary. The water can be conditioned with a commercially available non-ionic buffering and conditioning agent. You can use rain water, distilled water or clean dehumidifier water.  Insecticidal soap is also more effective when it dries slowly, so it is best to apply it at dusk, particularly on hot, dry days.

Botanical Insecticides
There are several classes of botanical insecticides. The botanical insecticides with the fewest negative effects are those based on neem (using the seeds of a tropical tree). The active ingredients in these insecticides are azadirachtin and/or neem oil, and they work by interfering with insect molting and oviposition, and also by deterring feeding. Because of their effect on molting, neem insecticides are most effective when used against the immature stages of insect pests. Neem has very low toxicity to humans and wildlife (neem extracts are even used in soap and toothpaste for human use), but can harm beneficial insects, particularly in the immature stages.

The effectiveness of neem products varies among different products due to differences in extraction and formulation. A recent survey of tests of neem in agricultural systems (Caldwell et al, 2005) found that the products Agroneem®, Ecozin® and Bioneem® had little effect on pests, while other products such as Align®, Amvac Aza®, AZA-Direct®, Azatin®, Fortune Aza®, Meem Azal® and Neemix® were effective against such pests as armyworms and aphids.

Pyrethrum is another botanical insecticide. It is made using the flower heads of certain species of daisies grown in Africa and Australia. Pyrethrum is a broad-spectrum insect neurotoxin that paralyzes insects on contact. It kills a wide variety of insects but is allergenic and neurotoxic to humans, especially when inhaled, and is toxic to wildlife, particularly fish. Pyrethrum is not allowed on Massachusetts school grounds because it is a carcinogen and should not be used on Connecticut school grounds.

« Last Edit: April 29, 2011, 11:01:11 AM by admin »