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The Garden Plot for May 02, 2008
3:55 PM - 4:00 PM
[Program Website]
Today's Highlight: “Beneficial Insects”
The first aphids are hatching and lady bugs are appearing to eat them up. Bright-red lady bugs are easy to notice, but have you seen all the other garden-helper beneficial insects in your garden? If you design your garden well, it should fill up with predators and parasites, beneficial insects that take care of garden pests without charging a dime.
Predators chew up or fatally pierce plant-eating insects. Parasites lay their eggs on or near other insects. When parasite eggs hatch, baby parasites eat insects from the inside out – a little like invasion of the body snatchers. Predators increase in gardens that provide season-long, sequentially-blooming pollen and nectar sources. They move into gardens early, if you provide spring bloomers such as willow, wild strawberry, and golden currant. They will stay late, if you plant fall flowering plants, such as asters and our native, perennial: Maximillian sunflower. There should always be something booming – don’t make predators go hungry. They move on to where there are better pickings, when food gets scarce. Predators also want safe places to spend the winter, such as undisturbed hedges, and borders of shrubs and perennial flowers.
Specific predators like particular plants. Everybody’s favorite, the Lady Beetle, is happy in gardens where willow, yarrow, annual alyssum, and sunflowers bloom. Ladybug larva are worm-like bluish grubs with orange-red spots. Ladybug pupa (the transition stage between larva and adult) are solid orange to yellow orange and shaped like a hunched over, curled up animal.
Predatory true-bugs, such as the tiny black and white pirate bug, like native grasses, yarrow, and sunflowers. Shiny-black ground beetles, who feed on soil-dwelling pests, such as cutworms and slugs, want undisturbed (meaning un-tilled) areas with thick ground cover. Agricultural researchers are studying “beetle banks” to increase predator ground beetles. Beetle banks are areas of permanent mixed grasses kept unmowed. A Mowed lawn does not count as a beetle bank. A border of ornamental or native grasses next to the garden might make a pretty good beetle bank. Or, leave an unmowed area under a fence, where it’s hard to mow anyway.
Parasites in Montana are most often wasps and flies. There are several species of parasitic wasps. Most are tiny and dark colored. Evidence that parasites have been busy in your garden can be seen by aphid mummies; these are tan-colored puffs, the size of a swollen aphid. Aphid mummies may still look a little like aphids, but thanks to the parasitic wasp that ate its way out of the aphid, nobody’s home. Parasitic wasps require abundant pollen and nectar sources. They are especially fond of plants in the carrot family (such as coriander), plants in the mustard family (such as alyssum), as well as yarrow and sunflowers. New research indicates that flower shape is most important to parasitic wasps. They prefer flat-topped, wide flowers such as our fall-blooming native shrub rabbit brush.
An insect-resistant garden starts with habitat for predators and parasites. Once they are present in the spring, avoid harmful gardening practices that can disturb or kill them. General insecticides that kill the good guys as well as the bad guys should be avoided, especially later in the spring when beneficial insect populations start to build. Cultivation and field burning also disturb and reduce beneficial insect levels. Ground beetle and spider populations are especially reduced by cultivation and tillage. These two predators are important to encourage if you have garden pests that spend all, or a part of, their life cycles in the soil, such as flea beetles and root maggots.
For more information on pesticides that are and are not compatible with biological control using beneficial insects, go to the Montana Public radio website.
Adapted from Cliff Sadof, Purdue University and Michael Raupp, University of Maryland “Midwest Biological Control”
PESTICIDE COMPATIBILITY COMMENT
Abamectin
(actinomycete derived) Not compatible Available for microinjection but sub lethal doses reported to harm mite predators; broad spectrum.
Acephate (organophosphate)
Not compatible Available for microinjection and in soil applied granular formulation; broad spectrum.
Azadirachtin (botanical)
Compatible Insect growth regulator derived from seeds of neem tree; kills immature stages; pupal stage parasitoids not affected.
Bacillus thuringiensis (bacterial insecticide) – Bt var. aizawa, var. kurstaki, or var. morrisoni.
Highly compatible Three strains that target caterpillars.
Bt var. israelensis
Highly compatible Targets gnat-like flies including dark-winged fungus gnats and mosquitoes.
Bt var. tenebrionis
Highly compatible Targets beetle grubs.
Beauvaria bassiana (mycoinsecticide)
Compatible Kills some soft-bodied predators; short residual; broad spectrum.
Bendiocarb (carbamate)
Not compatible Very long residual; broad spectrum.
Bifenthrin (pyrethroid)
Not compatible Very long residual; broad spectrum.
Carbaryl (carbamate)
Not compatible Repeated used may stimulate spider mite reproduction; broad spectrum.
Cyfluthrin (pyrethroid)
Not compatible
Dicofol (organochlorine)
Not compatible Very long residual miticide; kills mite predators.
Dienochlor
(chlorinated hydrocarbon) Somewhat compatible Short toxicity to predatory mites but not toxic to predatory beetles.
Diflubenzuron
(insect growth regulator) Somewhat compatible Moderate residual; kills immature stages; pupal stage parasitoids are not killed.
Dimethoate (organophosphate)
Not compatible Long residual; broad spectrum.
Disulfoton (organophosphate)
Not compatible Long residual systemic; broad spectrum.
Fenitrothion (organophosphate)
Not compatible Long residual; broad spectrum.
Fluvalinate (pyrethroid)
Not compatible Very long residual; broad spectrum.
Heterorhabditis bacteriophora (entomophagous nematode)
Compatible Very low toxicity to human and non-targets; wasp parasitoids with silken cocoons are not killed.
Hexythiazox (thiazolidine)
Highly compatible Kills only spider mite nymphs and eggs; long residual; does not kill predators.
Horticultural Oil
(petroleum oil) Compatible Inactive when dry; kills soft-bodied insects; pupal stage parasitoids not killed.
Imidacloprid (chloronicotinyl)
Not compatible Ability to kill predaceous plant bugs can cause spider mite outbreaks; long residual when systemically applied.
Insecticidal Soap (soap)
Compatible Inactive when dry; kills soft-bodied insects; pupal stage parasitoids not killed.
Lambda-cyhalothrin (pyrethroid)
Not compatible Very long residual; broad spectrum.
Lindane
(chlorinated hydrocarbon) Not compatible Very long residual; broad spectrum.
Malathion (organophosphate)
Not compatible Moderate residual; broad spectrum.
Methoxychlor (organochlorine)
Not compatible Very long residual; broad spectrum.
Neem oil
Compatible Insect growth regulator derived from seeds of neem tree; kills immature stages; pupal stage parasitoids not killed.
Oxythioquinox (dithiocarbonate)
Not compatible Long residual; broad spectrum miticide.
Oxydementon-methyl (organophosphate)
Not compatible Long residual; broad spectrum.
Permethrin (pyrethroid)
Not compatible Long residual; broad spectrum.
Phosmet (organophosphate)
Somewhat compatible Reportedly low impact on spider mite predators in orchards with long history of pesticide use; effect on predators in landscape unknown.
Pyrethrins (botanical)
Somewhat compatible Very short residual but very broad spectrum; prevents additional injury and sets the stage for future conservation and augmentation efforts.
Spinosad (naturalyte)
Compatible Very short residual; toxic to adult wasp parasitoids; not toxic to some important predators.
Steinernema carpocapsae (entomophagous nematode)
Highly compatible Very low toxicity to humans and non-targets; wasp parasitoids with silken cocoons are not killed.
Trichlorfon (organophosphate)
Not compatible Long residual; broad spectrum.
Helen Atthowe's new short program of gardening tips
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