Chemicals and Trichogramma

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Trichogramma pretiosum

• General info • Release strategies • Methods • What to expect • Chemicals • Monitoring •

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Chemicals and Trichogramma

Introduction to chemicals
Key to toxicity ratings
Insecticides table
Other considerations
Some IPM issues
Fungicides table

Which chemicals can be used?

Many chemicals are hazardous to Trichogramma wasps. However, in recent times a number of "soft" biological and chemical insecticides have become available and these have made it easier to incorporate Trichogramma and other beneficial insects into IPM programs.

Although Trichogramma are sensitive to many chemcals they are often found in crops that have been sprayed with "hazardous" chemicals. How have they survived? Several factors are at work. Trichogramma spend much of their lifecycle developing inside the host egg and as such are protected to various degrees from chemical applications. Adult wasps may be killed by a spray but those developing in eggs may get through.

Also, spray penetration is rarely perfect - eggs under leaves and in crevices may not be covered by the chemical.

Further, parasitised heliothis and looper eggs typically yield 2 or 3 wasps while cabbage moth eggs usually 1 or 2. If chemical residues are present on the moth egg, the first wasp that chews out of the egg may die but those following may survive.

Although Trichogramma may survive in crops where broad spectrum chemicals are used, the use of "hazardous" products is undesirable if you wish to get the full benefit from the wasps.

The table below gives a guide to the effects of some products in use:

Key to toxicity ratings

Applied = toxicity of chemicals when sprayed on the beneficials in the field. The rating is a general overall toxicity allowing for the impact on the population of the beneficial.

Low toxicity = nil or low impact on beneficials.

Moderate toxicity = beneficial activity significantly reduced but can recover in a week or so.

High toxicity = a high proportion of the beneficial population is killed and re-establishment will not be possible for several weeks.

( ) = estimated toxicity, based on anecdotal information and known impact on similar organisms.

Residual = suggested waiting time after application of the product before introducing beneficials.

Insecticides
Product	Trade names	Toxicity to Trichogramma
		Applied	Residual*
Bt products	Dipel	nil	nil
NPV products	Gemstar, Vivus	nil	nil
Methoxyfenoxide	Prodigy	very low	1 day
Indoxycarb	Steward, Avatar	low	3 days
Novaluron	Rimon	low	3 days
Diafenthiuron	Pegasus	low	3 days
Pyriproxifen	Admiral	low	3 days
Abamectin	Agrimec	low to moderate	3 days
Emamectin	Affirm	low to moderate	3 days
Pymetrozine	Chess	low to moderate	3 days
Imidacloprid	Confidor	moderate	5 days
Thiomethoxam	Actara	moderate	5 days
Fipronil	Regent	moderate	5 days
Spinosad	Tracer, Success	moderate to high	3 days
Broad spectrum pyrethroid, organophosphate and carbimate insecticides are generally "highly" or "very highly" toxic to Trichogramma and should be avoided if possible. Applications of these products will severely reduce Trichogramma numbers which may take several weeks to recover. Typically 7 to14 days needs to elapse after using these products before releasing Trichogramma. There are some differences within these groups and research is ongoing to identify those less toxic formulations.
* Estimated time to wait before releasing Trichogramma. These ratings relate to one spray. Repeated sprays are likely to result in an accumulation of residues. This is most significant in indoor conditions where it may take several months before residues have dispersed and establishment is possible.

Other considerations
If the number of larvae and/or unparasitised eggs exceeds your threshold and its deemed that a spray is necessary then use the softer options.

Be aware that the higher the number of parasitised eggs per hectare the more robust will be the wasp population and the quicker they will recover from spraying of a moderately hazardous product. Adult wasps may be killed but wasps developing inside eggs are protected to some degree.

Conversely, low numbers of heliothis (and other hosts) will only support a low population of wasps so using hazardous insecticides during such periods will severely effect wasp numbers and recovery may be slow.

See also Monitoring and Environment

Some IPM issues for vegetable and field crop growers

Heliothis

If Trichogramma wasps are not reducing your viable egg pressure below thresholds (determined from a parasitism check, eggs per meter x % parasitism) then, consider the numbers of other natural enemies in the system before spraying. Next to trichogramma, the major natural enemies of heliothis are predatory bugs and beetles which attack the egg and/or larval stages. If there are more than 3 predators per meter this is likely to further reduce the numbers of eggs and larvae (but by how much is not clear).

B.t products (Dipel® etc) and NPV (Gemstar®, Vivus®) products have no impact on Trichogramma and can be used anytime. If Trichogramma activity is moderate to high then either of these products is likely to reduce heliothis below damaging levels. Various additives to these products (e.g. AminoFeed, milk powder) will improve their effectiveness. See the manufacturers recommendations.

In recent times a number of selective chemical insecticides have become available. The safest chemical products to Trichogramma are Prodigee® and Avatar®. Be aware that some selectivie insecticides may impact on some natural enemies e.g. Avatar/Steward® is hazardous to some predatory bugs while Success/Tracer® is hazardous to adult micro wasps.

Aphids

Aphids have many natural enemies including predatory lady beetles and bugs, green and brown lacewings, hover flies and parasitic wasps. Using soft options for aphids will enable these beneficials to move into the crop. Small numbers of aphids can be useful in this regard by luring natural enemies into the crop. Aphids also produce honey dew which is a food for parasitic wasps.

If aphids increase to damaging levels use the soft options if possible. These include soap and oil sprays. Soft insecticides include: Pegasus®, Chess® and Pirimor®. If aphids occur late in the crop, for instance in sweet corn after silks have browned, then the use of broad spectrum insecticides at this stage will not be an issue for Trichogramma as they have already done their job by this time.

Mirids and green vegetable bug

Insecticide sprays for plant feeding bugs can be very disruptive to Trichogramma and other natural enemies. Recent work by the QDPI has shown that by adding salt to the insecticide mix at 750 gram per hectare the concentration of the active ingredient can be reduced by up to 75% and still get a good kill. Such active concentrations have a much reduced impact on beneficial populations. The amount of salt is low. Much more comes down in rainfall.

Powdery Mildew

Powdery mildew is an issue for some vegetable growers. Sulphur is hazardous to Trichogramma. Mancozeb used as a protectorant is okay if rotated with a "softer" fungicide (see table below). Likewise, carbenzim is okay if used in rotation with softer options. Alternative control measures like milk (at 10% full strength) and baking soda (0.5% plus 0.5% spray oil) are relatively safe to Trichogramma.

Fungicides - Toxicity to Trichogramma
Disorder	Chemical	Trade Name	Toxicity to Trichs	Days to wait*
Powdery Mildew	Bitertanol	Baycor	low	2
	Benomyl	Benlate	low	2
	Bupirimate	Nimrod	low	2
	Fenarimol	Rubigan	low (?)	2
	Dimethirimol	Milcurb	low (?)	2
	Milk	-	low	2
	Thiophanate Methyl	Topsin	low	2
	Triadimefon	Bayleton	low	2
	Propiconazole	Tilt	low	2
	Penconazole	Topaz	low	2
	Triforine	Saprol	moderate	3
	Carbendazim	Spin	moderate	3
	Oxythioquinox	Morestan	moderate	5
	Wettable Sulphur	Various names	high	5
	Pyrazophos	Afugan, Curamil	high (?)	5
Downy Mildew	Copper Oxychloride	Various names	low	2
	Zineb	Zineb, Curit	low	2
	Metiram	Polyram	low	2
	Chlorothalonil	Bravo, Daconil	low	2
	Dithianon	Delan	low	2
	Propineb	Antracol	low	2
	Copper Oxy + Zineb	Zinox	low	2
	Mancozeb	Mancozeb, Dithane	low-moderate	3
Grey Mould	Iprodine	Rovral	low	2
	Dichlofluanid	Euparen	low (?)	2
	Vinclozolin	Ronalin	low	2
	Chlorothalonil	Bravo, Daconil	low	2
	Dicloran	Allisan	low	2
	Thiram	Thiram	low	2
Black Spot etc	All Copper type sprays		low	2
	Dichlofluanid	Euparen	low	2
	Benomyl	Benlate	low	2
	Bitertanol	Baycor	low	2
	Chlorothalonil	Bravo, Daconil	low	2
	Thiram	Thiram	low	2
	Ziram	Ziram, Fulisan	low	2
	Thiophanate Methyl	Topsin	low	2
	Metiram	Polyram	low	2
	Fenarimol	Rubigan	low	2
	Dodine	Dodine	low	2
	Dithianon	Delan	low	2
	Triforine	Saprol	moderate	5
	Mancozeb	Mancozeb,Dithane	low-moderate	3
* Days to wait after spraying before releasing Trichogramma. (?) Indicates that the rating is likely but not confirmed.
This Table is a GUIDE ONLY.
CHECK crop registrations before spraying.

For a list of chemical toxicities for other beneficial insects and mites see "The Good Bug Book - Second Edition"

Next - Monitoring for parasitism

• Intro Page • Pretiosum • Carverae • MacTrix • Crops • IPM • Links • Testimonials • BioInsecticides •

Trichogramma pretiosum

• General info • Release strategies • Methods • What to expect • Chemicals • Monitoring •

• Environment • Prices - Ordering - Delivery • More Info • Acknowledgements • Index •