GB2402336A - Use of Tagetes extract to protect plants - Google Patents

Abstract

A volatile extract from Tagetes is used to reduce or prevent infestation of above-ground parts of a plant by insects, particularly aphids. Thus, a method of reducing or preventing infestation of above-ground parts of a plant by insects, comprises ```providing a volatile extract from Tagetes, and ```positioning said extract adjacent the plant, whereby volatile compounds from the Tagetes extract diffuse around the plant.

Description

USE OF TAGETES EXTRACT

The present invention relates to the use of a composition for protecting plants against insect infestation. s

Companion planting is part of the folklore of gardening in many cultures. It involves interspersing a variety of plants to protect crop plants against insect attack as an alternative to the environmentally damaging pesticides.

However, there seems to have been little systematic and rigorous scientific investigation into the precise mechanisms at work in controlling insect infestations by companion planting. One group of plants commonly used in this way is Tagetes (Marigolds).

Tagetes ( family Asteraceae) is a genus of about 50 species of annual and perennial plants, originating from Mexico (Soule 1996, Mabberley 1997). Four annual species of Tagetes are commonly cultivated as ornamentals Tagetes erects L., Tagetes patula L., Tagetes tenutolia Cav. and Tagetes lunulata Ort (Soule 1996). Essential oil is produced mainly from Tagetes minute L., Tagetes patula L. and Tagetes erecta L. An extensive review of various uses of this plant has been recently presented by Vasudevan et al (1997).

Greenhouse and field experiments with Tagetes patula have shown a reduction in Meloidogyne incognita infestation and an increase in yield with tomatoes (Ploog 1999, 2002) and with potatoes (Kimpinski, 2000). There is also some scientific evidence of the effectiveness of the use of Tagetes (patula and erecta) as part of a tobacco crop rotation for control of root-lesion nematodes (Reynolds et al 2000). However, Powers et al (1993) reported no consistent differences in density of various nematode genera in squash ( Cucurbita pepo) and cucumber (Cucumis saliva) intercropped with Tagetes patula. Srinivasan and colleagues (1994) reported that the use of African marigold (Tagetes erects) reduced both eggs and larvae of Helicoverpa armigera in intercropped tomato, with a consequent reduction in the number of damaged fruits.

Broussalis and colleagues (1999) reported that dichloromethane and methanol extracts from Tagetes erecta have significant insecticidal activity against the stored product beetle Sitophilus oryzee. Tagetes minute extract showed significant activity against adult Mexican bean weevils (Coleoptera: Bruchidae) (Weaver et al 1994), and mosquito larvae and/or adults (Perich et al 1995, Wells et al 1992 and Macedo et al 1991). The toxic effect of Tagetes extracts on adults of the beetle Sitophilus zeamais (Coleoptera: Curculionidae) decreased after fractionation or photodegradation (Weaver et al 1997). Tagetes essential oils have also been shown to be effective against some stored product pests. The study from Keita and colleagues (2000) showed that Tagetes minute oil increased adult mortality of Callosobruchus maculates (F.) (Coleoptera: Bruchidae).

Attempts to produce plant-based insecticides from Tagetes cell cultures have been described from Hitmi et al (2000) and George et al (2000).

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US 5,662,915 describes use of Tagetes extract for killing subsurface and surface soil pathogens such as nematodes. It also describes methods for preparing Tagetes extract.

It has now been found that Tagetes volatiles reduce the feeding, reproduction and survival of certain insects, particularly aphids. Tagetes volatiles can therefore be used to control a population of insects in a plant's environment, especially by killing and/or repelling the insects. The Tagetes extract restricts the growth of insect populations and reduces the number of insects on the plant.

In a first aspect, the present invention provides the use of a volatile extract from Tagetes to reduce or prevent infestation of above ground parts of a plant by insects.

The volatile compounds from the Tagetes extract can be spontaneously dispersed into the atmosphere around the plant. The volatiles diffuse around the above-ground parts of the plant, to repel or kill insects that are on the plant or in its environment. The extract may present in a carrier oil or other liquid. The extract may be the oil of Tagetes, particularly the essential oil.

Conveniently, Tagetes essential oils are available from commercial sources.

Preferably, the plant is in an enclosed environment because this helps to keep the volatiles in the near environment of the plant. For example, the plant may be in a greenhouse (e.g. in the form of a glasshouse, polythene house, polythene tunnel, cold frame etc.) either on a commercial or domestic scale. The plant may be a houseplant and kept in the home or office environment.

In general, the invention is appropriate for plants whose above-ground parts are susceptible to infestation by insects. The plant may be a crop plant, preferably a fruit or vegetable crop plant. For example, a broad bean plant, tomato plant, cucumber plant, lettuce or a salad plant generally. The plant may be a decorative plant, grown for the appearance of its flowers or foliage. For example, plants commercially grown for sale of their flowers.

In particular, the invention relates to insects that feed on or damage above-ground parts of the plant, mainly plant leaves, flowers and/or stems. The invention is less suitable for soil pests or insects in or on the soil.

Preferably, the insects are sap-feeding insects such as aphids (Aphidae), e.g. the pea aphid Acyrthosiphum pisum, peach-potato aphid Myzas persicae and the glasshouse and potato aphid Aulacorthum solani. The aphids may be greenfly and/or blackfly. The insects may be insects that eat the leaves of the plant, such as caterpillars.

Preferably, the Tagetes is Tagetes minute, Tagetes erecta, Tagetes patula or Tagetes tenutolia.

Preferred and exemplary features of the first aspect of the invention apply also to further aspects of the invention.

In a further aspect, the invention provides a method of reducing or preventing infestation of a plant by insects, comprising providing a volatile extract from Tagetes, and positioning said extract adjacent to the plant, whereby volatile compounds from the Tagetes extract diffuse around the plant.

The extract may be provided in a controlled release formulation or package, to control the diffusion of volatile compounds from the extract. In some embodiments, for example, the extract may be provided on an absorbent/adsorbent material.

Tagetes extract can be absorbed on to the absorbent material, from where it spontaneously disperses and diffuses into the air. The absorbent material assists in the controlled release of Tagetes volatiles. The absorbent material can be a pad or a sheet. It may be a fibrous material, either woven or non-woven. Cloth can be used. In a simple embodiment, the absorbent material may be paper e.g. a strip or wad of paper.

The absorbent material can be attached to or positioned near the plant. An elongate member such as a wire or string can be attached to the absorbent material, so that it can be hung from the plant or from a nearby structure. Where the plant is in an enclosed environment, the absorbent material may be attached to a wall or other fixture of the enclosure, e.g. the framework of a greenhouse. Where the plants grow on supports, the absorbent material may be positioned on, or be incorporated into, the supports. The absorbent material may be positioned near the top of the plant. Frequently, a higher density of plant-feeding insects is found at the top of a plant because that is generally a growing point where there are young leaves and stems.

Other ways to control the diffusion of volatile compounds are well known in the art and include, for example, carrier oils and semi-permeable outer layers.

Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure. All documents mentioned in this specification are incorporated herein by reference in their entirety. In the case of inconsistencies, the present

disclosure will prevail.

Certain aspects and embodiments of the invention will now be illustrated by way of example and with reference to the figures described below.

Figure 1 Mean number (+SE) of offspring per leaf for the three tested aphid species in Petri dish experiments.

Aphids were exposed to 11 of three Tagetes minute essential oil from different suppliers. (a) pea aphid (Acyrthosiphum pisum); (b) peachpotato aphid (Myzus persicae); (c) glasshouse and potato aphid (Aulacorthum solani). Key to graphs: dark line and diamonds = control; squares = essential oil 1; triangles = essential oil 2; dotted line and crosses = essential oil 3.

Figure 2 Mean number (iSE) of adults per leaf for the three tested aphid species in Petri dish experiments. Aphids were exposed to 1,ul of three Tagetes minute essential oil from different suppliers. (a) pea aphid (Acytthosiphum pique); (b) peach-potato aphid (Myzas persicae); (c) glasshouse and potato aphid (Aulacorthum salami). Key to graphs: dark line and diamonds = control; squares = essential oil l; triangles = essential oil 2; dotted line and crosses = essential oil 3.

Figure 3 Mean number (+SE) of glasshouse and potato aphid (Aulacorthum solani) per leaf in Petri dish experiments, exposed to 1,ul Tagetes essential oil from different suppliers. Essential oils No 1-4 are Tagetes minute, No 5 is Tagetes patula and No 6 Tagetes erecta. (a) number of offspring) (b) number of parental aphids. Key to graphs: dark line and diamonds = control; squares = essential oil l; triangles = essential oil 2; dotted line and crosses = essential oil 3; solid line and crosses = essential oil 4 dotted line and circles = essential oil 5; plain mid-grey line = essential oil 6.

Figure 4 Mean number/+SE of offspring per leaf for the three tested aphid species in Petri dish experiments. Aphids were exposed to 0.1 and 1 Al of three Tagetes minute essential oil. (a) pea aphid (Acyrthosiphum pisum); (b) peach-potato aphid (Myzas persicae); (c) glasshouse and potato aphid (Aulacorthum solani). Key to graphs: dark line and diamonds = control; squares = 1 Ill; triangles = 0.1 Ill.

Figure 5 Mean number/+SE of adult aphids per leaf for the three tested aphid species in Petri dishes experiments.

Aphids were exposed to 0.1 and 1 pi of three Tagetes minute essential oil. (a) pea aphid (Acyrthosiphum pisum); (b) peach-potato aphid (Myzas persicae); (c) glasshouse and potato aphid (Aulacorthum solani). Key to graphs: dark line and diamonds = control; squares = 1 pl; triangles = 0.1 p1.

Figure 6 Mean numbers/+SE of offspring peach-potato aphid (Myzas persicae) and glasshouse and potato aphid (Aulacorthum solani) exposed to Tagetes minute essential oil. (a) glasshouse and potato aphid (Aulacorthum solani); (b) peach-potato aphid (Myzas persicae). Key to graphs: dark line and diamonds = control; squares = 1 pi no replacement; dotted line and triangles = 1 pi with replacement; crosses = 0.1 pi with replacement.

Figure 7 Mean numbers/+SE of peach potato aphid (Micas persicae) preexposed to Tagetes minute essential oil (1 or 0.1 pi) for six days. (a) peach-potato aphid pre-exposed with 0.1 pi Tagetes oil; (b) peach-potato aphid pre-exposed with 1 pi Tagetes oil. Key to graph a: dark line with diamonds = non-treated; crosses = control from 0.1 pi; dotted line with triangles = treated with 0.1 pi. Key to graph b: dark line with diamonds = non treated; crosses = control from 1 pi; dotted line with squares = treated with 1 p1.

Figure 8 Mean number of Pea aphids (Acyrthosiphum piston) exposed to Tagetes minute essential oil in glasshouse experiment and the percentage decrease compared to the controls. (a) and (b) source of volatiles near the base of the plant; (c) and (d) source of volatiles near the top of the plant. Key to graphs: dark line with diamonds = control; squares = 200 Al paper; dotted line with triangles = 200 ul vial; crosses = 20,ul paper.

Figure 9 Mean number/+SE of Glasshouse and potato aphids (Aulacorthum solace)) exposed to Tagetes minute essential oil in glasshouse experiment and the percentage decrease compared to the controls. (a) and (b) October 2002; (c) and (d) November 2002. Key to graphs: dark line with diamonds = control; squares = 200 pl; dotted line with triangles = 20 ul.

Experimental Aphids The following aphid species were used: Pea aphid (Acyrthosiphum pisum) Peach-potato aphid (Myzus persicae) Glasshouse and potato aphid (Aulacorthum solani) Essential oils Six Tagetes essential oils were tested. Four of them were Tagetes minute from different suppliers, one Tagetes patula and one Tagetes erects.

Plant material Broad bean was used as a host plant for pea aphid (Acyrthosiphum pisum) and tomato as a host plant for glasshouse and potato aphid (Aulacorthum solani) and for peach-potato aphid (Myzas persicae).

a. Essential oils from different suppliers or Tagetes species The aims of this experiment were to compare the effect on reproduction and/or survival of oils bought from different suppliers and/or produced from different Tagetes species.

Experimental method One host plant leaf was set onto the surface of 2% water agar layer in one half of the base of Petri dish (diameter 9cm) and five aphids were put on the leaf. The dishes were turned upside down and 1 Al essential oil on filter paper (Whatman) was placed on the base of the dish. The filter paper with the essential oil was replaced every 24 h. The Petri dishes (in plastic bags) were kept in an illuminated incubator at temperature 22 C and a light/dark period 12h/12h. The number of aphids (adults and offspring) was recorded daily.

Experiment 1 Three Tagetes minute essential oils from different suppliers were tested at the same concentration level.

The three aphid species were examined: pea aphid (Acyrthosiphum pisum), peach-potato aphid (Myzas persicae) and glasshouse and potato aphid (Aulacorthum solani).

One microlitre essential oil on filter paper (Whatman) was placed on the base of the dish. The filter paper with the essential oil was replaced every 24 h. Resul ts and discussion For each treatment the mean number of aphids per leaf and the standard error were calculated. No data were collected with one of the essential oils for Myzus persicae because of aphid infestation by parasitoids. The Mann-Whitney U test for two independent samples was used to compare the differences between treatments with each of the essential oil and the respective controls for the tested species of aphid.

Figure 1 shows the number of offspring (mean value per leaf) for the different aphid species exposed to 1,ul Tagetes oil.

A significant decrease in aphid number was found for all aphid species after four days of treatment or less (p<0.05, 95% confidence interval). Figure 2 shows the mean number of live parental aphids per leaf. Exposure to Tagetes minute oil volatiles decreases the survival of all tested aphids after six days of exposure or less (p<0.05, significance level 0.05). Most susceptible to the volatiles are pea aphids (p<0.01, significance level 0.05) after four day of exposure to the essential oil in terms of decreasing the number of the offspring as well the rate of surviving parental aphids. The differences between the oils were not significant (p>0.05, significance level 0.05).

Experiment two Six Tagetes oils were used. Four of the oils were Tagetes minute from different suppliers (three of them were the same as in Experiment 1), one Tagetes erects and one Tagetes patula.

Experimental method One host plant leaf was set onto the surface of 2% water S agar layer in one half of the base of Petri dish (diameter 9cm) and five aphids were put on the leaf. The dishes were turned upside down and adsorbent material strip (2x2mm) with 1 pl essential oil fixed on the top of the entomological pin was inserted into water agar in the other half. The source of the essential oil was replaced every 24 h. The Petri dishes (in plastic bags) were kept in an illuminated incubator at temperature 22 C and light/dark period 12h/12h.

The experiment was performed only with glasshouse and potato aphid (Aulacorthum solani). The number of aphids (adults and offspring) was recorded daily.

Results and discussion For each treatment the mean number of aphids per leaf and the standard error were calculated. The Mann-Whitney U test for two independent samples was used to compare the difference between treatments with each of the essential oil. Figure 3 shows the number of offspring Aulacorthum solani (mean value per leaf) treated with 1,ul of the different Tagetes oil. The significant and dose dependent decrease in aphid number was found for all tested Tagetes oil (p<0.05, 95% confidence limit) after four days of exposure. The mean number of live parental aphids per leaf is shown on Figure 3. Exposure to Tagetes oil volatiles caused significant and dose dependent increase in the mortality of all three tested aphid species.

We can compare the results from Experiments 1 and 2. In both essential oils 1, 2 and 3 were tested at the same level and they show similar trend in decreasing aphid reproduction.

The only difference between the experiments is the source of volatiles - a filter paper on the base of the Petri dish in the first and absorbent material strip (2x2mm) fixed on the top of the entomological pin in the second one.

b. Effect of concentration of the volatiles The aim of this experiment was to compare the effect on reproduction and/or mortality of different concentrations of essential oil volatiles on the tested aphid species: pea aphid (Acyrthosiphum Sioux), peach-potato aphid (Myzas persicae) and glasshouse and potato aphid (Aulacorthum solani). One essential oil ( Tagetes minute) was tested but in two different concentrations.

Experimental method One host plant leaf was set onto the surface of 2% water agar layer in one half of the base of Petri dish (diameter 9cm) and five aphids were put on the leaf. The dishes were turned upside down and the required amount of Tagetes minute oil (1 Al or 0.1 pl) on filter paper (Whatman) was placed on the base of the dish. The filter paper with the essential oil was replaced every 24 h. The Petri dishes (in plastic bags) were kept in an illuminated incubator at temperature 22 C and light/dark period 12h/12h.

The number of aphids (parental and offspring) was recorded daily.

Results and discussion For each treatment the mean number of aphids per leaf and the standard error was calculated. The Mann-Whitney U test for two independent samples was used to compare the difference between treatments with the essential oil and the respective controls for each aphid species. Figure 4 shows the number of offspring (mean value per leaf) for the different aphid species exposed to lul and 0.11 Tagetes oil respectively. The significant and dose dependent decrease in aphid number was found for all aphid species (p<0.05, significance level 0.05). The mean number of live parental aphids per leaf is shown on Figure 5. Exposure to Tagetes minute oil volatiles caused a significant and dose dependent increase in the mortality of all three tested aphid species.

c. Memory effect The aim of this experiment was to find out whether volatiles from Tagetes oil have continuing impact on aphids reproduction and mortality in the longer terms, after pre- exposed aphids were no longer treated with the oil volatiles.

Experimental method One Tagetes minute essential oil was tested.

The three aphid species were examined: pea aphid (Acyrthosiphum pisum), peach-potato aphid (Myzas persicae) and glasshouse and potato aphid (Aulacorthum solani).

One host plant leaf was set onto the surface of 2% water agar layer in one half of the base of Petri dish (diameter 9cm) and five aphids were put on the leaf. An absorbent material strip (2x2mm) with 1 or 0.1 ul essential oil fixed on the top of the entomological pin was inserted into the agar in the other half. The source of the essential oil was replaced every 24 h in the case of 0.1 ul treatment. With the higher concentration, two treatments were applied - in the first case the source of the essential oil was replaced daily and in the second the absorbent strip with the essential oil was kept in the Petri dishes without replacement.

After six days, five aphids from each replicate were transferred onto a fresh host plant leaf in a new Petri dish. Aphids exposed to 0.1 pl and 1, ul of oil without replacement, were treated in two different ways - they are either exposed to the same amount of the essential oil or kept as controls without essential oil. Aphids from the controls were transferred to another control dish. The number of surviving aphids exposed to 1 ul essential oil replaced daily was not sufficient to continue this part of the experiment.

Resul ts and discussion For each treatment the mean number of aphids per leaf and the standard error was calculated. The Mann-Whitney U test for two independent samples was used to compare the difference between treatments with each of the essential oil. Figure 6 shows the mean number of offspring aphids per leaf for peach potato and glasshouse and potato aphid.

Data show that Tagetes oil volatiles have a 'memory effect' on aphid reproduction and treated aphid produce fewer offspring even if they were no further exposed to the volatiles (Figure 7).

Conclusions

Tested Tagetes essential oils caused À Significant and dose dependent decrease in the number of offspring À Significant and dose dependent decrease in the survival rate for adults À Most susceptible to the volatiles are pea aphids À Volatiles have a 'memory effect' on aphid reproduction and treated aphid produce fewer offspring even if they are no more exposed to the volatiles d. Glasshouse experiment Pea aphid Experimental method One Tagetes minute essential oil was tested with Pea aphid (Acyrthosiphum pisum). Broad bean was used as a host plant.

An absorbent material strip (10xlOmm) was used as source of the essential oil volatiles. The strip was 'hung' near the base of the plant, i.e. hung so that the absorbent material strip was near the base of the plant. In one of the treatments 2001 essential oil was added and the same strip was kept till the end of the experiment. In the second treatment 201 essential oil was added and the strip with the essential oil was replaced daily. For the third treatment 200,ul essential oil was added to a small vial, the vial was kept in the pot during the experiment. Each treatment was replicated six times and ten aphids were added to each plant. The pots were put into netted cages and were kept in the glasshouse.

The experiment was repeated a second time but the paper strip was hung near the top of the plant.

The experiments were performed during August 2002 when the temperature in the glasshouse varied between 18 C and 35 C.

The aphid number was recorded daily visually on the Broad bean plants.

Results and discussion For each treatment, the mean number of aphids per pot and the standard error were calculated. The Mann-Whitney U test for two independent samples was used to compare the difference between each treatment and the corresponding controls. Figure 8 shows the mean number of offspring per plant for the two experiments. All differences were significant after six days of exposure (p<0.05, significance level 0.05) but fewer aphids were found if the source of the essential oil is at the top of the plant - approximately 45% decrease if the source is near the base of the plant and 75% if it is near the top respectively.

Glasshouse and potato aphid The same experimental design as described above was used but with glasshouse and potato aphid (Aulacorthum solani) on tomatoes as a host plant. Only the treatments with absorbent material as a source of Tagetes volatiles were prepared and the paper strips were hung near the top of the plant. The second experiment was set up to evaluate longer-term effects on aphid numbers.

Resul ts and discussion For each treatment, the mean number of aphids per pot and the standard error was calculated. The Mann-Whitney U test for two independent samples was used to compare the difference between each treatment and the control. Figure 9 shows the mean number of offspring per plant for the two experiments. All differences were significant after six days of exposure (p<0.05, significance level 0.05). The lower concentration of Tagetes oil tested (20ul), if applied daily could cause the same effect as the higher concentration (200ul) applied once.

Concl usions In glasshouse experiments, Tagetes oil caused; À Significant decrease in the number of offspring À The lower concentration of Tagetes oil tested, if applied daily could cause the same effect as the higher concentration.

References Broussalis AM et al (1999) Journal of Ethnopharmacology, 67, 219-223.

George J et al (2000) Critical Reviews in Biotechnology, 20, 49-77.

Hitmi A et al(2000) Critical Reviews in Biochemistry and Molecular Biology, 35, 317-337.

Keita S.M. et al (2000) et al Journal of Stored Product Research, 36, 355364.

Kimpinski, J. et al. (2000) Supplement to the Journal of Nematology, 32, 531-536.

Mabberley DJ (1997), The plant book: a portable dictionary of the vascular plants, Cambridge University Press Macedo ME et al (1997) Memorias do Instituto Oswaldo Cruz, 92, 565-570.

Perich MJ et al (1995) Journal of the American Mosquito Control Assosiation, 11, 307-310.

Ploog AT, Maris PC (1999) Journal of Nematology, 31, 62-69 Ploeg AT (2002) Plant Disease, 86, 505-508 Powers LE et al (1993) Journal of Nematology, 25, 666-673.

Reynolds LB et al (2000) Agronomy Journal, 92, 957-966 Soule JA (1996), Novel annual and perennial Tagetes, 546 551, In: J. Janick (ed.), Progress in new crops. ASHS Press Srinivasan K et al (1994) International Journal of Pest Management, 40, 56-63.

Vasudevan P et al (1997) Bioresource Technology, 62, 29-35 Weaver OK et al. (1994) Journal of Economic Entomology, 7, 1718-1725.

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Claims (21)

1. Claims 1. Use of a volatile extract from Tagetes to reduce or prevent

   infestation of above-ground parts of a plant by insects.
2. 2. Use according to claim 1, wherein the extract is Tagetes essential oil.
3. 3. Use according to claim 1 or claim 2, wherein the plant is in an enclosed environment.
4. 4. Use according to claim 3, wherein the enclosed environment is a greenhouse.
5. 5. Use according to any one of the preceding claims, wherein the plant is a crop plant or a decorative plant.
6. 6. Use according to any one of the preceding claims, wherein the insects feed on or damage plant leaves, flowers and/or stems.
7. 7. Use according to any one of the preceding claims, wherein the insects are aphids.
8. 8. Use according to claim 7, wherein the aphids are Acyrthosiphum pisum, Myzas persicae or Aulacorthum solani.
9. 9. Use according to any one of the preceding claims, wherein the Tagetes is Tagetes minute, Tagetes erects, Tagetes patula or Tagetes tenutolia.
10. 10. A method of reducing or preventing infestation of above-ground parts of a plant by insects, comprising providing a volatile extract from Tagetes, and positioning said extract adjacent the plant, whereby volatile compounds from the Tagetes extract diffuse around the plant.
11. 11. A method according to claim 10, wherein the extract is Tagetes essential oil.
12. 12. A method according to claim 10 or claim 11, wherein the plant is in an enclosed environment.
13. 13. A method according to claim 12, wherein the enclosed environment is a greenhouse.
14. 14. A method according to any one of claims 10 to 13, wherein the plant is a crop plant or a decorative plant.
15. 15. A method according to any one of claims 10 to 14 wherein the insects feed on or damage plant leaves, flowers and/or stems.
16. 16. A method according to any one of claims 10 to 15, wherein the insects are aphids.
17. 17. A method according to claim 16, wherein the aphids are Acyrthosiphum pisum, Myzas persicae or Aulacorthum solani.
18. 18. A method according to any one of claims 10 to 17, wherein the Tagetes is Tagetes minute, Tagetes erects, Tagetes patula or Tagetes tenufolia.
19. 19. A method according to any one of claims 10 to 18 wherein the volatile extract is on an absorbent/adsorbent material.
20. 20. A method according to claim 19, wherein the absorbent/adsorbent material is attached to the plant.
21. 21. A method according to claim 19 or claim 20, wherein the absorbent/adsorbent material is positioned at the top of the plant.