WO2000062619A1

WO2000062619A1 - A method for controlling nematodes

Info

Publication number: WO2000062619A1
Application number: PCT/IL2000/000233
Authority: WO
Inventors: Yuval Benyamini; Dan Orion
Original assignee: Luxembourg Industries (Pamol) Ltd.
Priority date: 1999-04-20
Filing date: 2000-04-19
Publication date: 2000-10-26
Also published as: IL129528A0; AU3986300A

Abstract

The invention provides a method for controlling nematodes in plants. The method comprising applying to the plants, or to the vicinity of the plants, a nematicidally effective amount of at least one phosphorous acid or salt thereof.

Description

A METHOD FOR CONTROLLING NEMATODES

FIELD OF THE INVENTION

This invention relates to a novel method for controlling nematodes.

BACKGROUND OF THE INVENTION Nematodes are tiny, unsegmented equatic roundworms that live in soil water or plant fluids and are generally transparent and colorless, with bodies ranging from 0.25 to 3.0 mm long. The nematodes^' rate of activity, growth, and reproduction increases as soil temperature rises from about 10°C to about 32°C. For many nematodes a complete life cycle, at optimum temperature, is about 4 weeks. Plant parasitic nematodes are usually of two kinds: ectoparasitic nematodes which live outside of roots and feed only on tissues which are accessible from outside the root; and endoparasitic nematodes that spend at least part of their life cycle inside the roots on which they feed.

Plant parasitic nematodes occur worldwide and most of them live most of their lives in the top soil layer. Several species of parasitic nematodes. including the root-knot nematodes belonging to the Meloidogyne species, the cyst nematodes belonging to the Heterodera species and Globodera species and other nematodes such as the Nacobbus species, cause severe damage and substantial crop losses. Some common crop hosts of root-knot nematodes are soybeans, corn, millet, tobacco, ornamentals, peach, and many vegetables, among them: cucumber, pepper, potato, cabbage, and tomato.

Damage by root-knot nematode results primarily from the invasion of the plant roots by larvae which, in a compatible relationship with the plant, develop into the reproducing female. After invasion the larvae induces the root cells to develop into giant cells, which serve as their feeding zone. Upon infection galls or knots are formed on the roots and the plant roots become disturbed, thickened and stunted, and thus are eventually physiologically dysfunctional in the uptake of water and nutritional elements, such a dysfunction leads eventually to damage of plant growth and development. The damage and/or yield reduction caused by root-knot nematodes has substantial effect on the total worldwide agriculture production. In individual stand yield losses can be as high as 25-50% of the crop.

Phosphorous acid and its salts are well known for their use in agriculture, especially as fertilizers and fungicides.

US 5,514,200 discloses fertilizers comprising a buffered composition of an organic phosphorous acid and salts thereof.

US 5.206,228 discloses a method for controlling arthropod pests comprises applying to the pests, or to an infested locus thereof, a phosphorous acid derivative. The method is said not to damage the plants and to be safe-to-use as well as environmentally friendly.

US 4,075,324 discloses fungicidal agents for combating fungal diseases in plants, which contain as active ingredients organic or inorganic compounds which release phosphorous acid. US 5,736, 164 discloses fungicidal compositions containing phosphite and phosphate salts and derivatives thereof.

GB 2,279,252 discloses fungicidal compositions containing phosphorous acid and/or its salts, and treatment of plant seeds with phosphorous acid or its salt to protect them against fungi.

SUMMARY OF THE INVENTION

The present invention is based on the surprising finding that potassium phosphite which has well known activity as a fungicide, was also effective in reducing the galling index of tomato roots infected with root-knot nematodes. Thus, the present invention concerns a method for controlling nematodes in plants comprising: applying to said plants, or in the vicinity of said plants, a nematicidally effective amount of at least one compound selected from phosphorous acid and salts thereof.

The compound applied is phosphorous acid (H₃P0₃) and salts thereof, including potassium salts, ammonium salts, aluminum salts and sodium salts. Typically, the phosphorous acid and salt are dissolved in water and the pH is adjusted to the range of 5 to 8. The term "controlling " refers to a method, which reduces or eliminates infestation of the plant by nematodes. The term "controlling " also refers to prevention of such infestation by nematodes before it occurs.

The term "plant " refers to agricultural crops including trees, such as banana, peach, vineyards, apple, and annual dicute crops belonging to families such as Solanacea, Cucurbitacea, Cruciferae, and to crops such as tomato, pepper, eggplant, tobacco, soybean, cucumber, cabbage and ornamentals.

The term "nematodes " refers to: nematodes from the order Tylenchida from families such as Pratylenchidae and Tylenchulidae, and genera such as Meloidogyne, Pratylenchus, Tylenchulus, etc. The method refers to application of the phosphorous acid or salts thereof on any part of the plant, such as the leaves, the roots etc., and by any method of application, such as drenching, spray application, etc.

The method of the invention also concerns application of the compound in the vicinity of the plant, for example in the soil surrounding the plant. Such application can be carried out by mixing the compounds in the soil prior to planting, by adding the compound to the irrigation water, or by direct spraying of the plant canopy. By one mode, application to the soil may be carried out by mixing the compound with fertilizers, which are used to fertilize the soil. The term "nematicidally effective amount" refers to an amount of the compound which causes substantial reduction of the galling index of the plant, to an index below 2.0 accompanied by a reduction of at least 30% of the female population compared to the female population of the untreated plant. Such a reduction should be accompanied by no substantial decrease in fresh weight of the host plant.

The concentration of the phosphorous acid in the water base formulation is 10% to 60%, preferably 25% to 55% and most preferably 48% to 52%. The dosage of application is of course appropriate to the species of the plant, and is correlated mainly with the size of the root system.

Generally, for young plants, 1 - 8 weeks old. the dose is 50mg to 1 OOOmg active ingredient per plant, preferably 250mg to 750mg a.i. per plant, most preferably 400 to 600 mg a.i. per plant. The method of the invention may comprise application of two different types of phosphorous acids and salts thereof, for example, a product that contains both potassium salt and ammonium salt of phosphorous acid. The phosphorous acid or salts thereof may be administered together with other pesticides intended to combat other plant infestation such as with other fungicides, insecticides, herbicides, etc. Preferably, the phosphorous acid or its salts may be applied in a mixture together with other nematicides.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, preferred embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 shows the effect of different dosages of L973, applied by soil drench, on the galling index;

Fig. 2 shows the effect of different dosages of L973, applied by soil drench on the development of nematode population; Fig. 3 shows the effect of different dosages of L973, applied by soil drench, on fresh weight host shoot;

Fig. 4 shows the effect of different concentrations of L973, applied to host foliage, on galling index;

Fig. 5 shows the effect of different concentrations of L973, applied to host foliage, on fresh weight of host shoot;

Fig. 6 shows a comparison between the effect of foliage spray and the effect of soil drench on galling index;

Fig. 7 shows a comparison between the effect of foliage spray and the effect of soil drench on fresh weight of host shoot; Fig. 8 shows the effect of different concentrations of L973 in the growth medium on the average number of galls in monoxenic tomatoes root culture;

Fig. 9 shows the effect of different concentrations of L973 in monoxenic tomatoes root culture, on the development of nematode population;

Fig. 10 shows a comparison between the number of galls per petri dish in tomato roots treated with different amount of L973 and tomato roots of a genetically resistant species;

Fig. 11 shows a comparison between the development of the nematode population in a genetically resistant species to the same development in non-resistant species treated with different amounts of L973; Fig. 12 compares the effect of soil drench of L973 (500 mg/plant) on galling index in roots of several different plants;

Fig. 13 compares the effect of soil drench of L973 (500 mg/plant) on the development of nematode population in different plants; and Fig. 14 compares the effect of soil drench of L973 (500 mg/plant) on fresh weight of the shoot in several different plants.

Fig. 15 compares between SEM image of giant cells in tomato's roots that were treated with L973 and similar images in control plants.

DETAILED DESCRIPTION OF THE INVENTION Experimental procedure

In all the following experiments an aqueous solution containing 500 g/lit phosphorous acid (active ingredient) as potassium phosphite salt, (in which K ions are in equilibrium with HP0₃ ^"2, and H P0₃ ^"') was used to protect Marmand tomatoes from nematodes of the species Meloidogyne javanica.

The above mentioned aqueous solution is referred to herein as L973, all the dosages mentioned referred to active ingredient quantity.

Three parameters were determined to evaluate the chemical activity of the composition: 1 ■ Galling Index:

A six grade scale (from 0 to 5) of the gall covered portion of the host roots. The scale is: 0 = no galls found, 1 = 0-10% of the root covered by galls, 2-10-25% coverage, 3=25-50% coverage, 4=50-75% coverage, 5=75-100% coverage. 2. Population Analysis:

The percentage of juveniles, females, and males in the nematode populations within the galls. 3. Fresh weight of the host shoot. In several cases the effect of the treatment on the morphology of giant cells was also studied.

Example 1 Effect of L973 on root-knot nematode and the host plant when applied by soil drench.

In a greenhouse experiment, at a temperature of 25 °C, three different dosages of L973 were applied to tomato plants that were infected by nematodes: 250, 500 and 750 mg L973 per plant. L973 was diluted in 50 ml water/plant, and applied by drenching twice: three days before inoculation with the nematodes and two days after inoculation.

The effects revealed six weeks later on galling index are shown in Fig. 1 ; a nematode population analysis is shown in Fig. 2; and the effect of the treatment on the fresh weight of host shoot is shown in Fig. 3. Fig. 1 shows that the galling index decreased from 4.5 in the control to between 1.5 - 2 in the two higher dosage treatments.

Fig. 2 shows the effect of the same treatment on the development of the nematode population. It is apparent from the figure that the female population was reduced from above 80% in the control to about 30%o in the 500 mg per plant treatment. In the two highest dosages of the compound tested most of the population was of juveniles.

Fig. 3 shows the effect of the same treatments on the fresh weight of host shoot. Here, a phytotoxic effect, expressed by plant weight being substantially lower in treated plants as compared to control, was evident when the highest dosage was used. Fig. 3 also demonstrates that in the 500 mg per plant treatment fresh weight of host shoots is much larger than in the controls, indicating that this dosage in fact improves the plant's physiological status, probably by decreasing dysfunction caused by nematode infestation.

The above three figures clearly indicate that at the dosages tested L973 can be nematicidally effective without harming the host.

Example 2 Effect of L973 on root-knot nematode and the host plant when applied on host foliage

In a greenhouse experiment at a temperature of 25 °C four different concentrations of L973 were applied: 0.02%. 0.04%, 0.08% and 0.16% (v/v) aqueous solution of the base formulation. Eight upper leaves of each plant were dipped in different concentrations of L973. Triton™ wetting agent was added to the solution before dipping, in order to improve the absorption by the leaves. One day after the treatment strong nacrosis was found: among the plants that were treated with 0.16% solution, about 80-90% of the foliage was nacrotic.

The nacrotic leaf area decreased as the concentration decreased and no nacrosis was found in the 0.02%o treatment. Three days after the treatment, the plants were infected with nematodes and the results are shown in Figs. 4 and 5. Fig. 4 shows that galling index was hardly affected by dipping application at concentration of less than 0.16%. Fig. 5 shows the effect of foliar application on fresh weight of host shoot.

Since the amounts of L973 needed in order to act effectively as a nematicide in foliar application caused severe nacrosis , it was concluded that soil drench application is to be preferred for protecting Marmand tomatoes from Meloidogyne javanica.

Example 3 Effect of L973 on root-knot nematode and host plant when sprayed on host foliage

In a greenhouse experiment at a temperature of 25 °C two different concentrations of L973 were applied by spraying on foliage: 0.04% and 0.08%>. These treatments were compared to soil drench of 500 mg L973 and untreated control. Fig. 6 shows the galling index of treated plants and control. As can be seen in the figure galling was reduced appreciably by the spray treatments although the soil drench treatment showed better results.

Fig. 7 shows the effect of the treatments on the fresh weight of host shoot. Phytotoxic effect seem to exist in the present spraying experiment, similar to the one found in the dipping experiment.

Example 4 Effect of L973 on root-knot nematode in a monoxenic tissue culture of tomato roots

The tissue culture experiment was aimed at isolating the effect of L973 on the plant while eliminating the effects caused by its interaction with physical, chemical, and biotic factors that exist in soil. In this experiment, food substrates for excised tomato roots were prepared according to the procedure suggested by Skoog Tsui and White as described in "A manual for Practical Work in Nematodology'^* by s'Jacob, J. J. Bezooijen and J. V. Benzooijen pp. 1-52. Different amounts of 5, 25, and 125 mg L973 were added per liter of the growth medium. Excised tomato roots were put on the growth media in petri dishes and nearby a cluster of root-knot nematodes eggs were placed. The petri dishes were incubated in 25°C for three weeks. Figs. 8 and 9 show the results obtained. Fig. 8 shows the average number of galls per culture and shows reduction of at least 50% in the galls number.

Fig. 9 shows the effect of the same treatment on the development of the nematode population and shows reduction in female population.

These two figures clearly show that the treatment of monoxenic roots culture by a compound of the invention results in strong reduction in the average number of galls per culture and in a decreased development of the female nematodes.

Example 5 Comparison between genetically resistant tomato plants and sensitive tomato plants that were treated with L973 in monoxenic culture

This experiment was conducted as described in Example 4, the difference being that the L973 examined concentrations were 62.5, 125 and a

250 mg/lt. The purpose of the experiment was to compare results obtained by the L973 application to those obtained by use of tomato plants, which possess genetic resistance to nematodes (var. Shorshat 199-2).

Fig. 10 shows the average number of galls per dish . and Fig. 11 shows the effect of the same treatment on the development of the nematode population, i.e. percentage of females in the population.

It is apparent from both figures that a concentration of 250 mg per liter of L973 gives results that are similar to the behavior of the genetically resistant tomato.

Example 6 Effect of L973 on root-knot nematode in various plants

The experiment was conducted in a glasshouse with controlled temperature of 25°C around the clock. 500mg of L973 were drenched in the soil surrounding each plant. The plants were cucumber, tomato and cabbage. Each was inoculated with about 2,000 eggs of root-knot nematodes, and was treated by L973 3 days before inoculation and 2 days after. The results achieved one month after planting are described in Figs. 12, 13 and 14.

Fig. 12 shows that in all three plant species the galling index was reduced to around 2. These results show that L973 can be nematicidally effective to other species rather than tomatoes.

Fig. 13 shows a substantial decrease in the population of female nematodes in cucumber and tomato and a less impressive decrease in the female population of cabbage. This figure also demonstrates that L973 is effective for controlling nematodes in various plants.

Fig. 14 shows the effect of L973 on the fresh weight of the shoot in various plants. It seems that some phytotoxic effect exists in each of them, including the tomato, which did not show such an effect in the greenhouse experiment. Therefore it may be suggested that the artificial conditions in the glasshouse are major contributors to the reduction in shoot weight, and that greenhouse experiments with cucumber and cabbage will also show nematicidally effectiveness with substantially no phytotoxic effect.

Example 7: comparison between SEM image of giant cells in tomato's roots that were treated with L973 and similar images in controls Fig. 15A shows a scanning electron microscope image of giant cells in tomato's roots. The plants were treated with 500 mg per plant of L973 applied by soil drench. It is clearly evident from the image that the giant cells are empty.

Fig. 15B shows a scanning electron microscope image of giant cells in a control tomato's roots. It is clearly evident from the image that the giant cells are full of active cytoplasm.

The comparison of Fig. 15 A to Fig 15B suggests that L973 causes the giant cells in treated plants to be empty, whereby it hinders the normal development of the nematodes.

Claims

CLAIMS:

1. A method for controlling nematodes in plants comprising: applying to the plants, or to the vicinity of the plants, a nematicidally effective amount of at least one compound selected from phosphorous acid and ₅ salts thereof.

2. A method according to Claim 1. wherein said salt is a potassium salt.

3. A method according to Claim 1. wherein said nematode is an endogenic nematode.

4. A method according to Claim 1. wherein said nematode is a root-knot 10 nematode.

5. A method according to Claim 1. in which the nematode is of the species Meloidogyne javanica.

6. A method according to Claim 1. wherein said at least one compound is of a concentration between 10 and 600 gr per liter.

15 7. A method according to Claim 1. wherein said at least one compound is of a concentration between 250 and 550gr per liter.

8. A method according to Claim 1. wherein said at least one compound is of a concentration between 480 and 520 gr. per liter.

9. A method according to Claim 1. wherein said nematicidally effective 20 amount is between 50 and 1.000 mg per plant.

10. A method according to Claim 1. wherein said nematicidally effective amount is between 250 to 750 mg per plant.

11. A method according to Claim 1. wherein said nematicidally effective amount is between 400 and 600 mg per plant.

25 12. A method according to Claim 1. wherein said at least one compound is applied to said plants or the vicinity thereof by aerosol.

13. A method according to Claim 1. wherein said at least one compound is applied to said plants or the vicinity thereof by mixing the soil with said compounds prior to planting said plants.

14. A method according to Claim 1. wherein said at least one compound is applied to said plants or the vicinity thereof by drenching the soil with said compounds prior to planting said plants.

15. A method according to Claim 1. wherein said at least one compound is applied to said plants or the vicinity thereof together with another pesticide.

16. A method according to Claim 14 wherein the pesticide is a nematicide.

17. A method according to any one of the preceding claims, wherein the plants are selected from tomatoes, cucumber, and cabbage.