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Duong Van Ha
“Study the resistance of three populations of Diamond back moth Plutella Xylostella L. in DaLat, TienGiang and HoChiMinh city”.
It is really not difficult to control Diamond back moth. To control effectively this insect, there are either the newly used insecticides like abamectin, or the unpopularly-used ones like phenthoate, B. thuringiensis var kurstaki, nereistoxin. However, it is shown that some insecticides which have been used widely now have just a little efficacy on this insect. This proves unsuitable to maintain the existing method of treatment.
The population of Diamond back moth in DaLat has resisted not only B. thuringiensis var kurstaki but also cypermethrin. Meanwhile, this in HoChiMinh city and TienGiang has also resisted cypermethrin.
Through 10 generations treated by abamectin, the resistance abamectin of the population of Diamond back moth in DaLat has increased rapidly. Through some generation, it is shown that the higher concentration of the insecticides, the quicher increase of the resistance of the insect.
The resistance abamectin of this population in DaLat has gone up greatly. However, it will decrease slowly in many late generations, although this insecticide is not used in this period.
Le Minh Dung
“Study on the biological and eco-biological features, of the leaf-mining fly (Liriomyza sp.) and on the integrated preventive methods to protect vegetables from damage caused by Liriomyza sp. in Ho Chi Minh city”
were carried out in Ho Chi Minh city from April, 2000 to April, 2001.
The results of study showed that:
In Ho Chi Minh city area, most of farmer grow cucumber, green peas, tomato in both rainy and dry season. Of which, from 41,7 – 72,7 percents of farmer grow vegetable in dry season. The unique method used to prevent the Liriomyza sp. is insecticides application as organicphosphate and pyrethroid. The use of plant protection insecticide bases mostly upon the manufacture’s instructions.
We have already recorded two popular Liriomyza sp. species in Ho Chi Minh city. These are Liriomyza huidobrensis Blanchard, Liriomyza trifolii Bergess. We have also found a species that bores bean stem is Ophiomyia phaseloli Tryon, belongs to Agromyzidae family, Diptera.
We investigated and recorded 15 vegetable plants that were attacked by the leafminer. Of which, tomato, cucumber, green peas are the most serious damaged plants by the pest.
It was recorded of 6-parasitoids of the Liriomyza sp. species in Ho Chi Minh city. The parasitize, however, ranged from 1,16 –30,43 % on cucumber, and from 0,32 – 16,13 % on green peas.
The pecentage of pupae developed to adult was from 4,34 – 46,72 % on cucumber and from 12,77 – 42,28 % on green peas.
In Ho Chi Minh city, adult and pupae of Liriomyza sp. leafminer found on different vegetables have different sizes. On tomato, body length of a female is 1.57 ± 0,42mm, and of a male is 1,42 ± 0,23 mm. On cucumber, body length of a female is 1,68 ± 0,27 mm, and of a male is 1,51 ± 0,31 mm. On green peas, body length of a female is 1,69 ± 0.22mm, and of a male is 1,61 ± 0.24 mm.
The Liriomyza sp. occurs from the beginning of the crop and develops toward the end of the crop. Damages caused by the Liriomyza sp. are more serious in dry season than in rainy season.
IPM methods have been proved to be effective in the control of the Liriomyza sp.. For example, they delay the development of the Liriomyza sp.. In addition, they bring back higher economic and technical effects compared to the traditional methods. Profits when applying the IPM methods are VND 424.000/ha on cucumber, and VND 6.518.000/ha on green peas.
Nguyen Ninh Phuoc
Effect of four kinds of herbicides on soil microbial activity and biomas carbon and nitrogen of rice cultivated soil in An Phong village, Thanh Binh district, Dong Thap province
A field experiment was conducted to study effect of four kinds of herbicides on soil microbial activity and biomass carbon and nitrogen of cultivated rice soil in An Phong village, Thanh Binh district, Dong Thap province in Summer – Autumn 2000 cropping season. The experiment was arranged a completely block randomized design with four replications and five treatments consist of four kinds of herbicide (Rafale, Tiller – S, Cantanil and Satunil) and control (handle weed control); total of twenty plots, every plot (20 m2 = 4 x 5m) was separately covered by dikes (0,5 x 0,5 m). Soil samples were taken at 6 times: 1 day after herbicide application, 3, 20, 40 and 85 day after sowing (DAS) and at the depth of 0 – 10 cm. Soil (10 gram) was diluted with a dilution series (10-4, 10-5, 10-6) for enumuration of bacterial, actinomycetal, fungal and algal propagules (Wardle and Parkinson, 1990b) by the Miles and Misra Drop – Plate count method (Vincent, 1970) and the Most Probable Number method (Alexander, 1982). Soil microbial biomass carbon and nitrogen were determined by Chloroform Extraction Method (CEM) (Houwath and Paul, 1994). Total of N and organic matter content of soil were analysed by the micro - Kejldahl method and Walkey – Black method after harvesting.
The results showed that four types of herbicides decreased bacterial, fungal, actinomycetal and algal propagule numbers and they also reduced soil microbial biomass carbon and nitrogen, Rafale and Tiller – S toxicity affted on bacterial and fungal propagule numbers seriously. Prologation of inhibition was caused by two kinds of herbicides (Rarale and Tiller – S) on soil microbial biomass carbon and nitrogen during rice cultivation time. Cantanil had no effect on microbial numbers and biomass but the rice yield of Cantanil application was the lowest. Nitrogen total of top soil reduced after hervesting in comparison to N total of before cultivation among N total of soil Cantanil application was smallest. On the contrary, organic matter content of soil had no change and soil of control treatment and Rafale application had the highest organic matter content.
Nguyen Phu Hien
“ The evaluation concerning the effect of IPM practice on rice farmers in Dong Thap province”
was carried out during the time from November, 1 st, 1999 to June, 1 st, 2001 at 24 villages of 8 districts in Dong Thap. It completed on December, 2002. With randomized survey method was applied, 309 households (belonging into 2 group: IPM trained farmers and non-IPM trained farmers) were interviewed.
The results showed that even not to be trained in any class of IPM, 81.0 % farmers of the second group get some IPM information. After receiving informatoin on IPM technology, there was 96.7 % of IPM farmers (already trained in FFS class) and 68.3 % non IPM farmers who agreed that IPM is a reasonable method for plant protection, there are 92.3 % IPM farmers and 50.4 % non IPM farmers who already practiced IPM in their rice field.
Among IPM technologies, the reduce of insecticide sprays and seed quantity were the most commonly applied by farmers and reasonable fertilizer appication, good water management, and resistant rice variety use took the second place in IPM technology practice.
The most commonly reasons why some farmers didn’t practice IPM technology concerning: the neighbors didn’t practice it (20.6 % IPM farmers and 11.7 % non- IPM farmers) and the caring about the yield loss (7.9 % IPM farmers and 7.2 % non- IPM farmers). Through these results, we can see that the community took a very important role in IPM practice.
The most change in the perception of the farmers was the knowledge concerning the natural enemies with 60.5 % of non- IPM farmers can recognize already the natural enemies in their field.
The best methods for IPM technology transfer were: demonstration fields ( 68.0 % IPM farmers and 31.9 % non IPM farmers), FFS training courses (60.5 % IPM farmers), workshop (40.2 % IPM farmers). For IPM technology transfer through the mass media, television took the most important place (29.3 % IPM farmers and 29.4 % non IPM farmers), followed by radio broadcast (16.8 % IPM farmers and 15.1 % non IPM farmers).
However, there are still 26.3 % IPM farmers and 64.2 % non IPM farmers who continue to spray immediately when insects appear in their fields and 14,3 % IPM farmers and 19.1 % non IPM farmers who practice preventive sprays.
In general, knowledge and attitude concerning IPM practice of almost interviewed farmers were good, when practice IPM technology, a lot of farmer gained a high yield and high benefit in their rice production. And by reducing pesticide use, the health of farmers was improved and the pollution of environment was reduced. Beside this, there was some farmers who, even having a good perception on IPM, still hesitate in practicing IPM technology by different reasons.
Nguyen Viet Long
“Effect of prevention and treatment of sheathblight disease on rice of two antagonistic bacteria isolates with Rhizoctonia solani on the field in Dong Thap province”
was executed from November, 1998 to August, 2001. Experiment is arranged in form of randomized complete block design with 04 replications.
Purpose of the experiment:
- Appraising effect of treating methods, determining number of spraying times, appropriate-spraying distance and researching influence of two antagonistic bacteria isolates with Rhizoctonia solani causing sheathblight disease.
- Surveying restricted ability and infection of sheathblight disease according to horizontal direction of the antagonistic bacteria isolate DP7L1-17 in the field. Simultaneously, appraising effect of prevention and treatment of sheathblight disease on rice of the antagonistic bacteria isolate DP7L1-17.
Preliminary results
- Treating the antagonistic bacteria by method of seed soak and seed soak plus two times of spraying antagonistic bacteria at interval of 05 days, gave bad effect of disease treament and it was equal to the control which did not use neither fungicide validacin 3DD nor antagonistic bacteria.
- The treatment of fungicide validacin 3DD gave better effect of than that of single antagonistic bacteria and the control which did not use neither fungicide Validacin 3DD nor antagonistic bacteria.
- Spraying antagonistic bacteria three times at interval of 05 days and spraying antagonistic bacteria three times plus half a dosage of validacin 3DD in first spray (25 days after transplant) protected rice from infection of disease during 40 days from the date when Sclerotia infected (the disease).
- Spraying antagonistic bacteria at time of 25 days after transplant (43 days after sowing or 05 days after inoculation Rhizoctonia solani) is an appropriate time to help antagonistic bacteria DP7L1-17 take effect in time.
Pham Minh Sang
“ The efficacy of antagonistic and plant growth-promoting bacterial product against rice sheath blight (Rhizoctonia solani Kuhn)
was conducted in Cuu Long Delta Rice Research Institute from October 2001 to August 2002.
The bacterial strains used in the experiments were: B 49, B 52, P 71, P 101, and B 177. Laboratory and green house experiments were laid out in a completely randomized design (CRD) with 3 – 5 replications. RCBD was used for field experiment.
Results showed that:
Five bacterial strains still maintained the antagonistic activity against Rhizoctonia solani by dual culture test. These strains were not rice pathogens through pathogenicity test. When used as seed treatment, these strains promoted shoot and root growth of rice seedlings and consequently increased dry matter by 31.8% - 70.1% as compared to untreated.
Nutrient Broth and rice bran extract were suitable liquid media for biomass production of five bacterial strains, while weed and rice straw extracts did not favor bacterial reproduction. Nutrient agar was the best solid medium, followed by rice bran and rice bran – rice hull media. Banana, soybean grain, soybean powder were not suitable solid media for biomass production.
Viability of bacterial strain B 52 in talc – based formulation during storage time was influenced by the ratio of carrier. Ratios of 10:100 (10ml of bacterial suspension containing about 108cfu.ml-1 homogenized in 100 g of talc) and 1:100 (1ml of bacterial suspension containing about 108 cfu. ml-1 homogenized in 100 g of talc) gave higher density of viable bacteria than ratios of 0,5:100 and 0,1:100 and bacterial concentration in these two treatments still remained high until 5 months of storage under room temperature condition (27 – 280C) .
Under green house condition, talc-based formulation of five bacterial strains, when sprayed twice at maximum tillering stage with bacterial density of 108 cfu. ml-1, reduced sheath blight incidence and markedly restricted sclerotial formation. No significant difference in the efficacy against sheath blight was found between five different bacterial strains applied singly or in mixture.
Under field condition, talc-based formulation of five strains suppressed horizontal development and reduced the rate of disease development over time. The efficacy against sheath blight was not significantly different among tested strains applied singly or in mixture and was equal to Validacin 3L treatment
Tran Minh Ton
Using parasitoid on biological control against Diamond Back Moth (DBM) Plutella xylostella, the biological agent Cotesia plutellae was examined. The experiments were conducted through the host-parasitoid relationship in the field and laboratory condition. This paper was carried out in order to investigate the real situation and to evaluate the parasitoid potential as a biological agent for DBM control.
On farm, C. plutellae appears at crucifer crops damaged by DBM. The frequency of appearance of this parasitoid was affected by weather variation which is depended upon yearly seasons, by pest and weed control applied by farmers.
Investigation of parasitization status has shown how the natural or human factors had affected to the appearance of this parasitoid. Thus, the added measures such as augmentative release and conservation of natural food source are actually necessary.
In the laboratory condition, the biological control effectiveness of this parasitoid was researched in bio-control terms through functional response experiment, in damaging terms through numerical response one.
As results, the mathematic model indicated the host-parasitoid correlation in parasitization was established.
Based on these models, biological controllers could predict the parasitization when the population variation of both host and parasitoid occurs at the same time.
To maximize the potential exploitation and the effectiveness in mass rearing as well as the place and time of release, the host age selection, the low temperature hardiness of pupal stage, the available food source for parasite adults have studied and have got essential results.
The host age selection allowed determining the appropriate time to arrange the exposure between host and parasitoid in mass rearing and field release.
The low temperature hardiness of pupal stage permitted to store and to transport, to satisfy demand of quantity for serving different release batches on schedule.
The food availability for adult is important in mass rearing and mass release, including the introduction of parasitoid to new geographic area.
Damaging status of DBM in the field really needed to different release methods for this parasitoid on biological control application.
How the effectiveness of release methods which are different from each other in suppressing pest was compared. Besides a lot of natural characteristics of a parasitoid species, therefore, the method of application decided strongly the own effectiveness.
Nguyen Ngoc Bich
“Initial survey and diagnosis of major virus diseases on tobacco in Taây Ninh province”, was carried out in Taây Ninh, in Chemical and Biological Analysis and Experiment Center of Noâng Laâm University and in Sub-Institute of Tobacco Technology and Economics. The experiment last from 10/2001 to 05/2003 with three major contents:
1. To survey of tobacco virus disease in four areas of Taây Ninh: Gia Loäc, Thaïnh Ñöùc, Bình Lôïi and Tieân Thuaän. Each of those, we choose an area of 30 ha and take 10 points on the crossline with 100 plants/point for periodical survey.
2. To identify and detect the major virus pathogens causing damage to tobacco planted in Taây Ninh province by using ELISA method with polyclonal antibody of kinds of kit: TSWV (Tomato spotted wilt virus), TMV (Tobacco mosaic virus) and CMV (Cucumber mosaic virus) that were carried out at Chemical and Biological Analysis and Experiment Center of Noâng Laâm University. Leaf samples with different symptoms were tested for each of kits or tested concurrently to examine presence of different viruses.
3. Experiments on tobacco seedlings in the greenhouse at two locations were Phöôùc Ñoâng (Taây Ninh) and Sub-Institute of Tobacco Technology and Economics headquarter. We collected from 3 to 5 adult thrips and released them on tobacco seedlings after transplanting.
Result
1. There were six viruses on tobacco planted in Taây Ninh province: Tomato spotted wilt virus (TSWV), Tobacco mosaic virus (TMV), Cucumber mosaic virus (CMV), Tobacco leaf curl virus (TLCV), Potato Y virus (PVY) and Tomato bushy stunt virus (TBSV). TSWV, CMV and TMV were identified successfully by ELISA method. TLCV, PVY and TBSV were by specific symptoms.
2. TSWV caused bud malformation of tobacco and severe outbreaks occured at many areas of Taây Ninh for two successive crops (2001 – 2003).
3. Analysing by DAS-ELISA method
3.1 Tobacco leaf samples from the field with symptoms such as bud necrosis, veinal necrosis, leaf yellow spotting and that of seedlings in greenhouse with or without disease symptoms showed positive reaction against polyclonal antiserum of TSWV in DAS-ELISA method but negative or weakly positive reaction with TMV and CMV. Other plants around tobacco field such as eggplant, tomato, dark tobacco, red pepper, pergularia, cucumber, pumpkin, passiflora, peanut, amaranth, black bean also showed positive reaction with TSWV.
3.2 Tobacco leaf samples with mosaic symptom and that of peanut, dark tobacco, black bean, okras, eggplant, pergularia showed positive reaction with TMV.
3.3 Tobacco samples with tumour, mottling symptom in the leaves of Coker 176, and that of red pepper, black bean, dark tobacco showed positive reaction with CMV.
4. Thrips palmi K. that was identified by the Centre for Agriculture and Biosciens, UK, is specific vector of Tospovirus. The greenhouse seedlings showed disease symptom at 5th day after released thrips on tobacco.
5. To isolate insect vector also prevents disease symptom.
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Last modify: 18-04-2011
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