3rd INTERNATIONAL WORKSHOP ON METHYL BROMIDE ALTERNATIVES
Heraklio of Grete Greece, 7-10 December 1999
Topic: Alternative methods of Methyl Bromide in tobacco crop in Greece.
A.P. Chryssochoou
Tobacco Institute of Greece (T.I.G.), Plant Protection Dep. GR. - 66100, Drama
SUMMARY
Methyl bromide (MB) as other soil disinfectants have been used for tobacco seedbeds disinfection in Greece
for many years with very good results. Proper preparation of soil and the followed right seedbed disinfection, are the
best actions for a successfull tobacco plantation. In this way, many soil diseases (fungi, bacteria), nematodes, insects
and the most weeds, except dodder (Cuscuta spp), white clover (Trfollium repens) and fieldbind weed (Convolvulus
arvensis)can be well controlled, resulting in producing many, uniform and healthy tobacco seedlings when they are
needed for transplsnting in the field. Hand weeding is difficult and expensive work.
Up to now, the following soil disinfectants have been tested by the Tob. Institute of Greece (T.I.G.) for
seedbed disinfection:
Methyl bromide (MB), Metham sodium (Vapam, Hellapam, Laisol).
Bunema (Nemapam), Dazomet) Basamid G). For the same purpose, soil solarization was tested some years ago.
From above soil disinfectants, MB either due to its cost or difficulties in application (e.g. plastic covers and
some sand are needed for airthght of soil) resulted this chemical not to be used by the total tob. farmers in Greece
(73.000), but in a mean of 8-10% of them. In the contrary, MB is used in greater % in some tobacco areas as: Central
Macedonia 25%, West Macedonia 25-30% and in a part of Sterea Hellas (Lamia area) 7-10%, In consequence the
problem that may appear in the fucture by its restricted use, would be analogous in severity and extend in the percentage
used in the areas.
The change of soil for seedbeds (every year or without fail every 2-3 years), the use of the rest of above
mentioned soil fumigants, the encouragement of use of soil solarization as weel as other technics (e.g. steam, burning
organic matter, bio-fumigation, possibility in the future use of Methyl l iodide CH 3I) would be good alternatives to MB.
PREPARATION - SEEDBED DISINFECTION
Soil fumigation is a standard practice in the production of tobacco (Nicitiana tabacum L.) seedlings in
plantbeds. The primary purposes are to eliminate weed competition and control soil-borne pathogens. For a succesful
fumigation, no mater which disinfectant is used, the following are needed: a) proper site selection and b) suitable soil
preparation.
A good plant bed location included the following:
- A deep, fertile, well-drained soil that warms up quickly.
- Exposure to sunshine, which protects from cold strong winds.
- A clean water supply for irrigation and sprays.
- To be near the house, in order to be shecked regularly.
- To be protected from animals, rid of diseases / insects and not close to horticulture crops (potato,
tomato, pepper) which are hosts of diseases (virus etc).
Heavy soils should be improved by adding river sand, while light ones are needed well composed sheep
manure. It is better, plantbed location to be changed every year or without fail ever 2-3 years. If the same location is
continiously used for plantbeds, then fumigation is necessary every year.
b) Suitable soil preparation
As soon as possible after transplanting plantbeds should be destroyed by the first ploughing in order all
remainting tob. seedlings to be decomposed completely as they are breeding ground for insect pests and tobacco
diseases. This culrural work is one of the most important for application of the Integrated Pest Management program,
I.P.M. A second and a third one ploughing is followed in Autumn and next Spring respectively, in order weeds and old
crop residue to be fully incorporated and decomposed before fumigation. Then the soil for plantbeds is seperated in
narrow bands and it is formed in small bounds for better drainage. After a few days and when soil moisture is good for
cultivation, plantbeds are flattened and the soil is splitting up in small pieces for uniform germination and growth of
tobacco seedlings.
The good plantbeds should be 25-30cm higher tham soil level, 1m width, 10-15m long and apart 50cm, in
order all cares concerning to be facilitated.
c) Fumigation
In well prepared as above mentioned plantbeds and when soil moisture is good for cultivation and soil
temperature is at least 50 degrecs F (10 oC) in a derth of soil 10cm, (e.g. in a sunny day at noon) fumigation is carried
out.
Right soil moisture and especially soil temperature during fumigation and some hours later, are the most important
factors for good fumigation.
Very often tob. farmers are in a hurry and they fumigate when soil moisture is high (wet soils) or when temperatures are
very low, resulting in failure with many problems (e.g. many pests, weeds etc).
Fumigation in Greece takes place according to the districts (early, late) during the months February (South) - March or
early in April (North).
Fumigation with each one of the fumigants referred above, is done as following:
MB is piped, using a simple special apparatus, to seedbeds under sealed airtightly plastic covers wich prevent the
fumigant escaping from the soil, two (2) days before seeding. The plastic covers remain for 24 hours, them they are
removed, plantbeds remain uncovered for other 24 hours for good aeration and after that the seeding is followed.
The fumigants Vapam and Bunema are applied each one diluted into water by means of a watering can. The
amount of water used (5l/sq.m) is suffiently to allow even application and wash the chemical into the soil to an
appropiate depth of approximately 15cm.
Four (4) days after application, the crust of the soil is broken up slightly using a rake to facilitataeration, and four days
after it follows the seeding. That is, seeding of plantbeds is done eight (8) days totally after fumigation.
Basamid G is applied by uniformly broadcasting on the surface of the plantbeds, it is incorporated by disking or a rake
to a depth of 10-15cm and them it is watered (2-3 l/sq.m). Plantbeds remain uncovered, undistubed in this situation for
five (5) days. After that the crust of the soil is slightly broken up using a rake to facilitate aeration for at least other 5
days and then follows the seeding. That is, seeding of plantbeds is done at least 10 days totally after fumigation.
Post - application time needed after the use of soil disinfectants
Discussion - results
From trials conducted by the Tobacco Institute of Greece (TIG) the following can be concluded:
Vapam. From table 3, and that can also be confirmed from its long use in practice so far, the following are ascertained:
The uniformity in growth is closely related to the time between application and sowing. When sowing was done 2 or 4
days after disinfecation a severe phytotoxicity was observed especially at the initial stage of seedling growth. These
treatments were significantly different from other ones and they were even worse than the control. The picture impoved
(uniformity fairly good) when sowing took place 6 days after disinfection. The last group (uniformity very good)
included 8-14 days between chemical application and sowing.
As concern the number of weeds per sq.m, all Vapam treatments gave excellent results.
The number of transplants was very low when Vapam was applied 2 days before sowing and that it was significantly
different from the rest treatments of Vapam, but not from the control plots. When sowing took place 4 or 6 days after
disinfection, the number of transplants was fairly good and significantly different from the control. Finally, the highest
number of transplants was given by those treatments which were sown 8, 10, 12 or 14 days after disinfection.
Basamid G. From table 4, the following are ascertained: (phytotoxicity N o of weeds, No of transpl.),
This chemical valued by three criteria together showed that the best results were when sowing had done 10 at least days
after disinfection.
Basamid valued by each one criteria showed as follow:
Phytotoxicity was severe when sowing had done 2 or 4 days after disinfection, as in the case of Vapam. It was fairly
good when sowing had taken place 6 or 8 days after disinfection, and it wasexcellent and significant different than the
other tretments, when sowing had place 10 and 14 days after disinfection.
As consern No of weeds / sq.m in both years (1985 & 86), all treatments of Basamid gave excellent results and they
were significatly different than the control.
As concern No of transplants / sq.m, they were very low, when Basamid G had applied 2 or 4 days after disinfection.
Generally. the greatest number of transplanting was given when sowing had been 8, 10, 12 or 14 days after disinfection.
MB. From table 5, the following are ascertained:
Methyl bromide generally evaluated, in all treatments and criteria gave excellent results and it differed significantly
than the control plots.
For this chemical, it is general accepted that two (2) days are needed for seeding after fumigation (one day covered by
plastic, plus one, for aeration).
Fumigation of manure
Manure which is usally used for ¨cover¨ of tobacco seed after seeding in plantbeds, should be also disinfected
in the same way by each one of above mentioned disinfectants. In this way, in addition to other benefits (control of
pests, weeds etc in manure), tobacco seed of other undesired cultivars which may be present in the manure are
destroyed, resulting in clean tob. variety crop. One (1) cub. in of manure is enough for covering 100-150 sq.m of
plantbeds.
TOBACCO CROP FIGURES IN GREECE
Table 2. gives some statistics about tobacco crop in Greece.
a) Good tobacco seed should be:
- clean genetically
- high emergence capicity (more than 85%)
- ¨strong¨ healthy and well developed
- Pure, not mixed with seed of other tob. varieties, weeds or foreign substances
- seed of The National Tobacco Board (NTB)
(1gr. of tob seed= 10-12 thousands of seeds)
b) Tobacco seedbeds / ha
Uniform emergence and growth are necessary to provide a high percentage of usable transplants.
The area of seedbed need for each ha dependes on:
- Type or variety of tobacco wich will be grown (No of tob. seedlings / ha)
- careful construction of the seedbeds
- method of transplanting
Usually tob. farmers under their are to have as many as possible tob. seedlings during the transplanting period
in each area, construct each year more seedbeds than are needed, even some times as much as double.
When tobacco is transplanted by machines (today 85% of tob. crop is done by machines) more seedbeds are needed.
c) Date of seeding
Date of seeding should be done 55-60 days before transplanting in each area. In South Greece (early crop)
suitable date should be in meddle of February, while in North Greece (late crop) during the March.
Germination of dry tob. seed may be done even in low temp, 5 oC. In 13-20oC germination of dry tob. seed is done in
10-15 days, for Oriental type tobacco, and in 15-20 days for flue-cured (Virginia) and Burley tobacco.
When plastic covers are used in plantbeds after seeding for 35-40 days (to avoid damage from cold or frost etc), this
protection results tobacco seedlings to be ready for transplanting earlier 10-15 days than the usual date.
The use of soil solarization in tobacco seedbeds compared to conventional disinfection
Discussion - results
From trials conducted by TIG some years ago, the following can be concluded:
From table 6, the following are shown:
a) Soil solarization (Jul΄87, treat. No2) gave very good results in all criteria except control of weeds.
b) M.B, in both dates of its application (Octob. 87, treat No 3 and March 88, treat No 4) gave excellent results in all
criteria of its valuation.
c) Vapam (March ΄88, treat No 6) also gave very good results in all criteria of its valuation, while Vapam (Octob. ΄87,
treat No 5) gave pretty good results, although they were significantly different than the control (treat. N o 1). All above
results are illustrated better in graph 1.
From table 7,the following are shown:
a) M.B. (March ΄89, treat No 6) gave excellent results in all of its criteria of valuation in comparison with the control
(untreated, treat No 1).
b) Soil solarization with transparent plastic in both applications (Aug. ΄88, treat. No 2 and Sept.΄88, treat No3) controlled
excellent damping-off, had very satisfactory development of tob. seedlings and number of tob. transplants was also very
satisfactory. Each one of these criteria deffered significantly in comparison with the control, while the number of weeds
in both treatments No 2 and No 3 was high, and no significant difference between these and control existed.
c) Soil solarization with black plastic in both applications (Aug.΄88, treat. No 4 and Sept.΄88, treat. No5) had pretty hight
infection from damping-off, very good to excellent growth, and it gave pretty satisfactory number of transplants. In
these criteria there was also significantly difference than the control. But as concern the number of weeds in both
treatments, it was not at all control, as it was also reffered in soil solarization with transparent plastic, and in some case
(treat. No4) weeds were more than the control.
Generally, with soil solarization, although it is achieved a very effective control against a wide
spectrum of weeds in other crops, the following weeds which are common in tobacco crop are not controlled. Avena
sterilis, Amaranthus spp, Portulaca olereacea, Xanthium (annual weeds) and Cynodon, Convolvulus, Sorghum
(perennials). All above results are illustrated better in graph 2.
CONCLUSIONS
Alternatives to Methyl Bromide in tobacco seedbed disinfection should be:
- The change of soil for seedbeds every year or without fail every 2-3 years.
- The right selection and proper preparation of the soil before disinfection.
- The right application of the soil disinfectants: Metham sodiium, Bunema (nemapam), Dazomet.
- The encourangement of use of soil solarization.
- The possibility of the future use of CH3I.
- Other technics (steam, burning organic matter, bio-fumigation etc).
BIBLIOGRAPHY
1. Chryssochoou, A.P., Preparation - disinfection of tobacco seedbeds.
Agricultural magazine: The ¨consultan of farmer, Jun -Feb, 1999 (in Greek).
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diseases caused by soil - borne pathogens. Phytopathology 66:683-688
3. Tjamos E. and Faridis A. 1982. Control of soil - born pathogens of vegetables and cotton by solar heating. (In Greek
with English summary).
Agricultural Research 6:393-401.
4. Tjamos E. 1983. Control of Pyrenochaeta lycopersici by combined soil solarization and low dose of methyl bromide
in Greece. Acta Hort. 152: 253-258.
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9th Interbalkanic Conf. for Plant Protection. Athens, Greece, Nov. 1983.
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after the use of soil disinfectationts.
Coresta, Agro/Phyto soint Meeting. Porto Alegre, Brazil, Oct. 1987.
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