relation of cotton cultivars to the cotton-pest problem in the sudan gezira

8
Euphytica 34 (1985) X49-856 RELATION OF COTTON CULTIVARS TO THE COTTON-PEST PROBLEM IN THE SUDAN GEZTRA 0. S. BINDRA Food and Agricultural Organixition of the United Nations. 00100 Rome. Italy Growing of irrigated cotton in the Sudan, in relation to pest control. entered the ‘crisis phase‘ around 1967-6X and the ‘disaster phase’ in 198OM I, At the cruxes ofthe pest-control problem lay the uncontrollable whitefly-Induced lint stickiness and the American bollworm (ABW). The paper gives the succession of cotton varieties in the Gezira and reviews the reports on higher incidence of the whitefly and ABW on newer varieties. Logical cxplanations offered for the higher pest incidence on newer varieties lead to the conclusion that as compared with Sakcl-type cottons, the Lambert-type cottons would have a greater build-up of the white- fly. while AC&I cottons would have not only larger populations ofboth whitelly and ABW but also increaxd losses from the latter. Changes in area under different types of cotton are shown graphically in relation to the pest-control situation and a case is made for the hypothesis that varietal changes in the Ge/;ira had profound ecological effects which favoured the whitefly and ABW. but made sprays less effective. leading eventually to the cotton-pest-control predicament. Finally. based on recent cxperiencc. a hope is cxpresscd that switching to cultivars less favourdblc to the pats and more suited for eflicicnt pesticide application would ease thecotton-protection problem. INTKODUCTION Growing of irrigated cotton, which occupies 93.7(i) of the nearly 0.4 million ha cotton area in the Sudan has been plagued by serious pest problems since the early 1960s. The deterioration in the pest-control situation is well documented (BINIIRA & RAHMAN, 1983a; EVELEEKS, 1983; RAHMAN & EVELEENS, 1980). It is sufficient to say, here, that cotton-pest control in the Sudan Gezira entered the ‘crisis phase’ in 1967-68 when cotton stickiness caused by the cotton whitefly, Bmzisiu tahaci GENN., and the Ameri- can bollworm (ABW), Hrliothis urt+pu (HUB.) continued unabated and cotton yields dropped despite increased frequency of spraying. The new strategies of area- wide sequential ultra-low-volume spraying based on synoptic surveys, in the ‘package deal’, eventually failed miserably (EVELEENS, 1983) and ‘disaster’ came in the season 1980-81. It was marked by (1) an almost complete failure of whitefly and stickiness control despite more frequent spraying (upto 12 times per crop season), (2) highest, so far, insecticide-import cost and mounting of pest-control bill to 28”,, of the produc- tion costs which consumed 853;, of the cotton revenue, (3) reduction in cotton yields

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Page 1: Relation of cotton cultivars to the cotton-pest problem in the Sudan Gezira

Euphytica 34 (1985) X49-856

RELATION OF COTTON CULTIVARS TO THE COTTON-PEST PROBLEM IN THE SUDAN GEZTRA

0. S. BINDRA

Food and Agricultural Organixition of the United Nations. 00100 Rome. Italy

Growing of irrigated cotton in the Sudan, in relation to pest control. entered the ‘crisis phase‘ around 1967-6X and the ‘disaster phase’ in 198OM I, At the cruxes ofthe pest-control problem lay the uncontrollable

whitefly-Induced lint stickiness and the American bollworm (ABW). The paper gives the succession of cotton varieties in the Gezira and reviews the reports on higher incidence of the whitefly and ABW on newer varieties.

Logical cxplanations offered for the higher pest incidence on newer varieties lead to the conclusion that as compared with Sakcl-type cottons, the Lambert-type cottons would have a greater build-up of the white- fly. while AC&I cottons would have not only larger populations ofboth whitelly and ABW but also increaxd losses from the latter. Changes in area under different types of cotton are shown graphically in relation to the pest-control situation and a case is made for the hypothesis that varietal changes in the Ge/;ira had profound ecological effects which favoured the whitefly and ABW. but made sprays less effective. leading eventually to the cotton-pest-control predicament. Finally. based on recent cxperiencc. a hope is cxpresscd that switching to cultivars less favourdblc to the pats and more suited for eflicicnt pesticide application would ease thecotton-protection problem.

INTKODUCTION

Growing of irrigated cotton, which occupies 93.7(i) of the nearly 0.4 million ha cotton area in the Sudan has been plagued by serious pest problems since the early 1960s. The deterioration in the pest-control situation is well documented (BINIIRA & RAHMAN,

1983a; EVELEEKS, 1983; RAHMAN & EVELEENS, 1980). It is sufficient to say, here, that cotton-pest control in the Sudan Gezira entered the ‘crisis phase’ in 1967-68 when cotton stickiness caused by the cotton whitefly, Bmzisiu tahaci GENN., and the Ameri- can bollworm (ABW), Hrliothis urt+pu (HUB.) continued unabated and cotton yields dropped despite increased frequency of spraying. The new strategies of area- wide sequential ultra-low-volume spraying based on synoptic surveys, in the ‘package deal’, eventually failed miserably (EVELEENS, 1983) and ‘disaster’ came in the season 1980-81. It was marked by (1) an almost complete failure of whitefly and stickiness control despite more frequent spraying (upto 12 times per crop season), (2) highest, so far, insecticide-import cost and mounting of pest-control bill to 28”,, of the produc- tion costs which consumed 853;, of the cotton revenue, (3) reduction in cotton yields

Page 2: Relation of cotton cultivars to the cotton-pest problem in the Sudan Gezira

0. S. BINUKA

Table I. Release of cotton varieties for commercial cultivation in the Sudan Gezira

Cotton species Varieties and types

Year of release

Domains Sakcl Bar 14!‘25 VSI Tayiba VSA Maryoud

I927 1952 I967 I969 1972 1978

Lambert Type X I73OA 19.39 Bar XLI 1952 Barakat I969 Huda I976

Go.r.sypiwn lzirsutunl Acala Type Acala 4-42

Barac (67)B Barac (69)2

1958 I972 1979

to the lowest of the last 17 years, (4) reduction in cotton area, and (5) cotton exports being lowest since 1970. with plummeting of the share of cotton in the value of the Sudanese exports ( BINURA & RAHMAN, 1983a).

At the cruxes of the said ‘crisis’ and ‘disaster’ were the following two developments: (1) the cotton whitefly which used to be a minor early- and mid-season pest became an annually recurring uncontrollable all-season major pest, and (2) the ABW which used to be an occasional minor pest attained the status of a regular major pest. The causes of these developments have been the subject of much speculation and discussion (AMIN & BALLA, 1983; BALLA, 1982; EVELEENS, 1983; GAMEEL, 1982; RAHMAN, 1983; RAHMAN & EVEI.EENS, 1980). Interestingly enough, the various factors considered did not include a change in cotton varieties, even though BASHIR (1974) had earlier specu- lated that the introduction of the variety Barakat had aggravated the whitefly problem. This paper aims at examining the hypothesis that varietal change was one of the factors causing this pest problem.

MATERIAL

Cotton vurieties irz the Su&n Gezira. The Sudan Gezira has been famous for its extra- long staple, Gossypiutn harhudense, cottons. These are of two types: (I) Sake1 Type ~ tall, open canopy, and (2) Lambert Type ~ bushy, dense canopy. In the late 1950s the medium-staple. G. hirsututn, Acala cottons were introduced into commercial culti- vation. The varieties cultivated since the start of cotton growing in the Gezira are listed in Table 1. The cultivars now grown on a large scale are Bakarat, Barac (67)B and VSA. These occupied 68.53::. 30.880;; and 0.58:{ respectively f the 215000 ha. cotton area in the Gezira in 1983-84 (MURSAL, 1983).

850 Euphyrictr 34 ( I OH5 )

Page 3: Relation of cotton cultivars to the cotton-pest problem in the Sudan Gezira

COTTON PhST C'ONTKOL

RESULTSANDDTSCUSSION

W/lit<fly. JOYCE (1955) and HASSAN (I 970) mentioned that Lambert cotton cv. X 1730A was more prone to whitefly infestation than Domains Sake]. Further. GAMEEI, (1965566) reported that the tall, more open, Sake1 cotton cv. Bar 14125 was always more lightly attacked by the whitefly than the bushy Lambert cotton cv. Bar XL1 that replaced X 1730A. He also stated that Acala cotton, being bushy, provided shelter for the whitefly after the end ofoctober and, hence, supported high populations. KHA- LIFA (1982) showed that the above was reflected in lint stickiness in different cottons. Thus, Acala cotton had significantly higher mean stickiness (mg of sugar/100 g lint) than the long-staple cottons. Further, among the long-staple cotton, Lambert cv. Barakat and Huda (having bushy plants and closed canopy) had higher mean sticki- ness than Sake1 cv. VSA and Maryoud, which have open canopy.

Factors which make a cotton variety more prone to whitefly infestation are bush- iness, hairiness and larger leaf area. Bushiness and hairiness make cotton varieties suitable for the build up of populations of the whitefly ( BINDRA, 1983; MOUND, 1965; SIPPELL et al.. 1982, 1983a. 1983b). This explains the high build-up of the whitefly on the commercial Acala cotton, Barac (67)B, which is not only bushy but also more hairy than the commercial long-staple cottons in the Sudan. Further, bushiness and larger leaves provide protection to the whitefly against inclement weather and pesticide sprays.

BURHAN & TAHA (1974) determined the leaf-area indices in three harhcrckcxw cottons. viz. Sake1 cv. Tayiba and Lambert cv. Bar XLI and Barakat. They found that leaf-area indices were higher throughout each of the three seasons (1970-71 to 1972-73) in the two Lambert cultivars than in the Sake1 cv. Tayiba. Month-wise means of the leaf-area indices during the three years in the three cultivars (Fig. I) reveal that the leaf-area index of Bar XL1 was considerably higher than that of Tayiba throughout the season. Further, the leaf-area index of Barakat was higher than that of Bar XL1 throughout the season, except in January and February. It may be noted that Barakat replaced the previous Lambert cv. Bar XLI and also occupied much of the area earlier planted to the Sake1 cottons (Tayiba and its predecessors).

Arwricun holhwm. Acala cottons represented by Barac (67)B are more susceptible to ABW damage than hurhdense cottons like Barakat (BALLA, 1979). The former had consistently heavier ABW infestations than the latter, both in terms of numbers of larvae + eggs and rates of damaged fruiting parts (EVELEENS & RAHMAN, 1979). The differences may be due to (i) higher oviposition by ABW moths on hairy surfaces (GILHAM, 1963: LUKEFAHR et al., 1965, 197 1) of the Acala cotton, (ii) higher deterrence and toxicity of gossypol to ABW larvae (HEDIN et al., 1974; LUKEFAHR & HOU(;FI- TALINC;, 1969; USDA, 1980) on hurhurknsc~ cottons in view of their higher gossypol content (BAHIELDIN et al., 1978), and (iii) greater damage to Acala than to Barakat owing to better attunement of ABW to fruiting development in the former than in thelattercotton (EVELEENS& RAHMAN, 1979).

Page 4: Relation of cotton cultivars to the cotton-pest problem in the Sudan Gezira

0. S. BINI)KA

3.5

3.0

2.0

BARAKAT /\_, 6, I \

Sept. Oct. NOV. Dec. Jan. Feb.

MONTHS

Fig. I. Monthwise mean Icaf-arca indices of three cotton varieties during seasons 1970-71 to 1972.-73 (After BUKHAN & TAHA, 1974).

Conclusion. From the above, it is concluded that in comparison with Sakel-type cottons, the Lambert-type cottons would have a greater build-up of the whitefly, while Acala cottons would have not only a greater build-up of the whitefly and ABW, but also higher losses from the latter. Further, sprays against the whitefly on Lambert-type cottons (and also on the Acala cotton), particularly later in the season, would be ineffi- cient as compared with those on Sake]-type cotton.

Chunges in varic~tyn~isr cotton urea and its possihlr irnpuct on crop protection. Changes in area of different cottons in the Sudan Gezira are shown in Fig 2. Until 1958-59, hardly any G. hirsuturn was grown. G. hurhadensr covered the entire area; its two types (Sake1 and Lambert) sharing the cotton area almost equally. Thereafter, the share

Page 5: Relation of cotton cultivars to the cotton-pest problem in the Sudan Gezira

COTTON PEST CONTROL

- Package Deal -

100 1 DDT Spraying z

60

Lombert Cotton: (WF susceptible 1

ABW widespread and serious __+ Lint stickiness serious

20

0

- I Sokel Cotton:

Acala Cotton: (WF and ABW susceptible)?, I

-co-o-fJ-o-o-o-

0 : z ? z c E

: 1 2 co 2 2

(D (D r-

Years

Fig. 2. Changes in area undcrdifferent types ofcotton in the Sudan Gwira and cotton pest-control situation during the last 30 years.

of the Sake]-type cottons (open canopy, harbouring fewer whiteflies and well-suited for efficient pesticide application) in the cotton area declined to 2 1 T<, in 196465, below 1 Oy, in 1976677 and a mere l.l7’j/, in 1982-83. Conversely, the area under the Lambert- type cottons (large leaved, closed canopy, harbouring high whitefly numbers and not well-suited for efficient pesticide application) increased greatly by 1964-65 and has. since then, averaged about 77;<; of the total cotton area. As a result of these changes, the average cotton-leaf area per hectare in the Gezira must have increased and the canopy become denser, because the Lambert cottons had greater leaf-area indices than Sake1 cottons whose area they occupied since 1959-60, and because the new Lambert cv. Barakat had greater leaf-area index than Bar XL1 which it replaced rapidly and completely, since its introduction in 1969.

In view of the effects of cotton varieties on cotton whitefly outlined above, the said changes in variety-wise cotton area in the Gezira, specially from 1959-60 to 1964-65, would have made conditions in the cotton fields more favourable for the whitefly but adverse for efficient pesticide application against this pest. This belief is further supported by the fact that during the 1982-83 season, open-canopy okra-leaf Acala cv. Sudac-K needed only three pesticide sprays against six sprays required by normal- leaf Acala cv. Barac (67) B, or Barakat, the commercial long-staple cotton (KHALIFA, 1983).

The whitefly became a major pest in late 1950s in the wake of DDT spraying against the cotton jassid, Empoasca l~?Ccu DE BERG. Initially it was only an early-season and

Page 6: Relation of cotton cultivars to the cotton-pest problem in the Sudan Gezira

0. S. BINDKA

mid-season pest. But in 1967, three years after the area under Lambert cottons in- creased to about 77:; in 1964-65 (from around 50’:;; in 1958-59) it attained the status of the most damaging pest active until late in the growing season. The resulting unac- ceptably high lint stickiness made the marketing of the Gezira cotton very difficult. Two additional sprays were recommended late in the season to control cotton sticki- ness. This meant increased selection-pressure on the whitefly for pesticide resistance. The end result was a virtual failure of the chemical control of the whitefly during 1980-81 when even the best efforts of a well-known chemical company could not keep the whitefly under control, and there was a disaster in cotton production in the Gezira (BINDRAALRAHMAN, 1983a,1983b).

The area under Acala cotton increased more recently. At first, it increased gradually from 0.7”,, in 1972273 to X.7”,, in 1977778, but thereafter, the increase to 30.9”1;) in 1983384 was rather quick. This cotton is susceptible to both whitefly and ABW, as discussed earlier. Thus, an increase in its area in recent years in the Gezira (as also in the El Rahad, El Suki, Blue Nile and White Nile Schemes) must have aggravated the problem of both these pests. Further, this cotton is planted early and produces squares, flowers and bolls in September-October when populations of ABW are at their peak. Consequently, it requires spraying earlier in the season than hurhc~&tz.sc cottons. Spraying early in the season is known to destroy the parasites and predators, and to commit the crop manager to a chemical-control programme for the rest of the crop season. An all-season pesticide spraying would eventually be followed by the various well-documented adverse effects of unilateral dependence on pesticides. The increase in area under Acala cotton occurred too late to be blamed for the emer- gence of whitefly and ABW as major pests in late 1950s and 1964 respectively. How- ever, the effect of increase in area under Acala cotton would have only worsened the bad pest-control situation instead of improving it.

Thus, from the above discussion one may surmise that the said changes in cotton varieties in the Sudan favoured an increase in whitefly and ABW numbers, as well as in losses from Heliothis, and decreased the efficiency of sprays; particularly against the whitefly; thereby accentuating the cotton-protection problem. This factor. impli- cated rather casually by BASHIR (1974) might have been important in worsening the cotton-protection problem in the Gezira during 1960-1980 - perhaps more important than at least some factors implicated since 1980 by others (AMIN & BALLA, 1983; BALLA, ~~~~;EVEIXENS. 1983; GAMEEL, 1982; RAHMAN & EVELEENS, 1980; RAHMAN, 1980) e.g. growing of Philipsrrtr.

To end the discussion with an optimistic note, the above analysis and the experience gained so far indicate that switching back to cultivars less favourable to the pests and more suited for efficient pesticide application will ease the crop-protection prob- lem in the Sudan Gezira. In this behalf, it may be mentioned that Sudac-K (an open- canopy glabrous super-okra whitefly-resistant Acala cotton) was multiplied on an area of 200 ha during 1983-84. and has since been released for commercial cultivation. Burhudmse cotton cultivars with similar traits should also soon become available from the breeding programme startedin 1981 (BINDRA, 1983).

854

Page 7: Relation of cotton cultivars to the cotton-pest problem in the Sudan Gezira

(‘OTTON PI-ST CONTKOL

ACKNOWLEDGEMENTS

This paper was prepared at the end of the author’s assignment as FAO Host-Plant- Resistance Expert in GCP/SUD/NET Project, ‘Development and application of inte- grated pest control for cotton and rotational food crops in the Sudan’, hnanced by the Govt. of the Netherlands and executed by the FAO, Rome at the Gezira Agricul- tural Research Station. Wad Medani, Sudan. The author is thankful to the FAO for the opportunity afforded and for permission to publish this paper. Further, he expresses gratitude to Prof. Hassan Ishag, of the Agricultural Research Corporation of the Sudan, Wad Medani for useful discussion, and to Mr Idris El Turafi Mohamed. Statistician, Sudan Gezira Board, Barakat for allowing access to unpublished data on variety-wise cotton area in the Gezira.

REFERENCES

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BAHIELUIN. I. M., H. KHALIFA, H. A. FAKI & A. W. KHIDIK, 1978. Variation of gossypol content in some species of Gos.yr/>iunr. Sudan J. Fd. Sci. Technol. IO: 37 44.

BALLA, A. N., 1979. Ann. Rep. (Entom.). Gezird Res. Stn & Substns, 1979. Wad Medani, Sudan. BALLA, A. N., 1982. Progress in research and development for Heliotlzis management in the Sudan. In:

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KHALIFA. H.. 1983. Sudac-K, a prospective medium-staple cotton cultivar resistant to whitefly, B~misitr tcrhtrci (GENN.). Proc. FAO Symp. on IPC for Cotton in the Near East, Adana, Turkey, Sep. S-9, 1983; p. 49-5 I.

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8.56 Euplz.vtictr 34 ( IYHS )