EFFICACY OF DIFFERENT INSECTICIDES FOR THE MANAGEMENT OF STEMBORERS OF MAIZE IN UGANDA
T. Kalule , M.W. Ogenga-Latigo^1 and V.A.O Okoth^2
Namulonge Agricultural and Animal Production Research Institute, P.O. BOX
7084, Kampala, Uganda.
(Recieved 9 May, 1997; accepted 2 August, 1997)
Evaluation was made of the efficacy of commonly available insecticides for control of stemborers on maize. Insecticide application influenced the occurrence and extent of stemborer damage on maize. In the early stages of crop development, the lowest stemborer incidence was recorded on Furadan treated plots, although its efficacy decreased with time. Overall, Sevin treatments effected better control compared to other treatments. A well timed granular application of Sevin could fit well in the integrated stemborer management system and reduce maize yield losses caused by these pests.
Key Words: Chemicals, Lepidopteran stemborer, Zea mays
L'efficacite des insecticides communement disponibles dans la lutte contre les insectes terebrants des tiges du mais a ete evaluee dans la presente etude. L'application de l'insecticide a influence l'existence et l'importance des degets causes par les insectes terebrants sur le mais. Au cours des premiers stades de developpment de la culture, la plus faible incidence de l'insecte terebrant a ete enregistree sur les parcelles traitees avec du furadan, bien que son efficacite ait diminue avec le temps. Dans l'ensemble, les traitements avec du sevin ont produit un meilleur control par rapport a d'autres traitements. Une application granulaire du sevin mieux chronometree conviendrait mieux dans le systeme integre de la gestion de l'insecte terebrant et reduisait les pertes de la productivite du mais causees par ces pestes.
Mots Cles: Produits chimiques, lepidopterous stembores, Zea mays
Maize (Zea mays L) is a crop which can be grown in a wide range of environments and has multiple uses. Presently, it is the most widely grown and consumed cereal crop in Uganda. However, the factors which limit its production are also diverse. In Uganda, lepidopteran stemborers are some of the major constraints to maize production. The species that are destructive to maize are the maize stalk borer Busseola fusca (Fuller) and the pink stalk borer Sesamia calamistis (Hampson), both Noctuidae, and two pyralids, Chilo partellus (Swinhoe) and Eldana saccharina (Walker) (Girling, 1978).
Although the build up of stemborer populations on maize is usually limited by use of appropriate agronomic practices such as proper field sanitation, adjustment in time of planting and the activity of biotic mortality agents, these insects often attain population densities that cause substantial crop losses (Warui and Kuria, 1983). When stemborer population build-up to levels that threaten to cause economic losses, chemical control remains the only method by which immediate losses can be averted.
There has been conflicting reports on the effects of applying insecticides on the incidence and severity of stemborers on maize and on yield performance. Some workers have obtained reduced damage levels with significant yield increases (Swaine, 1957; Warui and Kuria, 1983) while others have not recorded similar responses (Ingram, 1958). A possible reason for this variation is the critical time of maize infestation and its relationship to time of insecticide application.
Based on trials in Uganda (Coaker, 1956) and Kenya (Warui and Kuria, 1983), effective control of stemborers has been reported. Warui and Kuria (1983) reported that Furadan (carbofuran) granules when applied during planting and Dipterex (trichlorphon) granules applied at 2-3 weeks after plant emergence (WAE) are effective against stemborers. Application of these pesticides, coupled with proper management practices, could reduce the quantity of chemicals to a level where it is economical to the small farmer.
To-date, information on proper use of chemicals for the control of maize stemborers in Uganda, is inadequate. This deficiency was brought to light in 1988 when a serious outbreak of stemborers destroyed maize in Masaka district and there was no proper chemical to use (Anon., 1990). In this study, we evaluated the efficacy of insecticides commonly available in Uganda for the control of stemborers on maize. Identification of a suitable insecticide is a crucial factor in the development of an integrated pest management programme for these insects.
MATERIALS AND METHODS
The study was carried out at Namulonge Agricultural Research Institute (NAARI) located 27 km north east of Kampala at latitude 0 degrees 31'N, longitude 0 degrees 32'E and an altitude of 1,200 - 1,300m above sea level. The study was conducted during the long and short rains of 1992. Maize variety Longe 1, was planted on 10th April during the long rains and on 19th September (short rains). The experiment consisted of six treatments established in a randomised complete block design with four replications. The treatments were carbofuran 5G (Furadan) at 0.5 kg a.i ha^-1 applied at planting, esfenvalerate 2.5% (Sumi-alpha) foliar insecticide at a rate of 1 litre ha^-1 applied 2-4 and 6-8 WAE, fenpropathrin 1 % E.C (Danitol) foliar insecticide applied 2-4 and 6-8 WAE at a rate of 1 litre ha^-1, carbaryl 5G (Sevin) at 0.5 kg a.i ha^-1 applied in the maize funnel at 2-4 and 6-8 WAE, chloropyrifos 5D (Dursban) at 0.5 kg a.i ha^-1 applied in maize funnel at 2-4 and 6-8 WAE, and a control where no insecticide was applied.
The contact pyrethroids, Sumi-alpha and Danitol were applied using a CP15 Knapsack sprayer while Furadan was applied in the planting holes (furrow). Sevin 5% granules and Dursban 5% dust were applied using package applicators (Rhone-Poulenc Kenya Ltd.). Plots measured 5.5 x 3.75 m, with 1 m alleys, and the maize was planted at 75 and 50cm inter and intra-row spacings, respectively.
To assess stemborer infestation on maize, sampling was carried out one day before the chemical applications, and 13-14 weeks after plant emergence, based on random selection of 10 plants per plot. First and second instar stemborer larvae were recorded by careful examination of maize leaves, while older larvae were counted after uprooting ten plants at random and splitting each stem length-wise.
The extent of stemborer damage on maize leaves or its severity was assessed by taking damage scores from four uppermost leaves. A scale of 1-5 was used whereby 1= 1-20%, 2= 21-40%; 3= 41-60%; 4 = 61-80%, and 5= 81-100% damage (Anon., 1990).
Damage on stems was assessed by counting the number of stems showing borer damage per 10 plants in each plot and by measuring the length of stem borer tunnels. Tunnel length per plant was expressed as a percentage using height of stem to the top most ear point as recommended by Bosque-Perez and Mareck (1991). The number of nodes below the top-most ear damaged by stemborers was also counted and expressed as a percentage.
The number of cobs damaged by the borers was counted on 10 plants per plot selected at random. Visual assessment of damage was based on a scale of 1-5, where 1= 0-5%; 2 = 6-10%; 3 = 11-20%; 4 = 21-40%; and 5 > 40 % of grain consumed. At crop maturity and field drying, 10 ears were randomly harvested from plants in the three middle rows in each plot. After shelling, the grains were dried to 15% moisture content and grain weight calculated by dividing total grain weight by the number of plants. Data on insect populations and damage proportions were subjected to appropriate transformations (square root and arc-sine ) and analysis of variance to determine the significance of the various treatments. Means were compared using the Newman-Keuls test.
Sampling at 3-4 WAE during the long and short rains showed that some insecticides significantly (P=0.05) reduced the occurrence of stemborers on 21 day-old maize (Table 1). The lowest incidence during the long rains was from the Furadan and Sevin treated plots, while during the short rains, Furadan, Sumialpha and Sevin were effective. The second generation borers sampled at 7-8 WAE were significantly (P=0.05) reduced in Furadan, Sevin and Dursban treated plots compared to the control during the long rains, while the same three plus Danitol were effective during the short rains (Table 1).
In the early stages of crop growth, no significant variation in the level of foliar damage was observed for the various insecticide treatments (Table 2). Further observations in the later stages of crop development showed that the number of stems damaged at 7-8 WAE did not vary significantly despite the relatively higher numbers from the control plots (Table 2). Only later in the long rains (11-13 WAE) were Sevin, Sumialpha and Dursban found to be superior to the other insecticides in suppressing stem damage. In both seasons, Furadan failed to show any marked effect and was not better that the control (Table 2).
During the long and short rains, significant variations (P=0.05) in stem tunnelling were observed in 50 day old maize. The unsprayed plants suffered the greatest tunnelling followed by Furadan and Dursban treated plants. The shortest tunnel length were from Sevin and Danitol treatments (Table 3).
No significant variation was observed in the number of cobs damaged for both the treated and control plants (Table 4). Cob damage scores varied from 3.0 for Danitol treated plots during the long rains to 2.0 for Dursban treated plots during the short rains.
No yield differences were observed during the long rains. In the short rains, only Danitol did not prevent a yield loss (Table 5). The lowest yields during the long rains were from the control plots, the highest being 163gm plant-1 for the Sevin treated plants. Sevin, Sumialpha, Dursban and Furadan treated plants produced significantly better yields than the control in the short rains (Table 5). The highest increase in grain yield over the control was recorded for the Sevin treated plots during the long and short rains (12.4% and 31.3%, respectively) (Table 5).
Some of the tested chemicals suppressed stemborer infestations and damage on maize, efficacy depending on the type of chemical used and the timing of application. These results are in agreement with earlier studies which showed that greater control of stemborers depended on time of chemical application, which should be at 2-3 weeks after plant emergence (Dabrowski et al., 1984) such timing of application reduces the build up of the first generation stemborers.
Our study also revealed that the effectiveness of Furadan decreased with time. This decline in effectiveness against the target pest has been also observed by other workers. For example, Egwuatu (1982) reported failure of Furadan to control leaf-eating flea beetles, Podagrica spp., on Okra during late stages of crop development.
The most effective chemical in this study was Sevin. Its greater effectiveness against stemborers may have been largely due to its mode of appli-cation . By applying granules in the unfolding maize leaves or funnel, where during early crop growth stem borer activity is confined, contact between the pest and the insecticide was enhanced. On the contrary foliage presents a barrier for sufficient foliar spray to penetrate into the funnel (Mathews, 1979). Placement of chemicals in funnels tend to deter entrance of larvae in the stem, especially the first and second instars which are very vulnerable to insecticides (Jotwani, 1983). Similar observations were made in Tanzania, where spot treatment was effective in control of maize stemborers (Walker, 1960).
Our results show that 12-31% grain yield loss can be prevented through insecticide application, as was reported in Kenya (Warui and Kuria,1983). Yield losses obtained in this study justify the use of insecticides to control stemborers either in spot applications, or when wide-spread infestation occurs.
A pest management system for control of stemborers could involve a well timed granular application of Sevin introduced 2-3 weeks after plant emergence in the maize whorl. This ensures separation in time and space of natural enemies from the insecticides (Greathead, 1989). This approach, coupled with continuous monitoring of the borer populations together with adoption of practices that reduce pest population and damage to crops, could constitute an effective integrated management programme against these pests.
Financial assistance was provided by the United States Agency for International Development (USAID)/Manpower for Agricultural Develo-pment Programme (MFAD).
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Copyright 1998, African Crop Science Society
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