Sustainable control of Striga hermonthica in maize (Zea Mays L.) by the use of Parkia biglobosa based products and post-emergence herbicides.Introduction
Parasitic weeds of the genus Striga (Scropularianceae) strongly affect host crops such as maize (Zea mays L.), sorghum (Sorghum bicolar (L.) Moench), pearl millet (Pennisetum americanum (L.) Beeke), rice (Oryza sativa L.) and cowpea (Vigna unguiculata L. Walp) as a consequence, these weeds are important growth reducing factors in crops in vast areas of the Savannah zone in Africa . Of all Striga species, Striga hermonthica (Del.) Benth is the most economically important parasitic weed in the Nigerian Savanna [7,16,14,20]. Yield reduction caused by S. hermonthica can be up to 79% even under good management .
Management approaches for control of Striga in Nigeria are generally based on cultural control strategies such as trap cropping, appropriate rates of fertilizer and suitable herbicide application, hand pulling and hoe-weeding , and host plant resistance [16,20]; Chemical [4,5] and biological control [23,19,21]. However, the use of plant products for the control of S. hermonthica is limited, though the effect of plant materials especially neem (Azadiractha indica) products have been reported to significantly control some organisms e.g. insects, fungi and to some extent nematodes [11,12,6,9,2,1].
The use of powder from the fruits of Parkia biglobosa has been reported to be beneficial to the soil agrochemical properties and inhibited the germination of S. hermonthica seeds in Burkina Faso . An in-vitro culture method analysis showed the presence of steroids, triterpenes, carotenoids, tannins and polyphenolic compounds in Parkia fruits . Tannins are the main secondary oxidates in Parkia and are toxic to animals especially in aquatic areas [8,18]. Earlier researchers have reported germination inhibition of 97-100% and 92% of Striga seeds when untreated powder extract and decorted powder of Parkia were used, respectively . In Nigeria,  reported 29.1 and 38.8% less Striga emergence in field and green house when Parkia products were used, respectively. The present study focuses on the assessment of the effects of maize seeds soaked (as a pre-plant treatment) in two Parkia products suspension and post-emergence herbicides in the control of S. hermonthica in the Nigerian Savanna
Materials and methods
Collection and Preparation of Parkia based products
Matured and dried Parkia fruits were collected from North Bank, Makurdi. The Parkia pods were pealed and the pod powder and seed separated. The pod powder and seeds were allowed to dry under sunlight for about 14 days. Thereafter, they were separately ground into fine powder (<1mm) and stored dry until required.
Two experiments were conducted in 2008 and 2009 cropping seasons at the Teaching and Research Farm of the University of Agriculture ([07.sup.0] [14.sup.1]N, [08.sup.0] [37.sup.1]E) and the Model Extension Village, Danka-Sarki, Lafia ([08.sup.0] [3.sup.1]N, [07.sup.0] [31.sup.1]E) in the Southern Guinea Savanna of Nigeria. The two sites were naturally and heavily infested with S. hermonthica.
The two experiments were established on the 28th May and 16th June in 2008 and 2009, respectively. In each year, the two experimental sites was ploughed, harrowed and ridged at 0.75m apart. Local maize variety was planted at 50m apart. Before planting, the maize seeds were soaked for a period of 20 minutes in different concentrations of Parkia based products. Maize seeds were added to the slurry and mixed thoroughly in order to obtain bio-fortified maize at 400g/litre of the concentrations of Parkia fruit powder and the Parkia seed powder. Another 1000 maize seeds were soaked in one litre (1L) of water as the control. The two trials were planted in a spite-plot design with three replications. The three Striga control methods consisting of post-emergence (POE) Triclopyr, 2, 4-D (each at the rate of 0.36 kg a.i/ha) and a hoe-weeded check at 3 and 6 (WAS) formed the main plot treatments, while the maize seed soaking (soaking for 20 minutes in Parkia fruit powder suspension, Parkia seed powder suspension and distilled water as control) were the sub-plot treatments, respectively. The gross and net plot sizes were 9[m.sup.2] and 4.5[m.sup.2] (4 ridges and 2 ridges of 3m length each) respectively. Spot application of fertilizer was carried out at 120 kg N/ha, 60 kg [P.sub.2][0.sub.5]/ha and 60kg [K.sub.2]O/ha to maize using 15-15-15 N-P-K compound fertilizer at 3 WAS and later top-dressed with urea at 6 WAS. The post-emergence herbicides (2, 4-D and Triclopyr) were applied at 6 WAS at 20% Striga infestation using a knapsack sprayer ([CP.sub.3]) with spray volume of 2501/ha.
Observations made included number of days to first Striga emergence, number of maize plants infected by Striga, Striga shoot per unit area, crop vigour score, number of capsules per Striga plant, maize plant height, weight of 1000 grains and grain yield. The data collected were subjected to analysis of variance (ANOVA) and means were compared using Least Significant Difference (LSD) at 5% level of probability.
Results and discussions
Number of days to Striga emergence was not significantly affected by the different treatments, but seed soaking (Table 1). Although not significant, the trend indicated that in 2009, there was a delay in the emergence of Striga (46 days after sowing, DAS) as compared to 2008 (42 DAS). Similarly, Makurdi delayed the emergence of Striga by 45 DAS as compared to Lafia 42 DAS. Maize seeds soaked in distilled water significantly initiated early emergence (36 DAS), than the Parkia fruit powder and seed powder (50 and 45 DAS, respectively). The use of Parkia fruit powder delayed the emergence of Striga the most. In respect of the different Striga control methods, the trend indicated early emergence with the hoe-weeded check.
Number of maize plants infected with Striga differed significantly at 6, 9 and 12 weeks after sowing (WAS) among the various treatments, except location effect (Table 1). Throughout the period of observation, the trend indicated significant difference in the infestation of maize plants with Striga in 2008 than the 2009. Although, throughout the period of observation, no significance difference was observed, the number of infected plants with Striga was higher in Lafia than in Makurdi. The number of maize plants infected with Striga was significantly affected by seed soaking in Parkia products throughout the period of observation (Table 1). Seeds soaked in Parkia products (fruit and seed powder) resulted in significantly lower number of maize plants infected with Striga as compared to the use of distilled water check. The results obtained support farmer's practice in Nigeria where they use neem and Parkia products for Striga control, among other practices such as the use of brine (Nacl) solution . The results also supported the work of Kambou et al  where they reported inhibition of the germination of S. hermonthica seeds in Burkina Faso when different concentrations of Parkia pod extracts were used. The Striga control methods were significantly affected by the different treatments at 6, 9 and 12 WAS (Table 1). The hoe-weeded check resulted in significantly higher number of maize plants infested than those plots that received post-emergence (POE) application of either Triclopyr or 2, 4-D each at the rate of 0.36 kg a.i/ha only at 9 and 12 WAS. But at 6 WAS, there was no significant difference between the hoe-weeded check and POE applied 2, 4-D. This result is in conformity with earlier works that hormonal type of herbicides such as 2, 4-D, Triclopyr when applied POE has been reported to significantly reduce the number of emerged Striga . Triclopyr herbicide kills the target weed by mimicking the plant growth hormone (indole acetic acid). The exact mode of action of Triclopyr has not been fully described, but it is believed to inhibit cell division and growth.
Table 2, presents the result of Striga shoot count that was significantly affected at 6, 9 and 12 WAS by the various treatments. The lowest Striga shoot count was recorded at 6 and 12 WAS in 2009, but at 9 WAS, it was the reverse in 2008. At 6 WAS, Lafia recorded significantly higher Striga shoot count than the Makurdi location; however, at 9 and 12 WAS, the lowest Striga shoot count was observed with Lafia location as compared to Makurdi. Throughout the period of observation, the Striga shoot count was significantly reduced in maize seeds soaked in Parkia products as compared to the highest recorded with distilled water (check). Maize seeds soaked in Parkia fruit powder recorded significantly lower Striga shoots than those soaked in Parkia seed powder during the period of observation. This goes to show that Parkia based products posses a strong allelopathic potential as it resulted in reduced Striga shoot count. A number of allelochemicals identified in dodder (Cuscuta spp) plant, including terpenes, phenols, phenolic acids, long-chain fatty acids, and lactose are similar to those in Parkia based products . These chemicals have been previously reported to inhibit plant growth [3,22]. It has also been suggested that the fatty acids are responsible for the strong inhibitory activities of Parkia based products against the emergence and subsequent growth of Striga. In the Striga control methods, it was only at 9 and 12 WAS that significant Striga shoot count was observed (Table 2). The POE application of either Triclopyr or 2, 4-D each at the rate of 0.36 kg a.i/ha resulted in significantly fewer Striga shoot count as compared to the hoe-weeded check. This result agrees with earlier work . There were significant interactions between year and location at 9 WAS (Table 4) and between location and the Striga control methods at 12 WAS (Table 5) on Striga shoot count. At 9 WAS the interaction between Makurdi X 2009 produced the highest Striga shoots, while the lowest was recorded with Lafia X 2009 and Makurdi X 2008 interactions (Table 4). At 12 WAS, irrespective of the location, the Parkia products (fruit and seed powder) resulted in significantly the lowest Striga shoot count when compared to the highest recorded by the hoe-weeded X Makurdi location which was followed by the hoe-weeded X Lafia location (Table 5).
Number of Striga capsules per plant was significantly affected by the various treatments (Table 2). The year, 2008 recorded significantly higher number of capsules/plant (93) when compared to 2009 (76). Makurdi, recorded the lowest number of Striga capsules/plant (78) as compared to Lafia (90). The maize seeds soaked in Parkia based products (fruit and seed powder) produced similar Striga capsules/plant, but significantly lower than the highest obtained by the distilled water (75, 80 and 98, respectively). Similarly, plots that received POE application of either Triclopyr or 2, 4-D recorded similar, but significantly lower number of capsules/plant as compared to the highest recorded with the hoe- weeded check (76, 80 and 96, respectively). This may be attributed to the fact the applied POE of 2, 4-D or Triclopyr affected the flowering process of the Striga plants in the treated plots, consequently resulting in lower number of capsules/plant. There was a significant interaction between year and locations on the number of Striga capsules/plant (Table 4). Irrespective of locations, the year 2008 interactions recorded greater Striga capsules/plant than the year 2009.
The effects of the various treatments on crop vigour score at 6 and 12 WAS are shown in Table 3. It was only at 6 WAS, that the year and Striga control methods effects did not record any significant effect on crop vigour score (Table 3). But at 12 WAS the year 2009 produced more vigorous maize plants than those of 2008. Throughout the period of observation, more vigorous maize plants were observed at Lafia than Makurdi. This may be attributed to higher Striga shoot count recorded at Makurfi location in the later stage of the crop life-cycle. Maize seeds soaked in Parkia based products resulted in significantly more vigorous maize plants when compared to the distilled water throughout the period of observation. Similarly, in the Striga control methods, the POE application of either Triclopyr or 2, 4-D resulted in significantly more vigorous plants than the hoe-weeded check at 12 WAS. This could be attributed to suppressive ability of the applied herbicides on this parasitic weed, which then allowed for good growth of the maize plants. It is a well established fact that prior to emergence, Striga depends entirely on its host for nutrients and even emergence, two-third, (2/3) of its requirements still comes from its host. This may account for reduced growth of the host and possible reduction in photosynthetic activity as a result of competition for growth factors as earlier reported .
The effect of the various treatments on plant height was only significantly affected by seed soaking and the Striga control methods at 12 WAS (Table 3). The year 2009 and Makurdi location, although not significantly different, the trend indicated taller maize plants than in 2008 and Lafia water gave significantly shorter maize plants than those soaked in Parkia based products. Similarly, the hoe-weeded check recorded significantly shorter maize plants than those that received POE application of Triclopyr or 2,4-D each at 0.36 kg a.i/ha.
The weight of 1000 grains was significantly affected by the different treatments (Table 3). Grains produced in 2008, was significantly heavier than those of 2009. Makurdi location resulted in significantly heavier grains than Lafia. This result is similar to that earlier reported . In the seed soaking, Parkia fruit powder produced significantly heavier grains as compared to the least obtained by the distilled water. In the different Striga control weight was obtained with the POE Triclopyr at 0.36 kg a.i/ha and the hoe-weeded check, respectively.
Maize grain yield was significantly different among all the various treatments except location effect (Table 3). The highest maize grain yield was produced in 2009. Although not significant, Makurdi had more maize grain yield. The use of Parkia products (fruits and seed powder) significantly resulted in increased maize grain yield than the distilled water check. The long time suppressive ability of parasites by the allelochemicals contained in the Parkia products might have been responsible for the better performance of the maize plants treated with these products and thus increased grain yield. In the Striga control methods, the lowest and highest grain yield was obtained by the hoe- weeded check and POE application of Triclopyr at the rate of 0.36 kg a.i/ha, respectively. This result agrees with earlier reports that Triclopyr or 2, 4-D when applied POE, significantly reduced the number of emerged Striga and subsequently increased maize and sorghum grain yields .
The study results demonstrate the high potentiality of using Parkia based products as pre-sowed treatments and thereafter followed by POE application of herbicides like 2,4-D or Triclopyr each at the rate of 0.36 ka a.i/ha. The Parkia trees are abundant within the Savanna and thus their fruits can easily be procured. This implies that farmers could adopt the tested methods for a sustainable management practice to enhance the control of S. hermonthica.
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(1) E.I. Magani, (2) A. Ibrahim and (1) R.I. Ahom
(1) Department of Crop and Environmental Protection, University of Agriculture, P.M.B. 2373, Makurdi, Nigeria.
(2) Department of Agronomy, Nasarawa State University Keffi, Nasarawa State, Nigeria.
E.I. Magani, A. Ibrahim and R.I. Ahom: Sustainable Control of Striga Hermonthica in Maize (Zea Mays L.) By the Use of Parkia Biglobosa Based Products and Post-emergence Herbicides: Adv. Environ. Biol., C(C): CC-CC, 2010
Table 1: Effects of Parkia and Post-emergence herbicides on number of plants infected and time of emergence of Striga. Treatments Number of days to first Striga Emergence Year 2008 42 2009 46 LSD 3.44 Location Lafia 42 Makurdi 45 LSD 3.44 Seed Soaking Parkia fruit powder 50a Parkia seed powder 45b Distilled Water 36c LSD 4.21 Striga Control Method POE Triclopyr (0.36kg a.i/ha) 45 POE 2,4--D (0.36kg a.i/ha) 45 Hoe weeded (check) at 6 WAS 41 LSD 4.21 Interaction(s) YR x LOC NS SCM x LOC NS All Possible interactions NS Treatments Number of Maize plants infected with Striga/Plot 6 WAS 9 WAS 12 WAS Year 2008 1.56 2.67 (a) 3.22 (a) 2009 1.20 2.11 (b) 2.87 (b) LSD 0.33 0.37 0.33 Location Lafia 1.65 2.28 3.06 Makurdi 1.11 2.50 3.04 LSD 0.33 0.37 0.33 Seed Soaking Parkia fruit powder 0.58 (c) 1.19 (c) 1.89 (c) Parkia seed powder 1.11 (b) 1.97 (b) 2.47 (b) Distilled Water 2.47 (a) 4.00 (a) 4.78 (a) LSD 0.40 0.45 0.40 Striga Control Method POE Triclopyr (0.36kg a.i/ha) 1.17 (b) 1.78 (c) 2.36 (c) POE 2,4--D (0.36kg a.i/ha) 1.39 (a) 2.22 (b) 2.78 (b) Hoe weeded (check) at 6 WAS 1.58 (a) 3.17 (a) 4.00 (a) LSD 0.40 0.45 0.40 Interaction(s) YR x LOC NS NS NS SCM x LOC NS NS NS All Possible interactions NS NS NS Means in a column of any set of treatments followed by different letters are not significantly different at 5% level using LSD. POE = Post--emergence WAS = Weeks after sowing. Table 2: Effects of Parkia and post--emergence herbicides on Striga shoot count and number of seed capsules. Treatments Striga shoot count/plot 6 WAS 9 WAS 12 WAS Year 2008 2.13 (a) 3.63 (b) 8.15 (a) 2009 0.91 (b) 4.50 (a) 6.33 (b) LSD 0.43 0.71 0.90 Location Lafia 1.87 (a) 3.52 (b) 6.28 (b) Makurdi 1.17 (b) 4.61 (a) 8.20 (a) LSD 0.43 0.71 0.90 Seed Soaking Parkia fruit powder 0.56 (c) 1.33 (c) 2.75 (c) Parkia seed powder 1.22 (b 2.61 (b) 5.67 (b) Distilled Water 2.78 (a) 8.25 (a) 13.31 (a) LSD 0.52 0.87 1.10 Striga control method POE Triclopyr (0.36kg a.i/ha) 1.33 2.25 (c) 4.75 (c) POE 2, D--D (0.36kg a.i/ha) 1.47 3.00 (b) 5.78 (b) Hoe weeded (check) at 6 WAS 1.75 6.94 (a) 11.19 (a) LSD 0.52 0.87 1.10 Interaction(s) YR x LOC NS 0 NS SCM x LOC NS NS 0 All Possible interactions NS NS NS Number of Treatments Striga capsules/plant Year 2008 92.6 (a) 2009 75.6 (b) LSD 4.63 Location Lafia 90.10 (a) Makurdi 78.10 (b) LSD 4.63 Seed Soaking Parkia fruit powder 74.7 (b) Parkia seed powder 79.6 (b) Distilled Water 78.0 (a) LSD 5.67 Striga control method POE Triclopyr (0.36kg a.i/ha) 75.5 (b) POE 2, D--D (0.36kg a.i/ha) 80.4 (b) Hoe weeded (check) at 6 WAS 96.3 (a) LSD 5.67 Interaction(s) YR x LOC 0 SCM x LOC NS All Possible interactions NS Means in a column of any set of treatments followed by different letters are not significantly different at 5% level using LSD. POE = Post emergence WAS = Weeks after sowing. Table 3: Effects of Parkia and Post-emergence herbicides on crop reaction, plant height, weight of 1000 grains and maize grain yield. Treatments Crop vigour score (1) Crop height (cm) 6 WAS 12 WAS 12 WAS Year 2008 7.9 7.5 (b) 181.6 2009 8.0 8.0 (a) 184.4 LSD 0.13 0.14 4.81 Location Lafia 8.3 (a) 7.8 (a) 182.0 Makurdi 8.0 (b) 7.6 (b) 184.0 LSD 0.13 0.14 4.81 Seed Soaking Parkia fruit powder 8.6 (a) 8.3 (a) 190.7 (a) Parkia seed powder 8.0 (b) 7.9 (b) 187.3 (a) Distilled Water 7.8 (c) 7.1 (c) 171.1 (b) LSD 0.16 0.18 5.89 Striga Control Method POE Triclopyr (0.36kg a.i/ha) 8.5 7.9 (a) 188.2 (a) POE 2, 4--D (0.36kg a.i/ha) 8.5 7.9 (a) 186.3 (a) Hoe weeded (check) at 6 WAS 8.4 7.4 (b) 174.5 (b) LSD 0.16 0.18 5.89 Interaction(s) YR x LOC NS NS NS SMC x LOC NS NS NS All Possible Interactions NS NS NS Treatments Weight of Grain yield 1000 grain (kg/ha) (g) Year 2008 285.9 (a) 1755 (b) 2009 280.4 (b) 1885 (a) LSD 4.81 82.70 Location Lafia 278.9 (b) 1809 Makurdi 287.4 (a) 1831 LSD 4.81 82.70 Seed Soaking Parkia fruit powder 293.9 (a) 2168 (a) Parkia seed powder 283.6 (b) 1923 (b) Distilled Water 271.9 (c) 1368 (c) LSD 5.89 101.30 Striga Control Method POE Triclopyr (0.36kg a.i/ha) 290.6 (a) 2201 (a) POE 2, 4--D (0.36kg a.i/ha) 281.9 (b) 2005 (b) Hoe weeded (check) at 6 WAS 276.9 (c) 1255 (c) LSD 5.89 101.30 Interaction(s) YR x LOC NS NS SMC x LOC NS NS All Possible Interactions NS NS (1) rop vigour score scale (1-9); where 1 = completely killed plants and 9 = most vigorous plants. Means in a column of any set of treatments followed by different letters are not significantly different at 5% using LSD POE = Post emergence WAS = Weeks after sowing Table 4: Interaction between year and location on Striga shoot and number of Striga seed capsules/plant Year Striga Shoot count Number of Striga Seed (9 WAS) capsule/plant Location Location Lafia Makurdi Lafia Makurdi 2008 4.04 (b) 3.22 (c) 94.4 (a) 90.7 (a) 2009 3.00 (c) 6.00 (a) 85.7 (b) 65.4 (c) LSD 1.00 6.55 Means in a column of any set of treatments followed by the different letters are not significantly different at 5% level using LSD. Table 5: Interaction between Striga control method and location on Striga shoot count at 12 WAS Striga control method Location Lafia Makurdi POE Triclopyr (0.36kg a.i/ha) 4.33 (c) 5.17 (c) POE 2, 4--D (0.36kg a.i/ha) 5.83 (c) 5.72 (c) Hoe weeded (check) 8.67 (b) 13.72 (a) LSD 1.56 Means in a column of any set of treatment folat 5% level using letters are not significantly different LSD.