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EXPERIMENTAL METHODS
Experiments were carried out at the Forestry Research Institute's experimental nursery about 5 km south of the
University of Science and Technology, Kumasi, Ghana. The area is within the moist semi-deciduous forest zone (Hall and
Swaine 1983), a common tropical forest type in West Africa that generally supports populations of Milicia excelsa. Seedlings
used in the companion planting and shading experiments were collected from a single parent tree (AA 17) from the village of
Abofour in the Ashanti Region of Ghana. Other studies have indicated that this particular provenance is of intermediate
susceptibility to Phytolyma lata (Cobbinah and Wagner 1994). Seedlings used in the fertilizer trial were of mixed origin.
Seeds were collected in 1991, sown on raised beds, and transplanted into polyethylene bags. Trees were kept under shade
and watered regularly until used in the experiment. The spacing on all experiments was 1m x 1m.
Companion Planting Trial
The companion planting trial was established in September 1991. The trial consisted of four rows of 10 (40 total)
Milicia excelsa planted in alternating rows with Gliricidia sepium cuttings and four rows of 10 Milicia excelsa planted
without G. sepium. At periodic intervals the following data were collected: seedling height, number of leaves, number of
galls/plant. Regression analysis was used to estimate the number of galls in large gall masses as described by Cobbinah and
Wagner (1994). For this experiment, the data were averaged for each row of 10 trees to reduce variability, consequently n = 4
for both treatments.
Shading Trial
The shading experiment was established in October 1992. The shade was created by supporting commercial shade
cloth (Hummerts International) over wooden structures. Four levels of shade were established: full sun = no shade, light
shade = 33% shade cloth, medium shade = 57% shade cloth, and deep shade = 82% shade cloth. Under each shade level, 50
seedlings were planted in five rows of 10 seedlings each. Data collection was as indicated above. For this experiment, n =
50 per treatment.
Fertilizer Trial
The fertilizer experiment was established in December 1992 and ran for 6 months. The effect of fertilizer was tested
using a randomized complete block design with four replicates (25 seedlings/plot and 100 seedlings/block) and four treatments:
control (no fertilizer), NPK ® (15-15-15), Phostrogen ® (10-4-22), Sampi® (8-3-3). Fertilizer was applied in the
irrigation water at the rate recommended by the manufacturer. Seedlings were kept under shade. Data were collected as
above and the average number of diebacks was determined.
Statistical Analysis
Data for the companion planting trial were analyzed using a paired t-test on STATGRAPHICS software. Each row of
10 trees was treated as the sample unit. Data for the shading trial were transformed [Logl0(x+l)] to meet assumptions of
homogeneity of variance and were analyzed using an ANOVA on STATGRAPHICS software. Data for fertilizer trials were
analyzed using ANOVA and LSD multiple range test using STATGRAPHICS software. The P value to reject the null
hypothesis was set at 0.05.
RESULTS
Companion Trial
Milicia excelsa seedlings growing together with the nitrogen fixing Gliricidia sepium were not significantly taller
(Fig. 1) and they did not produce more leaves (Fig. 2) than Milicia excelsa seedlings growing alone during any sample
period. However, there were significantly fewer galls during two sample periods on Milicia grown with Gliricidia (Fig. 3).
There was also a tendency for fewer galls in the presence of Gliricidia for most of the 1992 sample periods (Fig. 3).
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