Table 3.

Effect of wireworm damage on maize yield as a percentage of the number of plants attacked (any symptom) on maize yield. Dataset covers 29 years

Plant damage (%)	No. of cases observed	Land (ha)	No. of yield reduction cases	Land with yield reduction (ha)	Mean yield reduction (t/ha) (LS-means ± se)a	Probability of yield reduction (range) %	Probability of yield reduction (mean) %	Risk ratio	95 % confidence interval	P chi-square test
<15	151	260.85	0	0	–	0–1	0.4	ne	ne	ne
15–20	11	20.32	2	1.2	1.28 ± 0.63 b	2–16	7	0.43	0.07–2.52	0.3195
20–30	19	11.67	11	4.88	1.86 ± 0.31 b	17–62	37	3.46	1.65–7.24	0.0031
30–40	9	5.97	6	4	2.43 ± 0.34 a	62–94	81	5.51	2.92–10.39	<0.001
>40	23	34.17	22	33.67	2.72 ± 0.12 a	>94	98	29.21	15.90–93.66	<0.001
Tot	213	332.98	41	43.75

ne not estimable

^aLS-means ± se = least square means ± standard error; means with different bold letters are significantly different for P < 0.05