Forages to be ensiled for subsequent feeding to dairy cows are often contaminated with spoilage microorganisms that negatively affect feed quality and feed safety. Aerobic instability due to these spoilage organisms can cause heating and significant DM loss. L. buchneri improves aerobic stability, but because it grows slowly it is often combined with homofermentative strains to achieve a fast reduction in pH early in fermentation. Efficacy of silage inoculants can vary depending on forage type, harvest time, management etc. In the current study it was aimed at keeping the experimental conditions equal between experiments and to test the efficacy of a dual-purpose silage inoculant. Three samples of chopped whole maize were collected from farms in 2012 and 2013 on the day of harvest. Aerobic stability, microbial population and dry matter loss of the maize was measured using the same methodology. Briefly, maize was inoculated with a combination of L. buchneri and L. lactis (150,000 cfu/g) or pure tap water and allocated into 1 kg bags, vacuum packed and stored for 15 weeks at 25°C. Then silage was placed in a polystyrene container (1.2 L; 274 kg/m³) with 1 cm diameter hole in top and bottom. The change in temperature was recorded continuously for 6.5 d using a data logger placed in the middle of each sample. Results showed that the pooled freshly harvested maize was very similar in microbial composition between the farms and years. All samples were highly contaminated with yeast and mold, while epiphytic total lactic acid bacteria were lower than the inoculated. The effect of the silage inoculant varied considerably among the 3 maize samples. Acetate concentration after 15 weeks of anaerobic fermentation was significant (P < 0.05) for all inoculated samples compared with control. The aerobic stability varied considerably between the different control samples (46 h, 75 h, >156 h). Inoculation significantly increased (P < 0.05) aerobic stability of the unstable samples (72 h, >156 h, >156 h). This study showed that maize with similar quantities of spoilage organisms in the fresh maize can vary widely in their aerobic stability.