Moisture of corn stover was field monitored under southeast U.S. ambient conditions to aid biomass collection decisions. Timing to collect stover at low moisture depended on elapsed time on field, elapsed time after precipitation, time of day, contact with soil, and conditioning effect by combine header. Grain had been combine-harvested at kernel moistures of either 25% or 15% wet basis (w.b.). Stover moisture was determined by weighing large in-situ baskets for a month and with frequent grab samples. Experiment controls included stover dried under tent shelter and mower-cut stover for combine-conditioning effect. Stover moisture asymptotically declined over time from approximately 70% (w.b.) to an equilibrium of approximately 20% (w.b.) for 25% (w.b.) grain harvest. Moisture reduction was not constant due to daily diurnal variation of eight percentage points (w.b.), and light precipitation that re-hydrated the stover. Stover moisture was significantly greater in the morning compared to afternoon and was greater for stover in contact with soil. A combine corn stalk conditioning effect reduced mean moisture (approx. 10 percentage points) for high-moisture stover at early harvest, yet conditioning increased moisture for a period after light precipitation. Correlation of daily stover moisture with the corresponding day's evapotranspiration factor was not as strong as correlations with other combinations of environmental factors. Stover moisture generally peaked two days after rain events, so correlations and regressive predictions used previous data (2-day delay) for rainfall, air relative humidity, and evapotranspiration data. In addition to mechanical harvest method (stalk conditioning effect), the strongest environmental/timing correlations to predict stover moisture on the field after grain harvest included the following daily-averaged factors: elapsed time (days) after sowing (collect later for reduced moisture), time of day (evening collection preferred over morning collection), soil moisture, 2-day previous rainfall amount, 2-day previous relative humidity, and 2-day previous evapotranspiration factor. Thus, increased elapsed time after sowing/harvest, evening harvest times, and the immediate (2-day) exposure history of corn stover to available moisture and drying potential are useful in determining strategies to collect corn stover with minimum moisture content.