|Abstract:||The objective of this study was to determine the effects of harvest cut height and foliar fungicide application on brown mid-rib (BMR) whole plant corn silage (WPCS) yield, chemical composition, and in situ degradability. Foliar fungicide (prothioconazole and trifloxystrobin; Delaro, Bayer CropScience) treatments were randomly assigned to one of sixteen 0.21-hectare plots as follows: control (CON), plants received no application; treatment 1 (V5), plants received one application at corn vegetative stage 5 (V5); treatment 2 (V5R1), plants received two applications at V5 and corn reproductive stage 1 (R1); treatment 3 (R1), plants received one application at R1. At reproductive stages R1 and R5, 12 corn plants per plot were evaluated and the number of yellow leaves was recorded. At R5, corn plants in R1 and V5R1 had less (P = 0.0001) yellow leaves (0.35 and 0.47; SEM = 0 .19, respectively) than CON and V5 (0.63 and 1.08; SEM = 0.19, respectively). Ten random plants from each plot were evaluated for disease at stages V5, R1, and R5. Disease prevalence was recorded as percent of the total individual plant infected. Fungicide application had no effect (P = 0.5922) on disease prevalence (1.62%, 1.07%, 1.23%, 1.48%; SEM = 0.30 for CON, V5, V5R1, and R1, respectively). On August 30, 2017, WPCS was harvested at 34.0±1.6% dry matter (DM). Each plot consisted of 16 rows; 8 of which were harvested at a low cut height of 30.5 cm (LC) and 8 of which were harvested at a high cut height of 56 cm (HC). Fungicide application had no effect on WPCS DM, gross yield, or DM yield (P > 0.51). Fungicide application had no significant effect on fermentation profile, chemical composition of WPCS (P > 0.06), but significant two way interactions of fungicide application × days ensiled were observed. Fungicide treated corn ensiled over time had higher VFA scores (P = 0.02), and higher lactic acid (P = 0.02), acetic acid (P < 0.0001), and total acid concentrations (P = 0.03). Dry matter of WPCS was higher (P = 0.0012) in HC than LC (34.57% and 33.43%; SEM = 0.39, respectively). Gross yield of WPCS was lower (P = 0.0023) in HC than LC (38,281 and 41,931; SEM = 1,050; kg/ha, respectively). Dry matter yield of WPCS was lower (P = 0.0284) for HC than LC (13,234 and 14,004; SEM = 362; kg/ha, respectively). Increasing the chop height from 30.5 cm to 56 cm resulted in an 8.7% gross yield loss, but only resulted in a 5.5% loss of dry matter yield content. Raising cut height resulted in decreased acid detergent fiber (ADF) and acid detergent lignin (ADL) concentrations and increased effective degradability (ED) of crude protein (CP) in the rumen.
In conclusion, fungicide application had no effect on disease prevalence in corn plants, but did reduce the number of yellow leaves. Fungicide treated corn ensiled over time had higher VFA scores, and higher lactic, acetic, and total acid concentrations. Cut height reduced gross yield and DM yield of WPCS, but increased the DM of WPCS. Raising the cut height had no effect on NDF concentrations or VFA score, but reduced ADF, ADL, lactic acid, acetic acid, and total acid concentrations.