An increasing global population, decreasing amount of arable land available for crop production in the United States, and an increased global demand for protein in the human diet encourage crop and livestock producers to seek solutions to improve the efficiency of producing large crop yields. The interaction of fungi and corn plants in the field threaten yields, decreasing the efficiency of food production and the nutritive quality of feedstuffs for ruminants. Fungicides can assist corn plants in protection from fungal infection by limiting yield losses and increasing the nutritive quality of the plant material. However, little is known about how various applications of fungicide on corn change the nutrients of individual parts of the corn plant, alter the fermentation of corn silage once ensiled, and affect the milk production when fed to dairy cattle. Therefore, the objectives of the present study were to investigate various applications of fungicide on: corn associated with the nutritive profile and growth of corn leaves, ears, stalks, and flag leaves; once ensiled, on the nutritive and fermentative profile of corn silage; and when corn silage is fed to dairy cattle on milk production, milk components, blood metabolites, and cow health. Corn from two growing seasons, 2014 and 2015, with different fungicide treatments was included in this study. Corn grown during the summer of 2014 was ensiled and fed to dairy cows, while corn grown during the summer of 2015 evaluated the plant and corn silage. In 2014, treatments were as follows: corn silage with no application of foliar fungicide (CON); corn silage received one application of pyraclostrobin and fluxapyroxad (PYR+FLUX) foliar fungicide (Priaxor®; BASF Corp.) at corn stage V5 (V5); corn silage received one application of PYR+FLUX at corn stage V5 plus another application of PYR+FLUX at corn stage V8 (V5/V8); corn silage received one application of PYR+FLUX at corn stage V5, one application of PYR+FLUX at corn stage V8, plus a third application of pyraclostrobin and metconazole (PYR+MET) foliar fungicide (Headline AMP®; BASF Corp) at corn stage R1 (V5/V8/R1). Corn was harvested at 31.2% DM and ensiled for more than 200 d before feeding. Treatments were fed to cows for 5 wk with only the last week being used for statistical inferences. Three contrast statements were used: contrast 1: CON vs. TRT compared control to the average of treatments fed corn silage sprayed with foliar fungicide (V5, V5/V8, and V5/V8/R1); contrast 2: V5 vs. V5/V8 compared the treatment fed corn silage sprayed at V5 to the treatment fed corn silage sprayed at V5 and V8; and contrast 3: V5/V8 vs. V5/V8/R1 compares the treatment fed corn silage sprayed at V5 and V8 to the treatment fed corn silage sprayed at V5, V8, and R1. No differences in DMI (19.5, 19.5, 20.8, and 20.4 kg for CON, V5, V5/V8, and V5/V8/R1, respectively) or milk yield (30.5, 31.2, 29.1, and 29.3 kg/d) were observed. However, cows in V5 when compared with cows in V5/V8 tended, to produce more 3.5% fat corrected milk (FCM; 32.42 and 28.58 kg/d, respectively) and energy corrected milk (ECM; 31.35 and 27.76 kg/d, respectively). Concentration of milk lactose tended to be greater for cows fed corn silage treated with foliar fungicide when compared with CON. In 2015, the study was split into two parts, but the fungicide treatment was the same for both part one and part two. Treatments were as follows: control (CON), corn receiving no foliar fungicide application; treatment 1 (V5), where corn received a mixture of pyraclotrobin and fluxapyroxad foliar fungicide (Priaxor, BASF Corp.) corn vegetative stage 5 (V5); treatment 2 (V5+R1), where corn received two applications of foliar fungicide, a mixture of pyraclotrobin and fluxapyroxad at V5 and a mixture of pyraclostrobin + metconazole foliar fungicide (Headline AMP; BASF Corp.) at corn reproductive stage 1 (R1), and treatment 3 (R1), in which corn received one applications of pyraclostrobin + metconazole foliar fungicide at R1. Evaluators at R1 and R3 reported signs of Gray Leaf Spot and Northern Leaf Blight on the foliage. In part one, 24 individual corn plants from each treatment were collected R1 and R3 for weight and length measurement. At each collection, treatment corn plants were disassembled into leaves, stalks, flag leaf, and ears for nutrient analysis. The effect of foliar fungicide treatment, corn growth stage, and treatment by growth stage was evaluated on a dry matter basis. Interactions of fungicide applications on corn by collection time point were observed for the number of yellow leaves (0, 0, 0, and 0 at R1 and 0.85, 0.77, 0.42, and 0.44 for CON, V5, V5+R1, and R1 at R3 respectively; P = 0.03) and the height of the stalk (2.89, 2.94, 2.92, and 2.96 m at R1, and 2.50, 2.91, 3.05, and 2.80 for CON, V5, V5+R1, and R1 at R3; P = 0.02), with greater values for corn treated with fungicide than untreated. Corn stalks from corn treated with fungicide had greater concentrations of lignin compared with untreated (46, 56, 64, and 50 g/kg DM for CON, V5, V5+R1, and R1, respectively), with the greatest value from corn in V5+R1. Corn leaves from corn treated with fungicide had lower concentrations of ADF (333, 331, 283, and 330 g/kg DM for CON, V5, V5+R1, and R1, respectively) and NDF (569, 584, 524, and 554 g/kg DM for CON, V5, V5+R1, and R1, respectively) compared with untreated, with the lowest concentrations of ADF and NDF from corn in V5+R1. Interactions of applications of fungicide on corn by collection time point in corn leaves were observed for ADF (329, 335, 338, and 336 g/kg at R1, and 337, 326, 228, and 304 g/kg at R3 for CON, V5, V5+R1, and R1, respectively; P = 0.008), Na (14, 12, 10, and 7 g/kg at R1, and 6, 5, 7, and 5 g/kg at R3 for CON, V5, V5+R1, and R1, respectively; P = 0.02), and Cu (12, 12, 11, and 13 PPM at R1, and 15, 15, 18, and 17 PPM at R3 for CON, V5, V5+R1, and R1, respectively; P = 0.03). In part two, the effect of treatment, ensiling time, and treatment by ensiling time was evaluated on a laboratory scale. Samples of the chopped corn were collected at harvest, prepared as 0.9-kg silos, and vacuumed sealed (28 × 36 cm). Chopped corn ensiled for 0 d was frozen on the day of harvest, while silos for 30, 90, and 150 d were left in the vacuum-sealed bags for each respective time frame and frozen for later analysis. Applications of foliar fungicide on corn ensiled as corn silage decreased dry matter (335, 319, 315, and 317 g/kg DM for CON, V5, V5+R1, and R1, respectively), but increased crude protein (81, 85, 82, and 87 g/kg DM for CON, V5, V5+R1, and R1, respectively), water soluble carbohydrates (38, 40, 46, and 52 g/kg DM for CON, V5, V5+R1, and R1, respectively), and lactic acid (46.5, 50.1, 50.9, and 55.0 g/kg for CON, V5, V5+R1, and R1, respectively). Applications of fungicide at R1 had the lowest lignin compared to treatments (20 g/kg DM for R1 vs 24, 24, 26 g/kg DM for CON, V5, and V5+R1, respectively), and corn silage in V5 had greater milk kg/MT DM (1631 kg/ton DM for V5 vs. 1511, 1585, and 1576 kg/MT DM for CON, V5+R1, and R1, respectively; P = 0.04). Length of ensiling postharvest affected the dry matter (327, 314, 325, and 320 g/kg for 0, 30, 90, and 150 d, respectively; P = 0.03), crude protein (81, 85, 84, and 86 g/kg for 0, 30, 90, and 150 d; P < 0.0001), and pH (5.74, 3.75, 3.80, and 3.80 for 0, 30, 90, and 150 d; P < 0.0001) of corn silage. Significant interactions between foliar fungicide applications on corn ensiled as corn silage and length of ensiling postharvest were observed for water soluble carbohydrates (80, 91, 111, and 125 g/kg at 0 d; 16, 17, 19, 22 g/kg at 30 d; 25, 25, 26, and 32 g/kg at 90 d; 31, 28, 27 and 32 g/kg at 150 d for CON, V5+R1, and R1, respectively; P = 0.03), and lactic acid (1.0, 0.5, 0.4, and 0.5 g/kg at 0 d; 54.3, 67.8, 64.4, 71.9 g/kg at 30 d; 63.4, 68.5, 69.2, and 71.1 g/kg at 90 d; and 62.7, 63.7, 69.7, and 76.6 g/kg at 150 d for CON, V5+R1, and R1, respectively; P = 0.03). In conclusion, fungicide application on corn affected the nutritional profile differently depending on the part of the plant. Once ensiled, fungicide application on corn impacted the nutritional composition and fermentation of corn silage ensiled for varying lengths of time postharvest. Finally, corn silage from corn receiving foliar fungicide fed to cows impacted milk production and composition. Cows fed corn silage receiving foliar fungicide treatment at V5 had greater FCM and ECM than cows fed corn silage receiving foliar fungicide treatment at V5 and V8. Results from 2015 corn indicate applications of fungicide on corn reduced the number of yellow leaves and increased the height of the corn stalk. Applications of fungicide on corn atV5 and R1 resulted in the greatest concentration of lignin in the stalk, but applications of fungicide on corn at both V5 and R1 reduced the concentration of ADF and NDF in the corn leaves. Applications of fungicide on corn ensiled as corn silage reduced the DM content, and applications of fungicide at R1 resulted in the lowest concentration of lignin in corn silage. Foliar fungicide treated corn and, then corn silage, increased the nutritive quality of the plant material and corn silage by decreasing the fibrous content, and resulted in increased FCM and ECM when fed to dairy cows.
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From field to rumen: foliar fungicide application on corn and its effects on the corn plant, corn silage, and Holstein cow performance
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