Jourdan Bell, Kevin Heflin, Vanessa Corriher-Olsen, and Pete Dotray

In response to increasing silage demands, Texas producers are growing more corn and forage sorghum for silage.  In recent years, some producers are also making late season decisions to harvest corn intended for grain as silage due to favorable silage markets. As producers make preplant agronomic decisions, it is important to select herbicides that are labeled for the silage crops if there is a contingency plan to chop a grain crop for silage.

Although it is commonly believed that weeds contribute to forage tonnage, weeds can reduce tonnage. Massinga and Currie (2002) confirmed that Palmer amaranth (Amaranthus palmeri) reduced corn forage yield up to 30%. Weeds can also negatively impact forage quality. The palatability and nutritive value vary between weeds species and growth stage (Kirilov et al., 2016), and some weeds can be toxic. Palmar amaranth (Amaranthus palmeri L.), redroot pigweed (Amaranthus retroflexus L.), lambsquarter (Chenopodium album L.), silverleaf nightshade (Solanum elaeagnifolium Cav.), and johnsongrass (Sorghum halepense L.) are nitrate accumulating weeds. While nitrates can be reduced 45-70% during the ensiling process (Chunsheng et al., 2022), research in sorghum silage confirmed that variability in degradation is a function of the storage temperature, packing density, and fermentation characteristics of the silage. By controlling weeds in the field, a producer can minimize risks of nitrate “hot spots” within the silage pile and optimize forage yields.

When making herbicide decisions for silage crops, it is important to confirm that the herbicide is labeled for forage, fodder, or both. While crops grown for silage are commonly referred to as forage crops, many herbicide labels distinguish between forage and fodder. Forage crops are plant materials directly grazed by livestock while fodder crops are harvested plant materials for livestock feed including hay and silage. Although ensiling is the process of preserving a forage crop, silage may be considered fodder on the herbicide label. Therefore, it is important to know the end-use and how the crop is defined when reading herbicide labels, because usability and harvest intervals can vary depending on the intended use. For example, Liberty 280 SL cannot be applied within 60 days of harvesting corn for forage and within 70 days of harvesting for corn grain and corn fodder. Additionally, just because the herbicide is labeled for corn or sorghum grain, does not mean it is labeled for corn or sorghum silage (forage or fodder). Most corn herbicides are labeled for corn forage or fodder, but there are exceptions, and many herbicides labeled for grain sorghum are not labeled for forage sorghum.

It is the pesticide applicator’s responsibility to ensure that all products are used according to the registered intended use. When making herbicide selections for corn and forage sorghum silage crops, the pesticide applicator should:

1. Confirm that the herbicide labeled for a forage or fodder (silage) crop.
2. Confirm the harvest interval for livestock.
3. Follow harvest restrictions from the date of the last herbicide applied or the longest harvest interval of tank mixed herbicides ensuring latest date.
4. Refer to the label of each product used when tank mixing and follow the most stringent label.

References:

Chunsheng, B. P. Gang, L. Ruoxuan, N. Wenhua, Y. Jiyun, S. Juanjuan, Y. Zhu, L. Zhigang, X. Yanlin. 2022. Effect of Ensiling Density and Storage Temperature on Fermentation Quality, Bacterial Community, and Nitrate Concentration of Sorghum-Sudangrass Silage. Frontiers in Microbiology. doi: 10.3389/fmicb.2022.828320

Kirilov, A., N. Georgieva, and I. Stoycheva. 2016. Determination of Composition and Palatability of Certain Weeds. Int J Agric Sc Food Technol 2(1): 041-043. doi.org/10.17352/2455-815X.000013

Massinga, R. and R. Currie. 2002. Impact of Palmer Amaranth (Amaranthus palmeri) on Corn (Zea mays) Grain Yield and Yield and Quality of Forage. Weed Technology. 16(3):532-536 doi.org/10.1614/0890-037X(2002)016[0532:IOPAAP]2.0.CO;2