Sudangrass has relatively thin stems. It tillers extensively, when conditions permit, and can regrow rapidly. Thus, it is better suited to pasturing than other types of sorghum. Hybrid sudangrass crosses usually yield slightly more than true sudangrass varieties in multiple-cut harvest systems. While prussic acid poisoning is possible, the risk with sudangrass usually is less than with sorghum-sudangrass or forage sorghum.
Sorghum-sudangrass hybrids are the most numerous of the various types of summer annual grasses. They are high-producing forage grasses, but more than 50 percent of their yield usually comes from the stems. Forage quality tends to depend highly on harvest timing, as quality declines rapidly as plants mature. Their rate of regrowth after repeated clippings or grazing is lower than that of sudangrass. Thus, sorghum-sudangrass hybrids are best suited for hay or greenchop.
Forage sorghums are usually tall growing and mature late in the growing season. Sometimes called “cane,” many forage sorghums have sweet and juicy stems. Many also have relatively small grain heads.
As silage, forage sorghums usually yield more dry matter per acre than dryland corn and will yield similarly to corn under irrigation. However, yields of TDN (total digestible nutrients) per acre are usually lower from forage sorghums than from corn.
Grazing forage sorghums is not recommended. They have a much higher risk of prussic acid poisoning than other summer annual grasses and can be dangerous to graze even when plants are completely headed, especially when young shoots are present. Forage sorghums can be cut for hay, although their stems dry very slowly after cutting.
Foxtail millet has relatively coarse stems yet dries quickly following cutting. It has a short growing season and is more dependable than other summer annuals on light, sandy soils. It will often produce higher hay yields than other summer annuals following a late planting.
Foxtail millet does not root securely into the soil during early growth and is slow to regrow following grazing. Thus, it is not recommended for grazing except in an emergency. It is used best as a short-season or emergency hay crop.
Foxtail millet is a host to the wheat curl mite, which is the carrier of the wheat streak mosaic virus. While foxtail millet is not injured seriously by the virus, use proper precautions when planting foxtail millet and wheat in close proximity.
Pearl millet has become increasingly popular for grazing in recent years due to the development of commercial varieties adapted to more northern climates. It is very leafy, regrows well after grazing, yields about the same as sudangrass and does not cause prussic acid poisoning.
Pearl millet is fairly drought tolerant, but it has thicker stems than foxtail millet, so it dries down more slowly when cured for hay. Its sensitivity to cool weather limits its usefulness to only the hottest times of the year.
Teff has very fine stems, grows rapidly once established, regrows rapidly in midsummer and has a high leaf-to-stem ratio. It is fairly drought tolerant once established. It can be harvested 45 to 55 days after planting. It is used most commonly for hay, especially for horses and similar recreational animals. Grazing can result in some uprooting of the shallow crop, especially early in the growing season. Teff is not known to cause either prussic acid or nitrate poisoning.
Crabgrass produces abundant thin, decumbent stems of high quality, very palatable forage. Although considered a weed in many cropping systems, crabgrass is gaining popularity as a forage for grazing or hay. It is only moderately drought tolerant and has poor tolerance to poor drainage.
Crabgrass is somewhat unique among summer annual forage grasses because it often can reseed itself naturally, thus reducing or eliminating the need to plant it every year.
Last (at least for this article) but certainly not least is corn, which is a summer grass. As forage, corn is used most commonly as silage but can be a viable choice for grazing, especially as new hybrids with added tillering potential become available. In many areas, it is both the most productive and highest quality summer grass available. The standing crop retains its nutritional value into winter better than other summer forages due to its grain production, so it can be grazed successfully from summer through winter.
Further complications – enhanced traits
The differences in the usual characteristics of these summer annual grasses are not the only factors that complicate making the best choice. Recent advances in unique genetic traits give added complications.
BMR (brown mid-rib) traits reduce lignin so plants are more digestible. Brachytic dwarf shortens plants without reducing yield, thereby improving standability. Male sterile plants do not produce pollen and potentially no grain, while photoperiod-sensitive plants may not produce a seed head at all. And high sugar types can increase palatability and energy content. Combinations of these traits can be found in some varieties or hybrids. FG
Bruce Anderson is an extension forage specialist with the University of Nebraska – Lincoln.