Fall Forage and Frosts

 I will start with the first question. Many of us are concerned about watering our forages in the fall because of the potential of ice forming on the crop. For the most part, ice usually does not harm the crop. I have changed pipe in icy fields many times. Ice formation on a plant does not mean that the plant froze. In fact fall irrigation of forage fields is a good idea. At this time of year evaporation is reduced and you will be able to “bank” more of the water you apply. Fall irrigation also helps forages to grow better the following spring.

At this time of year I receive many calls concerning fall management of forage crops. The questions usually fall into three categories. These are: when can I cut the forage; when can I graze the forage; and when can I irrigate the field.

 Cold nights and frost do however, affect the forage. Harvesting or grazing a field that has sustained a light frost is not advised due to the toxic substances that build up in the plants. When forages freeze, changes occur in their metabolism and composition that can poison livestock. Alfalfa can sometimes concentrate nitrates ( following a frost) in high enough quantities to poison livestock. Alfalfa that has had a frost can also increase the chances of bloat. It is best to wait until these toxic substances have been reduced in the plant prior to cutting or grazing.

 Milo, sorghum, and sudangrass can also become toxic following a frost. The ice crystals that form in plants during a frost will puncture and break cell membranes. This breakage allows prussic acid to be released.  Livestock that consume frozen sorghums can get a sudden, high dose of prussic acid and may die. If we delay grazing the prussic acid will eventually turn into a gas and dissipate into the atmosphere. It is recommended to wait 5 days after a freeze before grazing these crops.

Oats and other grains can also build up toxic levels of nitrates after a frost. The extension office can test forage for high nitrates. The test is qualitative, and can be used to alert the grower to a potential hazard. Raising the cutter bar on the swather and delaying harvest a few days, along with mixing frozen forage with low nitrate forage can go a long way in ameliorating the effects of frost.

Fall tillage in the Garden

Many farmers have given up the plow, and converted to no-till farming in order to reduce soil erosion. Since soil erosion is so devastating to agriculture we might ask; why did we plow our fields in the first place?

The answer  is that plowing helps decompose plant materials left over after harvest, makes it easier to prepare a good seed bed the next spring, helps the soil warm up faster in the spring, kills many weeds, and reduces insect populations. I would like to focus on the benefit of insect control.

Insects go through four stages in their lifecycle. These are the egg, larvae, pupa, and adult stages. The adults are hard to kill. They will not ingest or take in pesticides, are hard to damage mechanically, and survive many of our control methods. May larvae are usually present on the leaves of the crop itself and therefore it is difficult to use mechanical control measures against them.  Eggs and pupae are another story. These two life stages are critical in insect development. Eggs and pupae are easily damaged by moving, rolling, smashing, or crushing. This is the type of damage that cultivation, especially disking and plowing causes.

Many insect species bury their eggs to protect them. Insects also bury themselves in the ground prior to pupation. Tillage will bring these insects to the surface, where they will be eaten by predators or damaged by the sun, wind, and rain. Fall tillage of cold soils has an even greater effect on insect control than summer tillage possibly due to the damage cold temperatures has on eggs and larvae. These two life stages have a narrower window of environmental conditions under which they can survive.

When gardening, do not forget to use tillage for insect control.