Forage Stands – Assessing Flooding Injury

There is no precise way to predict the flood damage to perennial forage fields. It is known that alfalfa is not very resistant to flooding, but reed canary grass can withstand prolonged flooding. Commonly used forage species are between these two extremes. Every field will react differently, depending on the degree and duration of flooding, the species present, the age of stand, the health and vigour, fertility level, stage of development of the plant at the time of flooding and the temperature.

Alfalfa can generally withstand 1 to 2 weeks of flooding when it is dormant. Fortunately, cool spring weather may help to maximize the survivability. The extent of flood damage to fields can best be determined when the fields become dry enough to walk on. By this time, growth will have started where life still exists. Evidence of this growth will be short, green shoots at the base of the plants. If the stand has been severely damaged, the only practical solution is to cultivate the field and re-seed. Where the stand has been only partially damaged and is judged worth saving, weed control will become a problem because of the thinning-out of the land.

Re-seeding alfalfa--if necessary--should be done by mid-June. To increase the chances of establishing a stand at this later-than-normal seeding date, these fields should be seeded with a companion crop to protect the seedlings from hot weather. To minimize the competition effect, a crop such as oats should be used, as it can be cut and baled as green feed or grazed off when it is in the "shot blade" stage.

Grasses as a group tolerate flooding more than alfalfa. Bromegrass will generally withstand over 3 weeks of flooding, while meadow fescue and timothy can withstand 6 weeks or more when they are still dormant. However, if the stand has been severely damaged and cultivation is deemed the only solution, re-seeding of the grasses should be delayed until early August. This will allow for good seedbed preparation, and hopefully increase seedling survival with the fall rains.

Annual Forages

If producers are left without enough hay or pasturelands to meet their needs, annual forages can be used to fill the gap. Oats seeded at 1.5 to 3 bu/ac (55 to 115 kg/ha) can be cut at the late milk to early-dough stage (about 8 weeks after planting) for green feed, hay or silage. For pasture, a mixture of 10 lb./ac (11 kg/ha) of annual rye grass and either 1.5 bu/ac (53 kg/ha) of oats or 0.3 bu/ac (20 kg/ha) of fall rye will provide abundant high-quality pastures when well fertilized. With reasonable growing conditions, either pasture mixture should be ready for grazing about 6 to 8 weeks after planting. Both mixtures will give excellent pasture late into the fall. The mixture containing the fall rye has an added advantage: with a fall rest period, it can provide an early pasture for the following spring.

For further information, contact your GO Representative.