A bi-monthly news publication of The Ohio State University Extension, Editors: Clif Little and Mark Sulc
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Contents:

• Grazing Dairy Heifers on Winter Annual Forages
• Frost Injury to Alfalfa – Issues and Concerns
• Stand Establishment Problems in Late Summer Seeded Alfalfa
• Boosting Forage Production After Winter Damaged Alfalfa
• Chemical Weed Control in Pastures
• Prevent Grass Tetany

[top] Grazing Dairy Heifers on Winter Annual Forages - Mark Sulc, Giovani Stefani Fae, John McCormick and David Barker

We’ve had an interesting late autumn and early spring grazing experience on the Waterman Dairy Farm at The Ohio State University Columbus campus. Early last September we no-till planted two annual forage treatments right after corn silage harvest. We wanted to compare Marshall annual ryegrass to a mixture of Armor oat plus Aroostook cereal rye for grazing dairy heifers.

Besides forage and animal performance, we will evaluate how the winter forage cover influences root growth in the winter forages, soil compaction from animal treading, and changes in soil organic carbon. We think any negative impact of animal treading during grazing (compaction) will be offset by improvement in soil structure and soil carbon provided by the winter annual forages.

The forages were grazed from November 20 to January 4 with Holstein heifers weighing around 700 pounds and Jersey heifers weighing around 600 pounds. The oat naturally winterkilled late last fall. The Holstein heifers gained 2.1 pounds per day and the Jersey heifers gained 1.4 pounds per day during that period.

The surviving cereal rye was grazed from March 26 to April 10. The annual ryegrass came on more slowly, and we grazed it from April 2 to April 10. The forages were grazed this spring by pregnant Holstein heifers weighing 1160 pounds and pregnant Jersey heifers weighing 750 pounds. The Holstein heifers gained 1.2 pounds per day and the Jersey heifers gained 0.9 pounds per day.

The early April cold snap and preparations for early corn planting restricted the grazing period this spring. Cereal rye grew 10 times faster during the warm days in late March than it did in early April. The annual ryegrass slowed its growth by one-third during the early April cold snap.

The annual ryegrass could be grazed into June if it weren’t for the plan to have corn silage in this field again this year. But we are working to see how much grazing we can get between successive corn silage crops. We will apply herbicides and plant the corn as soon as the soils are fit.

The oat + cereal rye treatment provided 88 grazing days per acre per heifer for the early winter plus early spring grazing periods. Total live weight gain was 132 pounds per acre, at a cost of about $86 per acre. So the cost per pound of gain was 65 cents. Annual ryegrass provided 72 grazing days per acre per heifer. Total live weight gain was 120 pounds per acre, at a cost of about $60 per acre. The cost per pound of gain was 50 cents.

We had very wet weather during both grazing periods, which was a challenge. This field has been in no-till for at least 10 years, which helped provide more solid footing than a tilled field. We also moved the animals more quickly or spread them out over a larger area when the soil was very wet.

We will plant the corn no-till by the end of April, weather permitting. The wetter areas of the field were tracked up some by the heifers. Time will tell how the corn establishes and produces in those areas. We will keep you posted.

Editor’s Note: This article was adapted from one that first appeared in Farm & Dairy Magazine on 19 April 2007.

[top]Frost Injury to Alfalfa – Issues and Concerns - Mark Sulc, OSU Extension Forage Specialist

The early alfalfa growth from late March has been killed back by the frigid early April temperatures across most of the state. Some fields show green leaves and small surviving shoots in the lower canopy, but the taller stems have collapsed from the freeze.

I really don’t expect to see permanent damage to established, healthy alfalfa stands from this late freeze. Back in 1992 we had similar conditions of alfalfa breaking dormancy early in March, followed by cold temperatures that killed the shoots back to the crown. Alfalfa reinitiated growth that year and first-cutting yields were near normal, although the first harvest was delayed by 7 to 15 days.

Established stands of adapted varieties should initiate new growth with the warming temperatures, especially if the fields have good drainage and adequate fertility. If fertility is low, make corrective applications as soon as soils are firm enough to support traffic.

In late summer 2006 seedings, the frost may cause greater problems depending on extent of seedling establishment achieved last fall. Plantings made by early August 2006 will likely have less long-term damage than those made much later. Plant roots should be observed. If the inner root tissue is soft, spongy, or discolored, then severe injury has occurred. In contrast, healthy root tissue will be firm and white.

Weak stands, especially those under waterlogging stress, will likely have a more difficult recovery this spring and yield levels will be lower than normal. Keep a close eye on those fields.

We also have to keep a very close eye now on alfalfa weevil injury. Start scouting fields immediately, as few weevils were killed by the frost, and they have less plant material to feed on now.

I’ve been asked three questions related to managing frost-injured alfalfa: Should the frosted alfalfa growth be cut? If not clipped, won’t the dead alfalfa stems interfere with new shoot development? Will forage quality at the first cutting be harmed by the dead alfalfa stems?

My answer to all three questions is “No”. I think cutting at this stage will be an added stress that will further drain the vigor of the plants and do more harm than good. In addition, any surviving stems in the lower canopy could get clipped off, setting the plants even further behind.

The frost-killed stems should have negligible effect on the growth of new shoots and forage quality at first cutting. They probably won’t even be picked up during harvesting. I think we should save fuel and be patient for plant recovery.

My best guess now is that we will have to delay first harvest by 7 to 15 days. A delayed first harvest will give the crop time to recover and produce higher yields. Forage quality should follow normal changes in relation to crop maturity.

The delay in first harvest this year will mean that only three cuttings will be possible for stands where four cuttings are normally taken. Later this summer, the alfalfa should also be allowed to mature to 40 to 50% bloom stage, which will help the stand regain full vigor.

Despite the potential for one less cutting (3 rather than 4 cuts) this year, overall yields could still be near normal provided weather conditions favor good alfalfa growth the rest of the growing season. Research has shown that alfalfa cut three times is often higher yielding than when four cuts are made. Forage quality is usually lower with three cuttings as compared with four; however, it’s usually acceptable for dairy animals, provided the stand is pure alfalfa and not mixed with grass.

For mixed grass-alfalfa stands, the tricky management issue may be that the grass will recover more rapidly and be ready for harvest much sooner than the alfalfa. So should grass-alfalfa mixtures be clipped to slow down the grass growth? Again, I don’t think so. Young alfalfa shoots are growing again, and removing them now could do more harm than good to the alfalfa.

[top]Stand Establishment Problems in Late Summer Seeded Alfalfa- Mark Sulc, OSU Extension Forage Specialist

I’ve heard reports of stand establishment problems in alfalfa planted last summer, especially in northwest Ohio where standing water reduced stands over the winter. What can be done about it?

If the thin spots are not too numerous and are relatively weed free, alfalfa can be interseeded with a no-till drill to thicken up the stand as soon as soils are fit. Alfalfa planted just last summer will not yet be old enough to cause autotoxicity.

Interseeding to thicken up the 2006 summer seedings will only be successful if the surviving plant density is very low and will provide minimal to no competition to new emerging seedlings. Use careful judgment before attempting to interseed where there is surviving alfalfa stand.

If winter annual weed populations are high in the areas with stand loss, a glyphosate treatment to eliminate that competition will be important before trying to interseed. Raptor and Pursuit are not an option where alfalfa is to be reseeded within 3 to 4 months.

If stand thinning is severe throughout the field, especially if winter annual weeds are a concern, then it will be best to start over. Kill the entire stand and replant as if it were a new seeding.

[top]Boosting Forage Production After Winter Damaged Alfalfa- Mark Sulc, OSU Extension Forage Specialist

Interseeding alfalfa is an option to thicken up stands if the alfalfa was seeded last summer. In stands that are 2 years old or older, interseeding alfalfa to thicken up the stand usually does not work. New alfalfa seedlings may emerge and look good early on, but they often die out over the summer due to competition, diseases, and autotoxicity present in the existing alfalfa stand.

To extend the life of winter damaged alfalfa stands beyond this year, consider interseeding red clover or a grass such as ryegrass or orchardgrass. The yield benefit from perennial species may not be great until the second year, because they require some time to establish. Perennial ryegrass would likely provide an earlier yield boost because of its rapid establishment. Perennial ryegrass and red clover are slower to dry, so curing times will be lengthened compared with orchardgrass-alfalfa mixtures.

If forage supplies are very critical for this year, consider interseeding with a cereal grain (oat, beardless barley, wheat, spring triticale) or annual ryegrass into alfalfa. All these annual grasses are quick to establish and will compete well in a thin alfalfa stand. The forage may need to be put up as silage or balage rather than as hay, but yields will be high and forage quality can be very good if cut in late boot to very early heading stage.

There are numerous annual species for boosting forage supplies for this year alone, corn silage being one of the best. The following are excellent sources of information on annual forages and managing alfalfa where winter injury is an issue:

• The Ohio Agronomy Guide, Chapter 7 (section on Annual Forages) http://ohioline.osu.edu/b472/0008.html

• Articles on Univ. of Wisconsin Website: http://www.uwex.edu/ces/forage/news/current/winterkill2005.htm

[top]Chemical Weed Control in Pastures- Keith A. Diedrick Extension Educator, Wayne County

The Problem. Well, it never fails. We go out with the perfect plans and plant the perfect pasture. In seemingly no time at all, undesirable plants find a way to grow with our crop. We used to say back in school that weed science held a lot of job security for us; weeds sprouting up in the wrong places are one of life’s certainties (along with death and taxes). The longer our pasture soils remain somewhat undisturbed, the more biennial and perennial weeds we will see. Some weeds are simply annoying, some aggressively crowd out our forages, and some can be downright deadly to our livestock. For this column, let’s discuss a couple of the principles of chemical weed control in pastures.

Identification of the Weed and Choice of Control: It sounds like common sense, but when a 2,4-DB application doesn’t seem to injure Canada thistle all that much, we ought not be surprised, since Canada thistle isn't even on the 2,4-DB label! Picking the right chemical and rate is very important. As with any herbicide, read the label all the way through. Labels have lists of “labeled crops,” “weeds controlled,” and “weeds suppressed.” Make sure your pasture fits the bill in terms of both crops and weeds. The labeled rates are a good guide to control, and reducing the recommended rate by a large margin may reduce control by an equally large margin. Do your weeds tend to reside in patches? Maybe a spot application of a cheaper, non-selective chemical (like glyphosate) would be preferable to spraying a large area with a more expensive selective chemical, saving time and money, to boot.

Timing of Control: Recently, a plant pathology professor related some great wisdom to me: “if we don’t know much about the pest’s life, how can we expect to control it? During the pasturing season, I get at least three calls a week about chemical control failures of Canada thistle, and my first question to them (after “what and how much did you use”) is “when did you spray it?” If the answer is “July” or “August,” that’s part of the problem. We’re trying to kill a thistle when it’s not nearly as susceptible as it is right before and during budding (and that goes for most broadleaf perennial weeds). Larger perennials and biennials are most vulnerable in the fall. Perennial grass weeds are most susceptible to herbicide action from boot to seedhead growth stages. Pick the right time and method, and our control dollars stretch further and are used more effectively.

Grazing Restrictions. Please take note of grazing restrictions that some chemicals might have at specific application rates; that information is contained in the label. If you use two chemicals tank-mixed, use the longer of the two restrictions.

Final Thought. Good grazing and fertility management should accompany any chemical weed control program. Otherwise the same weed problems will soon redevelop.

Editor’s Note: This article first appeared in Farm & Dairy’s “All About Grazing” column, 22 March 2007

[top]Prevent Grass Tetany- Mark Landefeld, Extension Educator, Monroe County

As the weather continues to warm and pastures grow, farm managers should be aware of the term hypomagnesemia or “grass tetany”. Turning cows or sheep out to new lush pastures can cause the lowering of blood levels of magnesium and an imbalance of electrolytes. This dangerous and unwanted condition is increased in pastures if nitrogen is applied in spring, if soils contain high levels of potassium, or low soil pH conditions exist. There is a relationship between soil phosphorus content and magnesium uptake in forages too. If phosphorus is low, even if soil magnesium is adequate, the plant may not take up magnesium in ade-quate amounts to meet the cow's needs.

Grass tetany is more common on grass pasture than legume pastures. Legumes tend to have higher magnesium levels in their leaves. Grass tetany is associated with cool weather in spring and fall because the metabolism of the plant is slower and its mineral uptake from the soil is lower, leading to lower magnesium in the forage that the cow is eating.

Early symptoms of grass tetany are muscular weakness, followed by incoordination that progresses until the animal can no longer get up. Animals do not store magnesium in their bones as they do other minerals. Magnesium is stored in soft tissue and must be ingested on a daily basis. Cattle most likely affected by grass tetany are the older cows and high producing animals after they have calved. Grass tetany can generally be avoided by feeding minerals with high magnesium content or supplemental magnesium. Commercial mineral mixes that are effective in preventing grass tetany are available, commonly called high-mag mixes; these minerals contain 12 to 14 percent magnesium.

Magnesium oxide is an inexpensive source of magnesium if you want to formulate your own mix. However, mag-ox is not well liked by animals so it needs to be incorporated with something readily accepted such as dried molasses, minerals, concentrated feeds or salt supplements. Magnesium oxide is about 60 percent magnesium, so the cow should consume approximately 1-2 ounces of mag-ox per day to maintain acceptable levels of magnesium in their diet during spring and fall. Intake of supplemental magnesium should be monitored regularly to be sure lactating cows are consuming proper amounts during the high risk periods.