NEWS--May 1997--Oklahoma Alfalfa

Hopefully you got your first cutting up without too much rain on it. It is time to make decisions about summer weed control. Some of the early-emerged summer weeds were frozen back, then the alfalfa shaded the area enough to prevent any more seedling emergence. So expect a big crop of weeds to germinate after the first or second cutting if the soil is wet at harvest.

If you still have a good alfalfa stand (more than 30 stems/sq. ft.), you may not have any summer weed problems this year. Your alfalfa will essential shade out and out-compete the emerged annual weeds and none will be in the hay. On the other hand, if your stand is thin and/or you are not keeping it fertilized properly, expect summer weeds to start showing up in the third harvest. However, it may require using a herbicide after your next cutting to get the best results.

Here are your summer weed control options:

1. Do no weed control. This may be the most profitable option, especially if you need hay for your beef cattle or you have a beef producer who will give you a fair price for it. Hay from the first and second cuttings usually do not have any summer weeds because the weeds are still small. Then, if it is dry in July, there will not be that much growth of the annual weeds the rest of the summer. If weeds do grow, they can be utilized. A mixture of alfalfa-grass is an excellent hay for beef cattle. Also, producers should consider grazing weedy alfalfa. Weeds in alfalfa minimize bloat problems and some good gains can be obtained by grazing (see Alfalfa Harvest Management Discussions with Cost-benefit Analysis. OSU Circular E-943).

2. Herbicide options include:

PURSUIT. It is most active on broadleaf weeds. At 4 oz/A, small pigweeds and some other broadleaf weeds are listed as being controlled. However, it may only suppress some of the grasses at this rate. In our trials, we have had good season-long control of pigweeds with 4 oz/A applied after first harvest. However, grass control has been erratic. Producer's satisfaction with PURSUIT has been mixed. I believe producers may be expecting too much, and possibly are not applying it at the best time. Weeds need to be small and actively growing when PURSUIT is applied. PURSUIT has both postemergence and good residual activity, so you can expect summer-long weed control of susceptible weeds with

an after first-harvest application. Also, be aware of rotational crop guidelines after using PURSUIT. It is 4 months for wheat and 18 months for sorghums (see label for other crops).

SINBAR. It gives fair to good control of pigweeds when applied after 1^st harvest. However, grass control has only been fair. SINBAR should be applied at 0.7 to 0.9 pounds of product/A as soon as the hay is off of the field. A 1-inch rain is required to move the herbicide into the soil so it can be taken up by the roots of the weeds.

GRAMOXONE EXTRA. It is a contact non-residual herbicide that can be used to control emerged weeds between harvest. Most alfalfa will be browned-off with application, so it should be applied within 5 days of cutting to minimize damage. Small emerged pigweeds are killed, but poor control of emerged grasses and the emergence of new weeds after spraying can be a problem. Best use for Graxomone Extra has been for dodder control after second cutting.

BUTYRAC 200 (2,4-DB). It is a non-residual herbicide that can give good control of small pigweed. If you spray them when they are small (2 to 4 inches tall) and actively growing, then 2 pints is just about as good as 3 pints. Do not expect to kill large pigweeds sighted during swathing. Also, control of some summer broadleaf weeds is only fair, so read the label for listing of susceptible broadleaf weeds before spraying.

POAST PLUS. It is a non-residual herbicide that can give good control of most emerged summer grasses. It is essential that 1 quart of crop oil concentrate/acre be added to the spray mix. It is important to use the rate listed on the label for the various grass. Be sure to scout your fields about 10 days after each cutting and spray the weeds when they are small.

Note: For both BUTYRAC 200 and POAST PLUS, weeds should be actively growing (good soil moisture and temperature) when herbicide is applied. Applications should be made between cuttings when the alfalfa regrowth is about 3 inches tall and there are enough emerged weeds to merit control (1 to 2/sq. ft.). The first application for both herbicides is normally made after the second cutting in mid-June, but if your regrowth after first harvest does not have a good canopy already, then better check your fields for emerged summer weeds. Since both of these herbicides have no residual, it will be necessary to scout the field for new emerged weeds and respray in each cutting if season-long weed control is desired.

ZORIAL received label clearance on alfalfa, and it has potential for giving season-long residual weed control of summer grasses if we can develop a cost effective and reliable way to get it applied and activated before the summer weeds germinate. Our research indicates that summer grass control was good with 2.5 pounds of ZORIAL, applied during the dormant season. However, the $40 per acre cost would be difficult to justify for most producers.

-- Jim Stritzke
Alfalfa Weed Control Specialist

Alfalfa hay quality is important to animal performance and hay marketing strategies. Livestock producers should utilize forage testing to reduce feed costs and maximize production by incorporating test results in ration formulation. For commercial hay producers, a system of selling the best hay and feeding the remainder is generally a profitable and efficient use of alfalfa.

Therefore, a hay quality test is a good investment.

The number of forage samples received by OSU Soil, Water and Forage Analytical Laboratory (SWFAL) was over 4,000 last year; and the majority of samples were alfalfa. SWFAL routinely tests forage samples for acid detergent fiber (ADF), neutral detergent fiber (NDF), crude protein (CP), dry matter (DM), nitrate, and calculates net energy from ADF and relative feed value (RFV) from ADF and NDF. The types of analysis performed on all the samples in 1996 are shown in the following figure (Routine analysis includes DM, CP, ADF and NDF):

The average testing results of each category for alfalfa during 1996 (values do not include research samples) are shown in the following table; this may give you some idea about the range of quality of alfalfa produced in Oklahoma.

Laboratory results are only as good as the sample submitted, therefore, it is extremely important to obtain a random but representative sample of hay for testing. See Extension Facts No. 2589 for more details about Collecting Forage Samples for Analysis. We do our best in the laboratory to reduce turn-around time and to ensure

high precision of the testing results by implementing a comprehensive quality assurance and quality control program and by better training our technicians.

We have been participating in the forage testing certification program sponsored by The National Hay Association and The American Forage and Grassland Council in recent years. SWFAL is again certified for 1997 on all the chemical analysis. As a matter of fact it is the only certified lab in Oklahoma by this program.

Test	CP	ADF	NDF	TDN	RFV
Ave. Value	20.8	33.8	47.7	62.8	132
Ranges	5.1-32	20-51	26-82	49-73	55-262

--Hailin Zhang
SWFAL Director

PRODUCER'S QUESTION: My hay yields are not as good as they used to be. What is hurting the yields? Cutting machinery, variety, fertility,....?

SHORT ANSWER: It is unlikely that harvest management practices are the cause of this reduced alfalfa hay yield. Most likely, low soil fertility is the cause of the problem. Early symptoms of low soil fertility are low yields and slow regrowth.

EXPLANATION: Cutting frequency, height, date, etc., can vary widely and seldom cause drastically reduced alfalfa hay yields. Poor decisions having to do with variety, insecticide, herbicide, and site selection usually cause stands to thin quickly.

After a few years stands thin more quickly under low soil fertility. It is likely this stand has not yet reached that point, but will soon. Unfortunately, most producers first suspect factors other than low soil fertility or low soil pH.

Good alfalfa production for several decades removes large amounts of fertilizer elements from the soil. Many good fields in Oklahoma were highly fertile for several decades after the prairie was first plowed, but soil fertility has slowly declined. With a relatively small decrease in fertility each year, it is difficult to notice that the soil can supply only a fraction of the amount of phosphorous and/or potassium necessary for good alfalfa production.

Current soil test calibrations predict about 10% yield response when a deficiency of 60 lb/A P₂O₅ is alleviated. For a good field of alfalfa that represents about ½ ton/A increased yield. Conservatively, this is $40/A income increase from fertilizer that cost $12 to $15/A to purchase and apply -- cost/benefit ratio of about 1:3.

Each alfalfa field should be soil tested annually. Soil testing is the only way to know if (or how much) fertilizer should be applied. It is a good idea (and inexpensive) to check the fertility level every year, even when no obvious problem exists and twice a year when there is a problem. Once the fertility has become limiting, large amounts of fertilizer must be applied every year to maintain high yields.

RELATED COMMENTS: Low soil pH can be corrected with a single application of agricultural lime before establishing the field; however, it may be necessary to reapply lime after 6 to 8 years of production. Lime applied after establishment will take longer to correct the low pH problem.

Soils "severely" deficient in phosphorous or potassium, on the other hand, are more difficult to improve quickly. Even when recommended amounts of these materials are applied before establishment, it will be necessary to apply phosphorous and potassium each year.

A certain amount of phosphorus applied as fertilizer is absorbed by the soil and is not available for plants. In addition, large amounts of phosphorus and potassium are removed each year in hay. Five tons of alfalfa hay contain approximately 70 lb P₂O₅ and 300 lb K₂O. This amount is removed as part of the hay crop and must be replaced by fertilizer or soil weathering. Soil weathering is a complex process whereby chemically bond minerals are released by the soil. Regular soil testing is the best way of accounting for how well soil weathering restores crop removal of phosphorous and potassium.

Low fertility and pH have far-reaching effects on alfalfa. In addition to reducing yield and shortening stand life, as noted above, they can exaggerate the effects of pests. Low fertility conditions result in weak alfalfa plants that do not compete well with weeds. Plant stress caused by low fertility coupled with insect infestations can result in losing an alfalfa stand in a short time. In contrast, well-fertilized alfalfa plants without insects, compete with broadleaf and grassy weeds very well, resulting in very little weed encroachment for several years.

This question and the answer was taken, with slightly modification, from Alfalfa Harvest Management Discussions with Cost-benefit Analysis. OSU Circular E-943.

PRODUCER'S QUESTION: Will I lose my stand if I cut alfalfa before it blooms?
SHORT ANSWER: Cutting alfalfa before it blooms from time to time will not result in stand loss.

EXPLANATION: Recommendations on harvest schedules for alfalfa for many years suggested cutting at 10% to 25% bloom. This is a good time to harvest since there is a good balance between forage quality and yield at this growth stage. Blooming signals that root reserves have been replenished and plants are prepared to regrow rapidly without sacrificing vigor.

Cutting before bloom is essential for reliable production of high quality dairy hay. Research conducted in Oklahoma over the last 15 years indicates that cutting at the bud stage does not severely damage stands. Harvests can occasionally be taken before the plants begin to bud without serious damage; however, repeatedly cutting at prebud may shorten stand life. Frequent cutting at prebud may not allow plants enough opportunity to replenish root reserves between harvests; thus, over a period of several harvests, stand decline may be hastened.

If cutting often at the prebud stage causes stand life to be reduced by a year or so, this result in reduced profits because of having to establish a new stand earlier than planned. A premium price must be received for hay to offset the loss of profit due to reduced stand life. Economic analyzes of alfalfa forage production indicate that 2 years are needed to recover establishment costs and begin making a profit from alfalfa.

OSU surveys indicate dairy managers are willing to pay more for higher quality alfalfa hay. In general, dairies will pay $5-$15 more for --

2 to 5 percentage points higher protein,

5 to 10 percentage points higher TDN, or

15 to 30 points higher RFV.

Any factor that reduces productive stand life must be offset by increased profitability during the remaining years to keep the entire enterprise operating at a profit.

RELATED COMMENTS: In Oklahoma, cutting at 10% bloom is not a good indicator for determining cutting time of the first crop of alfalfa forage. Weather conditions are often cool and wet enough in Oklahoma to delay blooming.

A much better indicator is to cut when new growth can be seen at the base of alfalfa plants. Harvesting at this time results in higher quality hay and reduces drying time 1 or 2 days. If you want high quality hay, therefore, it is important to cut in the bud stage or as soon as crown bud growth begins.

Timing of first harvest can also be set by the calendar for healthy stands. Vigorous alfalfa stands can be harvested about April 15 in the southern part of Oklahoma and about May 1 in the north.

This question and the answer was taken, with slightly modification, from Alfalfa Harvest Management Discussions with Cost-benefit Analysis. OSU Circular E-943.

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