Possible Causes of Yellowing Alfalfa

Alfalfa fields may periodically exhibit yellowing of foliage. There are several possible causes for such symptoms.

Leaf spot diseases. During springtime, several leaf spotting diseases–including Lepto leaf spot and summer black stem & leaf spot—are common in alfalfa. Very wet weather in spring and early summer favor activity of leaf spotting diseases in first and second cuttings.  Wet and humid weather during summer favor other leaf spotting and blighting diseases.  In all such cases, leaf spots and blights weaken the plant but alfalfa often outgrows the damage in later cuttings. Maintain a regular cutting schedule, cutting at 30- to 35-day intervals.

Potato leafhopper. Potato leafhoppers are common in Kentucky alfalfa fields. Information on recognition, scouting, and control are available from UK’s Entomology Extension program. See our previous article or your county Extension office.

Soil compaction. Wet soils this spring during preplant operations or hay harvesting operations can result in severe compaction in some fields. Check for soil compaction by digging and examining both root systems and soil structure. If the compaction is so severe that the taproot cannot pass through the compacted zone, yields will be reduced significantly and plowing and replanting might be the only option. Remember, it is much easier to prevent than to alleviate soil compaction.

Potash deficiency. High quality alfalfa removes a large amount of potassium from the soil each year. Soil test K levels should be monitored closely and fertilizer K should be applied whenever it is recommended. It is possible that some plants in your field may exhibit mild potash deficiency symptoms even if potash levels in the soil are adequate, since roots that are limited by compaction and/or root rots will be less effective at taking up potash. Maintaining soil test levels and preventing soil compaction will help to assure maximum productivity and stand longevity.

Root rots. There are a variety of root-rotting diseases of alfalfa that are favored in the saturated soils. The most damaging is Phytophthora root rot; which can attack any part of the root system of plants of any age.  Aphanomyces and Pythium organisms are also known to attack the fine feeder roots of mature plants of alfalfa when soils are saturated. Always select varieties with R or HR ratings to Phytophthora and Aphanomyces root rots when seeding alfalfa in Kentucky.  Unfortunately, there is no known resistance in commercial cultivars to Pythium infection, but improving soil drainage and minimizing soil compaction will help with all three diseases.

Poor nodulation. Check nodulation of new seedings by carefully digging and washing root systems and examining for nodules. Poor nodulation of roots may be the result of root-rot infections or of poor viability of the Rhizobium bacterium on the seed.  If poor viability on the seed is the cause, an inexpensive practice to improve the chances for nodulation can be found at: http://plantpathology.ca.uky.edu/files/ppfs-ag-f-04.pdf.

Crown rot diseases. Dig plants and cut into the crowns. Those that are showing brown discoloration are exhibiting crown rot.  A variety of soil-boirne fungi can cause crown rot.  Adapted varieties of alfalfa can sometimes recover from crown rots.  However, if severe, crown rots can be a significant problem for long-term health of the stand. Thus, if you see a high frequency of crown rot in a particular field, that is usually a flag to rotate.

Probably the best indication of when to rotate is stand density. Approximate guidelines as to economically acceptable stands from Dr. Garry Lacefield, UK Forage Agronomist, are:

3 crowns per square foot for hay

1 crowns per square foot for grazing

Dr. Lacefield points out that these are approximate guidelines. For example, a beef cattle producer often will meet his/her production goals well with a much lower density of alfalfa crowns than a hay producer. He also indicates that, for the Upper Midwest, for high-quality dairy hay productions, the standards are based on stem density, since this more closely correlates to forage production than crown density.:

55+ stems per square foot: no yield reduction

40-55 per square foot: some yield reduction

Below 40 per square foot: give consideration to replanting

If stands are less than needed for your yield goals, plan a rotation away from alfalfa followed by re-seeding.

~ Drs. Paul Vincelli, Chris Teutsch and Kiersten Wise, revision from an early extension article on this topic by Paul Vincelli and Greg Schwab.

KFGC Annual Field Day- August 7- Daviess County

Tim Taylor will host the 2017 Kentucky Forage and Grassland Council Annual Field Day Mon, August 7th on his farm in Daviess County. Registration begins at 4:45 with farm tour and educational sessions at 5:30 and a meal at 7:30. Topics include Grazing Corn, Annual Forage Systems, Pasture Re-Establishment and Maximizing Beef Profit Per Acre. 8706 Hwy 81, Owensboro, KY To register, call 270-685-8480.


Dung Beetles: Underground Allies

Dung beetles are important allies. Most beef producers are aware of these insects but few realize the range of benefits that they provide. About 30 species are important managers of livestock manure in the eastern US. These usually dark brown or black beetles and their grub-like larvae work out of sight to provide pasture management and pest management services that generally go unnoticed. Adults use their flat, shovel-like front legs to bury nutrient-rich manure that will serve as food for their developing larvae. Without dung beetles, manure pats would deteriorate very slowly, reduce productive pasture area, provide undisturbed breeding sites for pasture flies, and enable passage of intestinal parasites within herds.

Dung Beetle Services

Nutrient recycling – A significant proportion of the nutrients consumed by cattle is excreted in their manure. Using their strong sense of smell, dung beetles quickly detect and fly to fresh manure and immediately begin move it down into the soil. This helps to reduce nitrogen loss that can occur through ammonia volatilization and enables mineralization by soil microorganisms.

Soil mixing, aeration, and permeability – Several dung beetle species dig underground tunnels with expanded brood chambers where their larvae will develop on stored manure. These beetles bring large amounts of soil to the surface during the excavation process. Their tunnels allow oxygen and water to penetrate more deeply into the soil.

Improved plant growth – Dung beetle activity has a positive impact on plant growth. Studies have reported increased height, greater biomass, and higher protein levels and nitrogen content in plants grown in soils worked by dung beetles compared to sites where the insects were excluded.

Suppress internal parasites and pasture flies – Eggs of most internal parasites pass through the manure and ultimately the infective larvae are ingested by grazing animals. Aeration by burrowing beetles allows dung to dry more rapidly, resulting in death of many of their eggs. Burying or dispersal of manure affects pasture flies, too because it denies them the fresh cow manure that is their only breeding site.

Preserving pasture land – Most ruminants will not graze close to manure pats of their own species. If left to weather away, lingering cattle manure can reduce available grazing area by 5% to 10% per acre per year.

Managing for Dung Beetles

Some pesticides used to control internal parasites and pasture flies can affect dung beetle development or survival. However, there are management practices that will help to reduce adverse effects. Use fecal egg counts to determine when internal parasite control is warranted. Unnecessary treatments can contribute to resistance problems and may affect dung beetles. When deworming is needed, read product labels carefully. Some pass through in forms or at levels that can affect dung beetle development or survival. Insecticides used for pasture fly control can be excreted at levels that affect dung beetles. Use insect treatment guidelines to prevent unneeded treatment. When fly control is needed, limited use of oilers or forced-use dust bags can provide the protection needed with least harm to dung beetles. ~ Dr. Lee Townsend, UK Extension Entomologist, full article published in Grazing News.

Other Grazing News articles of interest: Annual Lespedeza for Grazing and Tips for Managing Grazed Forage Crops


2017 Fall Kentucky Grazing School

UK Agriculture Extension will be hosting their Fall Grazing School at the Woodford County Extension office in Versailles, KY September 27-28th. The fall grazing school will focus on the hands-on setup and management of rotational grazing systems and on warm season and cool season forage crops for cattle and small ruminants. Our goal is to educate farmers to make the most efficient use of their farm and to encourage beneficial grazing practices. Contact Zach Workman at (859) 257-7512 or zewo222@uky.edu to register. Fee includes all materials, manuals, snacks, and lunch for both days of the program.


Don’t Overlook Johnsongrass in Your Pastures

Livestock producers in the southern United States should not overlook johnsongrass in their pastures. For one thing, under certain conditions it can kill your cattle. Another reason not to overlook johnsongrass is that it is excellent forage – if you can get over the fact that it can kill your cattle!

Positive Aspects of Johnsongrass

As far as nutritive value is concerned, johnsongrass is tough to beat. One study conducted at the Noble Research Institute in Oklahoma showed that the quality, expressed as percent crude protein (% CP), and digestibility, expressed as percent total digestible nutrients (% TDN), of johnsongrass is as good as any of the forages tested (Figure 1). In this study, bermudagrass was neck and neck with johnsongrass in terms of % CP and % TDN. The bermudagrass was a managed stand and was fertilized with 50 to 100 pounds per acre of actual nitrogen. The johnsongrass was unfertilized and unmanaged.


In another Noble Research Institute study, the palatability of several warm-season grasses was evaluated by yearling steers. In the study, three yearling steers had access to plots containing pure stands of 14 different warm-season perennial grasses (both native and introduced).

Johnsongrass came out near the top in this study. Alamo switchgrass was the only other grass in the study that had more bites taken of it than johnsongrass in year one (9,262 versus 6,062, respectively). A testament to the preference for johnsongrass by livestock can be seen while driving down the road; pastures that are continually grazed generally won’t have any johnsongrass, but you will see it all along the roadside – out of reach of the fenced-in cattle.

Negative Aspects of Johnsongrass

Johnsongrass is on the noxious weed list in several U.S. states (including Kentucky) and has even made the list of the 10 most noxious weeds in the world. Johnsongrass can accumulate nitrates during the summer if exposed to several dry, cloudy days in a row. It can also produce prussic acid (hydrogen cyanide) after stressful conditions such as drought, freezing weather or exposure to a herbicide that kills grasses. If your johnsongrass is subjected to any of these conditions, keep cattle away for about a week to allow the prussic acid to dissipate. ~ Chan Glidewell, Noble Research Institute

Featured Publication: Alfalfa Analyst, third edition

Alfalfa is a vigorous and productive crop. Like all crops, however, alfalfa is subject to stand and yield loss from diseases, insect injury, nutrient deficiencies and other environmental stresses. Prompt and accurate diagnosis of a problem can allow early treatment to modify or correct the situation before yields are seriously affected or stands are lost. The purpose of the Alfalfa Analyst is to provide an identification guide to some of the more important alfalfa yield and stand limiters. Please use it to help identify any alfalfa problems you may have. Then secure specific up-to-date management recommendations from your local Extension service. ~ Download the full publication at Alfalfa.org.

Novel Tall Fescue Workshop August 15th

UK Extension Service will be hosting a Novel Tall Fescue Field Day Tuesday, August 15th at John Thomas’s Madison County Farm at 5pm. Program includes:

  • Novel Endophyte Fescue Breeding/Development
  • Establishment
  • Grazing and Hay Management
  • Effects on Beef Cattle Performance
  • Rainfall Simulator and Soil Heath Cover Crops

A meal will be provided. This workshop qualifies as a CAIP cost-share educational program. Call the Madison County Extension Office at 859-623-4072 for registration.