Plant Pathology
Factsheet

Frequently, stunted and yellowed legumes are thought by growers to be diseased. Close examination often reveals that such "diseased" plants are poorly nodulated. Agronomy colleagues have provided the following information to help growers overcome poor nodulation problems in legumes.

"Emergency" inoculation refers to an inoculant application after the crop has emerged and shows nitrogen deficiency symptoms. A developing crop may need this type of inoculation either because no inoculant was used initially or because soil conditions were too hot and dry, resulting in plants with few or no nodules on the roots. "Emergency" inoculation should not be necessary if you use good quality inoculants and inoculation methods to start with - but there are times when something unforeseen does happen and "emergency" inoculation is neccessary. Two types of inoculants can be used as "emergency" inoculants in an attempt to alleviate these problems:

HUMUS-BASED inoculant can be applied in one of three ways: 1)The humus inoculant is coated onto sand or a similar coarse material just as it would be coated onto the seed. A sticking agent, such as Inoc-U-Stik is used to help inoculant adhere to the carrier. Approximately 75 lbs of carrier with 1 lb of inoculant is broadcast per acre. One-half of the carrier/inoculant combination should be broadcast going in one direction across the field and the other half should be broadcast in the perpendicular direction. This will give more uniform coverage with less streaking. 2) The humus inoculant can be mixed with a carrier such as cottonseed meal. Use 40-50 lbs of meal as the carrier for 1 lb of inoculant and broadcast over 1 acre. 3) A fine slurry can be made and then sprayed. One lb of fine humus inoculant should be well mixed in 40 gal of water. Normal nozzles can be used, although they should be checked and cleaned more often than usual. Nozzles with larger orifaces and continued agitation in the spray tank may be necessary if large acreages are to be sprayed. It will also help to remove the screens from the nozzles.

LIQUID BROTH cultures of Rhizobium inoculants can be ordered from a number of inoculant companies. Be sure to ask for any specific directions which the company may have for it's use. The commercial liquid inoculant should be applied at a rate of 1 gal/10 acres. Dilution rates of 1 gal commercial inoculant in 10-20 gal of water are recommended but this can be varied according to the equipment available. Regular nozzles can be used as long as good coverage is obtained. Applications should be done during the cool times of the day and preferably before a rain. Liquid inoculation is a viable alternative to humus inoculation, as long as the liquid inoculant is treated as a living, heat-sensitive biological material.

IMPORTANT NOTE: The pH of the soil can also be a deterrent to nodulation. In this case "emergency" inoculation would not be a solution as long as the pH is also a problem. If the soil pH is below 6.0, some type of lime application should be used to adjust the pH. Remember that the application of limestone does not immediately raise the soil pH and so a well thought- out liming program is necessary for optimum legume growth on acid soils. Make sure the soil pH is not a problem prior to using emergency inoculant.

This information was provided by Dr. Garry Lacefield, Extension Forage Specialist

IF YOU HAVE ANY QUESTIONS REGARDING "EMERGENCY" INOCULATION CONTACT YOUR COUNTY EXTENSION AGENT OR A UNIVERSITY OF KENTUCKY EXTENSION AGRONOMIST