Seminole Crop E News

Agricultural News for Farmers and Agribusiness in SW Georgia

Question of the Week – Sunn Hemp

Posted by romeethredge on December 17, 2015

Last week I had a photo of a plant I wanted you to identify. It is Sunn Hemp, Crotalaria juncea, not to be confused with Showy crotalaria, Crotalaria spectablis.

The old Showy Crotalaria was planted here many years ago as a rotation crop, it is a legume. I believe the shade tobacco growers used it some.  The only problem is that it is poisonous to livestock. I still often see some volunteer plants growing in many locations. Here’s a link to a post I made about it a while back.


Sunn Hemp is used in some cover crop mixes for summer use. University of Florida has some useful information about it in their brochures, Management of Nematodes and Soil Fertility with Sunn Hemp Cover Crop1and Sunn Hemp for a Cover CropFullscreen capture 12142015 115654 AM

 Here’s some excerpts.

“Sunn Hemp is a rapidly growing crop that is used for fiber production in India and Pakistan. It is most popular as a green manure in many tropical and subtropical areas in the world as an organic nitrogen source. Recently, there is a growing interest in rotating sunn hemp with cotton in the southern United States and in using sunn hemp as a summer cover crop in Florida and other southeastern states. Sunn hemp suppresses weeds, slows soil erosion, and reduces root-knot nematode populations . When plowed under at early bloom stage, nitrogen recovery is the highest. Under optimum growing conditions such as in Hawaii, ‘Tropic Sun’ sunn hemp can produce 134 to 147 lb/acre of nitrogen (N) and 3 tons/acre air-dry organic matter at 60 days of growth at 40 kg seed/ha (Rotar and Joy, 1983).

In northern Florida, sunn hemp is usually grown in the summer and can produce 2.4 tons/acre of dry biomass and 98 to 125 lb N/acre (Marshall, 2002). In southwestern Alabama, plants grown for 9 to 12 weeks produced 2.6 tons/acre dry-matter and 112 lb N/acre (Reeves et al., 1996). Although in the tropics, ‘Tropic Sun’ grows and produces seed year-round at elevations of 0 to 900 ft, and in summer up to 1800 ft, sunn hemp does not set seed well in Florida (R. Gallaher, personal communication). Sunn hemp is usually planted in summer in Florida (Rotar and Joy, 1983), but it is suitable as a green manure crop as far north as Maryland.

Suppression of plant-parasitic nematodes by Crotalaria spp. has been known for decades. Godfrey (1928) noted that sunn hemp had few root galls from infection with root-knot nematodes. Most of the plant-parasitic nematodes suppressed by Crotalaria are sedentary endoparasitic nematodes, which are nematodes that remain and feed in one place within the root system. These include root-knot, soybean cyst  and reniform  nematodes (Wang et al., 2002). Some migratory nematodes such as sting , stubby root , dagger, and burrowing nematodes were also suppressed by other plants in the genus Crotalaria…”

This week I have another question for you. What is this insect and is it good to have on the farm or not?


2 Responses to “Question of the Week – Sunn Hemp”

  1. Tom W. Smith said

    Looks like a lace wing, one of the Neuropterans that is a beneficial insect in our row crops.

  2. Scott said

    Green lace wing, the larvae are predaceous on many soft-bodied insect pests (aphids).

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