Desmodium uncinatum (Jacq.) DC.

Silverleaf desmodium (Australia), silverleaf Spanish clover (Kenya).

Large rambling perennial, cylindrical or angular stems densely covered with short, hooked hairs which make the stems adhere to hands, clothing, etc. Leaves trifoliate, with short brown stipules that fall off early, and with a petiole 2 to 7 cm long. Leaflets ovate, 3 to 6 cm long and 1.5 to 3 cm wide, the terminal one on a petiole 5 to 15 mm long. Leaflets are dark green on the upper side with an area of white shiny surface near the central vein, often surrounded by a dark shiny area; lower side is lighter green and uniform in colour, both sides hairy.

Flowers in long paired racemes on stalks up to 1 cm long. Flowers 1 cm long, widely open when flowering, pink becoming bluish after flowering. Sickle-shaped pods easily break transversely at maturity into four to eight segments 4 to 5 mm long and 3 mm wide, light brown at maturity, densely covered with minute hooked hairs so that the segments adhere to clothing. Seed olive-green, triangular-ovate, 3 mm long, 2 mm wide and over 1 mm thick (Bogdan, 1965). It originally came from Deodora, Brazil, and was introduced to Kenya via CSIRO, Australia, as CPI 8990.

Distribution

There are some 350 species of Desmodium in the tropics. D. uncinatum is indigenous to northern Argentina, Brazil and Venezuela and is now widespread in pastures and nursery plots throughout the tropical and subtropical world. It is not common in tropical Brazil, being limited to an area of 1 000 m elevation at about latitude 10°S (Bryan, 1969).

Usually in excess of 900 mm (Bryan, 1969). It did not persist in alluvial soils under a rainfall of 3 000 mm in Fiji.

Horrell (1958) recorded its dry-season production as poor at Serere, Uganda, and Australian experience is similar.

Fairly tolerant of flooding and poor drainage. Performs better than D. intortum in low-lying land with a water-table close to the surface.

It is adapted to a wide range of soils, from sands to clay loams; is productive on red basaltic loams and on gleyed podzolics (Mears et al., 1964) . It is not as successful on sands as D. intortum. Does well on soils with an open texture and not so well on compact heavy clays. Will grow at pH 5.0 (Andrew and Bryan, 1958), do well at pH 5.5 to 6.5 and grow up to pH 7.0. Anderson and Naveh (1968) stated that it was fairly tolerant of soil acidity in Tanzania. Does not tolerate salinity (Andrew and Robins, 1969).

Use a specialized "Desmodium" group Rhizobium. The current Australian inoculum is CB 627. It will cross-inoculate with some other species, e.g. D. intortum and Neonotonia wightii (Diatloff, 1968), but not with others. Peak nodulation occurs 1 month before flowering (Whiteman, 1969).

Seed pods attach to clothing and the coat of animals and spread widely. In suitable soils (e.g. deep latosolic clay loams) it can spread vigorously.

Will perform best in a well-prepared cultivated seed bed, but will establish on roughly cultivated land. Luck (personal communication) has established it at Cooroy, Queensland (lat. 26°S, rainfall 1 400 mm), by treating the existing pasture of Axonopus and Paspalum with Dalapon at 6 kg./ha and sod-seeding D. uncinatum into them.

Sow using a drill, ground broadcasting, aerial seeding or sod-seeding. Some seed cover after sowing is desirable. Very little success has been achieved by oversowing into existing pastures. Sow in early summer at the rate of 2.2 kg./ha, no deeper than 1 cm (Suttie and Ogada, 1967). Whiteman (1969) found that December sowings gave higher nodule weights than later sowings in February and April.

198 000 to 220 000. Percentage of hard seed is low. Seed treatment before planting. Machine-harvested seed usually does not need treatment to break dormancy. For inoculation, use special "Desmodium" culture; the present Australian culture (1970) is CB 627. Lime pelleting stimulates the growth of this species (Norris, 1958).

D. uncinatum responds readily to fertilizers; it performs very poorly without phosphorus, potash, sulphur and molybdenum.

• Calcium: 

A calcium concentration of 1.3 to 1.8 percent of the dry matter of the tops was measured by Andrew and Hegarty (1969). Andrew and Norris (1961) found that D. uncinatum gave 25 percent of its maximum yield in the absence of calcium, maximum yield being at 1 000 kg./ha. D. uncinatum is one of the least efficient at calcium extraction of the tropical legumes and is only slightly better than white clover.

• Copper: 

D. uncinatum is very efficient in extracting copper from the soil, probably because of its deep root system. In the absence of added Cu it gave 60 percent of its maximum yield­the best performance of ten legumes tested. The copper content of the seed is 6.3 ppm (Andrew and Thorne, 1962). Symptoms of copper deficiency are outlined by Andrew (1963): at an early stage of growth (approximately four weeks), deficient plants, particularly the young growth, become pale- to greyish-green in colour, but this is not associated with interveinal chlorosis. With increasing severity-of copper deficiency, the youngest fully expanded leaves show marginal necrosis, especially toward the tip of the leaflets. This is not preceded by interveinal or general chlorosis or by necrotic spotting. Necrotic material tends to curve inwards bilaterally and also from the tip to give a dished effect. Progressively, younger expanding leaflets are pinched and necrotic at their tips and become completely necrotic on expanding fully. With increasing severity of copper deficiency,. the young shoots are damaged, malformed, fail to expand, and finally die. Following the death of the young shoots, secondary growth starts from axillary buds, but this also succumbs. Affected leaves abscise early, leaving stems almost devoid of leaves. No visual symptoms occur on the roots or on the mature stems. Growth habit is changed from a prostrate to a semierect form.

• Phosphorus: 

The critical level for P in the dry matter of the leaves at the immediately preflowering stage is 0.23 percent (Andrew and Robins, 1969a, b). D. uncinatum yielded 53 percent of its maximum yield at the equivalent of 250 kg./ha, the maximum yield being achieved at the equivalent of 1 250 kg./ha of single superphosphate.

• Potash: 

Andrew and Bryan (1958) found that in the field at Beerwah (south-eastern Queensland) visual symptoms of potash deficiency occurred when the potash content was below 0.50 percent of dry matter. Plants fertilized with potash contained 0.91 to 1.14 percent K and showed no deficiency. Andrew and Robins (1969c) found deficiency symptoms when the K content of the dry matter fell below 0.72 percent. Andrew and Pieters (1970a) have presented colour plates showing healthy leaves with 1.64 percent, and leaves from plants showing potash deficiency containing only 0.29 percent K in the dry matter. They record that deficiency commences as necrotic spotting on the mid- to lower leaves of the plant. The spots are initially of pinhead size, irregular in shape, and situated interveinally toward the leaflet margins. They are equally visible on both surfaces of the leaflets, and in the early stages create a halo effect around the entire leaflet margin except in the vicinity of the base; in more advanced stages, necrotic spotting occurs secondarily in the full interveinal tissue. Areas of necrotic spotting are preceded by a light form of chlorosis while the remainder of the leaflet is normal green in colour. Very little spotting occurs on the silver-coloured portion of the leaflet; however, in leaves which are severely affected by deficiency, the silver-coloured portions are not discernible. As the deficiency increases in severity, the areas of necrosis enlarge and coalesce, particularly in the distal marginal areas of the leaflets. At this stage, there is a general chlorosis of affected leaves. Associated with the severe form, the lamina of the leaflet curls inwards and there is some degree of surface puckering.

Fairly tolerant to 2,4-D and, even from 3/2 weeks of age, 1.65 kg. acid equivalent per hectare can be used. Early resistance to Diquat is not as good as with greenleaf desmodium, but at 0.275 kg. of cation per hectare it is safe to spray established swards (Bailey, personal communication) .

It is not very vigorous in the seedling stage. It comes away quickly in the spring, a few weeks earlier than D. intortum and two months earlier than Macroptilium atropurpureum (Whiteman and Lulham, 1970); also gives an earlier response in spring than glycine. Gives vigorous growth in early summer, again in late summer and autumn, then declines.

Whiteman (1969) showed strong nodule development and nitrogen fixation during summer; although a few nodules remained during the winter, they were not active in nitrogen fixation. Hence, the amount of nitrogen fixed is governed by the length of the winter dormant period. Suttie and Moore (1966) showed that when Pennisetum purpureum and Tripsacum laxum were grown with D. uncinatum, their crude protein contents rose by 18 and 51 percent and that of the mixture of grass and legume by 63 and 112 percent respectively. Henzell et al. (1966) found that a stand of D. uncinatum in Queensland provided approximately 110 kg. N/ha/year in the available forage, and that a similar amount was added to the soil. Suttie (1968) estimated that D. uncinatum contributed 160 kg. fertilizer N in association with grasses in Kenya; in Malawi the estimate was 90 kg./ha where the legume comprised 30 percent of the sward. Over a four-year period on a nitrogen-deficient soil, Bryan (1962) obtained a mean yield of N in the plant tops of 176 kg./ha/year in grass/D. uncinatum swards in south-east Queensland. Henzell (1962) in sand cultures found that about 80 percent of the N fixed by D. uncinatum was in the plant tops. Richards and Bevege (1967) found that D. uncinatum had an adverse effect on exotic pines but with native Agathis robusta and Araucaria cunninghamii it trebled the amount of surface litter, doubled tree height and increased dry matter tenfold. Whiteman (1969) has published figures for nitrogen fixed per plant of D. uncinatum during the season.

Whiteman (1969) showed that cutting or grazing to a height of 5 cm caused D. uncinatum to disappear from a Rhodes grass/ Desmodium sward.

D. uncinatum pastures should be well established before grazing is begun. Cattle eat the young terminal shoots, the leaves and finally the stolons if grazing is continued. As new growth arises, the axillary buds should be protected to allow for rapid regrowth. Weed competition should be reduced in the early stages by slashing, and grazing should commence after about 16 weeks. Top growth should be eaten down rapidly and the stock removed for four to eight weeks between grazings.
Whiteman (1969) showed that close grazing by sheep to a 5-cm height eliminated D. uncinatum from Rhodes grass/D. uncinatum pasture in four years. In New South Wales, Australia, D. uncinatum pastures have survived grazing for at least five years (Bryan, 1969) and at Beerwah, Australia, for eight years (Bryan, 1968).

Will recover from moderate fires if it is well established.

Self-fertile; pollination is improved by tripping the flowers. Chromosome number 2n = 22 (Pritchard, personal communication). It has been successfully crossed with D. intortum (Hutton and Gray, 1967).

Whiteman (1969) recorded a dry-matter yield of 4 670 kg./ha/year at Samford, south-east Queensland. Bryan and Shaw (1964) measured 730 kg./ha/year of D. uncinatum in association with grass which yielded 1 650 kg./ha/year over a period of four years in south-east Queensland. In Swaziland, l'Ons (1968) obtained 3 700 kg./ha of dry matter from D. uncinatum; Risopoulos (1966, Zaire) 15 tonnes of dry matter per hectare in a total of five cuttings. Anderson and Naveh (1968) obtained an average yield from five sites in northern Tanzania of 7 020 kg./ha.

Luck (personal communication) recorded some useful hay at Cooroy in south-east Queensland. There does not appear to be any record in the literature of the use of D. uncinatum for silage.

In frost-free environments, some standover feed is retained, but where frosts are severe, losses can be heavy. Whiteman (1969) recorded a 71 percent loss of dry matter over the winter compared with the amount present at the end of summer. The lower leaves tend to drop when the sward becomes dense.

Cattle graze the plant readily and intake is good, even after frosting (Milford, 1967). Leaves and shoots are mainly eaten (Bryan, 1966). Chemical analysis and digestibility. Luck (personal communication) recorded a crude protein content of 15.88 percent for hay from a first cutting (12 September 1967) and 18.75 percent from the second cutting (27 September 1967). Crude fibre percentage was 42 percent. Milford (1967) gives detailed analyses and digestibility figures for D. uncinatum grown on a heavy black clay at Lawes and a sandy soil at Beerwah, at different stages of growth. Mears, Murtagh and Wilson (1964) quote Holder's figure of 54.5 percent digestibility of the crude protein, which was 15.5 percent of the dry matter.

None recorded from grazing. Hutton and Coote (1966) found 3.6 percent tannin in the leaves. Bindon and Lamond (1966) found no toxic symptoms in mice fed on leaves and seeds. Minute amounts of oestrogens have been found in Desmodium species but not enough to cause adverse effects in the grazing animal (Bryan, 1969).

The greatest amount of seed is obtained by mowing when 50 percent of the seed is ripe, allowing it to dry in a swath for 10 to 14 days and then threshing. Wind is a danger to both Desmodium uncinatum and D. intortum with the plants vulnerable to pod shatter while seed heads are standing; they are protected when laid down in a swath and any seed drop will be caught in the crop. Satisfactory yields can be obtained from direct heading in the field. Use a slower drum speed for silverleaf desmodium­just sufficient to thresh the pods without undue seed cracking (about 200 rpm; less than for greenleaf desmodium). Use an adjustable sieve on a fairly close setting or a 2.5 mm punched-hole sieve.

Suttie and Ogada (1967) obtained 330 kg./ha cleaned seed in Kenya. In Queensland, 220-275 kg./ha are harvested.

There is only one cultivar in commercial use­cv. Silverleaf.

It is susceptible to little-leaf (Hutton and Grylls, 1956). In Georgia, United States, Wells and Forbes (1963) found it susceptible to anthracnose caused by Colletotrichum dematium f. truncata.

A robust grower which spreads readily and persists well in pastures, it commences growth early in the spring and has a long growing season. It is adapted to a wide range of soils and fixes nitrogen effectively.

It has lower digestibility and drought tolerance than D. intortum.

Southern boundary about 30°S (Tucuman, Argentina ­ Burkart, 1952) extending to about 19°N at Vera Cruz, Mexico (Bryan, 1969).€

When established, it competes fairly strongly.

It can be severely damaged by the Amnemus weevil (Amnemus quadrituberculatus), the adults of which feed on the foliage in summer and the larvae on the root tissue in winter. In two experiments at Wollongbar, New South Wales, Mears (personal communication) found that the annual dry-matter production of D. uncinatum and D. intortum declined from 4 400 to 6 600 kg./ha to 165 kg./ha over three years. The foliage can be sprayed with dieldrin at 1.1 kg./ha acid equivalent, but residues may be a problem. Whitefringed weevil (Graphognathus leucoloma) causes similar (but less) damage. Leaf-eating beetles, caterpillars and grasshoppers are common in moist climates. DDT at 0.55 kg./ha active ingredient can be sprayed onto the foliage to control leaf-eating caterpillars, but after spraying an interval of 30 days should elapse before the pasture is grazed. A pod-borer attacks the pods in Brazil. Colbran (1963) recorded that the nematodes Meloidogyne javanica and Radopholus similis attack the roots in Queensland, though damage is not severe.

Manganese: Andrew and Hegarty (1969) determined the toxicity threshold value for manganese of D. uncinatum as 1 160 ppm; hence, the plant is fairly tolerant of high manganese levels in the soil. Andrew and Pieters (1970b) recorded a colour photograph of D. uncinatum showing symptoms of toxicity and described the symptoms. The dominant effect of manganese toxicity in this species is chlorosis, which commences on the young shoots and newly expanded leaflets as a light interveinal chlorosis. With increasing severity of toxicity, the degree of chlorosis increases; in the extreme case, young leaves are devoid of chlorophyll upon expanding. Older leaves, which show slight interveinal effects initially, continue to exhibit these through to maturity but the thickness of the leaves increases with age (the young chlorotic leaves are very thin). Associated with the decrease in thickness of the latter are a development of a few irregularly shaped brown spots adjacent to the veins and also a narrow band of leaf marginal necrosis with slight inward curling of the leaflet margins. Restricted growth of the primary shoot gave rise to axillary growth which was affected by toxicity (in the same manner as above), resulting in a bushy habit of growth.

Not high; stock take some time to get used to it.

Short days induce flowering in April to May (Queensland); seed usually sets in June, before winter frosts (Davies and Hutton, 1970). Whiteman and Lulham (1970) found that D. uncinatum flowered in 181 days when planted in October and in 132 days when planted in September in south-east Queensland. It is more shade-tolerant than D. intortum and Macroptilium atropurpureum.

Summer-growing perennial, starting growth early in the spring. Whiteman (1968) found the optimum temperature for growth to be 30/25°C &177; 3°C. It wilts during the high temperatures of summer (Douglas and Luck, 1964). It is fairly cold-tolerant (Huang, 1967). Whiteman and Lulham (1970) put the growth minimum at about 15°C. Ludlow and Wilson (1970) found that D. uncinatum at 20°C yielded 23 percent of the dry matter it yielded at 30°C, 42 percent of the relative growth rate and had 14 percent of the leaf area. It is susceptible to frosts but more tolerant than siratro. Heavy frosts affect the tops, but in warm weather the plant recovers quickly (Huang, 1967). Spring and autumn growth is good.ern Q

Grows from sea level to 2 400 m in Kenya. In Zaire it occurs from 1 500 to 1 800 m. The order of altitude response is silverleaf desmodium, Neonotonia wightii, greenleaf desmodium and siratro. D. uncinatum is much more tolerant of high altitude than other tropical twining legumes (Middleton, personal communication).

Combines well with Setaria spp., Panicum spp., Paspalum spp., Pennisetum clandestinum, Chloris gayana and Pennisetum purpureum. Bryan (1968a, b) showed that at Beerwah in south-east Queensland it invaded pastures of Digitaria decumbens, Chloris gayana and four species of Paspalum.

Seventy percent germination and 94.5 percent purity are the standards required in Queensland.