Elaeagnus pungens
(thorny olive)

E. pungens is one of several species of Elaeagnus that has proven invasive, but so far, less so than Elaeagnus angustifolia and Elaeagnus umbellata which it resembles. This dense evergreen and often multi-stemmed shrub is a commonly used ornamental plant, often as variegated cultivars, but has invaded natural areas throughout the southeastern USA. It is very tolerant of wind, salt and shade, but will invade both in open areas and in forests. The fruit is widely consumed by animals and can spread rapidly.

E. pungens is native to China and Japan. It has been introduced to the eastern and southeastern USA were it is widely reported, is noted in New Zealand, and also in some European countries with unconfirmed reports from others. Noting its ornamental value and tolerance to drought and saline conditions, it is likely to be present in many more countries than is indicated, especially in northern Europe, but also around the Mediterranean, western USA, Canada, and elsewhere.

E. pungens is on the Florida and South-East Exotic Plant Pest Council list of invasive plants (USDA-NRCS, 2008), and is also on exotic pest lists for several other states including Alabama, Georgia, South Carolina, Tennessee and Virginia. As a highly valued ornamental it is highly likely to continue to be introduced as any number of the existing or future selected cultivars.

In its native range, E. pungens is often found on open slopes, roadsides or thickets, often near the sea and generally below 1000 m (Flora of China Editorial Committee, 2008). Where introduced and invasive it is also found in scrub and shrublands, and natural forests.

A number of cultivars have been selected and propagated, mostly for variegated foliage. Of these, cv. Maculata and cv. Dicksonii are slower growing variegated forms that also produce good fruit crops, cv. Frederici has especially large fruit 25 mm long, and there are other cultivars including Aurea, Clemson Variegated, Fruitlandii, Gold Rim, Hoksuba Fukurin, Tricolor and Variegata. Frederici is an old cultivar and may have been the original sent to the Netherlands by von Siebold in the mid 1800s (Houtman, 2004). The cultivated hybrid Elaeagnus x ebbingei arose from a cross between E. macrophylla, and pollen from E. pungens and was distributed in 1938 through M Koster and Sons of Boskoop, the Netherlands (Houtman, 2004). Chromosome numbers are not reported.

The scented flowers are hermaphrodite and are pollinated by bees.

Although commonly described as an evergreen, it may be deciduous in some circumstances. In its native range in China it flowers in September-December and fruits in April-June (Flora of China Editorial Committee, 2008). Where invasive in the USA it flowers in November-February and fruits in April-May. It is a nitrogen-fixing species, via an association with actinomycete fungi. After germination it produces dense multiple stems, with short shoots and small leaves that become branched or unbranched thorns 1-4 cm long. In the second year, lateral branches are produced that are followed by flowers in the autumn (Miller, 2003). It is extremely wind resistant and salt resistant (Houtman, 2004).

Associations

It is a nitrogen-fixing species, in association with actinomycete fungi, Frankia spp. (Dommergues et al., 1999), that also nodulate Hippophae and Shepherdia, but not by strains that colonize other actinorhizal plants such as Casuarina and Alnus. Inocula is available for Elaeagnus species, although inoculation may not be necessary since most plants spontaneously nodulate in the nursery or upon planting in the field, and unlike Rhizobium, Frankia survive in the soil for long periods without the presence of host plants. Specific E. pungens strains were identified by Fukumoto et al. (1995).

E. pungensis a species of warm temperate climates, and drought tolerant but can grow in most soils. It prefers a variety of soil types but prefers well-drained soils, and can tolerate infertile and very heavy soils, acid and alkaline conditions, and exposure to salt winds.

There are few records of pests and diseases specifically attacking E. pungens, though further investigation into horticultural diseases affecting ornamental plants would yield additional results. Colletotrichum gloeosporioides [Glomerella cingulata] was first identified as the causal agent of anthracnose in Argentina by Carmona and Wright (1999), and E. pungens was first identified as a new host record for Fusarium solani by Miller (1997).

Environmental

• Amenity
• Ornamental
• Wildlife habitat

Human food and beverage

• Fruits

Ornamental

• Propagation material

E. pungens closely resembles the two other commonly introduced Elaeagnus spp., E. angustifolia and E. umbellata but the latter are generally deciduous and have thin, non-leathery leaves.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Control

There are few reports of specific control methods for E. pungens, however, it could be assumed that cultural, mechanical and chemical treatments effective on the related E. angustifolia and E. umbellata would also be useful on E. pungens, especially those for E. umbellata as it occupies more similar climates and habitats. Control will need monitoring and repeated treatments to achieve success, and because seeds can be dispersed long distances by animals, it should also be eradicated in surrounding areas. Control can likely be achieved through eradication of individuals by hand pulling or spot applications of herbicide.

Cultural control

Hand-pulling of smaller plants would be effective, but as plants will resprout, mechanical or physical means that do not remove the roots are unlikely to be effective. Fire may also be appropriate (Munger, 2003).

Biological control

Zheng et al. (2006) have identified a range of natural enemies of E. pungens from its native range in China, some of which may prove effective as biological control agents.

Chemical control

Several herbicides have been used alone or in combination to provide effective control of E. umbellata and which may also prove effective on E. pungens (see Sather and Eckardt, 2001; Munger, 2003). Dicamba, glyphosate or 2,4-D (but not metsulfuron methyl) have been used as effective foliar-applied herbicides especially on shorter plants. On larger plants, glyphosate, triclopyr and/or 2,4-D are used effectively on regrowth; also basal-bark applications of triclopyr. In an invaded tree plantation in Illinois, USA, triclopyr reduced E. umbellata from 12.5 to 3.9 stems/m², but it is recommended that intensive control efforts focusing on relatively small areas in large well-established populations are only moderately effective and control efforts must be repeated every 5 years to achieve eradication (Edgin and Ebinger, 2001).

29/02/08 Original text by:

Nick Pasiecznik, Consultant, France