Galinsoga parviflora
(gallant soldier)

G. parviflora is a cosmopolitan fast-growing annual herb with the capacity to invade agricultural and other disturbed areas in most temperate and subtropical regions of the world (Holm et al., 1979). It is highly competitive and can spread quickly, often being the dominant species in a field. G. parviflora generates considerable economic impact on crop systems, greenhouses, gardens and nurseries. It is listed as an invasive and noxious weed in North America, Europe, Asia, Australia, and on islands in the Pacific Ocean (see Distribution Table for details). 

G. parviflora is an American weed, and its centre of origin is considered to be the mountainous area of Mesoamerica (i.e., Mexico and Central America; Vibrans, 2009). Because this species was first described from material collected in South America (a cultivated plant from Peru), it has been erroneously cited as native to this part of the world (Vibrans, 2009). Currently, G. parviflora is a cosmopolitan species widely distributed in North America, Europe, Africa, Asia and Australasia. It is considered a weed in at least 40 countries, mostly temperate and sub-tropical but also at higher altitudes in many tropical countries (Holm et al., 1979). 

Genetics

The chromosome number reported for G. parviflora is 2n=16 (Canne, 1983).

Physiology and Phenology

G. parviflora exhibits an early summer flush characterized by high peaks (Toit and Cout-de-Billot, 1991). Germination was observed from late March until early November, during which 3-4 generations took place. One plant produced 13,400 capitula in its lifetime and produced 400,000 seeds. Stem height and leaf area increased more in summer-germinating plants than plants germinating in the spring or autumn, growth rate of G. parviflora being dependent on season of germination.

Germination of exposed seeds is highest in the first year, suggesting that many seeds either germinate or die before the second year. Within two years all exposed seeds are dead. Laboratory tests confirm that exposed seeds lose viability more rapidly than buried seeds, and that the deeper the seeds are buried, the better they retain viability (Schwerzel et al., 1979).

Longevity

G. parviflora is an annual weed with a short life cycle, often less than 40 days, which can occur in the autumn, spring or summer in temperate areas and at any time of year in the tropics.

Population Size and Structure

Galinsoga parviflora exhibits density-dependent mortality, which increases at a higher nitrogen level. At lower densities the plant grows more vigorously in a mixture than compared to pure stands, but at higher densities it was completely suppressed by G. quadriradiata (Rai and Tripathi, 1986).

Nutrition

Shoot extracts of G .parviflora increased soil pH and reduced aluminium down to a depth of 20 cm when applied to the soil surface as a lime top dressing and leached with 3 pore volumes of deionised water (Meda et al., 2002).

Environmental Requirements

Sun species, among them G. parviflora, were more competitive with shade species at high light intensities, whereas at low light, the competitive ability depended on the initial weight of the plant (Corre, 1984). Rai and Tripathi (1986) showed that G. parviflora was very sensitive to shading.

G. parviflora is a C3 plant (Kissmann and Groth, 1993). High temperature seems to enhance growth, flowering and maturity. It is inferred that Galinsoga belongs to a type of weed of which the seed is light sensitive (Usami, 1976). Rate of germination is stimulated by alternating temperatures, with the highest rate at a day temperature of 30°C and a night temperature of 20°C, with a 16-hour photoperiod and 11,000 lux. The germination of irradiated seeds in the laboratory decreases as the red:far-red light ratio decreases in the range from 2 to 0.04 (Zweep et al., 1990).

Many of the natural enemies mentioned here are polyphagous species. Batra (1979) comments that host-specific natural enemies should be sought in the area of origin of the weed in the mountainous regions of Latin America.

Fungi: G. parviflora is a host to Plasmopara yunnannensis (Tao and Qin, 1987) and seeds have been found bearing more than 15 fungal species (among them Alternaria, Ascochyta, Penicillum, Phoma, Drechslera, Trichoderma, Fusarium and Botrytis sp.) (Lorenzi, 1986; Prete et al., 1986). Ten fungal species were identified infecting G. ciliata and G. parviflora, the most notable being Glomerella cingulata, the causal agent of anthracnose in G. parviflora (Gasich, 1997).

Viruses: Tomato spotted mosaic wilt virus on G. parviflora plants growing in nearby fields of vegetable crops has been reported in Belgium (Gofflot and Verhoyen, 1990) and Argentina (Gracia and Feldman, 1989). Cucumber mosaic virus was isolated in G. parviflora plants near a celery and lettuce field in the USA (Bruckart and Lorbeer, 1976). G. parviflora was reported as a new host of Turnip mosaic virus in Zimbabwe. Myzus persicae, Brevicoryne brassicae and Aphis fabae transmitted the virus from infected to healthy cabbage plants (Chivasa et al., 2002). Tomato spotted wilt virus infection was detected in the Czech Republic where the main vector Frankliniella occidentalis was also present (Mertelik and Mokra, 1998). A virus disease of sunflower caused by Sunflower mosaic virus had a very narrow host range, infecting only one weed host, G parviflora (Nagaraju et al., 1997).

Mites: several mite species have been found on G. parviflora in the USA (Batra, 1979).

Insects: Agrotis ipsilon, a serious pest of maize, sorghum, soybean, cabbage and rape crops in Brazil, develops its first-instar larvae in G. parviflora plants (Link and Severo-Pedrolo, 1987). Other noctuids, such as Heliothis, Plutella and Pieris spp., feed on G. parviflora (Rai and Tripathi, 1985). Thrips tabaci, the vector of tomato spotted wilt tospovirus, is usually found in G. parviflora plants in tobacco fields of Poland (Wegorek and Lipa, 1979). The host plant for the larvae of Dioxyna bidentis or Paroxyna bidentis is G. parviflora in southern Norway (Greve, 2001). G. parviflora was reported as a supplementary or alternative food for Arion lusitianicus (Kozlowski and Kozlowska, 2000).

In an extensive survey in the USA, 122 insect species were found on G. parviflora plants, among them 22 crop pests, including three virus vectors (Batra, 1979). Orthezia insignis, a serious eucalyptus pest in India, may be found feeding on G. parviflora (Srikanth et al., 1988).

Nematodes: species of the genus Meloidogyne (arenaria, thamesi, hapla, javanica and schachtii) and Globodera rostochiensis, that produce serious root damage in Hungary, Brazil (Lordello et al., 1988) and the Philippines (Zorrilla and Davide, 1983), have been found in G. parviflora.

Bacteria: results indicated that G. parviflora can maintain Ralstonia solanacearum (race 3 biovar) in the absence of potato as a source of infection in the following years (Barchend and Schmidt, 2002).

Parasitized aphids were observed on G. parviflora in Chile (Russo et al., 2000).

Human food and beverage

• Emergency (famine) food
• Flour/starch
• Food additive
• Spices and culinary herbs
• Vegetable

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical
• Traditional/folklore

G. parviflora is commonly confused with G. ciliata. The latter differs in being much more hairy, with many glandular hairs 0.5 mm or longer on the peduncles, whereas G. parviflora has only few, less than 0.5 mm long. Also G. ciliata has aristate (long-pointed) pappus-scales on the seeds; those of G. parviflora are not long pointed. G. ciliata may also be more shade-tolerant than G. parviflora (Rai and Tripathi, 1986b).

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.

22/04/14 Updated by:

Julissa Rojas-Sandoval, Department of Botany-Smithsonian NMNH, Washington DC, USA

Pedro Acevedo-Rodríguez, Department of Botany-Smithsonian NMNH, Washington DC, USA