Weeds
Ambrosia artemisiifolia L. - Common Ragweed
Systematic position.
Family Asteraceae, genus Ambrosia L.Synonyms.
A. elatior L., A. elata Salisb., A. paniculata Michx., A. longistyllis Nutt., A. media Rydb.Biological group.
Annual late spring weed.Morphology and biology.
Stem 20-200 cm in height, straight, paniculate branchy angular in upper part, with weak or rather strong accumbent spinose pubescence. The root is stalky, penetrates into ground down to 4?. Leaves 4-15 cm in length, dark green from above, almost naked, gray-green from below, with dense spinose pubescence; upper leaves are alternate, almost sedentary, pinnatipartite, lower ones are opposite, petiolar, bipinnatipartite. Flowers bisexual; staminal ones yellow, quinquedentate, collected in semiglobular or bell-shaped calathids of 3-5 mm in diameter, with pedicels of 2-3 mm in length. Calathids are collected in spiciform inflorescences. Pistillate flowers locating by 1-3 and more at the basis of staminal inflorescences and in axillaries of the top leaves, having no perianth, 4-5 cm in length, positioning one by one in accrete ovoid, narrowed and pointed at top envelope. Seeds 2-4 mm in length, ovoid or pear-shaped, triquetrous at base, winged along costulae, green-gray to black-brown, smooth, brilliant, located inside coalesced envelope. All those parts represent the false fruit having large process at top surrounded with 5-8 smaller ones. Shoots appear in May (or in April in the south). In a shoot phase the cotyledonous leaves are short-elliptic, 7 to 13 mm in length, punctate along margins, almost sedentary. The first leaves are pinnatipartite, opposite, pubescent, the following pairs of leaves are pinnatisected. Sub-cotyledonous part thickened, with dirty purple spots, about 10-15 mm in length. Blossoming in August - October. A. artemisiifolia vegetates till late autumn. On the average 1 to 25 thousand seeds are formed on a plant, and the most developed specimens can give to 100 thousand seeds. Fresh seeds almost do not germinate (biological hibernation lasts 5-6 months, and secondary one to 40 years). Shoots appear from seeds plowing-under on depth to 8 cm, but the greatest germination is observed from the soil layer 1 to 4 cm. The vegetative period lasts 150 to 170 days. A. artemisiifolia grows slowly in the beginning, passing 100 to 120 days from occurrence of shoots in spring till budding, and 50 to 60 days from budding till seeds ripening. It is spread by seeds only, with food fodder, seed grain, grain waste, and also with soil stuck to vehicles. Seeds are floating, easily transferring by thawed and rain waters.Distribution.
Northern, Central, and South America, France, Sweden, Switzerland, Belgium, Germany, Hungary, Romania, Poland, Yugoslavia, the Mediterranean, Iran, Japan, China, Australia, Africa, the European part of the CIS, the Caucasus, Central Asia, Primorskii Territory. The potential area of A. artemisiifolia distribution is to latitude 50-55?N. Borders of the area can constantly change, reduce due to control and quarantine measures or increase due acclimatization in new regions and in connection with transfer of seeds of A. artemisiifolia.Ecology.
Plant of short day, thermophilic and rather drought-resistant. A. artemisiifolia is a photophilous plant, therefore dense herbages of perennial grasses and winter cereals developing quickly in spring overtake in growth and development A. artemisiifolia growing slowly in this period, weaken and quite often kill the latter. There are optimum conditions for this weed development in tilling cultures. A. artemisiifolia differs in big viability; in particular, it grows after fivefold cutting. Fresh seeds sprout at light only and insignificantly. Shoots appear at temperature not lower than +6-8°?.Economic significance.
A. artemisiifolia is a quarantine weed, litters practically all field crops; it is especially harmful in vegetable and tilled crops. Having powerful root system, the weed strongly dries up and impoverishes soil. Animals eating Ambrosia produce milk and dairy products with unpleasant smack and smell. Pollen is dangerous to human health, causing sharp forms of pollinosis (autumn hay fever). Control measures include quarantine actions, i.e., prevention of Ambrosia import with grain from quarantine zones to areas free of the weed, regular inspection of agricultural lands, full cleaning of sowing material; land treatment, i.e., stubble shelling with subsequent plowing and surface soil treatment, on tilling crops - pre-emergence harrowing before formation of two pairs of Ambrosia true leaves, and repeated interrow treatments during a vegetative period, repeated mowing before fructification of the weed on nearby sites, correct alternation of cultures in a crop rotation, manual weeding, black fallow; chemical method (herbicides); biological method (Lygogramma suturalis, Tarachidia candefacta, planting perennial cereal grasses for two-three years, treatments with the biological products containing pathogens causing Ambrosia diseases, for example, White Rust.Related References:
Makarova V.A. 1955. Control of weeds. Rostov-na-Donu: Rostovskoe knizhnoe izdatel.stvo. P. 25-26 (in Russian).Maryushkina V.J. 1986. Ambrosia artemisiifolia and bases of its biological control. Kiev: Naukova dumka. 120 p. (in Russian).
Nikitin V.V. 1983. Weed plants in the flora of the USSR. Leningrad: Nauka. P. 358-360 (in Russian).