Imidazolinone Tolerant Maize

Zea mays L.

Synonyms - None.

Family: Poaceae.

Names:

Maize

Other Names:

Corn
Indian Corn

Summary:

An erect large leaved annual grass crop with male tassels on top and female silks lower that form seed cobs.

Description:

Cotyledons:

One

First leaves:

Single.

Leaves:

Rolled in the bud. In 2 opposite rows. Usually have some hairs.
Blade - 25-100 mm wide. Edges often wavy. 250-500 mm long. Flat when mature. Obvious mid-rib.
Ligule - Membranous. 2-4 mm high. Fine hairs.
Auricles - None.

Stems:

Solid, up to 4000 mm tall.

Flower head:

Separate male (tassel) and female heads on the same plant. Male, spike-like tassel, 150-300 mm long at the end of the stem. Female head is a cob, 100-300 mm long on a thickened woody or spongy axis, single in the axils of the lower leaves.

Flowers:

Female - 8-13 mm long. 8-30 rows of spikelets arranged in a cob and enclosed by numerous "leaves". Spikelets in pairs with no stalks. Grain pops out from the spikelet soon after pollination. Each spikelet has one fertile and one sterile floret.
Spikelets - Male - 8-14 mm long. 2 flowered. In pairs on one side of the axis. One is on a short stalk and the other nearly stalkless.
Florets - 2
Glumes - Male - 2 about the same size. Membranous. Lance shaped. Tapering pointed tip. 7-11 nerved. Hairy near the tip.
Female - Broad. Fleshy near the base. Rounded or with a shallow notch at the tip. 7-11 nerved. Hairy near the tip. Tip flat or with 2 lobes.
Palea - 2. Broad. Very thin and translucent. About the same size as the lemmas.
Lemma - 2. Broad. Very thin and translucent. 2 about the same size as the glumes. 3-5 nerved. Hairy at the tips. Remain as chaff on the cob after the seed is shed.
Styles - Long, up to 150 mm long and filamentous, often referred to as silks that form a mass of silky threads that hang out of the enclosing leaves or husks.
Stamens -
Anthers -5-6 mm long. 1.5 mm wide.

Fruit:

Cob.

Seeds:

Grain. Egg shaped. Flattened. Convex indentation at the top. Variable colour from yellow to reddish black. Up to 15 mm long and 5-10 mm wide. 2000-5500 seeds per kg.

Roots:

Prop roots grow from stem nodes near the base.

Key Characters:

Grain on a cob.

Biology:

Life cycle:

Annual. Pollen falls or is blown from the terminal male "tassel" flowers to the female "cob" flowers in the leaf axils below. Cobs are harvested 2-3 weeks after pollination when the kernels exude a milky juice on squeezing.

Physiology:

C4 plant.
Frost sensitive but will tolerate frost up to the 2-3 leaf stage. Requires 65-120 frost free days from emergence to harvest.
Optimum temperature for growth is 21-300C.
Pollination often fails when air temperature rise above 350C.
25 kg N required for each tonne of grain.
Intolerant of grazing and cutting.
Moderately sensitive to moisture stress.

Reproduction:

By seed.

Flowering times:

Summer.

Seed Biology and Germination:

Optimum temperature for germination is 21-270C. Seed won't germinate when soil temperatures are below 100C.
Little dormancy.

Vegetative Propagules:

None.

Hybrids:

Many have been bred to improve quality and yield.
Clearfield varieties.
Hycorn, 62IT, 53IT, PAC 338, Pioneer 3391IR.

Allelopathy:

Population Dynamics and Dispersal:

Spread mainly by intentional planting. Generally short lived and rarely naturalised. Most infestations are a result of grain from a previous crop.

Origin and History:

Tropical America.
Wild forms cultivated in America from pre-historic times.

Distribution:

ACT, NSW, NT, QLD, SA, TAS, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Temperate. Mediterranean. Sub tropical. In regions with good rainfall.

Soil:

Sandy loams to clay loams over a wide range of pH with an optimum of 5.5-7.
Grows well on rich alluvial soils.

Plant Associations:

Agricultural species.

Significance:

Beneficial:

Staple human food in Latin America and parts of Africa.
Staple stock feed in the USA as grain or silage.
Processed to produce industrial chemicals, starch, fuel from cobs and grain, alcohol, beverages, oils, syrups, adhesives paper (from spathes) and breakfast foods such as semolina and polenta.
Vegetable. Cobs eaten fresh, cooked, canned or frozen.
Honey plant for pollen.
Ornamental.

Detrimental:

It can be a weed of following crops.

Toxicity:

Occasionally toxic due to high levels of hydrocyanic acids or glycosides in the leaves.
Corn stalk poisoning due to nitrite toxicity.
May accumulate toxic amounts of nitrate under certain conditions or on some soils.
Moulds on the grain may cause poisoning.
Very high levels of nitrate may accumulate in the lower portions of stalks, within 150-200 mm of the ground. Nitrate levels fall during grain formation.
Toxic amount of gaseous oxides of Nitrogen may occur in silage. This may kill both animals and people working in silos. It is known as "silo-fillers disease" in man and "Pulmonary Adenomatosis" in ruminants.
Nitrosos may occur in ruminants.

Symptoms:

Silo fillers disease - broncho-pneumonia in mild cases. In acute cases, pulmonary oedema and death within a few days of exposure. Usually there is coughing and respiratory distress for 2-3 weeks then chills, difficulty breathing, dry coughing, incapacitation, cyanosis then death or spontaneous recovery.
Pulmonary Adenomatosis - Pulmonary oedema and emphysema, increased rate and depth of breathing, grunting during exhalation and a thick, brown, mucous discharge from the nostrils.
Nitrosos - excitement or depression and extensive internal haemorrhaging.
Mouldy corn poisoning - Genital hypertrophy, infection haemorrhaging and liver damage in pigs and haemorrhagic syndrome in cattle.

Treatment:

If coughing occurs after working with silage see a doctor immediately.
Don't feed mouldy grain to stock.
Avoid including lower stems in chopped stalk rations.
Test rations for nitrates, nitrites and nitrogen dioxide before feeding.

Legislation:

None.

Management and Control:

Grazing and cultivation provide good control. Usually disappears after a year or two because it has no effective seed dispersal method.
It does not tolerate weed competition.

Thresholds:

Eradication strategies:

None required or graze.

Herbicide resistance:

Tolerant to triazine herbicides.
Herbicide tolerant varieties have been produced.

Biological Control:

No planed bio control because of its commercial importance.
The main pests are Aphids, Corn Earworm (Helicoverpa spp.), Cutworms, African Black Beetle, Wireworms, Monolepta Beetle and Armyworm.
Diseases include Charcoal Stalk Rot, Fusarium Stalk Rot, Head Smut, Leaf Rust, Northern or Turcica Leaf Blight, Southern or Maydis Leaf Blight and Sugar Cane Mosaic Virus.

Related plants:

Dent Maize (Zea mays cv. Indentata)
Popcorn (Zea Mays convar. microsperma)
Sweetcorn (Zea mays var. saccharata or rugosa)

Plants of similar appearance:

References:

Beadle et al (1982).

Harden (1993) Vol.4, P427

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P355.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne). P292.

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #1295.1.

Reid, R.L. (1990) The Manual of Australian Agriculture. (Butterworths, Sydney). P79-83, 255. Diagrams.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.