Wild Radish Ecology, Population Dynamics and Dispersal:
Seedlings germinate soon after the first rains and quickly produce a large flat rosette of leaves that shade neighbouring seedlings. Flowering stems emerge from the centre of the rosette and rapidly elongate and branch to shade companion crops. A substantial taproot provides reserves to withstand periods of moisture stress, grazing or recovery from herbicide applications.

The plasticity of wild radish's life cycle, its tolerance of a wide range of conditions for germination and growth coupled with high levels seed production and varying dormancy make the population dynamics of this plant variable and difficult to manage.

The main source of spread is by contamination of agricultural seeds and produce. A survey in Victoria and southern NSW showed that 8% of wheat seed sown was contaminated with Wild Radish. The stems are brittle when dry and are blown in the wind carrying seed. The pod segments float, so water may be a significant dispersal agent in some situations. The Wild Radish "bush" and branches often entangle in machinery and vehicles spreading seed considerable distances. Stock eat and pass the seed in a viable form.

Around one sixteenth of the seasonal emergence of wild radish occurs in early autumn, three quarters emerges in the late autumn/early winter period and the remaining three sixteenths in late winter/spring. This pattern has been consistent in studies done in the Wimmera, NE Victoria and WA (Amor, 1985; Piggin et al, 1978; 773; 789). There is usually an emergence of seedlings after each rainfall event. Seedling densities of 300-800/m2 are common in cultivated situations for the main cohort. 30-40% of these seedlings normally die. In untreated continuous wheat or lupin/wheat rotations, wild radish builds up to 1,500-2,000 plants/m2 and has an annual seed set ranging from 1,500-16,000 seeds/m2. Where seed set is eliminated by herbicides Wild Radish populations dropped to about a quarter of their original levels (from 400 to 100/m2) over a 3-5 year period. 898 estimates that about 30% of the Wild Radish seed bank is lost each year in grass pastures with the half life of the seed bank about 1.5-2 years. 89 reports similar results in cereal cropping situations in WA. However, 899 found variable rates of decline depending on the age of the seed bank and the cultivation history.

900 has a model of spread for agricultural situations.

Competition between wild radish and barley for light increases rapidly up to 50 or 60 days after emergence reducing incident light for barley by 50% 798.

In Canola, Wild Radish seed production peaks at around 20,000-32,000/m2 (Moore,2002, 790

Where there are large quantities of seed in the soil, significant populations of wild radish will establish for at least 5 years even with very effective control programs. Some seed may remain viable for 20 years.

The food reserves of the taproot are used to survive poor growing conditions and to recover from control techniques such as herbicides, slashing, grazing and defoliation.

Seed is spread in manure 894.

Deer preferentially graze Wild Radish 901.

Leaf damage by Cabbage White Butterfly or defoliation of up to 50% has little effect on seed production 791.

902 showed insecticides had little effect on Wild Radish seed production but molluscicides increased it 2.6 times.

Crop rotations:

In unsprayed continuous wheat or wheat/lupin rotations radish built up to around 1500 plants/m2. In continuous wheat with 2 sprays per year (bromoxynil/MCPA followed by 2,4-D) populations levelled at about 100 plants/m2. In a wheat/lupin rotation with the above sprays in wheat and simazine in lupins the population gyrated between 200 and 1400 plants/m2 (Code et al, 1987). Populations decline in grass pasture with time but are still present after 20 years 898.

Cultivation:

Shallow cultivation in autumn encourages germination 903 904.

In the work of Piggin et al (1978), mould board ploughing resulted in 90 plants/m2, disc ploughing to 5 cm resulted in 323 plants/m2, disc ploughing to 10 cm resulted in 490 plants/m2 and direct drilling resulted in 207 plants/m2. In contrast, Code and Donaldson had 202 plants/m2 in direct drilled and around 100 plants/m2 in cultivated plots. Their best treatment was cultivation to 8 cm in the first two years then direct drilling in the second 2 years which left only 1 plant/m2 compared to 3-6 plants/m2 in continuously cultivated or direct drilled areas.

Mouldboard ploughing in Victoria greatly reduced Wild Radish densities. 905.

Tined cultivation usually increases Wild Radish prevalence 906.

In Spain, Wild Radish tends to build up in cultivated crops and decreases in minimum tilled crops 907.

Slashing:

This is usually ineffective because the Wild Radish regrows and sets seed below the height of cutting. Repeated slashings are required for partial control.

Swathing:

This is useful for reducing the effects of contamination by green material but has little effect on seed set or control. It may be useful to help collect seed but most harvesters need modification to be effective. Good yield responses in Lupins where swathing results in less delays to harvest were found by 908, 909.

Crop Topping:

2,4-D ester at 750 mL/ha (or 2,4-D amine at 1400 mL/ha) can be applied at the firm dough stage of the cereal (about 14 days before harvest) to turn green Wild Radish down so the crop may be harvested. It can reduce the viability of some of the Wild Radish seed also but is not an effective control technique.

Reglone at 2-3 L/ha can be used to desiccate green Wild Radish and other green weeds present at the time of harvest. It is applied at the firm - hard dough stage of the cereal (about 7-14 days before harvest). It is usually applied by aircraft. This treatment has little effect on the level of Wild Radish seed contamination of the cereal sample and is used mainly to reduce grain moisture content and harvest problems.

Crop topping is most useful for controlling Wild Radish that has emerged after the application of other treatments earlier in the season and is rarely effective by itself. Late applications of Logran, at 10-15 g/ha plus spray oil, just prior to flowering of cereals is far more effective.

910 has a model comparing crop topping with early post emergence control.

Burning:

This is most effective in heavy stubble when most of the seed is still on the plant rather than laying on the ground.

Nutrition

Long term nitrogen and calcium fertilization increases Wild Radish prevalence 911