Propyzamide gets to the root of the problem

November onwards is the usual time of year for the successful use of the residual-acting herbicide propyzamide in winter oilseed rape and this year should be no exception, according to Interfarm who market two propyzamide formulations, Engage and Flomide.

"Good weed control with Flomide or Engage in oilseed rape requires cold soils to provide long term residual persistence and wet conditions so that the herbicide is available to penetrate the soil and reach the weeds' root system. These conditions are usually achieved from November onwards and can last until the end of winter, which is why the label timing for propyzamide lasts until the end of January," says Dr. David Stormonth, Technical Manager for Interfarm UK Ltd.

"Trials over many years show that applications of propyzamide before November can work satisfactorily, providing soils are cold and moist. But this year October was just too warm and dry for optimum performance. The recent rains and cooler temperatures have provided more suitable field conditions and growers should be applying their propyzamide from now on. Soil temperatures of 8˚C or less are optimum for performance. The herbicide still works at lower temperatures, but when it is colder the weed control symptoms take longer to be seen. Frosts are not necessary for propyzamide to work but degradation of propyzamide in the soil is temperature-related, so lower temperatures mean longer persistence," says David.

Propyzamide is only absorbed by roots. As the weed roots grow into the treated soil near the surface, the herbicide is absorbed by the target weed. In the target weed the herbicide starts to interrupt cell division, leading to the typical symptoms of swollen root tips and stem bases.

"This year the variable growth stages of winter rape crops may be causing some growers concern when it comes to applying residual herbicides. Label recommendations for Flomide and Engage state that crops should be at or after the 3 leaf stage before application. But in practical terms there is no need to be concerned as this timing is just a guide as to when the crop root system will be below the herbicide residual layer. Trials have shown that the aerial size and stage of the crop is insignificant. As long as the crop's root system is below 3 cms, then crop selectivity will be good," says Dr. Stormonth.

"The use of propyzamide plays a crucial role in black-grass control. Whilst black-grass has become resistant to a number of herbicides, propyzamide has remained highly effective, even on the most difficult black-grass strains. In recent trials on a variety of resistant weed strains, propyzamide has still achieved total control. Tank mixes with suitable graminicides can speed up the control process by slowing down foliar growth and allowing the propyzamide to get to the root of the problem, stopping weeds in their tracks," says Dr. Stormonth.

Interfarm recommends using the higher label dose rates in order to gain maximum persistence and control of black-grass. For Flomide this is 2.1 litres/ha and for Engage 1.7kg/ha.

Propyzamide is available from Interfarm as Engage (50% WP) (which has been rebranded this year from Propose) and Flomide (400 g/litre SC). Both are recommended in winter oilseed rape, winter beans and a wide range of other crops for the control of cereal volunteers, annual meadow-grass, black-grass, brome, wild-oats, chickweed, bindweed, fat hen, redshank, small nettle, speedwells and black nightshade. Engage and Flomide are compatible with relevant pyrethroid insecticides, graminicides and fungicides including Quell Flo (mancozeb).

For further comment and information, please contact Dr. David Stormonth, Technical Manager, Interfarm UK Ltd. on 01354 741414 or 07818 036506 (mobile) or via e-mail david.stormonth@interfarm.co.uk