Tim O’Donovan of Teagasc looks at the optionsavailable to farmers
WITH the sowing of winter cereals virtually finished, except after root or maize crops, most growers will now be turning their attention to weed and BYDV control. Compared to the last few autumns, most crops have been well established into good seedbeds and conditions were good enough for rolling.
Knowing your targets is an important part of economic weed control. Knowing the most competitive weeds, when they germinate and when they become competitive is paramount to successful control. And as we move towards enforced integrated pest management (IPM) we must use this knowledge to develop alternative control strategies to minimise our problems.
Table 1 gives the relative competitiveness of a range of common weeds in winter wheat. This shows that cleavers and wild oats are the most competitive weeds and the biggest yield robbers. Other weeds, such as groundsel and fumitory, are much less competitive and low levels of these in a particular crop are not likely to cause economic yield loss. However, leaving these weeds slip through the herbicide net year after year will undoubtedly increase their numbers to levels that will make control essential.
Early post-emergence herbicide application tank mixed with aphicide at the 2-3 leaf stage has served Irish growers well and will be the main option chosen by growers this season. In trials carried out by Bryan Mitchell in Oak Park, this timing also provides the best chance of successfully using reduced rates, especially when crops are competitive. The small percentage of crops yet to be sown in November/December will probably receive herbicide in spring.
IPU is used mainly for grass weed control but it is only effective up to the early tillering stage. It will also control charlock, chickweed, groundsel, mayweeds, marigold and shepherds purse. Persistency can be an issue with early-sown crops in wet seasons. It is also used to help with wild oat and volunteer oat control.
Cougar (DFF & IPU) has been at the heart of weed control in winter wheat and barley for many years. It controls a wide range of the normal weeds but is weak on fumitory and poppy and will need to be used at a high rate for cleavers. Cougar is now being withdrawn from the market due to the availability of both actives individually.
Diflanil 500 / Hurricane (DFF) are generic products containing straight DFF. On its own DFF is primarily a broad-leaved herbicide so it needs to be used in conjunction with other products such as IPU or Defy to provide grass weed control.
Stomp Aqua (PDM) is a new formulation of the well-proven Stomp. It is normally mixed at 2.2 - 2.9 l/ha with IPU (1.5-2.0 l/ha). (You need 1000-1100g PDM for good broad-spectrum weed activity.) PDM is available as generic products but take note that different products are formulated at different concentrations.
Flight contains PDM and Picolinafen. The product works best when applied pre-emergence or early post-emergence. Many growers used Flight at 3.0 l/ha + 1.5 l/ha IPU at the two-leaf stage. The addition of IPU is warranted where high levels of annual meadow grass are expected or already emerged. Flight has better activity on cleavers, fumitory and poppy than DFF mixtures and better residual grass activity than IPU.
Firebird is based on DFF and Flufenacet. It shows good residual activity on grass weeds, especially annual meadowgrass. However, it must be used early for successful control of BLW. Application must be complete by the end of December. The full rate is 0.3 l/ha.
Defy contains Prosulfocarb and is applied at 2.0 l/ha, normally in conjunction with 0.1 l/ha of Diflanil (DFF). It has mainly residual activity and needs to be applied pre-emerge on winter barley and by the time the first tiller appears on wheat. It is good on annual meadowgrass and very active against cleavers and poppy.
Bacara is based on the active Flurtamone in combination with DFF for use on winter wheat, oats and barley. It is mainly used on oats. Target weeds include chickweed, mayweeds, speedwells, red deadnettle, field pansy and annual meadowgrass. Apply pre-emerge or early post-emerge of the crop from one-leaf to the end of December. However, in winter oats it is best to wait until the crop is ’hardened off’ and the weather is free from frost so as to minimise bleaching. Rate is 0.5-1.0 l/ha. Avoid overlapping. Best results achieved when the weeds are small. Some bleaching may occur after application, from which the crop will normally recover.
Alister is a mixture of DFF and reduced rates of the two sulfonylurea actives found in Pacifica; mesosulfuron and iodosulfuron. It is only for use on winter wheat as a post-emergence herbicide from GS 13 (three-leaf stage) up to GS 30. The full rate is 1.0 l/ha but is generally used at 0.75 l/ha.
At 0.75 l/ha it will supply the same amount of DFF as 1.1 l/ha of Cougar. It claims the same broad-leaved control as Cougar but with increased grass weed control, especially annual meadow grass.
SumiMax is based on a new active called flumioxazin. It is only for use on winter wheat at pre or post-emergence (up to GS 15). It has good activity on both grasses and on difficult broad-leaved weeds. Strong on cleavers.
Winter oats is generally very competitive against weeds due to its large canopy and also as its roots release chemicals which reduce weed growth --- known as allelopathy. Growers generally try to cut their spend of herbicides in oats but if cleavers, fumitory or annual meadow grass are poorly controlled then weed control in the following wheat crop will be difficult. Bacara and Lexus Class are the only grass weed control tools while there are many broad-leaved weed options (see table 2).