Tillage Farm Management Notes: 05/05/2009

Herbicide supplement

Michael Hennessy

Weed control in spring crops

Cereal growers across the length and breath of the country are optimistic by nature because if not few would have sown crops this year given the current price for grain. Good yields are required to break even and high yields are needed to turn a profit from all spring cereal crops.

Production costs must be kept to a minimum. Small nips and tucks in the overall spend will individually not appear to add up to much but collectively add quite a bit to the bottom line. Savings of €10-15 per hectare are possible with a well timed weed control strategy versus an ad-hoc approach.

The range of herbicides available this year is changed somewhat from last year. The gradual change from the familiar products like straight Ally and Cameo, etc. is more to do with the active ingredients of these herbicides now available in generic form as it is with the changing weed spectrum in fields.

The changes away from traditional packs (Ally, Cameo, etc.) should be embraced by growers as the increased active ingredients contained in each of the newer packs (Ally Max, Cameo Max, etc.) can represent excellent value for money if used in the correct way. Understanding the chemical, the weed and its growth pattern all contribute to successful weed control at a reasonable price.

Successful weed control

Crop density, sowing date and general growing conditions all impact on the success of weed control in cereals. Fundamentals such as rotation, weed identification and growing conditions around the spraying date remain at the heart of any weed control strategy. Timing of weed control and product selection is very important especially when using reduced rates. In Oak Park trials, reduced rates gave effective weed control when applied early (early tillering , GS 15) rather than late (flag leaf, GS 39).

The competitiveness of weeds varies considerably and this will influence the decisions as to the type of herbicide chosen for the field. Charlock is very competitive in spring cereals where as pansy or annual meadow grass are not very competitive. Identification of weeds is possible from a very early stage (cotyledon stage) and should be used in conjunction with the field history of difficult to control weeds. Identify the most numerous weeds in the field and then choose a herbicide by checking the susceptibility tables for the different herbicides. It is as important to identify weeds that the chosen herbicide is not good at controlling as it is often necessary to add another herbicide (CMPP, MCPA etc.) to control those weeds. In most cases the addition of a hormone type spray will give a better overall weed control.

In some cases a follow-up herbicide may be necessary if late germinating weeds come through such as volunteer potatoes, thistle, sow thistle, etc…

Apply herbicides early, at the 5 leaf stage to early tillering, for successful weed control in spring cereals.

Herbicide Choice

Sulfonylurea’s are the main products used for weed control but hormones are still the only products available for undersown crops. Cleavers, volunteer potatoes, thistles and wild oats will need particular attention in all crops.

Increasingly, growers have little choice but to switch away from the standard mix containing Ally. Mixtures of more than one Sulfonylurea (SU) type herbicide are now available with less and less straight products on the market (see table 2). These SU mixture (Ally Max, Cameo Max, Calibre Max, Harmony Max, etc ) products contain a higher total amount of SU than the straight products and when used at reduced rates (when conditions and weeds allow) can represent value for money. The mixing of these actives also brings increased control to a broader range of weeds than using one SU product on its own. Products like Ally Max SX and BiPlay SX are now becoming the standard treatment in many spring crops and offer better insurance for fields where you do not know the weed history.

All the SU products have different strengths and weaknesses in terms of the control of weeds (table 1). Generally SU should be mixed with a hormone type product (CMPP-P, HBN, fluroxypyr or Dicamba) or Galaxy to achieve full control of a wide variety of weeds and to prevent weed resistance.

Table 1 Selected Weeds and Herbicide Effectiveness

	ALLY MAX	BIPLAY	HARMONY M MAX	CMPP	GALAXY	HBN
CHICKWEED	S	S	S	S	S	MS
FAT HEN	MS	MS	S	S	S	S
FUMITORY	MR	MS	MR	MS	MS	S
IVY LEAVED SPEEDWELL	R	MS	S	MS	-	S
KNOTGRASS	MS	S	S	MR	S	S
PANSY	MS	MS	S	R	-	S
R=RESISTANT     S=SUSCEPTIBLE    M=MODERATE

All products have a latest time of application. Application after this timing may result in damage to the plants developing grain sites. Generally all weed control in cereals should be completed before the crop starts stem extension.

Timing of herbicides for spring wheat & barley

Crop Stage	Herbicides
2-3 leaves to flag leaf	Empire (Metsulfuron), Ally Max, Thor (Tribenuron), Cameo Max, Calibre Max, Harmony Max, BiPlay, Finish/Presite, Eagle, Boxer. Starane 2/Binder/Hurler/Reaper/Tomahawk
2-3 leaves to second node	Ally Express, Hussar, Oxytril CM, Stellox , Hobane
2-5 leaves to first node	CMPP, Foundation, MCPA, Undersown products

N. B.
Restricted range of herbicides for use on oats: - Herbicides include Empire, Ally Express, Ally Max, BiPlay, Finish/Presite, Galaxy, Boxer, Oxytril CM, Stellox, Hobane, CMPP, MCPA, Eagle, Foundation, Hurler, Starane 2, Reaper and Tomahawk,

Tank mixing Ally Max or BiPlay plus CMPP is very popular. CMPP will give improved control of Fumitory, Cleavers, Fat hen and Orache. Thor (Cameo) is particularly useful where Fumitory, Fat hen and Orache are numerous. A non-ionic wetter, e.g. Agral, Activator 90 should be added for these weeds where CMPP is not added. Thor can also gives useful control of Creeping Thistles and Annual nettles where emerged. Cameo Max will give better control of these weeds especially if advanced. Fluroxypyr (Starane 2, Binder, Hurler, Reaper or Tomahawk) will be the main active ingredient used for volunteer potato control. Use alone at 1.5-2.0 litres/ha when volunteer potatoes are emerged to 15-20 cm heights. Alternatively GEX 353 (Calibre +Starane in a dual pack). This gives very good control of volunteer potatoes including tuber cracking.

Wild oat control

Wild oats are a problem in almost every tillage field in Ireland. Realistically chemical control is the only option for reliable control. Growers need to achieve a minimum of 98% control each year to reduce populations of wild oats in the field.

Control wild oats in spring wheat with Puma Extra, Cheetah Super, Axial or Topik. All of these products can be used from the two leaf stage to flag leaf stage of the crop. Reduced rates (1/2 rates) can be used when applied early i.e. before the end of tillering. There are two products to control wild oats in spring barley; Axial and Puma Extra. Axial is a very flexible and mixable product as it can be used on wheat and barley up to the flag leaf stage. The full rate of Axial for the control of wild oats is 0.3 L/ha but a lower rate of 0.2 l/ha can be used when the wild oat is at a younger stage. Axial must be mixed with an Adigor at 0.5% of spray volume ( or 1.0 L/ha in most situations). Axial can also be used with a wide range of chemicals including SUs, HBNs, Fluroxypyr, fungicides, PGRs, insecticides and trace elements. This flexibility allows the control of broad leaved weeds with wild oats in the same tank. The full rate Axial must be used in these situations and growers should check compatibilities with other chemicals before use.

Canary Grass

This grass is becoming more prevalent and the damage it can inflict to crops is worrying. Its spread into new fields over the past two or three years is alarming and all growers should be vigilant to eradicate the plant before it becomes endemic on the farm. There are two species, lesser and awned canary grass. Both are equally as invasive. Lesser canary grass seems to be more prevalent in the south east and there are populations of the awned and lesser canary grass further south in Tipperary and Cork. The easiest way to distinguish between both species is the awned type sheds its seeds well before harvest but the lesser canary grass head stays intact. The canary grass emerges at the same time as spring cereal and can often out compete the cereal at an early stage through the sheer density of emerging plants. Control should commence at an early stage however it has been known to produce a couple of flushes of growth. Control in wheat can be achieved with a high rate of Topik or Puma Extra and in barley with Axial or Puma Extra.

Herbicide Resistance

Resistance is the naturally occurring inheritable ability of some weed within a given weed population to survive a herbicide treatment that should, under normal conditions, effectively control that weed population. In Ireland there are a few fields suspected to have corn marigold or chickweed resistance to SU chemistry. Where a weed becomes resistance a herbicide any other herbicide in a similar classification in equally ineffective, for example if corn marigold is resistant to Ally then Cameo, Calibre, Harmony, etc. will not kill it either.

The key to resistance management is to reduce selection pressure by using a combination of the following techniques:

Mixtures or sequences of herbicides with differing modes of action are important especially to prevent or overcome resistance based on target site differences. The addition of CMPP or Galaxy to Ally will give improved control of many weeds as well as providing an alternative mode of action.

Crop rotations may allow difference herbicides or cultivation techniques to be used and may also provide different competitive environments to shift the weed flora.

 

 

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