Herbicide programmes for peony crops

Devising a herbicide programme for peony crops depends on several parameters which are outlined below, and growers and agronomists should consider each of these as well as any other factors which may affect each farm or field (availability of equipment and type and number of equipment etc). The detail below provides information needed to devise programmes according to each specific crop situation including a guide to reduce the risk of crop damage and loss. It is not intended to provide a proven, safe spray schedule and growers should always take care when using new products in their programmes and test on small scale prior to wider use.

• Age of crop and flowering times

 Young and new plantations which have not entered the commercial cropping stage are low risk for possible crop damage and losses, provided treatments are carefully considered and total herbicides are used in appropriate timings. A robust herbicide programe is important for the early stages of establishment, as soil cultivations bring weed seeds to the surface which will proliferate very quickly in the first couple of years. Once these are controlled to desired levels and crops mature, the crop canopy will supress the weed pressure and help with better more efficient herbicide use. Mature crops tend to be more tolerant of herbicide damage and damage is often transient, but the risk of late herbicide applications and damage is greater as it can impact the bud, leaf and stem quality and therefore reduce marketable yield. The flowering times of each crop will determine the application timing of some of the pre-emergence and selective contact herbicides. For example, a young early flowering crop will always be at risk of herbicide scorch due to the earlier dormancy and therefore initiation of root and shoot sap movement in comparison to late or very late varieties.

• Type of soils for the planted crops

Soil type determines the likely weed range for the field and the behaviour of the herbicides used. Peony crops on lighter soils may require additional irrigation and if this is not provided, water availability can put the crops in stress and increase the risk of herbicide uptake during the time of applications. On lighter soils some of the highly soluble herbicide active substances such as metazachlor, metribuzin, lenacil and others tend to be easily washed into the rootzone increasing the risk of uptake and crop damage. Herbicide persistency is also affected by soi type. Heavy soils tend to bind to herbicide active substances more readily than lighter soils giving greater herbicide persistence and therefore improved weed control which will help extend the application intervals between treatments in the programmes.

• Weed species present and local background parameters

The herbicide choice is determined by the weed species present in each field and this should be considered carefully as many pre-emergence herbicides will control a similar range of weeds. In recent years herbicides efficacy has been decreasing due to weed resistances such as ALS resistance in groundsel, grass (black grass, annual meadow grass) and others. It is important to use more than one active substance which have different modes of action to control the same species of weeds and minimise the risk of resistance developing. This is particularly important where herbicides are used at a reduced dose to reduce risk of crop damage.

• Use of mechanical weeding machines 

Where mechanical weeding is used it is recommended to follow the mechanical weeders with herbicides and not the other way around.

• Fertiliser applications

Similarly granular or liquid fertiliser applications tend to break the herbicide layer, so it is recommended that the herbicide applications follow the fertilisers rather than the other way around.

• Crop handling and re-entry periods

Several herbicides have statutory handling or re-entry restrictions which need to be followed. This is particularly important around the de-budding phase as well as with some early flowering varieties. Herbicide choices should be carefully considered as many herbicides have very long handling or re-entry periods.  For example Devrinol has a 13 week handling restriction and if applied in late February could result in no access to the crop when it is ready to harvest.

• Spray equipment, nozzle choice, water volumes and dose rates

Spray equipment and nozzle choice are critical for herbicide efficacy and safety. Majority of the herbicide applications occur in late winter and early spring for pre-emergence options and spring and early summer for selective contact herbicides when weather conditions are unsettled, and wind can disrupt spraying plans. Compromising on drift reduction and coverage could result in poor weed control or crop safety. Particular attention should also be paid to recommended water volume and dose rates for products including active substances. Some actives will have restrictions to the amount of active substance applied per field/year in a given period of time, for example metazachlor has a limit of 1,000g a.s/ha in any three-year period. This tends to force the need for a different spray programme each year.