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Weed Control Starts in Wheat & Grass Reseeds

Autumn 2018 was again kind to us, allowing much of the winter barley and some winter wheat to receive a herbicide treatment during October and November. Mixtures of CRYSTAL and SEMPRA were widely used and by and large, performance has been excellent.

Control of Annual Meadow Grass (AMG) is the first priority in all crops if not already done with an autumn treatment. OTHELLO or HAMLET is an excellent contact solution for AMG in wheat in the spring, however there is no similar contact option for barley. None of the autumn products will control AMG beyond the mid tillering stage, yet they are the only AMG options for barley. Note that the actives in both HAMLET and OTHELLO that control AMG (iodosulfuron and mesosulfuron) will only control AMG that has already emerged; unlike the autumn actives these are not residual and have no pre-emergent activity. HAMLET provides a useful alternative to OTHELLO and is very effective on a wide spectrum of grass weeds. HAMLET has greater flexibility as the label allows a higher rate giving better activity in larger weeds. HAMLET works extremely well in cooler temperatures.

Both OTHELLO and HAMLET will also control a wide range of pre or early post emerged broad leaved weeds, but where these weeds have size then a contact product needs to be added to ensure larger overwintered BLW are controlled effectively. Where the AMG has been controlled in the autumn but for example over-wintered chickweed, cleavers or groundsel are problems weeds now, ZYPAR is a more effective option controlling these and most other emerged BLW.

Brome grass and wild oats

Brome grass infestations continue to be prevalent right across the province. Last season saw a decline in the numbers of infested fields, Effective control can only be achieved using a combination of cultural and chemical control methods. Cultural control methods (break crops, stale seedbeds).Chemical control then is a sequenced approach of an autumn treatment followed up with a spring treatment. CRYSTAL at 4lt/ha in the autumn was the first part, and should have been applied to wheat and barley. The follow-up then in the spring is BROADWAY STAR but note this product can only be used on wheat. There is no follow-up brome product available for barley and therefore in a severe infestation situation, only wheat allows effective control.

To avoid crop damage, do not spray any crop under stress. Note that performance of some wild oat/brome herbicides can be adversely affected by other herbicides used on the crop. To avoid these antagonisms, a minimum time interval must elapse between applications of the various herbicides.

Need a T0 Treatment?

Rhynchosporium and Septoria are the two most damaging cereal diseases in NI. Both have always been more effectively controlled protectantly, but in previous times where the curative properties of the azoles were able to rescue a bad situation later, particularly in wheat this is no longer the case. Growers must now change their approach, looking to keep ahead of both diseases by starting earlier than before and maximising the protectant activity of the chemistry available then right through to crop senescence.

In barley the lower leaves contribute more to grain fill than the upper leaves and therefore particularly in a year like this where crop was drilled early last autumn, plants are forward and disease is already present, so a relatively cheap T0 applied within the next few weeks will reduce the level of inoculum present keeping the newly emerging leaves clean and allow the T1 be better timed and protectant focused. Most of the azoles still have good curative activity on Rhyncho and the addition of morpholine will help control the high level of mildew present.

Treating Chickweed In Reseeds

There was a large amount of reseeding of poor performing grass fields last autumn. Now is a good time to check whether a herbicide spray is required to clean these fields up. Getting rid of annual weeds such as chickweed or seedling perennial weeds such as docks and thistles, is vital to ensure the investment in reseeding realises its full potential.”

Even though only an annual, chickweed is the most competitive and potentially damaging weed to new grass leys. This year’s mild winter has allowed chickweed to become very strong and competitive in the sward. If not controlled, chickweed levels will build up and will very effectively choke out the young grass; populations of 10plants/m2 can reduce the ryegrass population by as much as half. Therefore chickweed should be treated as soon as possible if ground conditions allow.

Whilst in the past many hormone herbicides had approvals for use on new sown leys, in recent years almost all of these approvals have been revoked, and the range of products today is limited to a handful. Product choice will be dictated first depending on whether clover is an important part of the reseed mixture or not. Where clover is important, broad spectrum product choice is limited specifically to TRIAD in mix with SPRUCE. Where clover is not important, the choice is essentially between ENVY and LEYSTAR depending on which weeds are to be controlled. Leystar from Corteva Agriscience has three effective active ingredients, fluroxypyr, clopyralid and florasulam, which combine to control a wide spectrum of annual weeds, such as fat hen, red shank and mayweeds, as well as seedling docks and thistles.

Leystar can be applied from 1 February to 31 August in new sown leys in 200 litres of water, so can be used on autumn-drilled and spring-sown grass reseeds. It has good grass safety, but will kill clover or any broad-leaved weeds that have not germinated when the herbicide is sprayed..

For best results apply to weeds that are small and actively growing, and when the grass has reached the three-leaf stage.

ENVY is an excellent herbicide choice for autumn reseeds as it works very well in cooler temperatures. ENVY can be applied between 1st February and 30th November. Trials done with ENVY have shown excellent results on chickweed much better than straight fluroxypyr.

Allow an interval of four weeks after application before cutting grass to optimise the effect of the herbicide. Do not roll the grass for ten days before or seven days after application. If the fields are to be grazed, animals can return just seven days after application. Farmers must be certified to use professional use herbicides on their fields.

 
 

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