Winter grass problem

It is hardly surprising that the herbicides you have used on your lawn have not affected the winter grass, Poa annua, for if they had they would have killed off your lawn as well. Selective herbicides for the control of weeds on lawns are designed to kill off broad-leaved annual and perennial weeds, not grasses.

The best way to control this annual grass is to use a pre-emergent seed ki I ler, propyzamide, regularly. The whole lawn should be sprayed every 4-6 weeks from March to June. It is also very important to try and keep the rest of the garden as free as possible from winter grass as this seeds so freely. If you are not sowing any seeds in the garden, you could spray the beds with propyzamide as well.

Weedkiller and fertiliser

The majority of selective herbicides used on lawns are systemic. This means that they act better and faster the larger the leaf surface of the weeds. Feeding the lawn with a high-nitrogen fertiliser such as 4:1:1 will make the weeds grow vigorously with plenty of leaf cover. The lawn should also not be cut for about a week after the herbicide has been applied. Some selective herbicides are quite slow acting and it may take a week or more before the weeds are affected. Rain or water within two

Hours of applying a herbicide will also diminish its efficacy. The grass cuttings from thefirst two mowings after the application of a weedkiller should be destroyed — don’t usethem as a mulch or compost them.

Applying weedkillers

As I simply haven’t the time to dig out all the weeds around my new garden, I would like to use a weedkiller, but I don’t want to damage any of my plants. How should I go about it?

All weedkillers should be used with great care as they are just what they say they are: killers of plants. Make sure that you have got the right type — see ‘Which kind to use’, p. 315 — and read the manufacturer’s instructions thoroughly.

Decide whether you are going to use a sprayer or spot-treat the weeds with a paintbrush or special applicator. Sprayers must only be used on a windless day or the spray could drift onto other plants and damage them. Spot treatment — treating individual weeds with small amounts of herbicide — is very time- consuming, particularly if you have a great many weeds in a large lawn area. However, it is certainly a much safer way of eradicating a few weeds than overall spraying — and it is the only method of eradicating grasses from in between vegetables and from shrub borders. When using a systemic herbicide, the weeds are not killed off immediately and may take a week or more before they start to wither, so don’t be tempted to spray again after a few days because the weeds do not seem to be dying.

You should always keep a separate sprayer for applying herbicides. If the sprayer is subsequently used for feeding or applying pesticides, the herbicide residue could easily damage garden plants, even though you may have washed the sprayer out thoroughly.

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