Controlling Weeds with Weedkillers for Growing Vegetables
Weeds and weedkillers
If weeds are not controlled they will at first compete with vegetables for plant foods and water, and may later overrun the crop altogether. However, their abundant presence does at least show that the soil is fertile.
There are three ways of getting rid of weeds: the hard way, by pulling them up by hand; the relatively expensive way, by drenching them with chemical weedkiller; and the simple way, by hoeing when they first appear.
Hoe regularly — at least weekly between April and July. A few minutes of regular attention are more effective than hours spent in clearing a badly overgrown plot.
In showery weather, rake up the weeds so that they do not get a chance to re-establish themselves, and put them on the compost heap. In dry weather, uprooted weeds may be left between the rows, as they will soon die.
The choice of hoe depends partly on the task and partly on the personal preference and needs of the gardener.
There are four main types: the draw hoe, which is especially useful for earthing-up potatoes; the Dutch hoe, which is ideal for destroying weeds between rows of vegetables; various types of patent hoes, which are mostly improved forms of the Dutch hoe; and the short-handled, or onion, hoe, which is excellent for accurate weeding close to plants.
Whatever type of hoe you use, make the most of hot, dry days — when uprooted weeds wilt and die almost immediately — and leave the surface loose and crumbly.
However carefully you use a hoe, some weeding will still have to be done by hand among close-growing plants, such as peas. Deal with the weeds when they are small, because if left too long their removal will disturb the roots of the vegetables.
Even in a well-tended garden, deep-rooted perennial weeds may get a hold among permanent crops such as asparagus, or among summer vegetables at holiday time. Get rid of them by easing the soil away with a trowel so that enough of the roots are exposed to pull them out cleanly by hand.
Such hand weeding is necessary where perennial weeds grow through a mulch.
Weeding a seed bed
In a seed bed, vegetable seeds and weed seeds have exactly the same conditions for. The seedlings may therefore, emerge at about the same time, and may confront the gardener with a bewildering green carpet in which vegetables are hard to distinguish from weeds.
Anticipate this problem at sowing time by inserting small canes at the ends of each row. When growth is about 1in (25 mm) high, tie string between the canes, so marking the seed row, and hoe to within 1in on each side.
Hand weed when the vegetables are clearly distinguishable, and thin them at the same time.
When sowing slow-germinating parsnip seeds, sprinkle radish seeds along the drill. The quick-germinating radishes will mark the row for weeding, and also provide a crop by the time the parsnips need to be thinned.
When sowing brassicas (plants in the cabbage family) , onions, swedes and turnips, the bed can be treated with propachlor to inhibit the germination of weed seeds.
Using chemical weedkillers
Chemical weedkillers are most effective in clearing paths, waste ground and the soil beneath fruit trees and bushes. Their use is more limited in the vegetable garden. Here, periodic digging and regular hoeing keep down both perennial and annual weeds. Nevertheless, for the gardener with little spare time, or who wants to return from holiday to a weed-free garden, chemical weedkillers have a part to play. There are three types: Total weedkillers, which destroy all plants and grasses.
Selective weedkillers, which kill weeds without harming the crop.
Pre-emergence weedkillers, which, on cleared ground, prevent weed seeds from germinating.
Simazine is especially useful for pathways, which it will keep weed-free for up to 12 months. The chemical remains in suspension in the top layer of the soil, and for this reason it can also be used as a selective weedkiller between soft fruit bushes whose roots are deeper than this.
It is sold under the trade names of Weedex and Boots Path Weed Control.
Simazine is mixed with diquat and paraquat in Pathclear; with aminotriazole in Super Weedex; and with MCPA and aminotriazole in Kilweed. The advantage of these mixtures is that they kill perennial as well as annual weeds.
Sodium chlorate is another total weedkiller, but it is liable to move sideways in the soil, killing any plants with which it comes into contact. There is a fire risk unless a brand containing a fire suppressant is used.
Grow nothing on treated soil for at least eight months. Do not put weeds killed by sodium chlorate on the compost heap; and do not use the chemical over tree roots. It is sold as ICI Sodium Chlorate and Liquisafened Chlorate.
Paraquat and diquat (sold as Weedol) are total weedkillers, in the sense that they kill all green plant tissue — other than liverworts and mosses — with which they come in contact. But as both chemicals are inactivated by contact with the soil, they can be used selectively by applying the solution to the weed foliage while keeping it off the cultivated plants.
This is easily done with a Weedol applicator, or by using a sprinkler bar fitted to a watering can.
A single application kills annual weeds completely, but repeated treatments are needed to kill the fresh growth made by perennial weeds.
Dalapon kills annual and peren- nial grasses, including twitch and couch. It may be used under fruit trees and bushes and in asparagus beds. It is sold as Battle’s Dalapon and Synchemicals Dalapon.
2,4,5-T is a powerful selective weedkiller for use on nettles, thistles, briars and woody or shrubby weeds. It does not kill grass.
It can also be applied by spot treatment — that is, dabbing weed leaves with a brush dipped in the chemical.
Do not use it close to tomatoes or store it in a greenhouse where tomatoes are growing. Do not put the dead weeds on a compost heap.
It is sold as Nettlekiller and Brushwood Killer.
Other widely used selective weedkillers include mecoprop (Clovotox, Supertox) and 2, 4-D (Dicotox). Dichlobenil (Casoron G) can be used selectively in established perennial crops, but has little selectivity when applied to annual crops.
Propachlor inhibits the germination of weed seeds for about six weeks, giving plants a better start. Unfortunately, it may be used only on a limited range of crops.
Propachlor may be applied immediately after sowing leeks, onions and brassicas, including turnips and swedes, and after planting brassicas. It is sold as Ramrod.
Store weedkillers out of the reach of children.
Never put liquid weedkillers in containers where they may be mistaken for something else. Read the makers’ instructions and carry them out carefully.
Do not use weedkillers in a high wind.
Keep the outlet of the can or spray close to the weeds being treated.
Wash out sprays and watering cans thoroughly after use.
Identifying garden weeds
Both annual and perennial weeds are relatively easy to control in ground that is cultivated regularly. But sometimes a gardener takes over a neglected plot or faces an invasion by a seemingly indestructible perennial weed from a neighbour’s garden.
Among the hardest of these intruders to eradicate are perennials that multiply by rhizomes —creeping underground stems that spread out from the parent plant and throw up fresh shoots to form a new plant.
The most diligent gardener might believe that he has cleared an area by digging, only to find the following spring that small pieces that he missed are throwing up new vigorous shoots.
For this reason it is important to be able to recognise weeds so that the most effective treatment can be given to destroy them.
Recommended chemical treatment is given for the control of each perennial weed. Use paraquat/diquat (Weedol) if you want to use a chemical weedkiller for annual weeds. But remember that hoeing costs nothing and can be just as effective if done frequently during the spring and summer.