Lawn Pests and Diseases
Perhaps the worst pest of grass is the larvae of the Cranefly (Daddy-long-legs), known by the familiar name of Leatherjacket; anyone who has tried to kill one of these larvae by stamping on it will know how well-named it is — the greyish skin is extremely tough and resilient. These larvae are an inch or so long.
Leatherjackets can do a great deal of damage to a lawn by feeding on the roots of the grass, just belowlevel, with the result that the grass dies off, creating large brown patches. The adult craneflies appear in late summer and lays its eggs in the soil in early autumn, and these hatch in about a fortnight to produce grubs which feed on the grass from then onwards and usually reach a peak of activity in early spring. It is then that the patches begin to be noticed. To confirm that it is leatherjacket damage, flood the area with water, and leave overnight, covered with sacking.
By the morning some of the leatherjackets present will have come to the surface, and can easily be swept up with a besom. Alternatively, BHC or DDT applied as a spray or dust will be found an effective control.
These animals do much good by devouring leatherjackets and other soil pests, but unfortunately they do a great deal of damage toat the same time by burrowing just beneath the surface of the soil and throwing up loose mounds of soil (molehills) at frequent intervals. Special steel traps are available from garden stores for setting in the runs. Gloves should be worn when this is being done as moles have a keen sense of smell, or mole smoke cartridges can be obtained. Also a few lumps of calcium carbide can be placed in the runs, the smell from these driving the moles out.
Some gardeners dislike having worms in their lawns because of the casts they produce, but it should be remembered that on the whole they do far more good than harm, aerating the soil very effectively. Where there are large numbers of them present, however, and sweeping does not provide the answer, worm killers of various kinds can be used. Derris will kill most of them in the soil, and has a lasting effect of several weeks; it is harmless to human beings and animals, but will poison fish so should be kept well away from pools containing the latter. Chlordane is another control which kills them in the soil. A good old-fashioned remedy is mowrah meal; this is an expellant and should be watered into the turf under strong pressure to make it froth. Worms will come to the surface within a few seconds, and can be brushed off or not as required. Mowrah meal also is poisonous to fish. It is most effective if used in spring and autumn, when the soil is moist and the weather mild, at which time the worms are likely to be near the surface. The treatment will need to be repeated.
There are several fungal diseases which affect lawns; the four main ones are Red Thread Disease (Corticium fuciforme), Fusarium Patch Disease (Fusarium nivale), Fairy Rings, caused by various fungi, and Damping-off, a problem for seedling grasses, also caused by various diseases, in particular fusarium and pythium species.
This trouble, known as Red Thread is not a killing disease, but it does weaken the grass considerably and render it susceptible to die off through some other trouble such as waterlogging, or invasion by. It appears most frequently during late summer and autumn, in the form of small circular patches of brownish-buff-coloured grass, which can coalesce if close together. The tips of the grass wither, and this gradually extends down the leaf blade, and a small red or pink thread-like growth about 1/4 in. long appears, growing out from the blade tip. This is the part of the fungus which gives it its common name and passes the disease on from plant to plant. These threads are rather difficult to see, and a very careful scrutiny of the grass has to be made in order to pick them out. It can be controlled by watering in a mercury-based fungicide, but as it is often found on lawns short of food, the addition of a quick-acting nitrogenous fertiliser as soon as the patches start to appear will do much to enable the grass to grow more strongly and overcome the attack.
Damping-off can be diagnosed when the grasscollapse, with rotting at soil level; they turn brown and the trouble can occur in patches several inches across. It is more likely to give trouble on damp soil or where the grass has been sown without putting on a well-balanced fertiliser beforehand. As soon as the trouble is seen, apply a solution of Cheshunt Compound, as directed by the makers.
You can often see rings of toadstools in fields and on lawns and although some may not harm turf, there are others, Marasmius oreades in particular, which will kill the grass and gradually extend outwards so that more and more is killed each year. The grass at the edge of the ring is likely to be a rich dark green. Getting rid of this trouble is rather involved. The simplest method is to skim off the turf from within the ring and to a distance of 2ft. outside it, and then to remove the soil for the same distance and to such a depth as is well outside that to which the white thread-like growth of the fungus has penetrated. For instance, if the white threads extend downwards for 6in. then remove at least 9in. of soil, and so on. Take the soil and turf completely away from the lawn, making sure that none of it spills on to the healthy grass — sacking placed over the full wheelbarrow will help to avoid spillage — to be the cause of a new infection and fill in the hole with fresh soil from another part of the garden.
Another method of control is to treat the grass with sulphate of iron mixed at the rate of 4oz. of sulphate of iron to 1 gallon of water and repeating this at half strength one week later. Further applications may also be necessary. This solution should be watered on after rain or after the grass has been well soaked with water.
This disease is rather more serious than Corticium, in that it will kill the grass and can spread very rapidly, causing a lot of damage before any treatment can be undertaken. It is most likely to appear during the autumn and spring, though sometimes mild attacks may occur during the summer, when the weather is cool and damp; however, these attacks are not serious and usually disappear as soon as the weather improves. When seen at other times the grass turns brown, and collapses. If grass is fed with a fertiliser having a high nitrogen content this is conducive to the production of soft growth which is liable to attack by this disease. The patches may be anything from an inch to a foot in diameter and sometimes round the edges a whitish fluffy growth is seen at the base of the grass. As with Corticium, a mercury-based fungicide can be used to control it; thereafter improve the drainage.