Lawn Diseases Caused By Fungus
Here we will see a number of diseases caused by parasitic fungi liable to affect the established lawn, and with certain non parasitic fungi causing ring formations.
Four well known diseases occur but only two of them, caused by Fusarium and Coticium, are common. All four are dealt with below:
Fusarium Patch Disease
Caused by F. nivale can be quite serious in its effects. It is a disease of highly cultivated grass and occurs mainly in autumn during muggy weather, though attacks sometimes occur in spring also. Small patches of yellowish dying grass appear on the turf and they may join together so that quite large areas are killed. The spores produced lead to further spread of disease. Virulent attacks are difficult to stop, and, of course, the damaged turf, if the attack is in autumn, will remain thin throughout the winter.
Prevention of the disease is better than cure, and this is best achieved by keeping the turf firm, not over fertilized and especially by avoiding forcing dressings of nitrogenous fertilizers in late summer or early autumn. Efforts should be made to keep the grass as dry as possible by switching off the dew, using, say, long bamboo and allowing as much air movement as possible over the turf. Annual meadow grass is most susceptible to this disease but other species may be attacked. Lawns which are closed in by tress, and therefore short of free moving air, are liable to suffer.
In some cases where a lawn is known to be prone to annual attacks, a preventative dressing of fungicide can be used, but this requires renewal at intervals of 7-10 days. Most people adopt curative treatment at the first sign of the disease and there are several reliable proprietary turf fungicides available for this purpose. A well tried and not expensive one consists of a combination of the dye malachite green and Bordeaux mixture. Other fungicides contain mixtures of calomel and corrosive sublimate, while a third type incorporates an organic mercury compound. Mercury fungicides are, of course, poisonous.
These fungicides should, of course, be applied in accordance with the manufacturers’ recommendation, those to be given in solution being applied with a suitable sprayer, while the dry ones should be dusted on evenly so that the whole turf area is treated. A useful emergency treatment for the amateur is to apply, with a watering can, a solution of ¼ oz. sulphate of iron in ½ gal. of water to 1 sq. yd. This may stop mild attacks or provide sufficient check to enable a supply of a more active turf fungicide to be obtained and applied.
Caused by Corticium fuciforme usually appears around mid to late summer but may persist into autumn. Patches of grass affected are not killed but seriously damaged and discolored, the grass taking on a bleached look with small pink branched needles of the fungus developing on the blades and sheaths. The fescues are more severely attacked, but other grasses may also suffer. Often a dressing of a nitrogenous fertilizer will be sufficient to help the grass through an attack but in serious cases a turf fungicide such as malachite green/ Bordeaux mixture should be given.
Caused by Ophiobolus graminis var. avenae is a ring disease found mainly on sports turf but its occurrence on lawns is by no means rare. Bent (Agrostis) is mainly attacked, fescue being resistant, and the patches often fill up rapidly with weed and coarse grasses. Many outbreaks follow applications of lime or lime containing materials to acid turf, but wet seasons seem to favor it. Small outbreaks can be best dealt with by re-turfing; larger ones are best countered with an organo-mercury fungicide plus fertilizer and renovation with seed.
Dollar Spot Disease
Caused by Sclerotinia homeocarpa was first found in UK in 1933. It attacks creeping red fescue, especially the sea marsh variety, but occurs sometimes on Agrostis. The symptoms are easily confused with early stages of Corticium, the spot produced being from 1-2 in. of diameter, roughly circular, but frequently running together. Inorganic and organic mercury fungicides give fair control, but preparations containing cadmium seem rather more promising. Identification of the organism is a matter for the specialist.
Fairy rings are the manifestation in the turf of the activities of the soil inhabiting fungi, mostly belonging to the Basidiomycetes (Cap fungi). These fungi grow in the turf, starting from a central point. They spread in every widening circles, the mycelium of the fungus ramifying in the soil between the roots of the turf grasses. The fungus is not parasitic.
The most disfiguring kind of ring is caused by Marasmius oreades and in it there is an outer green stimulated zone, a band of dwarfed or dead grass, and an inner green stimulated zone. Small brown caps – the fructifications – grow on the middle zone. There are several other species that cause rings of this type, but they are seldom found. The other types of ring where there is no dead area are caused by species of Lycoperdon (Puff ball) and Psalliota (Mushroom).
Eradication of Marasmius rings is not easy. There is no quick method by which something may be applied by to the surface of the soil so that the rings disappear. Most of the damage is due to the mycelium of the fungus waterproofing the soil, thus causing the grass upon it to die of moisture shortage. Therefore any material given for the purpose of eradication must penetrate this dry soil to be effective.
A method involving the use of formalin has been worked out and it is as follows:
- Prepare a solution consisting of 6 pints of 40% formaldehyde and ½ pint of non-ionic wetting agent, both stirred into 10 gal. of water. This does for about 10 sq. yds.
- Determine the farthest extent of the inner and outer green rings of the affected zone. Mark these out.
- Strip off the turf from the marketed area and remove it carefully from the site so as not to spill infected soil.
- Dig up the stripped area thoroughly, again being careful not to spread infected soil on to the turf.
- Apply the formaldehyde solution to the bare soil with a water can, being careful not to spill it on the surrounding turf. Soak the soil.
- Cover the treated area with sacks, tarred paper, or other similar material and leave the sealed up to fumigate for 7-10 days.
- Remove the sacks and stir the soil with a fork, leaving about two weeks for the formaldehyde to escape.
- After the formaldehyde has been allowed to dispense, add soil to restore the level, pre treat with fertilizer and sow or alternatively re turf.
The same method can be adopted against rings due to puff balls of mushrooms, but most lawn owners will hardly find these worth the trouble to eradicate.
Control of these rings has sometimes been effected by applying calomel corrosive sublimate fungicide after forking or by applying a solution of 1 oz. malachite green, with a wetting agent, in 28 gal. of water at the rate of 1 gal./sq yard after forking. Repetition is necessary.