WHEAT BLACK-MOULD.

Lyttelton Times, Volume CXXIII, Issue 15920, 4 May 1912, Page 15

WHEAT BLACK-MOULD.

(By A. H. COCKAYNE, in the " Agricultural Journal.") During wet summers it is not unusual for the wheat crop to become quite seriously damaged by a fungus known as tho wheat black-mould that manifests itself by the spotting and blackening of the ears. The very unfavourable weather that has been experienced during tho past harvest has accentuated the damage done by this disease, and a considerable loss both in yield and quality of the grain is reported. The wheat black-mould is caused by a fungus known as Cladosporium herbarum. This genus contains many destructive plant-parasites, the tomato-rust (Cladosporium fulvum) and verrucosis of lemons (Cladosporium elegans) being familiar examples. 1 Tlio wheat-mould is an extremely common fungus, and in normally dry seasons does but slight harm, being then found for the most part only on decayed and decaying vegetation. It is only when there is an excess of moisture, and when diseased seed has been used, that it attacks and is able to penetrate into living plant-tissues. Cereals of all kinds are liable to attack, but wheat and oats are the crops chiefly infested and in which the majority of the damage is done. By tho /ayman it is noticed only when tho grain is in ear, but, its presence can often bo detected much earlier in tho season when tho plants are quite small. After a comparatively dry spring followed by frequent rains tho wheatplants often assume a yellowish tint, followed bv a shrivelling and bleaching of tho leaves, which become covered with littlo blackish tufts, representing one of tho spore-bearing stages of the fungus. In certain instances many of tho plants are killed outright, leaving more or less circular bare or very thin patches here and there in tho fields'. During the past season this condition has not been unusual in Canterbury and the cause has in many cases been'erroneously attributed to the grass-grub (Odontria zealandica). Again, when the plants are not killed outright they may struggle on into ear, and, not having sufficient vitality to develop the grain, the stalks gradually die and become quite bleached, thus forming whitish patches that can be easily soon scattered through tho crop. The main damage, in New Zealand at any rate, occurs whon the ears are aro almost mature. The ears become spotted, and at times almost covered with blackish-olive tufts similar to those developed on the leaves. These tufts consist of masses of spores that germinate almost as soon as they are developed, and, provided there is sufficient moisture, continue the work of infection until tho whole of tho heads become completely coated with the fungus. v Tho mycelium of Cladosporium in eases of severe attack penetrates right into the wheat grains, and flour made from them has frequently :i very tuioleasant flavour and its value for

baking purposes is greatly, impaired. An examination of affected wheat shows that brownish patches are developed on the surface of the grains, sometimes forming quite distinct lines. When badly diseased the surface may even become cracked, due to the development of the fungus under the epidermis. Such diseased grain in many cases quite fails to germinate, and even when it does the resulting plants are always weakly, and. the leaves become spotted with reddishbrown blotches caused by the Cladosporium. In most seasons Cladosporium herbarum is often frequent on apple trees, causing at times quite a severe defoliation of the trees. When present on apples the fungus is often termed Dematium puelulans, but Jancezewski has proved experimentally that Cladosporium herbarum and Dematium puelulans are forms of the same fungus. CONTROL.

The presence of wheat black-mould as a parasite being almost entirely dependent on weather conditions, it is obvious that there can he no easy and effectual methods of control. Nevertheless, the damage caused by Cladosporium might be certainly lessened by attention to the following methods of restricting its power of infection:— (1) Never on any account sow seed that shows the least sign of disease. The use of affected seed will result in a diseased crop no matter whether dry or wet conditions prevail after sowing. (2) Avoid the growing on the same land of two grain crops in succession. An affected crop will leave the soil full of Cladosporium, spores, which will be liable to damage any cereal crop that may be resown on the same area. (3) The wheat-husks from a diseased crop aro capable of carrying infection. It is therefore a good practice to burn, all husks, refuso, etc., as soon as threshing is completed. (4) In cases of very bad attack all the straw should also bo destroyed by burning. • _.