Black point creeps north

Press, 25 May 1984, Page 17

Black point creeps north

Some farmers are finding this season that their wheat is being down-graded or rejected for milling because of black point. Normally this can be a problem in Southland and South Otago grain, but this season moist weather during grain ripening has led to the condition occurring in Canterbury crops. Black point is caused by common black moulds invading the wheat heads during moist, warm weather. Not only do they grow on the senescing flower parts and glumes, but they also invade the coat or testa of the ripening grain. When established, they give the grain a black, smudged appearance.

Investigation at the Plant Health Station has shown that this season the discoloration is caused exclusively by a fungus called Alternaria alternata. In any one sample the plumpest grain appears the worst affected and smaller grain are clean. The plumper grains matured earlier, on primary tillers, and were invaded during the wetter part of the summer. The smaller grain was from later maturing tillers and heads that

would have ripened during the subsequent drier period. Kopara wheat appears worst affected. Although this cultivar is susceptible to both melanism in the head, and basal glume rot which also blacken heads, it would appear that it is possibly 7 the ripening date of this cultivar that has predisposed it to the problem.

There was nothing farmers could have done to lessen the risk of crops becoming affected by the Alternaria fungus. It is simply unfortunate that the moist" weather in Canterbury this summer coincided with the ripening of the grain. The problem is primarily one of grain discoloration and no control is available.

What effect does the fungus have on the grain for baking or sowing? Baking score is not affected, and the milled flour is quite suitable for human consumption. However the flour is unattractive, dull and discoloured, and so is the crumb of the bread.

Lines with infection levels over 15 per cent should not be used as seed since infected grain can produce weaker seedlings. The fungus does not kill the emerging cotyledon, but may predispose it to other pathogens if establishment conditions are less than fav-

ourable. Grain with higher levels of infection that are required to be kept for seed should be sown only during ideal conditions for establishment.

The storage conditions for affected grain are important. Provided grain is maintained at not more than 15 per cent moisture content, and stored below 20deg. C and 70 per cent relative humidity, then there should be no further damage. Periodic checks should be made for grain heating and

on moisture content, grain viability and fungal activity. If sporulation occurs on the grain, then its value as feed decreases, since the airborne spores make the feed less palatable. Thus, under suitable storage conditions, blackpointaffected grain can be kept for long periods and is quite suitable for feed purposes. However, if farmers are in doubt as to the quality of their stored grain, they should contact their broker for resampling.