Leaf infection ﬁrst shows up as small spots which enlarge to form green or silvery grey elongated areas. Several of these may join together, forming long narrow infected areas. If conditions are favourable, several of these lesions may join until large leaf areas are affected. It is these long strips of infected leaf which give rise to the name leaf stripe.
In order to obtain any means of control over a fungus disease, it is necessary to know something of its source and conditions best suited to its development. Leaf stripe fungus is able to survive for many months on old corn stalks. Spores from this source become airborne and infect green tissue during the following growing season. Wet weather with showers or foggy conditions, or periods of heavy dews, provide ideal conditions for development. Moisture is very necessary for spore production. In dry seasons, then, we would expect leaf stripe to be of little importance; but in some seasons it could become more serious.
Destruction of the corn plant after harvest so as to destroy sources of re-infection, is one of the most important means of control. However, this would have to be done throughout the whole district. It would be of little use one grower practising careful crop hygiene if his neighbour left his corn stalks exposed throughout the winter and following spring.
Although burning of corn stubble is condemned in respect to maximum return of organic matter, it may have some merit. It would, of course, be better to turn the crop into the soil but complete coverage is necessary, particularly if another corn crop is to follow in the next season. A succession of crops in the same land would certainly increase the chances of re-infection, and is not recommended even though it has been done for many years in some districts.
Control by spraying in U.S A. is practised but has not been developed in New Zealand as yet. Work is also being done overseas in developing resistant varieties.
We acknowledge reference to “Leaf Stripe of Sweet Corn and Maize,” by I. G. Forbes, in the NZ. Journal of Agriculture, January, 1960
WORLD FRUIT STATISTICS
Published in “American Grower” recently and computed by Dana Dalrymple, of Connecticut University, are the following percentages of world fruit production. To anyone who has not travelled through Europe, the grape production comes as rather a surprise with 35.5 per cent. of all fruit production. Grapes are followed by apples with 14.6 per cent, a ﬁgure which is increasing rapidly.
Others include oranges 12.9 per cent, bananas 11.4 per cent, olives 5.5 per cent, peaches 4.7 per cent, pears 3.4 per cent, plums 2 per cent, lemons and limes 1.7 per cent, grapefruit 1.6 per cent, pineapples 1.6 per cent, dates 1.2 per cent, ﬁgs 12 per cent, cherries 1 per cent, apricots 5 per cent, nuts 5 per cent, and strawberries 3 per cent.
NEW ZEALAND PRODUCTION
The following is the New Zealand fruit production forecast for 1960, supplied by Horticulture Division ﬁeld ofﬁcers and published recently by the Department of Agriculture in the “Orchardist”: –
Apples in New Zealand are well in the lead with 3,900,000 bushels, or 65.51 per cent of all fruit production; pears 565,000, 9.4 per cent; peaches 759,000, 12.75 per cent; apricots 206,000, 3.46 per cent; nectarines 54,000, 91 per cent; plums 172,000, 2.89 per cent; cherries 18,000, 3 per cent; quinces 18,000, 3 per cent; citrus 261,450, 4.39 per cent. Citrus fruits were made up of 84,900 bushel cases of Standard lemons and 24,000 Meyer lemons. New Zealand grapefruit, 127,600 bushels, made up the bulk of other citrus, followed by sweet oranges with 13,800.
Sub-tropical fruit ﬁgures were given in tons, with tree tomatoes heading the list with 832 tons, followed by Chinese gooseberries with 452 tons, passionfruit 94 tons, feijoas 37 tons, persimmons 7 tons, a total of 1,422 tons.
The berry fruit crop is expected to yield 1,825 tons, made up as follows – Raspberries 833, strawberries 655, gooseberries 172, black currants 89, boysenberries 51 and loganberries 25 tons.