Plant health monitor

Press, 25 February 1983, Page 24

Plant health monitor

Soil and air temperatures are cooler compared with the same time last year but moisture stress is still a problem influencing plant health. Significant rain soon would be welcomed by most Canterbury farmers as the critical flushing period approaches. Growers should keep in mind the points made in the last issue of the Plant Health Monitor, especially on burning cereal stubble and sampling now for pasture pests. CEREALS Preliminary results of trials on stripe rust control are similar to last year's. Over-all the effect of stripe rust was reduced this season because of factors such as wide spread use of seed treatment, timely spraying, adoption of protective spray programmes, greater use of non-susceptible cultivars and unfavourable weather conditions. A new race of stripe rust has been identified recently by Australian scientists. This race (named 106E139) has developed from the common stripe rust (104E1377) and was found to cause rust symptoms on the previously resistant cultivar Oroua. Growers contemplating sowing this cultivar should be prepared to treat seed and spray foliage as recommended for susceptible cultivars such as Rongotea. Berry and pip fruits • Flights of leafroller moths are occurring now and eggs are being laid. Growers should be monitoring populations carefully especially on pip fruit crops. Peas • Paddocks that are to be planted in peas can now be tested for common root rot (aphanomyces). Growers should obtain instructions on soil sampling procedures from their local M.A.F. field officer or grain merchant. They will forward your samples to the Plant Health Diagnostic Station at Lincoln. The disease was not a problem this season because of the dry warm spring. A warm wet spring and early summer can lead to considerable losses. Lucerne • Continue to check for leaf spotting in lucerne especially if it is to be used for flushing or seed. Ring Agphone. 66887. Fruit • Keep checking for late season infections of black spot and mildew in apples.

• Maintain the brown rot control programme on stone fruit until just before harvest.

Tomatoes • Late blight is showing up in some crops and control measures such as applying ridomil plus mancozeb should be considered. • Spotted wilt virus (better known as bronze wilt) is widespread on tomato leaves. Adult thrips carry and transmit the disease so these should be controlled. • Autumn is a .time when leaf mould can become a problem. Regular sprays should be maintained. Potatoes • Some late blight has been seen and growers are advised to check crops now. Growers practising a protective spray programme should be able to contain the disease. However, if infection does occur the use of Metalaxyl should be considered. • Leaf roll virus is widespread this season and table potato growers who save

their own seed should carefully check their crops now. If infection is not above 5 per cent then roguing can be carried out, otherwise clean seed will have to be purchased. Ring Agphone, 66887. Brassicas • Stem weakening of brassica plants is still causing concern. Although Nysius wheat bug and possibly weevils could be causing the damage, fungi could also cause similar symptoms. In this case the use of an insecticide may not help. Irrigating the crop (if possible) will increase plant vigour and create an unfavourable environment for the dry-lov-ing insects. Current AgPhone Topics (ring 66-887): sampling for prina, ill thrift in lambs and hoggets, control of potato tuber moth, control of insect pests on lucerne and lotus seed crops, fungus levels and Argentine stem weevil damage to pasture, Nysius problems- in export berry fruit, seed treatment of brassica seed to control damping off, prevention of bacterial blight on peas,- control of trace element deficiencies and parasitism in lambs, treatment of lucerne leaf spot, and late blight and leaf roll in potatoes.