Plant health monitor

Press, 11 February 1983, Page 22

Plant health monitor

Harvesting and tidying up are now the main activities on the cropping scene. Growers are reminded of the importance of planning paddock rotations and practising good crop hygiene, e.g. thorough “burning off” to prevent carryover of pests and diseases. On grazing farms, the next few weeks are critical for next season’s lamb drop. Pasture management and care need to be carefully considered and any pests and diseases controlled to get maximum autumn growth. Some attention should also be given to pests and diseases on winter feed crops. Some growers are now considering whether to “burn” or not. Advantages of stubble burning are: • Reduced disease, pest, volunteer plants and weed carryover. • Low cost of straw removal. • Easier cultivation. • No nitrogen retention problems. Disadvantages include: • Reduced organic matter build-up. • Fire danger and pollution. • Patchy “burn off’ and headlands can still be a source of pests and diseases. • Weather and terrain can make a clean burn impossible. CEREALS • Stubble burning will only marginally control take-all. Warm soil temperatures combined with burning and early cultivation can stimulate early microbial breakdown. Further control is possible if barley follows an infected wheat crop. • Some oat crops have had pink straw at harvest. This could be caused by an earlier infection of barley yellow dwarf virus probably introduced by the rose grain aphid. This aphid may need controlling in autumn-sown cereal crops. • In the current damp conditions, cereal growers may be tempted to harvest grain for bulk storage at the acceptable maximum of 15 per cent. To prevent possible insect and mite problems a moisture content of less than 13.5 per cent is recommended. • Burning off is a useful follow-up to herbicide treatment for' wild oats. Delay cultivation after burning off. This leaves any remaining seeds on the surface where they are available to birds and prevents dormancy of the seeds. • Grass grub and porina damage can be expected soon, particularly if the weather remains cool and moist. Farmers should be sampling paddocks now and getting prepared to apply organo phosphate insecticides during or straight after heavy rain. • Argentine stem weevil has been damaging recentlysown Tama seedlings. Any annual grass and most perennials sown before the end of February should have phorate at 1 kg a.t. per ha sown “down the spout.” Examine any unprotected grass recently sown. If chewing damage on leaves caused by adults is obvious an insecticide such as diaziron, chlorpyrify or fenitrothion at 1 kg a.t. per ha may be worth while before too many eggs are laid. • Farmers will need to decide which perennial ryegrass cultivar to sow this autumn. Seed lines high in endophyte fungus will give Argentine stem weevil resistance but could cause ryegrass staggers in sheep and cattle. Lack of pasture per-

sistence due to weevil attack may occur if a low endophyte seed line is sown. Ring AgPhone 66-887 for details on endophyte levels of various grass seed cultivars. LUCERNE • Late summer, early autumn rain can induce leafspots in susceptible cultivars, e.g., Wairau, Washoe, ASI3R and Rere. This leads to defoliation and reduced seed yields. Spray at first signs with Benomyl plus Mancozeb. Remember to part the top canopy to examine the plant base as the disease often spreads from here to infect the productive top leaves. Ring AgPhone 66-887 for details. FRUIT • Late season infections of black-spot and mildew in apples can still occur. Control now will decrease winter carry over and fruit marking in late varieties. • Brown rot control programmes on stone fruit should be maintained until just before harvest, especially if moist warm weather occurs. BERRIES / • With the second crop of strawberries coming up, growers should look out for nysius (wheat bug) contamination. Check now and take appropriate action before picking begins. Ring AgPhone 66-887 for details. • Destroy any prunings of blackcurrants to prevent continuing development of currant clear wing larvae. Some adults are still present and will be laying eggs. Careful pruning can reduce baring damage from the resultant larvae. CUT FLOWERS • Thrips are still a problem and need to be constantly checked. Remember they are regarded as a non-acceptable contaminant in export flowers. Make sure sufficient chemical is applied. Use a minimum of 50 litres of a recommended insecticide for every 300 square metres. BRASSICAS • Large numbers of Nysius wheat bugs have been seen in many crops and may be causing seedling mortality. Damage can, however, be confused with wirestem disease, or wind damage. Insecticide control is suggested only when very high populations are seen, with obvious plant ill thrift. • Minor leaf damage on turnips has been reported. Older leaves affected more. Damage is not significant and no control is warranted. SUGAR BEET • Virus symptoms are now starting to show up on the trials at the Templeton Research Station. Up to 22 per cent infection rate has been reported on untreated plots compared with 6 per cent on the treated (fenvalerate) areas. AgPhone 66-887. Information on the following topics is currently available: sampling for porina, army Worm control in barley, ill thrift in lambs and hoggets, control of potato tuber moth, control oi insect pests on lucerne and lotus seed crops, endophyte levels and Argentine stem weevil damage to pasture, rosegrain aphid control on barley, Nysius problems in export berry fruit, seed treatment of brassicas to

control damping off, prevention of bacterial blight on peas, control of stored products pests, Xrace element deficiencies, parasitism in lambs.