MAF PLANT HEALTH MONITOR

Press, 20 December 1985, Page 20

MAF PLANT HEALTH MONITOR

causes glume blotching and gram rotting. This has only been a problem in highly susceptible cultivars, such as Oroua and Otane.

The disease spreads by water movement and plant contact and progresses slowly up the plant during wet, windy weather. Diagnosis is difficult in the field, since the symptoms resemble natural senescence and other minor diseases.

Fruiting bodies are only visible with a hand lens and after leaf wetting. See AgPhoto Page 10 for illustration and contact your local M.A.F. adviser or merchant for control management options.

BARLEY SCALD, NET BLOTCH AND RUST

® Prevailing climatic conditions have allowed scald to persist in crops longer than usual. The scald is still active and is causing serious damage, especially in second successive barley crops and where no control chemicals have been applied. There is still time to spray for this disease. © Some net blotch is still active and again may require attention. @ Leaf rust is coming into crops also as the weather warms up. This disease needs to be monitored carefully and controlled if it progresses up the plant ont'o the two .top leaves at any stage of growth up until grain filling. STRIPE RUST

Little can be done about stripe rust once it appears in the heads. Even though crops have been kept clean of the disease up until flowering, rust spores can come in from outside the crop and infect the heads. Head protection is difficult in susceptible cultivars (note that Advantage and Otane are head-susceptible). It is difficult to get adeSiate fungicide onto or into e glumes after flowering. Thus, heads can be at risk from infection even though good fungicide application practices have been carried out up until head emergence or flowering. Continued good growing conditions will alleviate the problem to some extent and allow normal grain filling to occur. However, any stress will mean that the diseased glumes will compete with the filling grain for moisture and nutrients, the grain will shrivel and reduced yields .will occur through lower thousand grain weights. ARMYWORM, CEREALS, SMALL SEEDS

Damaging populations of

Army worm caterpillars have been recorded this season. Crops at risk include cereals and ryegrass and lucerne for seed.

This problem needs to be recognised early and prompt corrective action is required before caterpillars cause economicc damage. Check crops, looking for notching on leaves and damage to heads. On cloudy days, caterpillars may be found feeding on plants, but they drop to the ground when disturbed.

If notching damage and caterpillars are easily found, a spray of fenitrothion at Ikg active ingredient per hectare should provide control. If sprays are required in lucerne crops in flower, use dichlorvos applied in the evening instead of fenitrothion. WHITE CLOVER

Pepper spot is common in white clover seed crops this season. Small black spots on petioles and leaves soon cause complete leaf colla P se -

Protection and control could be worthwhile. Benlate has been used with some success in the past,

although it is not registered for this use. LUCERNE SEED CROPS Before flowering, tank mix an insecticide with Benlate and apply as a clean up spray to control plant-sucking bugs and leaf spotting diseases. If insect control is needed in crops that are flowering, apply dichlorvos in the evneing to avoid killing bees. WHITE CLOVER SEED CROPS Sample crops for clover case bearer. Refer to AgLink FPP 620 for information on sampling and thresholds. Also check flower heads for aphids and apply control if aphid numbers exceed 5-10 aphids per head. Use dichlorvos to control both clover case bearer and aphids and apply during the evening when bees are not active. PEAS Common root rot of peas caused by Aphanomyces is likely to be a problem this season because of recent wet weather. Any pea crops grown in paddocks where the Aphanomyces soil index was found to be more than 50 will be highly susceptible to infection. Affected crops may be stunted and will

wilt under dry conditions. Root development will be poor and the main root will be soft and straw coloured. >

Yield losses will be great- -- est in crops infected early j in the season; those crops - - infected late may only suf-7 fer slight yield losses. » © The humid weather has favoured development of « downy mildew of peas, a ’ disease that in most years is t of minor importance. Under ' present conditions this s disease could cause signifi- ’ cant yield losses. c No chemicals are regis- r tered for use against downy ‘ mildew although some » growers have used Antracol ? or Ridamil for control. « There is some question as to ' the efficacy and/or cost ef- r fectiveness of these chemi- ’ cals.

STONEFRUIT * Brown rot will be a prob- ' lem in stone fruits nearing > maturity, because of adverse weather conditions. «. Growers should ensure that i the recommended fungicides are applied regularly. J

BLACKCURRANTS Currant clearwing moth ; flights are reaching peak » levels now. An application ' of insecticide to control cur- - rant clearwing should be applied immediately after» harvest. Mite control in blackcur-4 rants has generally been g excellent this season most growers are inputs of miticide although 7 mite populations should stfil« be monitored. PIPFRUIT

The second insecticide S spray of Gusathion or Lors- * ban for leaf roller and codl- J ing moth control should be «Y applied at the end of J December or in the first week of January. “