Plant health monitor

Press, 19 November 1982, Page 25

Plant health monitor

Although the cereal harvesting season is still a few weeks away farmers should be planning now to clean harvesting and transport machinery and particularly storage facilities. This is essential if infestation by stored product pests is to be prevented. Make sure all residues from cleaning are dumped or burnt to prevent reinfestation of newly harvested cereals. Despite the recent rains growers should be aware that high evaporation losses will still occur, over the next few weeks. Actively growing plants can easily become temporarily water stressed particularly during nor-west conditions. So if irrigation is available ensure it is used to its maximum. Plants under moisture stress are more susceptible to pests and diseases. As the warmer weather develops farmers should be on the watch for spotted alfalfa aphid in lucerne or clover crops. Suspect, samples should be sent to the Lincoln Plant Health Diagnostic Centre for identification. Lucerne • Bluegreen aphid numbers . are starting to decline after reaching peak population levels in the last two to three weeks.

• Bluegreen aphid numbers are starting to decline after reaching peak population levels in the last two to three weeks.

• Pea aphid numbers peak later and are still prevalent. An aphicide such as pirimicarb may be worthwhile if the crop is to be cut within the next week or so. , ’

• Sitona. weevil pupae are now present and plant chewing adults will be starting to emerge soon. If the stand is young,; yet. growing poorly, and extensive leaf notching is evident,, spraying with di-

azinon, fenitrothion or chlorpyrifos at Ikg a.i./ha during December may be worthwhile. Potatoes • Potato tuber moths are starting to fly. Keep the crop well moulded to prevent egg laying directly on tubers. Do not leave sacks of potatoes in paddocks overnight where moths can lay their eggs, as the resultant larvae will damage the' potatoes when

they are stored. • Greasy cut worm caterpillars can cause damage in dry seasons. If even one caterpillar is seen spray with fenitrothion at Ikg a.i./ha in high rates of water and dur- • irig the hours of darkness. Wheat • Farmers should stay on the lookout for stripe rust. The disease although well controlled in most crops, is . still a potential problem. Second sprays are now being | applied in some crops (particularly susceptible ones), as reinfestation is detected. If applied at the late boot stage no more sprays should be required. • Grain aphid will start to appear soon. Inspect crops regularly and spray if an average of five aphids per head are counted (see AgLink FPPSO9). • A new aphid identified as Rose/grain aphid, (Metapolqphium dirhodum) has recently, been found on wheat.

It is a yellow elongated aphid found about half way up the plant. Damage potential in New Zealand is unknown. , , • Some signs of barley yellow dwarf virus (BYDV) have been .seen. In most cases cereal aphid if still present is not worth spraying if the plants are in the late growth stages. • Bacterial blight is still evident. Other than ensuring a clean seed supply for next season, no control is possible. • Patches of stunted, distorted peas can be seen in some crops. These are caused by the aphid transmitted alfalfa, mosaic virus.

Brassicas • Cabbage aphid numbers are starting to build up. Young crops under moisture stress should benefit from an aphicide application such as demeton-S-methyl. Apples • Any orchardist who has released predatory mites ' should see an increase in numbers about now, and a subsequent decrease' in the two spotted mite population. Pip fruits » Growers should continue

the black spot and mildew spray schedule. Growers with varieties susceptible to “bitter fruit” Should begin the programme of calcium nitrate sprays. Berry fruit • Sprays are required on all berry fruit at the late blossom stage for Botrytis control.. Refer to your MAF export spray programme for further details. • Continue to watch out for mites on blackcurrants and strawberries. • Aphid populations can still build up on your berry crop. Apply an approved insecticide if populations are on the increase. Ornamentals • Keep checking for thrips aphids, mites and spittle bugs. • Adult grassgrubs are flying now and can strip grape vines, fruit trees and ornamentals. The application of a persistent insecticide, such as lindane or DDT should prevent damage. Pasture • Porina moths are still flying. Where heavy flights have occurred recently growers should plan to mob stock suspect pasture in midlate December.