MAF PLANT HEALTH MONITOR

Press, 7 February 1986, Page 13

MAF PLANT HEALTH MONITOR

BURNING CEREAL STUBBLE © Burning stubble can reduce carry over of many diseases. This season the moist conditions in many areas have allowed many usually minor cereal diseases to become significant, including glume blotch, eye spot, sharp eyespot, scald of barley and basal glume rot of wheat. Take-all and foot rot which have been widespread this season are little affected by stubble burning. Headlands or fire breaks should be closely mown, raked and worked as soon as possible to encourage stubble breakdown in these areas. PASTURE © Before sowing new grass think carefully about the seed line and consider the advantages and disadvantages of high versus low endophyte seed.

Argentine stem weevil adults will be feeding actively from about now until about the end of February and can cause significant damage to low endophyte ryegrass seedlings. All low endophyte seedlines sown before midFebruary should be protected with an appropriate insecticide sown down the spout. This is not required after February unless grass grub is a problem, or there is a potential for a stem weevil larval attack under direct drill or minimum tillage situations.

© Porina are causing visible damage now and this can only become worse if populations are left unchecked. Make sure paddocks are sampled for pasture pests, particulary porina, by the end of this month.

A couple of days sampling now may save thousands of dollars worth of ruined pasture later on. If an autumn drought is experienced the effects of high populations could well be devastating.

BARLEY © Two leaf spot pathogens are causing many barley crops to lose green leaf material prematurely. A “spot” form of the net-blotch fungus is occur-

ring throughout the South Island and causing a lesion similar to spot blotch (see Cereal AgPhoto page 13). A smaller lesioned blotching of leaves is caused by a fungus called ovularia. This fungus has been present for several years but was previously identified as a form of “physiological blotch”.

The spotting associated with ovularia has been controlled sucessfully in recent M.A.F. trials by timely applications of triazole fungicides, giving significant increases in yield and decreases in screenings.

More information on this complex should be available in the coming season and will be reported in the Plant Health Monitor then. LUCERNE • Most of the adult sitona weevils have left lucerne paddocks for summer hibernation outside the stands. Flight back into lucerne will start in March and will have finished by the end of May at which time it would be appropriate to apply an insecticide to suspectible stands. No action is required at present. LUCERNE SEED CROPS © Continue to check crops regularly for pests. If insecticides are applied post flowering, and seed is likely to be used for sprouting and human

comsumption, avoid using systemic chemicals, and adhere strictly to the witholding periods.

FORAGE BRASSICA • Check established crops for diamond back moth and cabbage white butterfly caterpillars. Thresholds for spraying will vary according to the season and general feed availability. As a rough guide consider insecticide application if an average of two cabbage white caterpillars or six diamond back moth caterpillars are found per plant after examining a total of 50 plants. Leaf miner damage has been reported and older leaves are usually affected.

This may cause premature death, but plants should be able to compensate for this loss if growing conditions are adequate. Control is not usually economic. Wheat bug (Nysius) populations are not expected to become high this year so damage to emerging seedlings should not be bad. However, still check maturing plants and look for strangled stems at ground level. RASPBERRIES AND BRAMBLES • Clean up programmes for bud moth should be complete by now or well under way. If picking, use dichlorvos and follow up post harvest with a spray of Gusathion or Lorsban.