Plant health monitor

Press, 26 October 1984, Page 24

Plant health monitor

The recent drying northwest winds have dramatically increased moisture stress in many crops and pastures although in the southern and foothill regions cooler, moist conditions still prevail so adequate growth is being maintained. In the dryer areas not only are crops wilting but the winds are causing physical damage which may be confused with disease. Growers should be able to recognise the difference so that unwarranted spraying is not carried out. CEREALS 0 Some crops may be infested by cereal cyst nematode which can cause purple-yellow colouration and stunted top growth. Third orr fourth successive cereal crops are most at risk. No control is available.

@ Manganese deficiency is showing up in many wheat and barley crops. It is found mostly in recently limed paddocks and particularly on corners where applications have overlapped raising the pH to deficiency inducing levels. Deficient wheat plants turn light green and become floppy and a little stunted. Lines of small tan spots or leaf death at the middle can cause leaf kinking. Barley plants also become stunted and floppy but the leaves become yellower or die at the tips and dark spots appear on leaf margins with blotches down the leaf blade. Apply a topical application of manganese sulphate at 10-15 kgm/ha in 200 litres/h & water. ® Successive warm, dry

north westerly winds have caused leaf damage in many autumn sown wheat crops. Physical whipping and leaf moisture deficits have caused leaf tips to brown off and lower leaves to prematurely die. If irrigation is available ensure that plenty of water is always available to plants during these dry periods. © Many farmers have been disappoihted at the amount of mildew still in Rongotea crops after spraying with Tilt or Bayleton. Several factors may be involved such as lower than recommended fungicide and water application rates, and dense crops preventing fungicide penetration into the base from where mildew can spread to newly developing leaves. Also complete and rapid control of this disease is difficult with any chemical especially under the present ideal environmental conditions favouring fungus development. Where mildew is still spreading and when using Tilt for rust control, consider adding Callixin at 350400ml/h a. Full rates (700 ml can produce phytotoxicity. Remember that stripe rust is the primary disease that requires con-

trol. Full rates of Bayleton applied now, even though it may be slightly early for rust, should give adequate control of mildew lurking on the top leaves. WHITE CLOVER SEED • Apply a herbicide now to control grasses. Paraquat will knock down all grasses but the selective grass killers such as Alloxol or Fusilade will give longer term control of most annual and perennial, grasses except Poa annua. PASTURE © It is now too late for effective spraying with M.C.P.B. (the recommended herbicide) to kill nodding thistle in pasture. Be prepared to spray in April ay next year. © To reduce barley grass seed head numbers, keep up the grazing pressure on infested pasture. Stock will eat the developing seed heads only when they are newly emerged and are still green and succulent. BRASSICAS © Seed crops are now forming pods and these must be protected from diseases. Black rot, a bacterial disease, ring-spot and Alternaria can all reducce seed yield and quality. If lesions are observed on pods and the peduncle between the pod and the stem, then an application of suitable pesticides should be carried out. Some farmers have used a mixture of Benlate and Kocide to good effect. © Insect pests could be a problem in brassicas being sown now. The use of seed coated with insecticide should be contemplated.