Plant health monitor

Press, 8 February 1985, Page 22

Plant health monitor

Familiar seasonal brown clouds and red sunsets are again appearing over the Canterbury plains as cereal growers burn off stubble. The very dry conditions should ensure a quick, hot bum, essential for good disease and pest control. Before burning stubble check with your local council for any fire restrictions. These dry conditions are in contrast to those, in the northern areas of the South Island where harvesting is being delayed because of the warm, humid weather. Cereals ® Growers should be planning crop rotation sequences now with special regard to recent disease occurrences. Diseases such as rusts, mildew, and even scald can be maintained on volunteer plants while others such as take-all, scald, speckled leaf blotch and eyespot can be stubble borne. A good stubble burn can reduce many of these diseases, except take-all, where most of the infected debris is underground. Burning or early stubble cultivation after harvest hastens crop debris breakdown and discourages volunteer plants. Growers should be particularly aware of take-all and eyespot when planning crop sequences. Take-all can attack barley following a wheat crop but is not usually as severe. If take-all has been serious use a brassica or legume break crop between cereal crops. If the disease was only scattered then barley can safely be planted. • Eyespot has carried over from the last season in

some South Canterbury cereal crops but the drier weather has kept it at low levels. Control measures may be required if conditions are wet next spring. © Take-all can spread to cereal crops from couch rhizomes, especially if the paddock has been treated with glyphosate. Check rhizomes for take-all symptoms (small brown flecks on the internodes) and if these are numerous plan to cultivate after spraying to hasten breakdown. Refer AgLink FPP 640. Seed Crops © Check for bug damage in lucerne and red clover seed crops. Make 20 sweeps with a net and count both nymphs and adults caught. Repeat the process once more in another part of the paddock. If an average of one bug per sweep (a total of 40 bugs) is caught apply a suitable insecticide such as bromophos. Remember to observe the usual precautions for bees. Pasture • Argentine stem weevil can still cause damage to most non-endophyte ryegrass seedlings. All seed lines without endophyte drilled before mid-February should be protected with an insecticide such as Thimet down the spout. Be especi-

ally careful when direct drilling or sowing into minimum tilled soil and keep checking the developing seedlings of all non-endophyte seed lines until mid-March.