Plant health monitor

Press, 9 November 1984, Page 20

Plant health monitor

Although some rain has fallen the drought continues to bite hard in many areas with obvious signs of crop stress and pasture browning.

Pasture growth rates have declined dramatically because of both moisture stress and seed head initiation. A careful balance between pasture control and overgrazing must be maintained over the next few weeks to ensure the best potential pasture growth. Although the majority of the early sown crops are still growing, later sown ones are struggling and strikes of recently-sown cereals and brassicas are poor. Cereals

© Despite moisture stress problems, growers should still be monitoring crops regularly for yield-reducing pests and diseases. Moisture shortage is producing leaf mottling, tip death and premature die-back of the lower leaves. These symptoms should be distinguished from those caused by stripe rust, mildew, leaf rust, scald, net blotch of barley and aphids. © Beware of rose grain aphid. Numbers are higher now on barley than at this time last year. If a fungicide is to be used soon apply pirimicarb as a tank mix, but only if five to 10 aphids per tiller are found before the booting stage. If there are more than 50 aphids a tiller at any time before the boot stage apply pirimicarb immediately. D.S.I.R. trials last season indicated little benefit in applying an aphicide after booting. Field Crops ® All small seed crops enetered for certification this season will be rejected at field inspection if yellow gromwell is found. From January 1 all laboratory

tested contaminated seed lots will be rejected but may be passed if redressing removes the yellow gromwell seed. Control in spring sown cereals can still be achieved with Glean, Buctril M or Brominal M. Long term, a period back in pasture will reduce the problem. In any field crop, small yellow gromwell infestations can be hand pulled or spot treated with Roundup before they seed. Peas

® Root rots caused by a variety of fungi, including Pythium, Ascochyta, Fusarium and Aphanomyces, are likely to show up soon. Their appearance' is dependant on cropping history, soil moisture and temperature. No controls are available although growers can avoid problems from Aphanomyces by using the M.A.F. pre-plant soil test service to detect this disease.

© Downy mildew is uneconomical to control in the field. Growers should however be aware that a seed treatment will soon be available to protect young plants from infection. © Note that there are few pea diseases that can be controlled in the field. Lucerne

0 A 15 per cent yield reduction has been recorded in the'first hay cut from a M.A.F. trial site v at Darfield. Sitona weevil larvae are blamed, although drought

may be contributing since there was no reduction recorded at this time last year. Sitona weevil numbers are also lower at 1500 to 2000 larvae a square metre. White clover, slugs, springtails © Low levels of chewing damage have been observed in white clover seed crops. This damage is attributable to slugs or, in some cases, to the green globular springtail or lucerne flea. If plants are growing vigorously, this damage is not likely to be economically significant. Pasture

® In many areas large flights of grassgrub brown beetles have occurred. These flights will continue for another two to three weeks so growers should mke sure valuable trees and shrubs are protected. Export horticulture Thrip numbers are increasing so susceptible export crops should be regularly inspected, especially those close to picking, and precautions taken. Contact a M.A.F. Horticultural Advisory Officer or Field Officer for information. Pipfruit

• Maintain sprays against black spot, as recent damp cool conditions may cause it to build up. © Mildew may also be a problem so carefully time spraying according to the M.A.F’s spray schedule.

Berry Fruit © Grey mould caused by Botrytis cinerea can cause major problems after flowering in many crops. The fungus uses the dying floral parts as a food source and entry site to healthy tissue. Check for the fungus especially in blueberries and black currants and spray if the mould is noted. See the M.A.F spray schedule.