MAF PLANT HEALTH MONITOR

Press, 6 December 1985, Page 22

MAF PLANT HEALTH MONITOR

The recent rain over much of the South Island means that many crop growers may have to change their approach towards disease and pest control.

Until now, careful crop monitoring followed by timely action have been stressed as essential for economic crop protection. With the likelihood of the present cool, damp conditions persisting, growers should consider insurance spraying for disease control, especially in spring sown crops. On the other hand, many crop insects, particularly aphids, do not thrive under these conditions so growers can expect a reduced need to spray for pests. The adoption of a different control approach does not mean that growers should relax from regular crop monitoring. To meet quality standards, especially for export crops, growers must carefully monitor pests and diseases until the product leaves the farm gate. CEREALS ® Continue to monitor crops for rose grain aphids. If populations were sprayed too early, numbers will have increased again, but

not if crops were treatea between flag leaf emergence and booting. Use of Pirimor insecticide will conserve natural enemies, and these will help to prevent population resurgence. Recently, Barley yellow dwarf virus has become evident in some spring sown crops. It is likely that Rosegrain aphid has been responsible for a good proportion of the infections.

Spraying to control virus carrying aphids is now too late except for late sown crops that have not tillered yet.

© Look for grain aphids in the heads from now onwards. Examine 50 heads and spray when an average of five aphids per head is found before the milky stage. It is not economic to Kfor grain aphid after dlky stage. See AgLink FPP 50y. © Thrips have been observed in the heads of cereals. These small (1.53mm long) elongated insects are not considered to cause economic damage. Adults are usually dark brown in colour, while juvenile forms vary in colour and can be brown, yellow or occasionally, red. OATS © Halo blight is prevalent this season. This disease causes small uark leaf spots which are surrounded by a water-soaked pinkish halo. Chemical control is uneconomic and plants usually grow out of the problem. LUCERNE © Check lucerne for aphids. If aphid infestations are heavy, spray straight after cutting to protect new growth. © Seed growers should be preparing to incubate their leaf-cutting bee cells in mid-December. STORED PRODUCTS PESTS © Any remaining stored grain should be checked frequently for pests or signs of deterioration, particularly as temperatures become warmer. © Any storage facility that is empty should be thoroughly cleaned now in readiness for the new harvest. Remove all grain residue using a vacuum cleaner if necessary and pay particular attention to corners.

and crevices. Do not forget to remove spilt grain and control weeds around silos. Apply an insecticide such as Baythion or Actellic EC to all inside surfaces. Use a high volume applicator to ensure good penetration of cracks. LOTUS SEED CROPS @ Use a sweep net to check for mirid bugs. Think about spraying the crop if one bug per 20 sweeps is found, and spray before numbers reach, 20 bugs per 20 sweeps. BRASSICAS @ Some seed crops are now showing black spots on the pods. This is caused by either the ringspot fungus or Altenaria species, both of which can be controlled with Bravo. PEAS ® The wet spring conditions have favoured bacterial blight of peas. There is no chemical control; the disease is best managed using clean certified seed and planned crop rotation. PIPFRUIT • As usual, early December is critical for European red mite and leaf-roller control. Apply a spray of Gusathion or Lorsban for leaf-roller control and a miticide other than Apollo for European red mite. Growers using Apollo should have controlled mites satisfactorily by now and further applications of miticide should not be necessary. BERRYFRUIT ® Recent wet humid conditions are ideal for Botrytis infection. The appropriate spray for control should be selected depending on the crop. If damp conditions persist, apply sprays as frequently as possible. Consult your M.A.F. berryfruit spray programme for details.

Strawberries • Black vine weevil is potentially a devastating pest in strawberries. There is no practical control in established beds. The best available method is to incorporate in the soil a persistent insecticide at planting as an insurance measure. Dieldrin is registered for this use provided a permit is obtained from the