Plant health monitor

Press, 17 December 1982, Page 18

Plant health monitor

In recent weeks soil moisture levels have improved dramatically. Although some pathogen and pest levels remain high their effect on plants has now lessened. Because weather plays such an important part in plant health. 5-day weather forecasts for Canterbury farmers will be available on “Ag Phone" 66-887 starting Monday, December 20. Provided with the co-operation of the Christchurch Meteorological Service, the forecasts will be updated Monday. Wednesday and Friday after 5 p.m. This and other agricultural information is available on Ag Phone between 8 a.m. and 8 p.m., Monday to Friday. The service will remain open over Christmas except .for statutory holidays. WHEAT

• A new race of stripe rust seems to have been found on Oroua. Fungicide treatment may be worthwhile if the crop is not beyond the mid flowering stage. Spraying of other susceptible cultivars is of doubtful economic value beyond the mid ' flowering stage, but with the higher yielding crops this period could be extended to the late flowering or milky ripe stages. • Grain aphids could be a problem up until the milky stage. Check regularly. See AgLink FPP 509.

•Do not confuse grain aphid (found in the head) with the new rose-grain aphid. Although present in high numbers in some late sown crops rose-grain aphid does not necessarily warrant specific control. • White heads in some crops may not be a result of pathogens such as footrots. Sudden changes during the recent weather are thought to be responsible. OATS

• Rose-grain aphid populations are high in many crops. If the crop has not reached the milky seed stage and an average of two adult aphids can be found on the top leaf, spray with pirimicarb at 300 g (product) per ha. Ring Ag Phone. 66-887 for updated information. BARLEY

• Many crops have symptoms of yellow dwarf virus, but it is now too late to spray for the cereal aphid which spreads this disease. • Infestations of rose-grain aphid are heavy in many crops. Control recommendations are the same as for oats.

• Net blotch continues to be found in a number of crops. If severe .in previous years, an application of Bayleton may be worthwhile. Tilt or Mancozeb can also be used but do not have a label claim in New Zealand.

• Black spots appearing on barley should not be confused with net blotch. The spots are symptoms of physiological stress. BRASSICAS

• Some crops have suffered

stem breakage. Wind damage. not Nysius bug, is the cause. Nysius populations have been high, but will decline temporarily with the damper weather.

CLOVER SEED CROPS

• Some growers are still spraying unnecessarily for springtails. Only aphids,, clover case bearer and myrids (sucking bugs) need your attention. The presence of a parasitic wasp together -with ladybirds should reduce aphid populations enough to eliminate the need for insecticides. BEANS

• Bean aphids could be a problem. Watch out for small black aphids appearing on the tips of plants. Apply insecticides such as pirimicarb. bromophos or dichlorvos when necessary. PASTURE

• High populations of twoyear life cycle grubs have been recorded around the Melhven area. They are feeding now, but not causing visible damage, and will have finished feeding by March. They should present no problem to existing or new grass from now on. • Mob stocking for porina control should be carried out before the end of the month in many South Island areas. See AgLink FPP 590. • White seed heads caused by stem boring Argentine stem weevil larvae will be seen from now on. Control is not possible. LUCERNE

• Sitona weevil adults are emerging in increasing numbers. In coastal areas, farmers with severe leaf notching should consider spraying with chlorpyrifos, fenitrothion or diazinon over the next two weeks.

LOTUS and LUCERNE seed crops • Over ■ the next two weeks check for bug populations (myrids). Insecticides such as bromophos, trichlorfon, dichlorvos or thiodan can be applied, but follow the label recommendations as these chemicals are toxic to bees. Ring Ag Phone 66-887 for details on sampling and spray thresholds. SUGAR BEET

• The aphid population has declined to about three to five per plant. This is Well down compared with last year. Heavy rainstorms have caused very high aphid mortality. Symptoms of virus infection have appeared however, and could still be severe this year. GARLIC

• Any crop showing signs of

stress, yellowing or stunting should be checked for the stem nematode Ditylenchus dipsaci. Crop collapse is possible and confirmed presence also prevents the crop being certified. For details on sampling. ring Ag Phone .66-887. NURSERY STOCK

® Young trees have sustained quite severe damage recently from adult grassgrub attack. In most areas flights have almost finished, but if you are still having problems apply a synthetic pyretroid such as Ambush. BERRYFRUIT

• Growers should keep up the regular botrytis sprays. Recent rain and cool weather favour the spread of this disease. If sprays are not timed properly there will be severe crop losses. ® High populations of Nysius bug are present in strawberries. Check carefully for any Nysius in export containers, any contamination will lead to rejection. See AgLink FPP 645 for further details. BLACKCURRANTS

• Large numbers of currant clearwing moths are flying now. Later varieties can still benefit from an application of gusathion. But remember the three-week withholding period before harvest.

@ Leaf roller larvae from the first summer generation are causing some damage at present. Sprays cannot be applied until after harvest. PIPFRUIT

• Watch out for Mills periods and spray for black spot as required.

© The first cover insecticide for control of codling moth should have been applied by now.

• Keep an eye out for powdery mildew on new growth. Use any of Pallinal, Morocide or dinocap until terminal growth ceases. Rubigan and Pallitop will also control powdery mildew, but have only a tentative' label recommendation. Remember the; waiting period before harvest for some of these chemicals. STONEFRUIT

• Growers aiming: for the export market should keep up with the recommended schedule. Those who have been badly hailed and now plan to sell on the local market should check with their local horticultural advisory officer before changing their spray schedule. VEGETABLES

© Poor germination, distorted plants and blind seedlings . experienced by growers are simply a result of cold nights and frosts. GLASSHOUSE TOMATOES • Growers having problems with fruit splitting should check for fluctuations in soil moisture. Water more frequently to prevent the soil from drying out. Another cause could be high humidity from under ventilation on the really hot days we have had interspersed with the recent cold weather.