MAF PLANT HEALTH MONITOR

Press, 26 December 1986, Page 15

MAF PLANT HEALTH MONITOR

Populations of both cereal and rose-grain aphids have increased dramatically on late-sown barley crops. If aphids can be easily seen on most tillers, a spray would be economic now if it is applied before the “booting” stage. WHITE CLOVER High numbers of bluegreen and pea aphids have been seen in some white clover seed crops. If numbers exceed 5-10 per head, a chemical control is economic. Dichlovos, applied during the evening when bees are not active, is suggested to control both aphids and any clover case bearer. Check two-year-old crops now for signs of clover case bearer moth and regularly monitor all red clover seed crops as flower heads develop. WHEAT

Stripe rust is evident in heads of many susceptible crops. Infection can come from outside sources even though crops have been kept disease free by timely sprays.

Control is difficult since it is not always possible to effectively apply a fungicide to the head. Once a crop has passed the watery-dough stage, . the withholding period becomes critical (42-49 days for Triazole fungicides). @ Many diseases are present on upper leaves of crops but are causing little damage at this stage. These include glume blotch, speckled leaf blotch, Ascochyta leaf spot and snow mould. Persistent wet, cool weather would allow them to infect heads and cause significant yield losses. Dry, warm weather should restrict, them to the foliage where they may cause some yield loss but not enough to justify a fungicide application. Some farmers may want to take "insurance” action, but this should be done before the “watery dough” stage. • Weka is showing symptoms of the bacterial disease-basal glume rot, but there is no control. Some losses may occur in areas that have persistent damp cool conditions.

Last season, two cereal ’B5 idiots at Lincoln had

heavy infection but they both still yielded to expectations. However, heavily infected crops around Methven were reported to suffer grain shrivelling through basal glume rot infection. BARLEY Classic physiological leaf blotch has been noted in some Triumph crops, but no action is warranted. The spot form of net blotch, Ovularia leaf spot and leaf rust could cause problems from now on. Later-sown crops could suffer from leaf rust. Control with fungicides may be necessary and these must be applied at first sign of infection. BAYFIDAN M In the plant health monitor which appeared in “The Press” on December 12, it was said that some of the phytotoxic effects had been caused by the Calixin component of Bayfidan M. This statement is incorrect, as Calixin, which is a trademark of BASF, is not a component of Bayfidan M although the active ingredient of Calixin, tridemorph, is included. BLACKCURRANTS Currant clearwing populations are approaching epidemic numbers in stands older than three years. Large flights of adult moths are occurring now. Apply a spray of azinphos methyl (Gusathion) immediately post harvest. Don’t neglect this spray if a pre-harvest insecticide was not applied. SITONA WEEVIL Populations of sitona larvae have been particularly high this year following the wet autumn and spring. Poor growth of young stands on light soils could have been caused by sitona if the stands were not sprayed with insecticides last autumn. Adult sitona are emerging now and some defoliation can be expected. Control is not warranted as these adults will leave stands in the next 23 weeks for over-summer-ing sites. ARMY WORM, CEREALS, SMALL SEEDS Check all crops for army worm damages- This

pest needs to be recognised early and prompt action is required. Look for notching on leaves and damage to heads and stems. If damage or caterpillars are easily found during the day use fenitrothion at Ikg active ingredient. Apply during the evening with maximum rates of water. STORED PRODUCTS PESTS Check any remaining stored grain for pests or signs of deterioration. Any empty storage facilities not already cleaned should be attended to now. Remove all grain residue, using a vacuum cleaner if necessary, paying particular attention to comers and crevices. Remove all spilt grain around silos and control weeds. Apply an insecticide such as Baythion or Actellic EC to all inside surfaces. Use a high volume application to ensure good penetration of cracks. © Check and clean all harvesting machinery, particularly headers and augers. PLANT CENTRE The Plant Protection Centre at Lincoln will be open on December 30 and 31 for diagnosis of plant problems and plant protection advice. The centre will reopen on January 5. The next issue of the plant health monitor will be published on January 9.

Evapotranspiration Christchurch: Thursday, Dec. 18 . . . 4.7 Friday, Dec. 19 3.9 Saturday, Dec. 20 . . . 6.0 Sunday, Dec. 21 ... . 4.5 Monday, Dec. 22 ... . 4.6 Tuesday, Dec. 23. . . . 5.6 Wednesday, Dec. 24 . . 2.9 Weekly total . . . . 32.2 Average for Dec. 130 mm Culverden: Weekly total .... N.A. Average for Dec. 125 mm Timaru: Weekly total 25.5 r Average for Dec. 125 mm Winchmore Irrigation Research Station: Weekly total 25.1 Average for Dec. 130 mm Kurow: Weekly total 27.1 Average for Dec. 130 mm