Glenmark’s sticky problems come before N.W.A.S.C.A.

Press, 21 February 1986, Page 20

Glenmark’s sticky problems come before N.W.A.S.C.A.

By

OLIVER RIDDELL

in Wellington

The future of the Glenmark irrigation scheme, still only partly operational 15 years after work started, should be decided at the next meeting of the National Water and Soil Conservation Authority in Wellington. Two reports will be considered in committee by the authority — one by consultants brought in by the Hurunui County Council to look at why dams were leaking, the other by the Ministry of Works and Development to review work to date.

Once it has seen the reports, the authority will then consider how . much money it is prepared to allocate to fix some of the problems that have bedevilled the project. It has taken those involved in the project two and a half years to reach this point after the water was first turned on, and some of the dams were found to leak, on September 15, 1983.

Since then the scheme has operated in fits and starts, and never over the whole of Stage I of the

project. Stage II work has hot even started. In a nutshell, five of the 10 dams built for Stage I of the Glenmark scheme still have leakage problems, and two cannot be used for water storage at all. This is principally because when the sites were bulldozed for the banks, the impermeable clay was dozed away and the dam base left of permeable shingly material, through which the water seeps.

It is not that the dams are unsafe; some of them leak uncontrollably. This makes them useless for the water harvesting the scheme is intended to provide. A number of small streams have been dammed to hold water for use until the summer; some of them do not hold water very well and so cannot be used for water harvesting. The Hurunui County Council, which now administers the scheme, wants more money to fix it up. It was originally estimated to cost SI.2M to irrigate 800 ha, but was finally approved at 1500 ha.

So far, $4.16M has been spent for a potential 24 farmers to have irrigation, but only 10 can and only eight do over an area of 700 ha, the Stage I of the scheme. Work has not yet started on the other 800 ha to be covered by Stage 11.

The money being sought by Hurunui County is partly to pay for remedial work already done, and partly for the extra work needed. Discussion of the amount of money sought and needed will also be held in committee.

With over three-quar-ters of the cereal crops now harvested, it has become obvious that quality is variable. Many barley crops have been disappointing with high screenings, reflecting problems experienced throughout the season, especially in the latter half. These have included take-all, foot rot, the spot phase of net blotch and Ovularia leaf spot. Wheat quality is variable also, depending on the time of harvest and cultivar. Late season diseases such as glume rot and basal glume rot have not affected quality as much as expected. Europeanbred feed wheats were hit heavily by glume blotch, but the effects have not

been fully investigated There is concern about the remaining crops , not harvested in areas experiencing wet weather over the last week or so. Harvesting should not be delayed once fitness 'is achieved since problems such as black point and sprouting can develop. BARLEY The spot phase of net blotch is a major concern to growers, advisers and researchers. Leaf damage has been extensive in many crops, even under full fungicide application situations. Observations indicate that triazole fungicides have not given the desired control levels, but further investigations are under way to determine why this happened. At this stage, the reason for the prevalence of this disease is not known, but every effort will be made to give growers guidelines for the coming season to avoid future problems. • Many crops have exhibited major damage from foot rot or Fusarium. This soil borne disease can attack or carry-over on a wide range of grass and cereal hosts, and be of little importance until conditions prevail that favour the disease. Alternating wet and dry soil conditions allow disease build-up and after experiencing losses a farmer should plan the crop- sequence away from grass or cereals for about two seasons to reduce disease inoculum. PASTURE Most grassgrub populations are well advanced and are actively feeding. High numbers are causing visible damage and this can be expected to increase in severity in many areas. Try to assess population levels in susceptible paddocks. Populations can only be assessed by digg-

ing. Pastures that are either three to four years old ' after ploughing and drilling, or have been trated with insecticide within the same time span are most likely to suffer damage. Management options are to: 1, Mob stock paddocks when moisture levels are high; 2, Heavy roll which may be a viable alternative to mob stocking; 3, Oversow damage once grubs have stopped feeding from June onwards and monitor populations to check the feeding status of the grubs: 4, Apply chemicals.— This may be seen as a viable option, but in general expense precludes its use BRASSICA Widespread dense flights of cabbage white butterfly have been reported. Damage to brassicas could become severe in many areas, but if the damp weather persists pathogens and predators will soon cause many populations to collapse. Keep monitoring crops for both diamond back moth and cabbage white butterfly caterpillars. Thresholds for spraying will vary according to general feed availability. Consider spraying if an average of two cabbage white caterpillars are found per plant after examining a total of 50 plants. If numbers are at, or above this number, delay spraying for a few days and check again before spraying to see if the population is collapsing as a result of natural enemies. BERRYFRUIT Two spotted mite populations are generally low. If mites are showing up in plantings, either control with miticide when the bulk of populations are immature, which is approximately now, or implement integrated mite control with predator mites.