Chemicals for higher profitability and yield for the cereal grower

Press, 1 May 1981, Page 18

Chemicals for higher profitability and yield for the cereal grower

(Contributed by Paul McCullough, technical officer with Bayer New Zealand ltd). Cereal growers are looking for higher yields and are relying more and more on agricultural chemicals to ensure the crop profitability is not eroded by weeds, pests and diseases. With increasing confidence in the ability of chemicals to provide this protection comes the demand for integrated strategies which save money and time, and one area of crop management where this approach is devel-

oping rapidly is in the control of cereal diseases. Farmers muht be prepared to participate in developing strategies which will serve them best; it is essential to consider local knowledge of soils, climate and varietal performance to enable identification of potential problems. Only when all this information is being considered in advance can objective planning be carried out. One of the first problems a farmer faces (having chosen the variety he will grow) is deciding what seed treatment chemical he is going to have applied to the seed. He must consider exactly what he is trying to achieve through seed treatment. The initial concept of fungicidal treatment of seed was to control diseases that were, carried on or in the seed and

which would, if allowed to develop unchecked on the growing seedling, impair the performance of the developing plant, or the quality of the grain produced from it. These diseases were principally the smuts, although some consideration has always been directed to foliar diseases carried on the seed as these may be a source of later necroses on the leaves, and thus may put stress on the plant by reducing the photosynthetic potential at a time when the number of

tillers that the plant may develop is being determined. So a farmer is faced with deciding whether he will adopt the most basic approach open to him: using captan to control seed-borne bunt (stinking smut) or if he should opt for the “best”. product available which would be Baytan Fl 7, a material which affords the broadest fungicidal spectrum of all seed treatments currently available. His first decision is important in that this may have quite a bearing on later applications of foliar fungicides. For example, last year many farmers who drilled Baytan treated seed in the autumn found that mildew did not build up to the same extent during the spring, and in some cases completely failed'to develop.

Trials have also identified a similar effect in reducing the infection of leaf rust in the spring where Baytan has been used on autumn sown wheat, resulting in yields of 16 per cent higher in Kopara and 19.9 per cent Karamu when compared to non-Bay-tan treated wheat.

Baytan is also effective against yellow rust, and while not yet a problem in Canterbury, it is important to realise that this disease must over-winter on the wheat plant to allow an infection build-up within the crop in the late spring to early summer period. As Baytan is highly systemic it provides protection as soon as the plant is through the ground and exposed to infection, and if the cycle can be broken at this point further infection may not occur until much later, and is reliant on re-introduc-tion of wind blown spores into the crop. If the farmer decides he will use the best that he can then unarguably he has bought a very inexpensive insurance policy, as the cost of Baytan for 1 acre of seed is less than the cost of 1 bushel of wheat. He has also reduced the chances of being faced with more than one application of Bayleton later in the season, and although he knows he may not eliminate the risk

from later infections of foliar diseases, he has made a deliberate decision to minimise this risk to the crop. Even while the seed is still in the bag, he has ensured that the crop will get off to the best possible start, through a decision which may be still paying off four to five months after the crop has been in the ground. From mid-July on, the farmer will be faced with the first potentially yield damaging disease which he can not plan for, and that is the infection of speckled leaf blotch. This has occurred through wind blown spores infecting the crop during the winter.

This infection period coincides with a very important phase of development of the wheat plant, which is now ready to switch almost all its resources into the process of reproduction. The embryo grain sites formed during tillering are develping the reproductive equipment needed for pollination and fertilisation of each floret on the ear, and if successful, grain may be produced. The recommendation for control of speckled leaf blotch is to spray with Bayleton or Benlate at the first appearance of symptoms and these may become evident any time from midJuly onwards, depending on the season and time of sowing. Both fungicides will give successful control of speckled leaf blotch and where this has been achieved the crop can develop unhindered by disease induced stresses. However, where Bayleton has been used for the control of speckled leaf blotch, the bonus of mildew control for up to six weeks after the time of application will be an additional benefit.

Many farmers found this “two diseases with one spray” approach most worthwhile, and this also eliminated the later worry of whether or not separate applications of fungicide later to control powdery mildew would have been economically worthwhile.

Later in the season, other foliar diseases may arise, the most economically important of which would be leaf rust. Control of leaf rust should be effected early, the recommendation being to spray with Bayleton when pustules are found on 50 per cent of the top three leaves.