Selection for winter-activity class
Highly winter-active cultivars produce more hay, at least in a three- to four-year term of production. They regrow quickly after cutting and frequently attain maturity before flowering. To maximise production, it is necessary to cut on four- to five-week intervals in the spring, summer and autumn and six- to eight-week intervals in the winter. This will produce about two cuts more each year than from semi-dormant cultivars.
If these cutting regimes are not maintained, new growth will start from the crown, and the older shoots will shed lower leaves, become stemmy, and result in poor quality hay. To produce attractive, leafy, high-protein hay from winter-active or highly winter-active cultivars, they must be cut when the crown buds begin to regrow, i.e. before the leaves begin to drop.
In haymaking studies it has been shown that the quality of hay produced during the spring, summer and autumn period by the more active cultivars such as Trifecta is equal to that produced by semi-dormant lines such as Hunter River. Newer cultivars such as Sequel HR (highly winter-active) and Pioneer L55 (semi-dormant) will behave in a similar way. During the winter months the quality of hay produced by winter-active cultivars is inferior. In the subtropics, rain is very likely to interrupt haymaking schedules between spring and autumn. Since semi-dormant cultivars retain leaf on their regrowth better, they maintain their quality through wet periods better than the more active cultivars.
Thus, the benefits of winter-active lines must be weighed up against the drawbacks, i.e. the production of more premium quality hay except in winter, against a greater management demand and the prospect of further reduction of quality in wet summers. If the producer wishes to make winter hay where premium quality is not required, highly winter-active cultivars produce more hay. If premium quality hay is required at all times, semi-dormant cultivars are more profitable.
The selection of a winter-activity class will depend on each farmer’s priorities. However, diversification over activity groups is worth considering.
Selection for disease resistance
Colletotrichum crown rot resistance
Haymaking is carried out under generally humid conditions, which, with warm summer temperatures, promote the development of the crown rot organism. Infection occurs mainly through the stems of mature plants. Susceptible cultivars produce high yields for only about two years before the stands thin and become grassy. Occasionally, whole stands can be wiped out by crown rot during establishment. For hay stands to remain commercially viable beyond two years, select for resistance to crown rot.
Crown rot resistance in the highly winter-active cultivars is generally lower than that of the most resistant semi-dormant cultivars. However, breeding has increased the crown rot resistance of newer winter-active cultivars, with Hallmark, Sequel HR, Pioneer L69 and Pioneer L90 considered to have high resistance (see Table 2.1). The productive stand life of the other highly winter-active cultivars is shorter and the hay becomes grassy more quickly. This is partly compensated for by the higher production potential of the winter-active cultivars, particularly in the first two years.
Phytophthora root rot resistance
The root rot organism multiplies in poorly drained soils (usually uniform, heavy clay soils or loamy surfaced soils with impermeable clay subsoils). In wet conditions on these soils, young stands of susceptible lines may be wiped out completely by the disease. In mature established hay stands under irrigation, plant death is less frequent, but the yield is significantly reduced. Most of the new lucerne cultivars possess high levels of resistance, and the range of resistances available can be matched with the soil types in individual paddocks. Under prolonged wet conditions, even the most resistant cultivars can suffer considerable plant death from phytophthora root rot. If root rot is a major concern in the area, the cultivar Aquarius should be selected because it has the highest resistance to the disease.
Leaf disease resistance
Leaf diseases are transient and usually seasonal. They are never lethal and their effects can be minimised by good cutting management. However, two diseases, stemphylium leaf spot and leptosphaerulina leaf spot (also known as pepper spot), have caused complete leaf loss in hay stands of new cultivars.
The highly winter-active lines are particularly susceptible to these diseases whereas the semi-dormant cultivars are less affected. A chemical treatment with the fungicide Rovral® is currently registered and provides some control in hay stands. The commercially available cultivar Quadrella has shown significantly lower levels of damage from these diseases in field and glasshouse studies. While damage will still occur, Quadrella appears to be able to avoid major damage from most leaf infections.
Selection for aphid resistance
Since the initial devastating infestations of lucerne aphids in 1977, subsequent outbreaks have been less severe due to the influence of introduced parasitic wasps and natural predators. Economic hay production depends on the use of insecticides, and insecticide technology for aphid control is well refined. Note that while spraying programs control aphids, they also increase the likelihood of insecticide resistance developing, and increase the cost of production. Be sure to use insecticides that have minimal affect on beneficial insects. It is always advisable to use aphid-resistant cultivars.
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