Pest and disease problems of Andropogon gayanus | [Problemas causados por plagas y enfermedades en Andropogon gayanus]

Forty-two different fungal pathogens and 26 species of nematodes have been described on A. gayanus and A. tectorum in Africa and tropical America, although the majority are in Africa. To date, no diseases caused by bacteria, mycoplasmas, or viruses have been found. Among fungal pathogens described from Africa: seven different rusts, including Puccinia, Ramularia, and Uredo; nine different smuts, including species of Balansia, Sorosporium, Sphacelia, Sphacelotheca, and Ustilago; and several leaf-spotting fungi including Ascochyta, Cercospora, Phyllachora, Sclerotium root-and-collar rot, and Myriogenospora twisted top have the potential to damage A. gayanus. In contrast, in tropical America only the fungi Rhynchosporium oryzae, the causal agent of scald, and Myriogenospora sp. have potential to cause damage. To date, no serious fungal disease has been detected on A. gayanus in Colombia. Nematode species of Helicotylenchus, Tylenchorhynchus, and Xiphinema were hosted by A. gayanus in Nigeria and Colombia. Although no serious nematode disease has yet been found on A. gayanus, the association of these parasitic nematodes with this grass merits further investigation. Six orders, 24 families, and 45 genera (50 species) of insects have been found associated with A. gayanus in tropical America. Among those considered as sporadic pests which can cause localized damage are the yellow aphid Sipha flava, and the foliage-feeding Lepidoptera Mocis latipes and Spodoptera frugiperda. The most important pest of A. gayanus in tropical America is the leaf-cutting ant, particularly species of Atta and Acromyrmex which have caused considerable damage during establishment and in well-established stands. At present, research is focused on further understanding this problem. Unlike many grasses in tropical America, A. gayanus is highly resistant to the major pest, spittlebug. Although little information could be found on specific insects associated with A. gayanus in Africa, with the exception of termites and migratory locusts, it has been established that very few of the insects associated with A. gayanus in tropical America are found in Africa. The exceptions include several hemipterous and coleopterous flower-feeders, lepidopterous foliage feeders such as Mocis and Spodoptera, and insect predators and parasites of the order Braconidae. The majority of insects associated with A. gayanus in tropical America are local. This grass is apparently free of its important African pests in tropical America. Because few important problems to date have been detected on A. gayanus, not a great deal of work has been done on the management of its pests and diseases. Cultural control has shown potential in the management of leaf-cutting ants. For the pasture establishment phase, both strategic soil preparation and, to a lesser extent, burning have been successful in reducing ant populations. Both burning and grazing management have shown potential in reducing various pests and fungal diseases; both could be further considered in solving future problems. Potential biological control agents have been identified for several pests of A. gayanus although further work is necessary to assess their roles in the pasture ecosystem. Resistance of A. gayanus to spittlebug has received considerable attention. Various studies have shown that resistance to this serious pest is based on antibiotic, physical, and anatomical factors. In addition, the natural diversity existing within the CIAT 621 population probably also encompasses diversity for resistance to pests and diseases. This should be maintained during any genetic manipulation of this accession. Andropogon gayanus is notably free from damaging pests and diseases throughout the major ecosystems of tropical America. It is of particular interest that the plant has apparently escaped its potentially damaging fungal pathogens and insect pests recorded in Africa. Because of this, considerable care must be taken with any future introductions of this grass and other grasses from their native habitat to prevent accidental entry of any African pest or pathogen