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Disease Management

The first step in BYD management is accurate diagnosis of the disease. BYD symptoms may be confused with those caused by other biotic and abiotic factors. Therefore, visual diagnosis is unreliable, and diagnosis by laboratory techniques is required. The diagnostic test most commonly used to confirm infection is a serological test called enzyme-linked immunosorbent assay or ELISA (Figure 15).

Figure 15

Genetic resistance

As for many diseases caused by plant viruses, the most effective control strategies aim to prevent infection of host plants rather than to cure plants that are already infected. The method most widely used to reduce crop losses due to BYD is planting tolerant or resistant cultivars (Figure 16). In tolerant plants, viruses are still able to multiply, but few symptoms are expressed. In resistant plants, the ability of viruses to multiply and/or spread is impaired, resulting in a reduction of disease symptoms. Genes for at least partial tolerance or resistance have been identified in many of the crop plants infected by the viruses. Some plant species also have been genetically engineered to express portions of the viral genome, and some of these transgenic plants display high levels of tolerance to the disease.

Figure 16

Vector management

Another management strategy, which is sometimes feasible, is to reduce the introduction or spread of the causal viruses by aphid vectors. The viruses that cause BYD may be introduced into crops by aphids that migrate at similar times each year. Aphid populations can be monitored by catching the migrating aphids in traps (Figure 17); these aphids can then be tested for the presence of the viruses that cause BYD by ELISA or other assays.

Figure 17

When aphid migration patterns are known, it is sometimes possible to alter the planting date so that crops are older and more resistant when the seasonal migrations occur. Another strategy which may be applied when aphid populations are monitored is to reduce the spread of aphid vectors in crops through the use of insecticides. Insecticide treatments may not prevent initial virus infections, but can greatly limit the secondary spread of aphids and, therefore, of viruses. The economic costs and benefits of insecticides must be carefully calculated before an insecticide is used, particularly in relatively low value crops such as small grains. Finally, the introduction of predators and/or parasites of the aphid vectors as biological control agents has, in some cases, successfully reduced aphid populations and BYD spread.

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