Interaction between phyllosphere yeasts, aphid honeydew and fungicide effectiveness in wheat under field conditions

Abstract

Aphid honeydew can reduce fungicide effectiveness against necrotrophic pathogens of wheat under controlled conditions. In 1988 and 1989, field experiments were carried out at different locations in The Netherlands, to assess the interference of honeydew with fungicide effectiveness under field conditions, and to establish whether honeydew consumption by naturally occurring saprophytes could prevent this effect. Different combinations of chemicals were used to create differences in saprophytic population densities and aphid populations, which were expected to result in differences in the amount of honeydew and other nutrients on the leaves. In two of the experiments, Septoria nodorum was the only necrotrophic pathogen present; in the other two the only necrotroph was S. tritici. On several sampling dates, the effect of the fungicides was significantly enhanced by addition of insecticide, most often when the saprophytes were reduced by maneb/anilazine. This effect of insecticide is ascribed to prevention of interference of honeydew with fungicide activity, and not to a direct effect of insecticide, as insecticide alone had no effect on necrosis. On the basis of the fact that interference of honeydew with fungicide activity was most apparent when saprophytic population densities were reduced, it is concluded that the naturally occurring saprophytes can generally prevent the effect of honeydew. The same interactions are likely to occur between other nutrients and fungicides, and it is therefore argued that the naturally occurring saprophytes should be protected by elimination of harmful chemicals.

Three‐way Interactions Between Plant Pathogenic Fungi, Herbivorous Insects and Their Host Plants

“…Honeydew can be utilized by other necrotrophic pathogens, including Septoria nodorum (Dik, Fokkema & van Pelt, 1991), that use nutrients from the phyllosphere for germination or superficial mycelial growth before penetrating the leaf (Dik & van Pelt, 1992)~ and appeared to stimulate the growth of Aspergillusfiavus on host foliage (Diener et al, 1987). T h e populations of four saprotrophic fungi on wheat were increased up to 10-fold by honeydew applications (Fokkema et al, 1983).…”

Changes of Scots Pine Phyllosphere and Soil Fungal Communities during Outbreaks of Defoliating Insects

“…It is known that defoliating insects contribute to the dispersal of bacteria on the phyllosphere [45]. Studies on honeydew-excreting aphids showed that C-rich insect excreta significantly increased the growth of phyllosphere bacteria, filamentous fungi and yeasts [16,17]. For example, heavy infestations of eastern hemlock (Tsuga canadensis L.) with hemlock wooly adelgid (Adelges tsugae A.)…”

“…In a pioneering study by Yang et al [15], DGGE revealed that microbial populations inhabiting the phyllosphere are much more complex than previously assumed. Studies on honeydew-excreting aphids suggest that C-rich insect excreta promote the growth of phyllosphere bacteria, filamentous fungi, and yeasts [16,17]. Beside excreta, the growth of microorganisms inhabiting the phyllosphere is enhanced by nutrient leaching from leaves damaged by folivorous insects [18][19][20][21].…”

The Plant–Aphid Universe

“…The coating of plants with honeydew can contribute to the spread of fungi that can damage plants (Reynolds and Volk, 2007). Honeydew produced by aphids has been observed to reduce the effectiveness of fungicides by obstructing their absorption (Dika and Van Pelt, 1992). The damage to plants, and in particular, commercial crops, has resulted in considerable resources and efforts being spent attempting to control aphid activities (McGavin, 1993).…”