Relationships of aphid and mite infestations to control of Botrytis cinerea by Clonostachys rosea in rose (Rosa hybrida) leaves

Infestations of aphids (Macrosiphum rosae L.) and of twospotted spider mite s (Tetranychus urticae Koch) were examined in relation to growth and sporul ation of Clonostachys rosea and Botrytis cinerea, and to suppression of the pathogen by the agent, in green rose leaves. Leaves were infested artifici ally with 10 aphids/leaflet for 3 h, or naturally with 15-30 aphids/leaflet for 7-12 days or with undetermined numbers of mites for 10-12 days. Leaves that had or had not been infested were inoculated with C. rosea, with B. c inerea, or with C. rosea plus B. cinerea. Germination incidence and germ tu be growth of C. rosea and B. cinerea on the phylloplane in most instances w ere much greater in leaves previously infested with aphids or mites compare d with noninfested leaves. After combined inoculation, C. rosea suppressed germination of B. cinerea from 47% to 19% in noninfested leaves, but in lea ves that had been infested the agent was ineffective and germination incide nce of the pathogen increased to 75-93%. Previous infestation with naturall y introduced aphids or mites, but not brief infestations of artificially in troduced aphids, markedly increased sporulation of C. rosea after the leave s died during an initial 7-15 days of incubation on a paraquat agar medium, regardless of whether or not B. cinerea was present. Sporulation of B. cin erea was similarly increased when inoculated alone. After 15-20 days, howev er, conidiophores of the agent or pathogen covered most of the leaf surface in these treatments. In leaves inoculated with C. rosea plus B. cinerea, t he agent suppressed sporulation of the pathogen almost completely in both p reviously infested and noninfested leaves. Thus, aphid and mite infestation s did not compromise the ability of C. rosea to suppress inoculum productio n by B. cinerea in the leaves. Increased nutrient availability on the phyll oplane through exudation or as honeydew or frass is proposed as a basis to explain effects of the pest infestations on C. rosea and B. cinerea.