Fertility Affects Susceptibility of Chrysanthemum to Cotton Aphids (Aphis gossypii): Influence on Plant Growth and Physiology

by Fred T. Davies, Jr., Chuanjiu He, Amanda Chau, Kevin M. Heinz, and Andrew D. Cartmill

This research details the influence of fertility on plant growth, photosynthesis, ethylene evolution, and herbivore abundance of chyrsanthemum (Dendranthema grandiflora Tzvelev var. Charm) inoculated with cotton aphids (Aphis gossypii Glover). We tested five fertilization treatments that consisted of 0%, 5%, 10%, 20%, and 100% (375 ppm N) of recommended nitrogen levels. After five weeks, plants were inoculated at five aphids per 6-in. pot containing four rooted cuttings. Plants were grown in growth chambers.

The cotton or melon aphid (Aphis gossypii Glover) is a serious economic pest of greenhouse crops such as chrysanthemum (Dendranthema grandiflora Tzvelev var. Charm) (2). High densities of cotton aphids can occur throughout the chrysanthemum production cycle because of favorable greenhouse growing environments and the prolific reproduction of aphids. Chrysanthemum cultivars differ in susceptibility to aphids (1). The greenhouse environment and cultural conditions contribute to host-plant resistance or susceptibility (6).

Fertilizers used in nursery - greenhouse industries are an important source of essential elements for both chrysanthemums and aphids. High nitrogen fertility can increase insect populations and decrease secondary metabolites, such as phenolics, reducing the chemical resistance of host plants to aphids. During commercial production, chrysanthemums are fertilized at high fertility (i.e., 375 ppm N for pulse feeding). However, unlike agronomic or other field crops, there is near zero tolerance for any aphids during greenhouse crop production of chrysanthemum. In short, strategies for optimizing greenhouse chrysanthemum nitrogen fertilization while simultaneously controlling aphid population development have led to mixed results (1).

Hence this study tested the hypothesis that moderate levels of nitrogen would better control cotton aphids on chrysanthemum. While aphids are known to reduce plant quality, there have been few comprehensive studies on plant response to aphid population dynamics.

SNA Research Conference. 48: 168-172. 2003.