Influences of fertilization on Aphis gossypii and insecticide usage.
by A. Chau, M. Heinz, and F. T. Davies Jr.
Fertilization levels for ornamental crops may influence pest population dynamics,crop quality,and pest
management strategy. We examined the effect of fertilization on population growth and within-plant distribution of
melon or cotton aphid, Aphis gossypii Glover,on potted chrysanthemum, Dendranthema grandiflora (Tzvelev). In terms of pest management implications, we also investigated the effect of fertilization on the number of insecticide
applications needed to control A. gossypii on potted chrysanthemum. Population growth rate of A. gossypii increased with fertilization levels from 0 to 38 ppm N and reached a plateau from 38 to 488 ppm N. Increased fertilization
beyond 38 ppm N, 10% of the commercial standard, did not result in higher aphid number. Aphids responded to
nutrient availability of plants by distributing themselves in areas with higher level of nitrogen. More aphids were found
in the apical and middle strata of the plants than the basal stratum, which had the lowest nitrogen content. Leaf
nitrogen content increased with increased fertilization level and was consistently higher in the apical and middle strata
than the basal stratum. Increased fertilization from 0 to 375 ppm N did not result in higher number of insecticide
applications. All three insecticides (bifenthrin, kinoprene or pymetrozine) were effective in keeping the aphid infestation
below a pre-determined level, ?ve aphids per plant, but pymetrozine required the least number of applications. For
chrysanthemum, a fast-growing crop and heavy utilizer of nitrogen, increased fertilization shortened the time to
flowering, which would allow growers to harvest their crop sooner and reduce the time for aphid population growth.
Reduction in time to harvest could result in signi ?cant reduction of insecticide usage by reducing the time for aphid
population growth. As a result, high fertilization together with minimal runoff may be a useful tactic to an integrated
pest management (IPM) programme for managing A.gossypii on potted chrysanthemums.
JEN, Vol. 129(2), pp. 89-97, 2005.