Influences of fertilization on population abundance, distribution,and control of Frankliniella occidentalis on chrysanthemum.
by Amanda Chau, Kevin M. Heinz, and Fred T. Davies Jr.
We examined the effects of fertilization on population abundance and within-plant distribution
of western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), on potted
chrysanthemum, Dendranthema grandiflora (Tzvelev). We also investigated the effects of fertilization
on the number of insecticide applications needed to control F. occidentalis on potted chrysanthemum.
Under greenhouse conditions, rate of change in population abundance of F. occidentalis increased
with fertilization levels from 0 to 100% of the standard fertilization level (375 ppm N) and was four
times higher on plants fertilized with the standard level (rate of change = 0.14) than on plants
fertilized with 0% during the first 4 weeks after thrips inoculation. Within-plant distribution of
F. occidentalis was influenced by the phenology of the plants rather than total nitrogen content of
plant tissues. Prior to flower opening, more F. occidentalis were found in the middle region of the
plants. When the flowers began to open, more thrips were found feeding inside the flowers than on
the leaves. We further showed that production time, the time from transplantation to flower opening,
shortened considerably with increased fertilization level. Production time was shortest, 12 weeks, for
plants fertilized with 100% of the standard fertilization level. When the fertilization level was reduced
to 20%, production time lengthened to 13 weeks. When fertilization level was reduced to 0%,
production time lengthened to 14 weeks. Increased fertilization from 0 to 100% of the standard level
did not result in higher numbers of insecticide applications. All three insecticides (acephate, bifenthrin,
and spinosad) were effective in keeping the thrips infestation below a predetermined level, five thrips
per plant, but bifenthrin required the most number of applications to do so. For chrysanthemum, a
fast-growing crop and heavy utilizer of fertilizer, fertilization influenced not only the population
growth of pest insects but also plant production time. As a result, optimizing fertilization level to
reduce pest population growth may be a useful tactic in an Integrated Pest Management program
for managing F. occidentalis on potted chrysanthemum. However, the effect of fertilization on
production time and plant quality should also be considered when implementing this tactic.
EEA, Vol. 117, pp. 27-39, 2005.