Effects of sustainable and conventional fertilizers on plant growth and insect life history traits
Abstract
Little is known about the effects on plant growth and pest abundance as sustainable fertilizers are becoming more common in greenhouse production. I conducted two studies to test the effects of sustainable production practices on plant growth and insect life history traits. In the first study, five species of bedding plants were produced under conventional or sustainable growing practices to measure their effects on plant growth. Significant differences in plant growth in this study favored the sustainable treatment, although overall, plant growth was not affected by treatment. In the second study, poinsettias (Euphorbia pulcherrima Willdenow ex Klotzch) were grown with five fertilizer treatments and infested with silverleaf whiteflies (Bemisia tabaci biotype B (Gennadius) (Hemiptera:Aleyrodidae)) to test the effects on plant growth and insect life history traits. The poinsettias were fertilized with sustainable water-soluble fertilizer (WSF), conventional WSF, weekly alternation of these, controlled-release fertilizer, or clear water. Here, poinsettias grown with the sustainable WSF did not grow differently from those grown with the conventional WSF. The clear water treatment greatly reduced survivorship of whiteflies compared with all other treatments, which suggests that nutritional deficiency is a cause, due to the limited plant growth observed on poinsettias in the clear water treatment. Fecundity was reduced on both the clear water and sustainable WSF treatments. The trend varies from that observed among treatments when survivorship was calculated, and poinsettias in the Daniels Plant Food treatment contained the highest amino acid concentration compared with the other treatments. This suggests that other explanations such as plant defense mechanisms may be involved. Plants in the clear water control exhibited the lowest concentration of free amino acids, while those in the sustainable WSF treatment exhibited the highest concentration of free amino acids. Whitefly survivorship was greatest on plants with intermediate levels of total free amino acids. In addition, the proportion of shikimic pathway amino acids was negatively correlated with whitefly survivorship. These observations suggest a combination of nutritional and plant defense effects on whitefly life history. Variation in amino acid concentration in petioles of plants treated with fertilizers makes it difficult to predict whether a particular fertilizer will produce plants with enough amino acids to deleteriously affect both survivorship and fecundity. However, my observations allow me to conclude that the use of this sustainable fertilizer will not cause increases in whitefly populations relative to plants fertilized with other fertilizers that deliver the same level of nitrogen to the plant.
Degree
M.S.
Advisors
Sadof, Purdue University.
Subject Area
Entomology|Horticulture
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