Soil management changes biological control and plant resistance to insect herbivores
Open Access
- Author:
- Rowen, Elizabeth
- Graduate Program:
- Entomology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 26, 2020
- Committee Members:
- John Frazier Tooker, Dissertation Advisor/Co-Advisor
John Frazier Tooker, Committee Chair/Co-Chair
Mary Ellen Barbercheck, Committee Member
Jared Gregory Ali, Committee Member
Armen R. Kemanian, Outside Member
Maryann Victoria Bruns, Outside Member
Gary Felton, Program Head/Chair - Keywords:
- Plant-insect interactions
fertilizer
manure
tillage - Abstract:
- Soil degradation threatens food security worldwide and has been conservatively estimated to cost $8 billion annually. In my Ph.D. thesis, I investigated the effects multiple soil health practices used to combat soil degradation (tillage, nutrient management, and cover cropping) on damage by insect herbivores to field crops. Understanding how management practices that benefit soil health affect pest management may increase adoption of these practices. Despite concerns about soil erosion, tillage is still used across much of the world to prepare fields for planting and manage pests. In Chapter 1, to evaluate how tillage practices affect abundance of invertebrate pests and natural enemies, Dr. Karly Regan and I conducted a quantitative analysis of studies published between 1983 and 2017 (a meta-analysis). Contrary to common perception, foliar pests were less abundant when tillage was avoided and communities of herbivores were different in less plowed fields. This may be due, in part, to an increase in abundance of predatory soil arthropods when soil was less disturbed by tillage. This meta-analysis offers evidence that decreasing tillage intensity may not cause as many problems for pest control as previously thought. Moreover, farm fields that experience less tillage, or do not get tilled at all, have potential to be better protected by predatory arthropods against invertebrate pests, indicating that low-disturbance farming provides an excellent base for conservation agriculture and reminding us that integrated pest management (IPM) and decreasing reliance on preventative insecticide use are key elements for maximizing some of the benefits that can be derived from no-till farming. Where farmers avoid tillage, pest management can interact with type of fertilizer used. Fertilizing with manure, for example, can increase soil microbial diversity and organic matter and improve pest management. In Chapters 2, 3, and 4, to better understand how manure can contribute to pest control, I studied how dry-stacked cow manure affected plant susceptibility to herbivores and whether manure altered biological control. Compared to synthetic fertilizer, I found, in greenhouse and field experiments, that fertilizing maize with manure decreased growth of two common caterpillar pest species (fall armyworm and black cutworm) by 8% and 40% respectively after 24h and reduced black cutworm growth by 30% after 6 d, suggesting that fertilizing with manure alters the nutritional value of plants or plant defenses against herbivore feeding. I also found, however, that manured, no-till plots tended to suffer more slug damage compared to conventionally fertilized plots. Because manure and cover crops increase residue on the soil surface, I expected these practices to increase ground predator abundance (Chapter 4). While I found manure and cover crops increased resources early in the season for predators, I did not see an effect of manure or cover on overall predator abundance. This lack of an effect may be because predators moved more in lower residue environments, but had a higher density in high residue environments (manure and cover crops). From these experiments, I found using manure as a fertilizer has pest-management benefits, but if farmers use manure in no-till fields, they should also adopt IPM to support predator communities so that they can help control slug populations. Fertilizing with manure can increase concentrations of micronutrients in the soil relative to chemical fertilization. About 50% of global soils are deficient in zinc (Zn), so farmers often apply Zn-containing fertilizer. In Chapter 5, I investigated the effect of Zn in soil concentrations found in PA on herbivore performance. Fertilizing maize with Zn increased concentrations of protein in maize tissues, which caused fall armyworm larvae to gain more weight on maize plants fertilized with more Zn. I repeated this experiment in the field, but Zn concentration in plant tissues remained low, and I did not observe effects on herbivore damage or performance. I conclude that a small increase in Zn, if taken up by the plant, maximizes plant growth without compromising plant resistance to fall armyworm. This research will help advise farmers how to increase pest resistance without using pesticides and decrease soil degradation. My results could encourage farmers to adopt soil health practices and reduce unnecessary fertilizer and pesticide inputs to save money and decrease environmental externalities.