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Fluid Journal : Fluid Journal 1996-1998
Fall 1996 Summary: Because soil fertility can impact root system growth, ag scientists are exploring the possibility that managed fertilizer applications could lessen the impact of rootworm larval feeding damage on the root function of corn. Recent research has shown that increased N fertilizer rates have resulted in larger root system size and reduced lodging in rootworm damaged corn plants. Root systems were also larger under split-applied banded N than under planting-time broadcast of N. Even at low levels of damage through infestation, lodging was reduced by split-applied banded N. The data suggest that N fertilizer management could play an important role in an integrated crop management strategy to improve rootworm tolerance. _______________________________ Damage inflicted on corn root systems by corn rootworm larvae can cause biological stress to the host plant. Reduced ability to absorb water and nutrients, reduced root hormone biosynthesis, and increased shoot lodging are important stresses that can cause grain yield reductions in root-damaged plants. Because of potential interactions between soil fertility and root system growth, experiments have been conducted to see if it is possible that fertilizer management can reduce stress and improve plant tolerance to rootworm damage. The theory behind these studies is that if improved plant tolerance could be consistently achieved across environments, then perhaps fertilizer management could play an important role in an integrated crop management strategy to reduce grain yield loss owing to corn rootworm infestations. The objectives of this report are to 1) review pertinent information on rootworm larval damage and nutrient relations in corn, 2) present data that relate root system damage to plant physical and morphological characteristics, and 3) present preliminary data on fertilizer placement effects on plant tolerance to rootworm larval feeding damage. Root absorption impaired In an average year, larval feeding begins about early to mid June and lasts until about mid to late July. A plot of nitrogen (N), phosphorus (P), or potassium (K) shoot concentrations (Figure 1, top) reveals that during the time of early larval feeding, both N and P have reached their highest tissue concentrations while K tissue concentration is still increasing. Plots of these data also reveal that the levels of all three of these nutrients are accumulating in the shoots at near linear rates throughout the larval feeding period (Figure 1, bottom). The graph suggests that if root damage caused by rootworm feeding impairs root absorption of N, P, or K, the concentration or level of these essential plant nutrients could be drastically less in shoots of rootworm damaged plants than undamaged plants. This contention is partially supported by research showing K shoot tissue concentration can be reduced by severe larval damage. While additional research has provided indirect evidence that corn rootworm damaged plants are not as efficient in absorbing nitrogen from the soil as undamaged plants, other research has shown that shoot N concentration is not reduced in plants severely damaged by larvae. Obviously, further work in this area is needed before a complete understanding of the interactions between soil fertility, root growth dynamics, nutrient absorption, and insect damage is achieved. Synchronization deadly Corn rootworm larvae pass through three subterranean developmental stages. First stage larvae are relatively small, but they perform an important role of establishment of the insect upon the host plant. Second and third stage larvae are progressively larger and more damaging to the root system than first stage larvae. Because one generation of insects Dr. Walter E. Riedell N Fights Corn Root Worms? Data from South Dakota research suggest that N management could play an important role in improving tolerance to corn root worms.
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