Laboratory Report

By: Robert D Raabe

Robert D Raabe is Professor Emeritus of Plant Pathology at University of California, Berkeley. He introduced a faster method of…

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Energy from Switch Grass

As early settlers moved west from the eastern forests, they encountered a head-high sea of grasses. The soils were high in organic matter and rich in nutrients, yet attempts to cultivate the soils were seldom successful, because the root systems of the grasses extended eight to ten feet deep. In 1837, the steel plow was invented, and that changed many things. Under cultivation, the soils were subjected to erosion, leaching, and nutrient and water depletion. In light of the current energy crisis, researchers are exploring the value of the land for raising plants high in cellulose, which can be used to produce ethyl alcohol (ethanol), thanks to advances in cellulose fermentation. Work in Washington’s Yakima Valley with switch grass (Panicum virgatum), grown on soils somewhat drier than those in the Great Plains, showed that switch grass and possibly other prairie grasses could be a viable resource for the production of ethanol.

Switch grass can be harvested twice in a season, yielding as much as ten tons of biomass per acre and one hundred gallons of ethanol. The advantages of this over ethanol from corn are many. The amount of energy derived from corn ethanol (made from the sugars in corn) is only twenty-five percent above the energy required to produce it. Cellulitic ethanol (made from the cellulose in grass leaves and stems) can yield four times as much energy as required to produce it. Switch grass is a perennial and needs replacing only every five to ten years. It can grow on much less water than corn, needs little or no fertilization, and has few insect or disease pests. It also is not a food crop. The use of corn as an ethanol source already has caused an increase in the cost of corn, which is reflected in the supermarket prices of meat, dairy products, cereals, and other foods containing corn and corn by-products. If all of the corn now grown in the US were used to produce ethanol, it would meet only twelve percent of our present energy needs.

Switch grass also improves the soil upon which it is grown and prevents erosion. It serves as wildlife habitat for birds and a number of small animals. The cultivation of switch grass on marginal lands, or on lands not generating much income, could provide farmers as much as five billion dollars in revenue per year. At the same time, this would reduce US greenhouse gas emissions by 1.7 billion tons per year. Switch grass alone cannot solve all of our energy problems, but it can make a significant contribution in combination with other sources of cellulose, such as other grasses, tree plantations, residue from logging operations, and leftovers from the harvesting of food crops—all of which are cheap and sustainable. Audubon September-October 2007: 81-86.

Ladybug Control of Powdery Mildew

A California researcher, working on biological controls for powdery mildews, became interested in a native North American, ash gray ladybird beetle (Psyllobora vigintimaculata) that had been discovered on roses and gerbera in greenhouses. The beetle was unable to survive on a typical ladybird beetle diet of insects and mites unless powdery mildew spores were also present as a food source. The beetle was found consuming isolated colonies of powdery mildews, nearly year around, on a range of at least thirty-nine different kinds of plants, including fruit trees, grape vines, ornamental trees and shrubs, annuals, and perennials. It was found that a single larva was capable of clearing powdery mildew from an area of approximately one square inch from the time the egg hatched until the larva pupated. IPM Practitioner 20 (516): 15-16.

A New Cranberry

The cultivated American cranberry (Vaccinium macrocarpon) is important, in part, because of its brilliant color, which is made up of many anthocyanins, a subclass of flavenoids. These anthocyanins have been studied for their possible health benefits, including their role as antioxidants. Vaccinium researchers in New Jersey found one species from Alaska (V. oxycoccus) that was so closely related to American cranberry that viable inter-specific hybrids could be made. They also found that anthocyanins are generally linked to glucose. In the case of American cranberry, its anthocyanins are bound to the less soluble sugars (galactose and arabinose), with less than five percent linked to glucose. Flavenoids bound to glucose are more readily absorbed by humans than those bound to the other sugars. In the hybrid cranberries, up to fifty percent of their anthocyanins are linked to glucose. In addition, the hybrids deliver proanthocyanidikins, which inhibit Escherichia coli (E. coli) bacteria from adhering to the bladder and causing urinary tract infections. Selections from among the hybrids have proven to be vigorous, adaptable, and productive. The next step is convincing growers to accept the new cultivars. Agricultural Research 56 (1): 22.

Insect Control by Cockroaches

The Asian cockroach (Blatella asahinal) was introduced to Florida in 1996 and, like most cockroaches, is now considered a pest. However, in 2006, an entomologist working on biological controls for cotton’s various insect pests found a large number of Asian cockroaches in a soybean field near Weslaco, Texas. The cockroaches were feeding on bollworm eggs but were not damaging the soybeans. By studying the feeding habits of the cockroach on soybeans and cotton, it was found that, although primarily nocturnal, the cockroaches provided good control of pests both day and night. Because it can become a household pest, there are no plans to release the Asian cockroach, but, because it already is there, entomologists are working on ways that the cockroaches can become more useful. Agricultural Research 56 (1): 11.