Physical Controls

V hen pests appear on plants, the most direct way to get rid of them is to pick them off. You can also handpick diseased leaves or other plant parts, limiting the ability of the infecting organism to further colonize them. In some cases this simple action effectively cures the host plants. 

Handpicking and other physical controls are among the most straightfonvard and safe techniques for protecting plants. Most such controls rely on the gardener s ability to remove or exclude pests from plants or to lure pests away from plants and/or into traps. 

In general, physical control methods are more often used to control insects than to control diseases. There is a wide variety of traps and barriers that thwart many common insect pests. Physical control of disease organisms is limited to removing diseased plant parts by hand or with pruning tools. 

Very few insects have mandibles strong enough to bite into human skin, although a few, such as the striped blister beetle, can cause skin irritation if you squash them in your hands. Likewise, few plant diseases cause corresponding human illnesses. Howes er. you can wear rubber gloves when handpicking pests if it makes you more comfonable with the job. You can also remove some types of insects with a small hand-held vacuum, while other types can be shaken off a plant onto a dropcloth. 

Besides the obvious benefits of trapping pests, you can use traps to warn of impending infestations. If you get early warning of the appearance of apple maggots, it will prompt you to quickly hang apple maggot traps in your trees. Traps like yellow sticky traps attract insects with color other traps use chemicals produced by insects (pheromones) or plants to lure the insects to the trap. 

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Physical controls are generally only applicable in lakes. The infinence of river morphology on eutrophication is not sufficiently well understood to be used effectively. The exception to this would be the short-term use of high flow to reduce the retention time to levels which limit growth rates of nuisance species such as cyanobacteria. 

Green, P.B., Erickson, R.O. Buggy, J. (1971). Metabolic and physical control cell elongation rate in vivo studies in Nitella. Plant Physiology, 47, 423-30. 

Gross motor impairment and lack of physical control. Blurred vision and major loss of balance. Euphoria is reduced, and dysphoria is beginning to appear. 

Sauerbom J, Linke KH, Saxena MC, Koch W (1989) Solarization a physical control method for weeds and parasitic plants (Orobanche spp.) in Mediterranean agriculture. Weed Res 29 391-397... 

The interplay of physical controls is less complicated in the Polar and Trade (tropical) domains. As shown in Figure 24.11a, only one phytoplankton bloom occurs in the Polar domain, but is larger in amplitude than at mid-latitudes (Westerlies). Phytoplankton growth in the subpolar region is prolific because uniformly cold atmospheric temperatures suppress density stratification of the water column. Abundant winds ensure that... 

The second assxmiption of the model that the characteristic buildup time is chemical-physical controlled, implies that this time is dependent on the chemical, physical and electrical properties of the foulant and the membrane but not on the flow. 

In this section we will develop the mathematical tools to describe mass transfer at diffusive boundaries. Again, it is our intention to demonstrate that diffusive boundaries have common properties, although the physics controlling them may be different. We will then apply the mathematical tools to the process of dilution of a pollutant cloud in an aquatic system (ocean, lake, river). Here the boundary is produced by the localized (continuous or event-like) input of a chemical that first leads to a confined concentration patch. The patch is then mixed into its environment by diffusion or dispersion. Note that in this case the physical characteristics on both sides of the... 

Feller, C., and Beare, M. H. (1997). Physical control of soil organic matter dynamics in the tropics. Geoderma 79, 69-116. 

Lorens R.B. (1978) A study of biological and physical controls of the trace metal content of calcite and aragonite. Ph.D. Dissertation, Univ. of Rhode Island. 

The physically controlled component ))7 S was estimated from viscosity measurements conducted on subsamples after passing through 0.20 pm pore size filters. The biologically induced excess viscosity >/Bio (cP) was subsequently defined from each water sample as ... 

When discussing diffusion, one inevitably needs to solve diffusion equations. The Laplace transform has proven to be the most effective solution for these differential equations, as it converts them to polynomial equations. The Laplace transform is also a powerful technique for both steady-state and transient analysis of linear time-invariant systems such as electric circuits. It dramatically reduces the complexity of the mathematical calculations required to solve integral and differential equations. Furthermore, it has many other important applications in areas such as physics, control engineering, signal processing, and probability theory. 

Soltwisch H., Stodiek W., Manickam J., Schlueter J., Proc. 11th Int. Conf. Plasma Physics Controlled Nuclear Fusion Research, Kyoto, Vol. 1, 263 (1986)... 

Computer modeling is a distinct type of scientific technique that bridges fimdamental theory with experimental observation on complex systems. Its success rests first on the fact that the basic physics controlling the behavior of matter at the atomic level has been established for over seventy years secondly on the development over the last twenty years of approximate but effective methods for implementing this physics in complex systems and thirdly on the ability of modem computers to handle the enormous demands regarding both processing power and memory required for realistic modeling of complex systems. 

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