Barrier crop

Spatial isolation Crops sown distant from pest or pathogen hosts, weeds, non-crop hosts removed, barrier crops or natural strips, physically distant from all coloniser pools Occasional Rare... 

Copper is not accumulated from soils by most crop plants, suggesting a soil-plant barrier for copper (Levine et al. 1989). Thus, com (Zea mays) did not accumulate copper from soils treated with 365 kg of copper per surface hectare (as copper-rich pig manure or copper sulfate) over a 13-year period. Com yield is not affected under these conditions (Reed et al. 1993). 

To determine the suitability of fluorinated HDPE containers as packaging material for the solvent-based formulations, the containers were placed in well-ventilated ovens at 50°C for 28 days. During this period the mass loss of the contents was monitored. To date more than 130 liquid crop protection chemical formulations have been evaluated at the AEC by this method with at least 91 of them having serious permeation problems through the untreated HDPE containers. In only two cases fluorinated containers did not have acceptable barrier properties. 

Keep out pests with barriers, traps, and crop covers. 

Shelter Protect exposed sites with pemianent or temporary windbreaks such as hedges, fences, or netting. Protect individuai crops with barriers, cloches, or other covers, especially when young. 

Larvae of the carrot rust fly will feed on the roots of all members of this family, but it is only a major pest of carrots. Barriers and crop... 

For farmers, controlling weeds in crops is absolutely essential. Lacy (1985) summarized weed control objectives as reducing the competitive ability of an existing population of weeds in a crop establishing a barrier to the development of further significant weeds within that crop and preventing weed problems in future crops either from an existing weed reservoir or from additions to the weed flora. 

Bio-control using pathogens holds promise mostly in non-cropland situations because of the slow pace of control of weeds and the wider window for control as compared with the shorter window of the cropping season and associated disturbances under cropland situations. However, in aquatic systems they appear to be more realistic, due to the absence of such cropping barriers and enhanced mode of dispersal in water. Among the wetland weeds, Echinochloa crusgalli and Cyperus rotundas are being... 

While the forest was a supply of timber for homes, fuel, and often times, food, they were also sometimes regarded as a barrier. The labor to cut and burn the forest, to eke out crop land and impediments to vehicular travel, were not regarded as a benefit. Thus, for years the migrants cut and burned their way until they crossed the Appalachians and began the process again at the Rockies after having crossed the Great Plains. 

The assessment of plant-available soil contents can frequently be achieved and validated by field experiments for nutritionally essential elements, and, for a few potentially toxic elements such as chromium, nickel and molybdenum, at the moderately elevated concentrations that can occur in agricultural situations. The validation of extraction methods, devised for agricultural and nutritional purposes, is much less easy to achieve when they are applied to heavy metals and other potentially toxic elements, especially at the higher concentrations obtained in industrially contaminated land. This is not surprising in view of the fact that for some heavy metals, for example lead, there is an effective root barrier, in many food crop plants, to their uptake and much of the metal enters plants not from the root but by deposition from the atmosphere on to leaves. In these circumstances little direct correlation would be expected between soil extractable contents and plant contents. For heavy metals and other potentially toxic elements, therefore, extraction methods are mainly of value for the assessment of the mobile and potentially mobile species rather than plant-available species. This assessment of mobile species contents may well, however, indicate the risk of plant availability in changing environmental conditions or changes in land use. 

Microencapsulation can be used to provide a temporary barrier between a chemical species and its surrounding environment see also Section 14.3). This permits controlled (slow) release of the active agents following application. Depending on the product and the situation, an active ingredient such as a pesticide may need to be released slowly at low concentration, or slowly at high concentrations. Such controlled release can both reduce the number of crop applications that are required and also help prevent over use and subsequent run-off. The barrier can be provided by a polymer film, in the case of suspensions [867], or a liquid membrane, in the case of single or multiple emulsions [865], Microemulsions have also been used [234,865],... 

The ozone layer around the Earth has provided us all a natural ring of protection from harmful UV radiation. However, multiple anthropogenic activities have acted as barriers and often caused damage to this shield. Less protection from UV light will, over time, lead to increased health problems and crop damage. Major health problems linked to overexposure to UV radiation by the depletion of ozone include skin cancer (melanoma and nonmelanoma), premature aging of the skin and other skin problems, cataracts and other eye damage, and suppression of normal immune system function.29... 

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