Resistance foliar

The most serious disease problems encountered in organic crops are blight in potatoes and seedbome diseases in cereals. Plant breeders are improving blight resistance in potatoes. As organically grown cereal seed cannot be treated, it is very important that it is tested for seed-borne diseases such as fusarium and smut. Foliar diseases in organic... 

Zlesak, D. C., Thill, C. A. (2004). Foliar resistance to Phytophthora infestans (Mont.) de Bary (US-8) in 13 Mexican and South American Solanum species having EBNs of 1, 2, and 4 and implications for breeding. American Journal of Potato Research, 81, 421 29. 

Chiang, M.Y., C.I. Yuan, and Y.J. Chiang (2004). Weeds resistant to foliar applied herbicides in Taiwan. 4th International Weed Science Congress, p. 61, S17MT08P07. 

Single tree injection is used to remove cull hardwoods from sites during site preparation, pine release, or for timber stand improvement. Tree injection is efficient on sites with a sparse distribution (100 stems per acre, or less) of hardwoods greater than 1 inch dbh. The method is useful for control of species resistant to foliar treatments or stems missed during foliar application. 

Insects have evolved resistance to Bt toxins in the laboratory, yet only one crop pest, the diamondback moth (Plutella xylostella), has evolved resistance to Bt toxins under open field conditions (Tabashnik et al. 2003). But this resistance was not caused by Bt crops, rather it occurred in response to repeated foliar sprays of Bt toxins to control this pest on conventional (non-GE) vegetable crops (Tabashnik 1994). Based partly on the experience with diamondback moth and because Bt crops cause season-long exposure of target insects to Bt toxins, some scientists predicted that pest resistance to Bt crops would occur in a few years. 

Another kind of environmental interaction may result when in a homeostatic adjustment to the pollutant, the plant sacrifices part of its capacity to respond to environmental fluctuations. For example, the metabolic adjustment to fluorides may increase the susceptibility to nutrient stress. This hypothesis could explain why some symptoms of chronic fluoride toxicity resemble those produced by Mn, Fe, or Zn deficiencies. If air pollution is one environmental factor that alters the susceptibility of the plant to other environmental stress, it would also be logical to expect an interaction between pollutants if the receptor is exposed to two or more of them. Such interactive effects have been found. Sub-threshold concentrations of SOL> and 03 or S02 and N02 produce foliar lesions when plants are exposed to both pollutants (34). Additionally, plants exposed to S02 differ from non-fumigated plants in their resistance to subsequent fumigations (35). Thus the plants susceptibility or capacity to adapt to a pollutant is altered by concurrent exposures to another or consecutive exposures to the same one. 

There is also the possibility that pollutants alter susceptibility of the plant to pathogens (36) or insect attack. Of the latter there is the decreased resistance of ponderosa pine to bark beetle attack caused by ambient oxidant exposure (37). The investigations of others with respect to the effects of fluoride on ponderosa pine indicated that although foliar injury was associated with increased resin exudation pressure, which could be interpreted as an increased capacity of the tree to overcome bark beetle attack, degree of insect infestation was not associated with amount of foliar injury (38). As more is known about pheromones, the botanical investigation of the secondary products of metabolism, such as terpenes and phenolics, may become more important in investigating the mode of action of pollutants in the entire plant. The switch to alternate pathways, while resulting in the same products, may reduce the intermediates needed in biosynthesis and thereby affect the plants resistance to disease or attractiveness to insects. 

Agronomic and other cultivated species would not be acutely impaired if future oxidant and sulfur dioxide levels remain as they are today. There appears to be sufficient genetic resistance to foliar injury within cultivated species that cultivars which are resistant to existing... 

Since most fungicides are applied as foliar sprays, they must be formulated so that when deposited on the plant, they are resistant to the effects of weathering. 

Its outstanding performance, strategy elements like limited number of applications or exclusive use of prepack mixtures against foliar pathogens were not easily accepted, particularly when resistance had not appeared In a given crop or region. It must be stressed that It Is of crucial Importance that a uniform, consistent strategy is applied In multinational companies. 

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