Calag Archive

Conservation is often perceived simply as “using less,” but most water conservation activities affect the state of the system in three other ways: First, these activities change the time in which the resource is used: for example, a storage dam changes water flows from the time of surplus in the spring to the summer, when water is scarce and has a higher use value. Second, reducing use through more efficient irrigation makes it possible to move the water saved to another location where its value in use is higher. Third, conservation is related to quality, the concentration of existing salts in irrigation water and addition of salts from the soil. Since concentrated salts cause taste problems and shorten equipment life, users of recycled irrigation water and urban wastewater operate at a cost disadvantage in comparison with those in other areas without these problems.

Late blight has become of increasing economic importance on tomatoes in California during the last few years. Previously, the disease, caused by the fungus Phytophthora in/estans, occurred mainly in coastal areas of California where environmental conditions favored its development. The disease may attack plants at any time during the growing season and, when it is severe, all plants in a field may be killed in a week or two. Late blight also results in great losses of tomatoes in transit, storage, and market.

The corral confinement system used for intensive dairying in the Central Valley and southern California subjects the cow to various types of stress, particularly following parturition and during peak lactation. The effect of weather on these animals is of primary concern, especially in the hot, dry summer, when temperatures average highs of 95° F, with numerous days over 100° F, and relative humidity averaging 33 percent. Winters in the area are usually cool and mild; spring and fall are moderately warm.

Phytophthora root rot has been a problem for several decades in cauliflower grown in the San Francisco Bay Area. About 2,000 acres are planted to this crop annually in Alameda County, where the disease is common and often destructive, particularly in the Fremont production area.

For centuries the art of keeping and breeding birds has been practiced by aviculturists, who enjoy the companionship, beauty, and behavior of canaries, finches, parrots, and other aviary and cage birds. The science of aviculture is, however, still in its infancy except for some gallinaceous birds (chickens, turkeys, pheasants, and quail), domestic pigeons and doves, and some ducks and geese. For these food and game species, our scientific knowledge is good or sometimes excellent; for example, the nutrient requirements of poultry are well known, as are the effects of deficiencies or excesses of nutrients. In contrast, most companion birds are poorly understood with regard to needs for growth, maintenance, and reproduction. Some reasons for this disparity in information reside in the nature of the bird business, with its diversity of species and sizes of production units; the dependence of dealers on the supply of certain imported, wild-caught birds instead of on local breeders; and the difficulties of studying altricial birds, which depend entirely on their parents for early care, as compared with precocial birds, which can feed themselves immediately after hatching.

Aphids occasionally cause substantial yield losses in California strawberries, usually as a result of honeydew accumulation from large populations of the pest. Honeydew deposits on the fruit permit development of sooty mold and attachment of the white skins shed by aphid nymphs; this contamination renders the fruit unmarketable. Many growers therefore apply pesticides regularly to prevent aphid population buildup. Viruses transmitted by aphids also can cause significant damage, but pesticide applications to reduce virus transmission are uneconomical.

The root lesion nematode causes a gradual decline and, if uncontrolled, a severe loss in production (quality as well as quantity) of greenhouse-grown roses. The disease progresses gradually; aboveground symptoms include lack of vigor, chlorosis, and generally sparse vegetative growth with shortened blossom stems. Diseased roots may have distinct small brown lesions at first, but these usually expand until they coalesce and the tissue deteriorates.