Crops early vegetable

Plants can also be pests that need to be controlled, particulady noxious weeds infesting food crops. Prior to 1900, inorganic compounds such as sulfuric acid, copper nitrate, sodium nitrate, ammonium sulfate, and potassium salts were used to selectively control mustards and other broadleaved weeds in cereal grains. By the early 1900s, Kainite and calcium cyanamid were also used in monocotyledenous crops, as well as iron sulfate, copper sulfate, and sodium arsenate. Prom 1915 to 1925, acid arsenical sprays, carbon bisulfate, sodium chlorate, and others were introduced for weed control use. Total or nonselective herbicides kill all vegetation, whereas selective compounds control weeds without adversely affecting the growth of the crop (see Herbicides). 

The increased use of IV-methyl carbamate insecticides in agriculture demands the development of selective and sensitive analytical procedures to determine trace level residues of these compounds in crops and other food products. HPLC is the technique most widely used to circumvent heat sensitivity of these pesticides. However, HPLC with UV detection lacks the selectivity and sensitivity needed for their analysis. In the late 1970s and early 1980s, HPLC using post-column hydrolysis and derivatization was developed and refined with fluorescence detection to overcome these problems. The technique relies on the post-column hydrolysis of the carbamate moiety to methylamine with subsequent derivatization to a fluorescent isoindole product. This technique is currently the most widely used HPLC method for the determination of carbamates in water" and in fruits and vegetables." " ... 

Maneb 486 (Figure 25) is an ethylene bis-dithiocarbamate (EBDC) fungicide used in agriculture for the control of early and late blights in potatoes and tomatoes, as well as many other diseases in fruits, vegetables, field crops, and... 

Some vegetables, such as cabbages, carrots, cauliflowers, leeks, lettuces, onions, and peas, have a range of cultivars for different seasons some can even be available to harvest all year, depending on the severity of your climate. Cultivars described as "quick" or "early" are especially useful at both the beginning and the end of the growing season, as they produce a crop more quickly than main crops. Others have been bred to tolerate cold conditions. 

Early field surveys depended on identification of a syndrome of responses that included symptoms on both native and cultivated plant species. Middleton and Paulus directed the first large-scale survey to determine the extent and severity of photochemical-oxidant effects in California on crops of agronomic importance. Th delineated four categories of crops (field, flower, fruit, and vegetable) and one of weeds. This was the most extensive survey of oxidant effects until the late 1960 s. The information was later used as a basis for subjective estimates of economic losses. This type of visual assessment of foliar injury has been attempted in many states and has been purposefully developed in some for use in economic estimates of damage to vegetation. 

The bioassay technique was developed to reduce the uncertainties associated with the use of native vegetation or cultivated crops. Plants can be started under controlled conditions and exposed under standardized conditions. Species and cultivars can be selected for oxidant sensitivity and symptom characteristics. The two studies just noted were the most closely controlled. Similar work has not been repeated. However, many investigators have grown plants under known cultural conditions and then transplanted them to field sites where they received special care. These plants can then be read for foliar symptoms throughout a given period, and the symptoms related to oxidant concentrations. The lack of apparent correlation in the two early studies could be due to the lack of specificity for the monitored oxidants, the presence of different concentrations of interacting oxidants at different times, or variations in cultural conditions between exposure times. 

In 1936 Sinox, a dinitro selective weed killer, was introduced and widely used, not only in cereal crops but in peas, onions, flax, and other important crops. In the early forties a private dealer in the Salinas Valley of California discovered the selective herbicidal use of stove oil in carrot crops. As war conditions made labor scarce and military demands called for increased production, this proved a great boon to the vegetable growers. 

The early statement that corruption is the mother of vegetation doubtless arose from the observation that manures, composts, dead animal bodies, and parts thereof such as blood, hair, hoofs, and so on, increased plant growth. John Woodward (cited by Russell, 1973), in a paper published in the Philosophical Transactions of the Royal Society (Vol. 21, p. 382), observed that the falloff in yields of crops grown in successive years on unmanured land could be rectified when supplied with a new fund of matter, of like sort with that it first contained which supply is made in several ways, either by the ground s being fallow some time, until the rain has poured down a fresh stock upon it or by tiller s care in manuring it. He considered that the best... 

As with human disease vectors, so DDT succeeded initially with some of the major agricultural pests. By the early 1970s over 4 billion pounds of the insecticide had been used--approximately 80j> of it on agricultural crops. It was also in wide use for pest control in home flower and vegetable gardens, and domestically as protection against moths and carpet beetles. 

Studies were conducted by Burgos and Talbert (1996) at the Main Agricultural Experiment Station in Fayetteville and the Vegetable Substation in Kibler, Arkansas, in 1992 and 1993 on the same plots to evaluate weed suppression by winter cover crops alone or in combination with reduced herbicide rates in no-till sweet com and to evaluate cover crop effects on growth and yield of sweet com. Plots seeded to rye plus hairy vetch, rye, or wheat had at least 50% fewer early season weeds than hairy vetch alone or no cover crop. None of the cover crops reduced population of yellow... 

Uses as fungicide to control early and late blights of potatoes and tomatoes anthracnose in cucurbits leaf spot diseases in many crops glume blotch of wheat also used on vegetables, ornaments, berry fruits, melons, coffee and tobacco, etc. 

The first survey to estimate the effects of photochemical air pollution on vegetation was developed in the mid-1950 s (I) for some areas of California. This survey used estimates derived from visible injury and included several major crop types and a single category of weeds, as they responded to certain pollutants. Although the pollutant list was not inclusive, this survey was fairly comprehensive for the crops studied and the California counties included. This survey did not estimate a monetary loss for the area of California covered. However, economic loss predictions have since been based on this early survey following superficial visual estimates of injury in several agricultural areas. These superficial predictions fixed an annual loss of approximately 8 million dollars on the West Coast and 18 million dollars on the East Coast by the early 1960 s for all types of pollutants (2). These estimates were then made countrywide, and yearly losses of between 200 and 500 million dollars have been suggested (3). 

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