Chemical weed control

Chemical weed control in cacao plantations with volatile weed killers is generally considered detrimental to pollinating insects and to the flower and fruit set. Recently Naundorf (28) and Oliver (33) in Colombia conducted tests with compounds derived from 2,4-D and with an ammonium salt of dinitro-o-cresol to determine the effect of these materials on the flowers. They found that dinitro-o-cresol can be used at the dosages commercially recommended, and that only the volatile 2-4-D derivatives at concentrations of 500 to 750 grams per plaza (6400 square meters) can be used. 

Rice. Rice, a major food crop in the tropics, is highly resistant to 2,4-D at most periods of growth. Although chemical weed control is widely used in the United States, relatively little has been done in the tropics. Some chemical weed control in rice has begun in Cuba (18), Philippines (39), Malaya (6), and Venezuela (16). Both dinitrophenol and pentachlorophenol were effective as pre-emergence treatments in Venezuela, and CMU gave very promising preliminary results. 

Chemical weed control in the tropics is still in an experimental stage in most crops. With the exception of sugar cane, few applications have been made on a commercial scale. Even in the sugar cane, where 2,4-D is used almost universally, there is considerable variation in the techniques, the kind of 2,4-D employed, and the use of subsidiary chemicals. This is partly due to different environmental conditions in operation at various times and situations, including the types of weeds present, age of the weeds and crop, soil, and rainfall. Personal idiosyncracies are also an important factor. 

Rapid growth of chemical weed control did not occur until after World War II when a herbicide was introduced by Jones in 1945 at the Imperial Chemical Industries of England 2,4-dichlorophenoxyacetic acid (2,4-D). Its utility has come from its ability to kill selectively broadleaf weeds in cereal grains, com, and cotton. It does not disturb the soil and is not persistent. 2,4,5-T was launched commercially by American Chemical Paint Co. in 1948 (now Union Carbide) to combat brush and weeds in forests, along highways and railroad tracks, in pastures, and on rice, wheat, and sugarcane. 

Summarizing the growth of the utilization of petroleum oils in herbicides, an evaluation is made of the present-day chemical weed-control methods in which oils are employed—as toxicants, as solvents, as filming agents, and as carriers. The unique properties of oil in the pest control of the future are also indicated. 

Surveying the field of chemical weed control today, it is found that oils fit into it in many ways ... 

In the utilization of petroleum oils in the field of chemical weed control, oils function as toxicants, as solvents, as filming agents, and as carriers. In view of the very effective synthetic compounds now used as toxicants (substituted phenols), the toxicity of the oils themselves is somewhat less important than it once was. Oils may serve as adjuvants in formulations involving 2,4-D, 2,4,5-T, dinitro compounds, trichloroacetates, and others. They have the unique property of aiding in the contact, spreading, and penetration of herbicides. In addition, synthesis of wetting agents, emulsifiers, and special herbicides may be dependent on petroleum products. 

How young an art was chemical weed control then For a long time man had evidently not felt himself so helpless against weeds as against other pests. It is not by chance that neither thorns nor thistles but mosquitoes, gadflies... 

While each of these milestones brought forth a renewed interest in chemical weed control and led to more research in the field, the use of chemicals for selective weed control in crops was very limited and not very successful until the discovery and development of 2,4-D, MCPA, and other phenoxyacetic acid herbicides in the 1940s. These compounds were the first truly selective herbicides that could reliably kill broadleaf weeds in cereal crops, including com, and they quickly developed widespread popularity and use after World War II. With this major milestone, new application technology emerged, including the low-volume sprayer, and new herbicide formulations were developed. 

Chemical weed control in sugarcane may have started in Hawaii. Sodium arsenite was first used in rubber plantations in 1913, but its most lasting impacts occurred in the sugar industry. At that time the Hawaiian industry was spending 750000 to 1 million annually for hand hoeing, but growers learned that they could apply sodium arsenite at 5.5kg/ha in 380L of water and achieve weed control at one-fourth the cost. 

Sugar production in Brazil dramatically increased after 1980 when the National Program of Alcohol was initiated to reduce dependence on petroleum imports. Over the past 20 years, sugarcane hectarage has doubled, yields have increased 50%, and ethyl alcohol production has tripled to more than 14 billion liters. A portion of these dramatic increases in Brazil is attributed to chemical weed control, which enabled better yield expression of new cultivars and improved use efficiencies in water and fertilizer. 

Hilton, H.W. and R.V. Osgood (1972). Chemical weed control for Hawaiian plantations. Int. Soc. Sugar Cane Technol. Proc., 14 1175-1184. 

Chemical weed control practices in citrus have been thoroughly reviewed by various researchers (Ryan, 1969 Jordan et al, 1977 Jordan, 1978 Tucker and Singh, 1983 Mersie and Singh, 1989 Singh el al., 1990 Sharma and Singh, 1999). Herbicides used in citrus can be divided into two groups soil-applied (preemergence) and... 

Abdel-Rehman, A.M., S.E. Salem, and S.S. Moustafa (1994). Studies on chemical weed control in citrus seed beds. Bullet. Faculty Agri., Univ. Cairo., 45 905-918. 

DelBosco, G.F., A. DeMichele, and B. Baratta (1974). Chemical weed control in Sicilian citriculture. In D.P.H. Tucker and R.L. Phillips, eds., Perennial Grass Control in Florida Citrus Groves. Murcia, Spain Ministerio de Agriculture, pp. 357-359. 

Kretchman, D.W. and J.T. McCown (1962). Chemical weed control in citrus groves. Agricultural Extension Service. Gainesville, FL University of Florida. Circular, 224. 

Mersie, W. and M. Singh (1989). Benefits and problems of chemical weed control in citrus. Rev. Weed Sci., 4 59-70. 

Perez, E. (1976). Chemical weed control in young citrus. 8th Reunion Argentina de Malezas y su Control ASAM . 3 172. 

Principles of Selective Chemical Weed Control in Trees, Vineyards, and Fruit... 

Brown, J.H, M.A. Spetich, and R.B. Heiligmann (1989). Effects of frequency of chemical weed control on growth and quality of Christmas trees. North. J. Applied Forestry, 6(1) 15-17. 

USDA-ARS has compiled agronomic, economic, and environmental data from a small Iowa farm that stopped chemical weed control in 1968, as well as from a neighboring conventional farm for comparative study (USDA NSTL, 1993). The information that follows describes the experiences of the small farm using nonchemical weed control methods. 

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