Mechanized production systems utilize a wide range of agrochemicals to manage peanut growth and development and minimize the impact of pests on peanut yield and quality (Lynch and Mack, 1995; Sherwood et al., 1995; Wilcut et al., 1995). Pests that can potentially impact peanut are diverse (Table 1). Yield loss from weed interference or from damage caused by insects, diseases, and nematodes can be substantial in peanut if pest control strategies are not implemented in a timely manner.
Monocotyledonous weeds, including annual and perennial grasses and sedges, as well dicotyledonous weeds, are prevalent in peanut production systems in the United States (Webster, 2009; Wilcut et al., 1995). Comprehensive herbicide programs, in combination with appropriate cultural practices, are employed to manage weeds and minimize interference and subsequent yield loss (Wilcut et al., 1987a 1987b 1990 1995). Herbicides are often applied in mixtures either prior to planting (preplant incorporated in conventional tillage or preplant to emerged weeds in reduced tillage), immediately following planting (preemergence), or after peanut and weeds have emerged (postemergence) (Burke et al., 2004; Clewis et al, 2007; Richburg et al, 1995 1996; Wilcut et al, 1994a 1994b 1995). Agrochemicals with efficacy against insects and plant parasitic nematodes are often applied in the seed furrow at planting and include organophosphate and carbamate insecticides (Brecke et al, 1996; Drake et al, 2009; Funderburk et al, 1998; Minton et al., 1990; Minton and Morgan, 1974; Riley et al., 1997). In-furrow insecticides also reduce incidence of tomato spotted wilt of peanut (caused by tomato spotted wilt virus, a Tospovirus vectored by several species of thrips) (Brown et al., 2003; Hurt et al., 2003). Pyrethroid insecticides are often applied to peanut foliage to control beet armyworm, corn earworm, fall armyworm, potato leaf hopper, and two-spotted spider mites. Chlorpyrifos can be applied at pegging, 45 to 70 days after peanut emergence, to control lesser cornstalk borer (Mack et al., 1989 1991) and southern corn rootworm (Brandenburg and Herbert, 1991; Chapin and Thomas, 1993).
Depending on environmental and edaphic conditions and a range of agronomic and pest management practices, application of insecticides may be needed throughout the growing season to protect peanut from pest damage.
Disease, caused by viruses, bacteria, or fungi, can reduce peanut yield considerably when not controlled (Sherwood et al, 1995). Fungicides are applied routinely to peanut to control foliar-borne diseases, including early leaf spot, late leaf spot, and web blotch (Brenneman et al., 1994; Culbreath et al., 2008; Shew and Waliyar, 2005). Fungicides are also applied to control the soil-borne disease stem rot and Sclerotinia blight (Brenneman et al., 1994; Culbreath et al., 2008; Smith et al., 1992). Although variation is noted among geographical regions, years, and environmental conditions, during a typical growing season fungicides are applied either singly or in combination beginning approximately 45 days after peanut emergence and continuing throughout the remainder of the growing season, which can approach 135 or more days (Sherwood et al., 1995; Smith and Littrell, 1980). Fungicide programs to control early and late leaf spot and stem rot often include bi-weekly sprays during this period. Fungicides applied to control these diseases provide protection for a period of two weeks under most environmental conditions (Shew and Waliyar, 2005). The soil fumigant metam sodium is often applied to peanut to control Cylindrocladium black rot (Cline and Beute, 1986). A period of at least two weeks between fumigation and peanut planting is required to allow the fumigant to dissipate, making weed control prior to planting challenging under some environmental conditions, especially excessive rainfall, that allow weeds to emerge between fumigation and planting operations (Van Gundy and McKenry, 1977).
The micronutrients boron and manganese are applied routinely to optimize peanut growth and development and, in the case of boron, to ensure proper kernel development (Gascho and Davis, 1995; Harris and Brolman, 1966; Powell et al., 1996). Because peanut is often grown on coarse-textured soils, boron can be deficient due to leaching. Single, and in some cases, multiple applications of boron-containing foliar solutions are applied 45 to 70 days after peanut emergence (Gascho and Davis, 1995). Manganese deficiency occurs frequently in peanut because of liming to achieve a target soil pH above 6.0. Correcting a manganese deficiency is achieved by foliar applications when visible symptoms become apparent, although some growers apply manganese irrespective of plant symptomology (Powell et al., 1996).
Excessive vine growth of peanut can reduce row visibility at digging and vine inversion (Mitchem et al., 1996). Prohexadione calcium is currently the only plant growth regulator applied to manage vine growth in order to facilitate efficient digging. Prohexadione calcium inhibits gibberellin biosynthesis in responsive plants (Grossman et al., 1994) and is applied when 50% of vines from adjacent peanut rows have met, and an application is repeated 2 to 3 weeks later (Mitchem et al., 1996). This timing of application is generally 70 to 90 days after peanut emergence (Mitchem et al. , 1996). In addition to prohexadione calcium, a wide range of products are available at the distributor level that contain micronutrient combinations, synthetic plant growth regulators, and other ingredients perceived to have value. Many of these products are not applied routinely to peanut.
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