Fresnel lenses are used to concentrate solar radiation to a line or point. A linear Fresnel lens (0.91 by 1.52 m, 0.74-m focal length, 0.01- by 1.52-m line focus) was investigated as a method for weed control. Field experiments were conducted to assess the effect of Fresnel lens concentrated solar radiation at various exposure times, stages of plant growth, and soil surface moisture conditions. On a dry soil surface exposure times of 1 to 10 s at 290 C resulted in control of redroot pigweed from 100% for a 1-s exposure at the cotyledon stage to 89% for a 10-s exposure at the 10-leaf stage. Redroot pigweed and kochia control was similar at exposures of 3 to 10 s, but less for kochia at 1 and 2 s. Green foxtail control was less than that of kochia and redroot pigweed. Control was reduced on a moist compared to a dry soil surface. Concentrated solar radiation holds the greatest potential for control of small dicot weeds on a dry soil surface.

Combinations of thifensulfuron with carbaryl, chlorpyrifos, malathion, and methomyl caused soybean injury that exceeded the expected injury based on effects of herbicide and synergists applied alone. Thifensulfuron-induced injury and growth reductions generally increased as insecticide rates increased from 140 to 560 g ai ha-1. TBPT and fenarimol also synergistically enhanced thifensulfuron injury in soybeans. Yellow foxtail control by thifensulfuron was enhanced slightly by all insecticides except carbaryl. Insecticides did not enhance kochia control by thifensulfuron.

A curved-linear Fresnel lens was investigated to test the effect of concentrated solar radiation on surface and buried weed seed. The lens produced a line focus 1 by 150 cm with a mean temperature of 309 C. A 20-s exposure to seed on the soil surface was 100% lethal to green foxtail, kochia, common lambsquarters, common purslane, and wild buckwheat. In a separate study, emergence from kochia and yellow foxtail seed was reduced 100% at 10 mm soil depth after 15 min in soil of 35 and 93 g/kg moisture and 20 to 40% at 178 g/kg moisture content. Concentrated solar radiation from a Fresnel lens has the greatest potential for affecting weed seed on the soil surface. A series of Fresnel lenses and/or larger lenses may be required for many practical field applications.