The effect of common cocklebur interference on snap beans was investigated at Bridgeton, NJ, in 1987 and 1988. Snap bean yields were reduced by increasing weed densities. Yields were reduced 8 to 44% in 1987 and 2 to 55% in 1988 by full-season in-row weed densities ranging from 0.5 to 8/m2. One weed and 4 weeds/m2 were the damage-threshold populations of common cocklebur with full-season interference in 1987 and 1988, respectively. The weed-free requirement, after planting, was to the unifoliolate stage of snap beans. Common cocklebur at 4 weeds/m2 did not affect yield when snap beans were maintained weed free until the unifoliolate stage of snap beans. The critical duration of interference for common cocklebur emerging with snap beans was between the emergence and full-bloom stage of snap beans. Snap bean yield was not reduced with weed removal at full bloom.

California arrowhead is a broadleaf weed widespread in water-seeded rice. Bensulfuron is the only herbicide currently available for use throughout the California rice growing region that provides complete control of California arrowhead; however, resistance to bensulfuron has been detected in California arrowhead and in several other weed species. Growers have herbicide alternatives for weed species other than California arrowhead but continue to use bensulfuron year after year for control because they believe California arrowhead reduces rice yields. However, damage thresholds have not been determined for this weed, and the crop may be able to tolerate relatively high California arrowhead densities. In this work, the damage thresholds for California arrowhead were determined in field and greenhouse experiments. Water-seeded rice was grown in mixture with California arrowhead in a 1992 greenhouse experiment and in field experiments in 1992 and 1998. Rice tiller density and grain yields were not affected by California arrowhead densities up to 200 plants m−2 in any year. Rice was taller than California arrowhead throughout the growing season in all experiments, and the weed senesced well before rice maturity. The ability of the crop to overtop the weed and grow weed-free during the latter part of the season may explain why California arrowhead is such a weak competitor with water-seeded rice. The results suggest that growers may be able to tolerate California arrowhead densities up to 200 plants m−2 without detectable yield losses. Implications for weed management are discussed.

Transmission electron diffraction patterns from ultra-thin aromatic and aliphatic organic films at beam energies of 200 eV–1 keV have been recorded in a custom low energy electron transmission (LEET) chamber. A significant reduction of the molecular damage cross-section, measured by fading of diffraction spots, was found for thin films of the aromatic perylene when the beam energy was reduced from 400 to 200 eV. The corresponding measurements for the aliphatic tetracontane showed a smaller “threshold energy” and the differences are discussed. Electron beam damage from other aromatic materials has also been studied at low energy. Comparison of the carbon K shell ionization cross-section and the measured damage cross-sections show that carbon K-shell ionization is strongly correlated with the damage observed in aromatics at beam energies higher than 284 eV. Calculation of the minimum number of unit cells needed for imaging a single molecule, and comparison of calculated elastic with measured damage cross-sections both indicate new possibilities for imaging biomolecules with low energy electrons.

The biology, insect density-yield loss relationships, genotype reactions, and consumption and utilisation of food by the legume pod borer, Maruca vitrata (Fabricius) on pigeonpea (Cajanus cajan) and Adzuki bean (Phaseolus angularis) were studied. Post-embryonic development was completed in 20.2 to 22.6 days. Grain yield in plants infested with 2 and 4 larvae was the same as that in uninfested controls, while plants infested with 8 and 16 larvae suffered between 50–68% grain yield loss in pigeonpea and 61–71% in Adzuki bean. Food consumption by third instars was highest on ICPL 90011. This genotype had the lowest approximate digestibility (AD) and efficiency of conversion of ingested food (ECI). The significance of these results in relation to economic damage thresholds is discussed.

The damage threshold of the green spider mite, Mononychellus tanajoa (Bondar) on cassava was determined in the greenhouse using four levels of mite infestation namely: 5, 10, 15 and 20 adult mites per cassava plant. Cassava cuttings were planted in plastic buckets in the greenhouse. The plants were artificially infested at 10 weeks old after planting.

Visible symptoms of mite damage appeared on cassava leaves at 4 weeks after infestation and at this period, the average number of mites was found to be eight mites per leaf. The mean number of active stages of M. tanajoa (larvae, nymphs and adults) was highest at the infestation level of 20 mites per plant, followed by that of 15, 10 and 5, in that order. The mean number of eggs was also highest at the infestation level of 20 mites per plant.