Tolerance of rhizoma perennial peanut to glyphosate and triclopyr

Rhizoma perennial peanut (RPP) is well adapted to the Gulf Coast region of the United States, but its varietal tolerance to glyphosate and triclopyr is not well defined. The research was conducted to determine the effect of various rates of glyphosate and triclopyr on established RPP, and the response of common RPP varieties to these herbicides. The RPP sward was approximately 7 yr younger at Zolfo Springs than at the Ona location. RPP showed moderate tolerance to glyphosate and triclopyr application, and injury level did not differ with the age of RPP sward. However, biomass production was negatively influenced by the age of the RPP sward. Overall, injury from glyphosate applications did not exceed 40% at either site. The glyphosate rate for 20% biomass reduction was predicted to be 0.53 and 2.17 kg ae ha−1 at Zolfo Springs and Ona, respectively. RPP injury from triclopyr was greater at the Zolfo Springs location than at Ona, and the triclopyr rate predicted to result in a 20% biomass reduction was 0.45 and 0.99 kg ae ha−1 at the Zolfo Springs and Ona locations, respectively. There was a difference on RPP varieties response to glyphosate and triclopyr application. ‘Florigraze’ and ‘Ona 33’ were less tolerant to glyphosate compared to ‘UF-Tito’ and ‘Ecoturf’ at 30 d after treatment. Likewise, UF-Tito and Florigraze were less tolerant to triclopyr compared to Ona 33 and Ecoturf. Overall, Florigraze showed highest injury and at least 2-fold reduction on biomass compared to the other three varieties from glyphosate or triclopyr application. Results from this research indicate that glyphosate and triclopyr appear to be safe to apply to long-established RPP stands, but herbicide rate and RPP varieties should be considered if stands are <5 yr old.

Manejo de la mustia hilachosa (Thanatephorus cucumeris (Frank)) en el cultivo del frijol comun (Phaseolus vulgaris L).

Several studies about web bligh control were carried out in Panama, the Dominican Republic, and Costa Rica. The pathogen´s genetic variability, bean varietal tolerance, chemical control, and sowing densities were evaluated. In Panama yield was increased through Benomyl applications and a greater sowing density. In the Dominican Republic Rhizoctonia AG 4, AG 2 2 and AG 1 groups were found. Several bean genotypes were evaluated, as well as populations from the web blight tolerant JB X MUS 14 cross. Between 20% and 40 % web blight severity was found in Costa Rica. Coverage and application of chemicals improved bean yield.

Pinto Bean (Phaseolus vulgaris) Varietal Tolerance to Imazethapyr

Field and laboratory studies were conducted to determine if differences existed in pinto bean varietal tolerance to postemergence application of imazethapyr under field conditions; if differences in tolerance were due to differential acetolactate synthase enzyme sensitivity or differences in14C-imazethapyr absorption, translocation, and metabolism; and the heritability of imazethapyr tolerance in pinto bean. All rates of imazethapyr injured Olathe, Sierra, UI-114, P89405, Aztec, and P90570 pinto bean varieties 7 d after treatment in 1991 and 1992, except 53 g ai ha−1of imazethapyr applied to Sierra pinto bean in 1991. Olathe was injured more than other varieties in 1991, and physiological maturity of Olathe was delayed more than Sierra in 1991 and 1992. Seed yields of all varieties were not reduced in 1991, and only P90570 had reduced seed yields from 53 g ha−1of imazethapyr in 1992. Differential sensitivity of the acetolactate synthase enzyme to imazethapyr was not the mechanism of differential varietal response. Olathe pinto bean absorbed and translocated 1.4 and 1.3 times more14C-imazethapyr, respectively, than Sierra pinto bean 24 h after application. No differences in14C-imazethapyr metabolism were detected between Olathe and Sierra pinto bean. Broad heritability of imazethapyr tolerance in pinto bean was calculated to be 0.85. The number of genes controlling the inheritance of imazethapyr tolerance in pinto bean was greater than one.

Protocol for Developing Weed-tolerant Crops

While there are published reports of varietal differences in competitiveness with weeds, no crop varieties have been specifically developed for tolerance to weed interference. We explored several methods that mechanistically compare potential sources of tomato varietal tolerance to purslane, velvetleaf, and black night-shade: 1) The influence of canopy structure and development was studied with a wide range of crop and weed germplasm with different growth habits. Leaf expansion rate and other morphological characters were used to select crop genotypes for more-detailed study. 2) Replacement series experiments with selected cultivars found that purslane and other species can adapt to avoid competition. The greatest varietal differences in competitiveness were with nightshade species that had a canopy structure similar to tomatoes. 3) Field measurements of canopy development and light interception found that competitive advantage shifted over time as height and leaf area of weeds and crops changed. 4) A systems analysis method, sensitivity analysis, found that changes in plant architecture over time were more important than initial or final crop characteristics in determining competitive outcomes.

A compendium of crop varietal tolerance to weeds

Genetic improvements in crop tolerance to diseases, insects, and other stresses have reduced or eliminated applications of pesticides and other inputs for many crops. However, little work has been done to examine the potential for increasing levels of tolerance to weeds, even though herbicides account for 69% of the pesticides used in the United States eachyear. This paper documents thatfor all 21 crops examined, varieties differ in their tolerance of non-parasitic weeds. Characteristics influencing varietal tolerance to weeds are summarized.

Varietal Tolerance of Rice (Oryza sativa) to Bromoxynil and Triclopyr at Different Growth Stages

This study was conducted to determine the tolerance of three cultivars of rice (‘Lemont’, ‘Mars', and ‘Tebonnet’) to bromoxynil and triclopyr. The effects of two rates of application (the labeled rate and twice the labeled rate) at three different growth stages (two- to three-leaf stage, four- to five-leaf stage, and panicle initiation) on percent visible injury rating and percent grain yield reduction of rice were investigated. Percent visible injury ratings for triclopyr averaged across all rates and application times, were 15, 16, and 25% (LSD = 3%) for Tebonnet, Mars, and Lemont, respectively, whereas ratings for bromoxynil were 11, 8, and 7% injury (LSD = 2%). Tebonnet was more tolerant than Lemont to triclopyr with an average percent grain yield reduction, across treatments, of 6% compared with 9% for Mars and 12% for Lemont (LSD = 4%). Bromoxynil did not decrease the average yield of any of the three cultivars.

BROCCOLI VARIETAL TOLERANCE TO DOWNY MILDEW

Downy mildew is a major concern to broccoli growers in the Sonoran Desert. Control measures include wide use of fungicide applications to prevent economic damage. Recent removal of EBDC type fungicides from the market and restrictions imposed on other registered materials has increased interest by growers and broccoli breeders in developing varieties tolerant to downy mildew. From 1984 to 1989 varieties were evaluated for tolerance to downy mildew in unreplicated trials conducted in commercial fields. In 1990, named varieties of current interest in desert production which showed tolerance to the disease in the previous trials were compared to standard varieties used by the industry. Varieties were replicated four times using a randomized complete block design. A rating scale from 1 to 5 was used to describe the severity of foliar lesions. The varieties Everest, Zeus, Legend, Pirate and Sultan showed significant tolerance when compared to the more susceptible varieties Arcadia, Emerald City, Emperor, Greenbelt, Packman, Commander, and NS 649.