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More than 70 biogenic hydrocarbon (BHC) compounds are known to be emitted by plants, but only a few are emitted in relatively large quantities. The magnitude of BHC emissions from individual trees is affected by ambient light and temperature, species-specific emissions rates, and leafmass. Like other volatile organic compounds (VOC), BHC emissions react with oxides of nitrogen (NOx) to form ozone and, thus, can contribute to urban air pollution. On average, BHC emissions are as reactive or more reactive than the VOC emissions from automobiles and can have higher ozone-forming potential. An accurate estimate of the overall magnitude of BHC contributions is important in formulating strategies to reduce peak ozone concentrations because an effective strategy will take into account the relative strengths of NOx and VOC emissions. The choice between NOx and VOC controls is crucial since an incorrect emphasis may result in non-attainment of ozone-reduction goals and control measures for either NOx or VOC involve enormous costs. As part of a program to develop a reliable BHC emission inventory for the Central Valley of California, a quantitative investigation of the leafmass of urban trees was conducted. Twenty-one trees in Bakersfield, Calif., were harvested and leaves removed, dried, and weighed. Leaf masses per tree ranged from 1.5 to 89.6 kg. Leaf mass densities (dry leaf mass per area of crown projection) ranged from 150 to 3200 g·m-2, as much as eight times greater than leaf mass densities for deciduous forests and more than twice those for coniferous forests. These data suggest the BHC contributions of urban trees may be underestimated if their foliar masses are calculated using forest-based leaf mass density data.
Roses are likely the most popular garden plant in the United States, and cultivars are also used as landscape plant materials. Three herbicide trials with two main objectives were conducted with rose plants. The first objective was to evaluate injury to the roses when over-sprayed at various stages of growth. The second objective was to evaluate the efficacy of the herbicides. All herbicides were used at label rates and applied over the top of rose plants. In the first trial, the pre-emergent herbicides pendimethalin, oryzalin, trifluralin, metolachlor, napropamide, and oxyfluorfen were applied to plots containing dormant roses with ≈1-cm shoots just pushing. Evaluations of shoot length taken over the next 6 weeks showed no differences in growth of rose plants, but weed populations were reduced. In the second trial, five post-emergent herbicides were applied to plots containing dormant roses. Herbicides evaluated included the grass herbicides fluazifop-p-butyl, sethoxydim, and clethodim. The nonselective herbicide glyphosate was included in the trial, as was a combination herbicide containing 2,4-D, mecoprop, and dicamba. There was no visible injury to rose plants until 6 weeks after treatment. At that time, roses treated with glyphosate had shorter shoots. Recovery from glyphosate appeared more rapidly than recovery from the combination herbicide. Weed control varied with each herbicide. The third trial evaluated the same five herbicides for control of bermudagrass in late spring. Injury to roses was noted immediately from the combination herbicide and glyphosate. All the grass herbicides and glyphosate were effective in controlling bermudagrass.
Moisture loss from bare-root plants during postharvest handling and storage can have a significant effect on plant growth and survival during establishment. Three film-forming antitranspirants and hot wax were applied to bare-root roses packaged after harvesting from the field and before three months of cold storage to determine effects on vegetative growth and flowering. Subsequently, during three weeks under display conditions, plants treated with hot wax resumed growth at the fastest rate compared to control or antitranspirant treatments. Hot wax-treated plants continued to grow at a faster rate than the other plants for two weeks following transplanting in the field. For the remaining 10 weeks of the experiment no differences in vegetative growth or flowering development were found between treatments. Over 70% of the plants treated with hot wax became sunburned, resulting in severe cane damage and plant dieback. Less than 20% of the plants from the other treatments were damaged.
The impending worldwide restrictions on the use of methyl bromide (MeBr) as a soil fumigant have prompted an intensive search for more-effective methods for delivering MeBr or replacement compounds. Although the majority of agrochemicals are applied in the solid phase or the liquid phase at ambient pressure and temperature, some chemicals, including certain soil fumigants such as MeBr, are gases under normal field conditions. Experiments were conducted to evaluate use of two types of commercial drip irrigation tubing to deliver gases to nontarped planting beds. Air moved through each tubing type immediately after burial; water was not necessary for inflation. Air was also able to move through 40 m of buried rigid drip tubing and through 90 m of buried flat tape that had been used for subsurface drip irrigation for more than 1 year. Mixtures of known ratios of propane and air were introduced into the buried tubing over several time intervals to evaluate gas movement from buried drip tubing into the surrounding soil matrix. Samples were collected from sets of three soil gas sampling tubes placed 15, 30, and 45 cm to the side of the buried tubing and at regular intervals along the length of the tubing, and propane concentrations were quantified by gas chromatography. Tubing lengths and run times affected the magnitudes and uniformity of propane concentrations. Results suggest gas-phase chemicals can be delivered via buried drip-irrigation tubing, but effective distances from the point of introduction will be limited by the low densities and viscosities of gases, and corresponding high rates of escape through tubing emitters.
Moisture loss from bare-root plants during postharvest handling and storage can have a significant impact on plant survival and growth during establishment. Three film-forming antitranspirants and hot wax were applied to bare-root roses (Rosa) packaged after harvesting from the field and before 13 weeks of –2C storage to determine effects on vegetative growth and flowering. Subsequently, during 15 days under simulated display conditions (22 to 32C), plants treated with hot wax resumed growth at the fastest rate compared to control or antitranspirant treatments. Hot-wax-treated plants remained at an advanced phenological stage compared to the other plants for 2 weeks following transplanting in the field. For the remaining 10 weeks of the experiment, vegetative growth and flowering development were similar for all treatments. More than 60% of the plants treated with hot wax developed moderate to severe cane damage and plant dieback. Less than 20% of the antitranspirant-treated plants were damaged. A laboratory experiment confirmed that hot wax treatment was most effective; it reduced weight loss from stem sections by 85% relative to the control. The other antitranspirants reduced weight loss by 27%.
Spider mites are the most commonly treated arthropod pest of roses grown for sale as plants in Kern County, California. One obstacle to possible reduction of acaricide use has been lack of a quantitative method for field evaluation of mite populations. A presence/absence (P/A) technique for mite sampling was evaluated in 1987-1991. Background data was collected in six fields of first-year and second-year rose plants in 1987 and 1989. A strong correlation existed between numbers of infested leaflets and leaves. P/A counts were similar among strata within first-year and second-year fields. A strong correlation existed between numbers of infested leaflets and leaves. In 1990 and 1991 P/A data was compared to mite counts obtained by brushing in replicated plots using leaves as sampling units. Acaricide applications have been made in the field on the basis of P/A count. Further work is underway to estimate the effects of treatment at several threshold levels of mite infestation as evaluated by P/A.