Eight clones of eastern white pine (Pinusstrobus L.) in three pollutant sensitivity groups (sensitive, intermediate, and tolerant) were exposed to 0.05 or 0.10 μL/L of ozone, sulfur dioxide, and (or) nitrogen dioxide 4 h daily for 35 consecutive days. Visible symptoms, length, and dry weight of 1st-year needles were determined to evaluate clonal response to these pollutants. A general response within sensitivity groups to all three pollutants, singly and in combination, was not observed. The sensitivity of the clones was dependent on the type of pollutant, its concentration, and the plant response used as the indexing factor. The amount of area injured was categorically differentiable among the three sensitivity groups but varied within the same group. Needle length was an inconclusive measure of clonal pollutant sensitivity, whereas needle dry weight was the parameter best associated with clonal pollutant sensitivity. These results demonstrate that a single response parameter is of limited value in determining plant sensitivity to air pollutants.

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The influence of metribuzin [4-ammo-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] on net photosynthesis of goosegrass [Eleusine indica(L.) Gaertn. ♯3ELEIN] and six cultivars of bermudagrass [Cynodon dactylon(L.) Pers. ♯ CYNDA cvs. ‘Common’, ‘Tufcote’, ‘Vamont’, and ‘Midiron’,Cynodon transvaalensisDavy., andCynodon dactylonXCynodon transvaalensis‘Tifway’] was evaluated. Metribuzin rapidly inhibited carbon dioxide (CO2) uptake within 1 h after application in both goosegeass and bermudagrasses. Very often, net photosynthesis was completely inhibited. Net photosynthesis in goosegrass was inhibited by lower rates of metribuzin than those required for similar reduction in bermudagrasses. Common, Tufcote, Tifway, andC. transvaalensisbermudagrasses were less sensitive to metribuzin than Midiron and Vamont based upon the degree of inhibition of net photosynthesis, the rate of its recovery, and the level of foliar injury. Recovery from inhibition of net photosynthesis was observed in both species 24 h after treatment with low metribuzin rates. High rates caused several days lag period before net photosynthesis resumed. After 10 days, 95% of the goosegrass foliage was injured (either chlorosis or necrosis) from 2 kg ai/ha metribuzin treatment. The threshold concentration for inducing leaf injury in bermudagrasses was 1 kg ai/ha. Inhibition of photosynthesis was initially rapid in both grasses; however, recovery was evident earlier and there was less foliar injury in bermudagrasses than in goosegrass. Selective control of goosegrass in bermudagrass may therefore be partially dependent upon rapid metabolism and/or inactivation of metribuzin in the bermudagrass.

The potential interactive effects between the herbicides chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl] benzenesulfonamide}, PP009 {butyl 2-[4-[5-(trifluoromethyl-2-pyridinyl) oxy] phenoxy] propanoate}, and BAS 9052 OH {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)-propyl]-3-hydroxy-2-cyclohexene-one} and the air pollutant ozone (O3) on the growth of sorghum [Sorghum bicolor(L.) Moench. ‘Funk G623rg’] and velvetleaf (Abutilon theophrastiMedic. # ABUTH) were examined. All three herbicides were applied postemergence either before or after a single 6-h fumigation of sorghum and velvetleaf seedlings with O3at 0, 0.1, and 0.2 ppmv. Chlorsulfuron was applied at 0, 0.06, or 0.12 kg ai/ha, while PP009 and BAS 9052 OH were applied at 0, 0.6, and 1.2 kg ai/ha. Two weeks after treatment, dry weight responses of velvetleaf seedlings revealed that PP009 interacted synergistically while chlorsulfuron and BAS 9052 OH interacted antagonistically with O3. The sequence of O3fumigation and herbicide treatment appeared to be an important factor determining the type of interactive effects of these herbicides with O3. The interactive effects of all three herbicides with O3on sorghum seedlings were additive regardless of the sequence of O3fumigation and herbicide treatment.

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