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Open access

Sharad C. Phatak and Casimir A. Jaworski


The herbicide metribuzin is registered for use on tomatoes (Lycopersicon esculentum Mill.). It is applied either preplant incorporated or postemergence. However, severe injury occurs when postemergence applications are made during low light conditions (1,2, 4, 5, 6). UGA 1113MT and UGA 1160MT are being released as sources of tolerance to metribuzin; both lines have exhibited excellent tolerance (no injury) to metribuzin applications (up to 16-times the recommended rate of 1.12 kg/ha) made during cloudy weather. Chemical name used: 4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4-H)-one (metribuzin).

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Martin M. Williams II, Loyd M. Wax, Jerald K. Pataky, and Michael D. Meyer

uninjured progeny were classified as tolerant and homozygous for an allele conditioning herbicide tolerance. Hybrids with sensitive and tolerant progeny were tested by χ 2 analysis for goodness of fit for segregation of tolerant:sensitive F 2 and testcross

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Thomas A. Bewick, William M. Stall, Stephen R. Kostewicz, and Kenneth Smith

Cupric hydroxide, copper ammonium carbonate, basic copper sulfate, mancozeb, and a combination of cupric hydroxide and mancozeb were applied to American black nightshade (Solanum americanum Mill) before treatment with paraquat at 0.6 kg a.i./ha. Paraquat efficacy was reduced by all fungicides/bactericides, except a flowable formulation of basic copper sulfate, when compared to the herbicide only control. Compared to a surfactant only control, efficacy 1 week after paraquat application ranged from 86% with paraquat only to 42% with a combination of mancozeb and cupric hydroxide. Mancozeb and mancozeb in combination with cupric hydroxide resulted in greater shoot dry weight than the paraquat only control when measured 2 weeks after herbicide application. Chemical names used: 1,1'-dimethyl-4-4'-bipyridinium ion (paraquat); Mn, Zn ethylene bis diethyldithiocarbamate (mancozeb).

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Howard F. Harrison Jr. and Mark W. Farnham

Clomazone herbicide is registered for cabbage (Brassica oleracea Capitata group) in the United States but not for other crop groups within the species. Greenhouse and field experiments were designed to compare the tolerance of broccoli (B. oleracea Italica group) and cabbage cultivars to clomazone to assess its potential for weed management in broccoli. Four broccoli cultivars (Captain, Green Magic, Legacy, and Patron) and four cabbage cultivars (Bravo, SC 100, Stone Head, and Vantage Point) were evaluated in all experiments. In a greenhouse experiment where seedlings were transplanted into potting medium containing clomazone at 0, 1.0, 2.0, and 4.0 parts per million (ppm), ‘Bravo’ cabbage was most susceptible. Its injury ratings and shoot weight reduction at 1.0 ppm were similar to ratings and shoot weight reduction for the other cabbage cultivars at 4.0 ppm. Among the broccoli cultivars, Patron was highly susceptible, exhibiting injury and shoot weight reduction similar to Bravo. Green Magic was the most tolerant broccoli cultivar, and it exhibited injury and growth reduction similar to the tolerant cabbage cultivars. In a field experiment where clomazone was applied pretransplanting at 0.25, 0.5, and 1.0 lb/acre, 0.25 lb/acre caused moderate chlorosis to the susceptible cultivars, Bravo and Patron. At 0.50 and 1.0 lb/acre, most cultivars exhibited chlorosis at 2 weeks after transplanting (WAT); however, tolerant cultivars recovered and injury was often not observed at 6 WAT. At 1.0 lb/acre, chlorosis persisted until maturity on ‘Bravo’ and ‘Patron’ foliage. Clomazone did not reduce mean broccoli head weight or the percentage of plants producing market-size heads. Mean cabbage head weight for ‘Bravo’ was reduced by clomazone at 1.0 lb/acre. This study indicates that the variability in clomazone tolerance among broccoli cultivars may be similar to that among cabbage cultivars and suggests that the herbicide can be used safely on tolerant broccoli cultivars at rates that are recommended for cabbage.

Open access

Edgar L. Vinson III, Kaitlyn J. Price, J. Raymond Kessler, Elina D. Coneva, Masuzyo Mwanza, and Matthew D. Price

Relatively few herbicides are registered in Alabama or in the southeastern United States for use in annual hill plasticulture production of strawberries. Acquisition of 24(c) special local needs status for certain herbicides could make more of these chemistries available to the strawberry industry. These herbicides, especially when applied as tank mixes pose potential risks to strawberry plant growth and fruit yield. Special local needs status for these herbicides has been granted for other states, but more evaluation of these products in Alabama soils under plastic mulch is needed. The objective of this study was to assess tank mix applications of preemergence herbicides with different modes of action on plant growth, crop yield, and fruit size of ‘Camarosa’ strawberry. A study was conducted at the Chilton Research and Extension Center in Clanton, AL, in 2018 and 2019. Pendimethalin (3.5 L·ha–1) and S-metolachlor (1.6 L·ha–1) were evaluated for potential phytotoxicity in ‘Camarosa’ strawberry when applied alone or in tank mixes with napropamide (8.6 kg·ha–1), sulfentrazone (0.3 L·ha–1), or terbacil (0.42 L·ha–1) by comparing them to a nontreated control. At 18 weeks after planting, pendimethalin tank mixed with napropamide reduced plant dry weight by 33% compared with the control, but this reduction was not significant. Additionally, tank mixes of pendimethalin with sulfentrazone, napropamide, and terbacil reduced shoot dry weight by 43%, 52%, and 43%, respectively, compared with pendimethalin alone. Pendimethalin + napropamide tank mix reduced relative growth rate by 95% compared with the control between 6 and 18 weeks after planting. All treatments were similar to the control in marketable yield. Differences in plant growth parameters did not appear to affect yield by the end of the experiment. All single applied treatments along with S-metolachlor tank mixed with napropamide and sulfentrazone; pendimethalin tank mixed with sulfentrazone and terbacil appeared to be safe for direct application to strawberry planting beds covered in polyethylene mulch.

Open access

C. L. Gupton


Several plants in a Vaccinium ashei Reade collection were tolerant of terbacil. To determine whether the tolerance is heritable, progeny of crosses between a selection from these plants and 3 rabbiteye blueberry cultivars were compared with progeny of 3 rabbiteye × rabbiteye cultivar crosses. Significantly less leaf damage by terbacil occurred in offspring of the selection than in those of rabbiteye cultivars. Tolerance to terbacil appeared heritable, suggesting that the tolerant plants constitute usable germplasm for a breeding program. Chemical names used: 5-chloro-3-(1, 1-dimethylethyl)-6-methyl-2, 4(1H, 3H)-pyrimidinedione (terbacil).

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Martin M. Williams II, Jerald K. Pataky, Jonathan N. Nordby, Dean E. Riechers, Christy L. Sprague, and John B. Masiunas

Nicosulfuron and mesotrione are herbicides from different chemical families with different modes of action. An association between the sensitivity of sweet corn (Zea mays L.) to nicosulfuron and mesotrione was observed when hybrids, inbreds, and S1 families (S2 plants) were evaluated for herbicide sensitivity in field trials. In 2003 and 2004, 50% and 53% of mesotrione-sensitive hybrids were sensitive to nicosulfuron compared with only 6% and 1% of mesotrione-tolerant hybrids that were sensitive to nicosulfuron. In trials with inbreds in 2003 and 2004, 88% and 78% of nicosulfuron-sensitive inbreds had some injury from mesotrione but 0% and 5% of nicosulfuron-tolerant inbreds were injured by mesotrione. Among S1 families, 77% of the mesotrione-sensitive families were nicosulfuron-sensitive but only 5% of the mesotrione-tolerant families were sensitive to nicosulfuron. Segregation of S1 families for response to mesotrione was not significantly different from a 1:2:1 pattern of sensitive: segregating: tolerant families (chi square value = 2.25, P = 0.324) which would be expected if sensitivity was conditioned by a single recessive gene. Segregation of S1 families for response to nicosulfuron was 15:23:26 (sensitive: segregating: tolerant) which was slightly different from an expected 1:2:1 ratio (chi square value = 8.84, P = 0.012). Segregation of S1 families probably was affected by the relatively small number of S2 plants sampled from each family. Similar responses of the S1 families to nicosulfuron and mesotrione lead us to hypothesize that the same recessive gene is conditioning sensitivity to both herbicides. Possibly, this gene is common in the inbreds and hybrids that were sensitive in these trials. These hypotheses will be tested by examining segregation in S2 families and other segregating generations and by conducting tests of allelism among sensitive inbreds and inbred parents of sensitive hybrids. Chemical names: 2-(4-mesyl-2-nitrobenzoyl)-3-hydroxycyclohex-2-enone, (mesotrione); 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide, (nicosulfuron).

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Matthew A. Cutulle, Howard F. Harrison Jr., Chandresakar S. Kousik, Phillip A. Wadl, and Amnon Levi

A greenhouse trial was used to evaluate 159 accessions of bottle gourd [Lagenaria siceraria (Mol.) Standl.] obtained from the U.S. National Plant Germplasm for tolerance to clomazone herbicide. Most accessions tested were moderately or severely injured by clomazone at 3.0 mg·kg−1 incorporated into greenhouse potting medium; however, several exhibited lower injury. Seeds were produced from tolerant and susceptible plants for use in a greenhouse concentration–response experiment. About three to four times higher clomazone concentrations were required to cause moderate injury to tolerant bottle genotypes in comparison with susceptible genotypes. The differences in tolerance among genotypes were observed with injury ratings, chlorophyll measurements, and shoot weights. Clomazone may be used safely on tolerant bottle gourd genotypes, but the herbicide may not be safe for susceptible genotypes. Also, tolerant genotypes such as Grif 11942 may be desirable for use as rootstocks in grafted watermelon production.

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Jialin Yu, Nathan S. Boyd, and Peter J. Dittmar

In Florida, cabbage (Brassica oleracea L.) is typically grown without a plastic mulch and as a result, weeds are a significant problem in most fields. Experiments were conducted from Nov. 2015 to Apr. 2016 in Balm, Citra, and Parrish, FL, to evaluate weed control and ‘Bravo’ cabbage tolerance to multiple herbicide programs applied pretransplanting (PRE-T), posttransplanting (POST-T), PRE-T followed by (fb) a sequential application at 3 weeks after transplanting (WATP), and POST-T fb sequential application at 3 WATP. PRE-T herbicide treatments of 277 g a.i./ha clomazone, 280 g a.i./ha oxyfluorfen, and 798 g a.i./ha pendimethalin and POST-T herbicide treatments of 6715 g a.i./ha dimethyl tetrachloroterephthalate (DCPA) were ineffective, and weed control never exceeded 70% in Balm and provided <50% weed control in Citra and Parrish at 6 and 8 WATP, respectively. POST-T applications of napropamide + S-metolachlor at 2242 + 1770 g a.i./ha, DCPA + S-metolachlor at 6715 + 1170 g a.i./ha, and S-metolachlor POST-T fb clopyralid at 1170 g a.i./ha fb 210 g ae/ha were the most effective herbicide treatments and consistently provided >70% weed control. In addition, results showed that all of the herbicide treatments evaluated except the PRE application of clomazone at 277 g a.i./ha are safe for cabbage with no adverse effect on yield.

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R. Thomas Fernandez, Ted Whitwell, Melissa B. Riley, and Cassandra R. Bernard

Canna ×generalis L.H. Bail. (canna), Pontaderia cordata L. (pickerel weed), and Iris L. × `Charjoys Jan' (`Charjoys Jan' iris) were exposed to a 5 mg·L-1 suspension of isoxaben or oryzalin or a water control for 9 days. Growth and photosynthetic responses were monitored throughout treatment and for an additional 22 d after termination of treatment. By the end of the experiment plant height of pickerel weed was reduced by oryzalin. Isoxaben resulted in lower height and reduced leaf emergence for all three taxa by the end of the experiment. Leaf CO2 assimilation (A) and transpiration (E) were lower for oryzalin-treated canna only 17 and 18 days after treatment, several days after treatment had been terminated. Leaf A and E were lower for oryzalin-treated pickerel weed and `Charjoys Jan' iris for most days after day 17. Isoxaben reduced A and E of all three plants for all days measured except day 6 for `Charjoys Jan' iris. Lower photosystem II efficiency (Fv/Fm) was found for isoxaben-treated canna from day 5 onward and days 7, 20, and 23 for pickerel weed and `Charjoys Jan' iris. Rapid reduction in A and Fv/Fm for all plants treated with isoxaben indicates a direct effect of isoxaben on photosynthesis. Reductions in growth and photosynthetic parameters due to oryzalin were minimal for all plants indicating these plants would be useful in phytoremediation systems where oryzalin is present. However, growth and photosynthetic parameters were reduced substantially for all plants exposed to isoxaben indicating the taxa studied would not perform well in phytoremediation systems with this level of isoxaben exposure. Chemical names used: isoxaben (N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyly]-2,6-dimethoxybenzamide); oryzalin (4-(dipropylamino)-3,5-dinitrobenzenesulforamide).