John O'sullivan

Sweet Corn (Zea mays) Cultivar Sensitivity to Mesotrione

Field studies were conducted in 1999 and 2000 at Simcoe, Ridgetown, and Exeter, Ontario, to evaluate the tolerance of nine sweet corn cultivars to mesotrione, applied preemergence (PRE) at 140 and 280 g ai/ha and postemergence (POST) at 100 and 200 g ai/ha. Urea ammonium nitrate fertilizer (28%) at 2.5% (v/v) and crop oil concentrate at 1% (v/v) were added to POST applications of mesotrione only. All cultivars were tolerant to mesotrione applied PRE. There was no injury, or reductions in plant height or yield with PRE applications of mesotrione at any location in either year. POST applications of mesotrione, particularly at 200 g/ha, caused significant phytotoxicity to ‘Calico Belle’ and ‘Del Monte 2038’. Other cultivars also showed phytotoxic symptoms; however, this injury was much reduced and did not occur at all locations each year. Sweet corn injury by mesotrione increased as rate increased. Del Monte 2038 also had significantly reduced plant height and yields. Other cultivars had no plant height or yield reductions because of POST applications of mesotrione. Nomenclature: Mesotrione; sweet corn, Zea mays L. Additional index words: Crop injury, plant height, triketone. Abbreviations: DAP, days after planting; DAT, days after treatment; HPPD, p-hydroxy-phenylpyruvate dioxygenase; OM, organic matter; PRE, preemergence; POST, postemergence; SU, sulfonylurea.

Effect of imazethapyr and imazamox soil residues on several vegetable crops grown in Ontario

Use of imidazolinone herbicides has often resulted in carryover effects on sensitive rotational crops. The effect of soil residues of imazethapyr and imazamox on several vegetable crops grown in rotation with soybean (Glycine max [L.] Merr.) was investigated over a 5-yr period in southern Ontario. Imazethapyr at 0, 100 and 200 g a.i. ha–1 was applied preemergence to soybean from 1991 to 1993. Imazethapyr at 0 and 100 g a.i. ha−1 and imazamox at 35 g a.i. ha−1 was applied postemergence to soybean in 1994 and 1995. Cabbage (Brassica oleracea L.), potato (Solanum tuberosum L.), tomato (Lycopersicon esculentum L.), sweet corn (Zea mays L.) and cucumber (Cucumis sativus L.) were planted each spring, 1 and 2 yr following preemergence imazethapyr application and 1 yr following postemergence imazethapyr and imazamox application. Potato and sweet corn showed visual injury symptoms 1 yr after preemergence imazethapyr application in 2 of 3 yr while cabbage, tomato and cucumber showed visual injury symptoms all 3 yr....

The Critical Weed-Free Period in Carrot

Abstract Seeding date and the duration of weed emergence influenced the duration of the critical weed-free period in carrot. The critical weed-free period extended up to 930 growing degree days (GDD), when carrot was seeded in late April. In contrast, the critical weed-free period was short and lasted 414 to 444 GDD, when seeded in mid to late May and weed biomass was less than 650 g m−2. It is important for growers to scout fields for weeds until 930 GDD to protect the yield potential of the carrot crop in earlier planted crops; however, for carrot planted in mid to late May, weeds emerging after 444 GDD did not reduce yield. A useful strategy to reduce reliance on herbicide application would be to delay planting until late in May. Nomenclature: Carrot, Daucus carota L.

Sweet corn (Zea mays) cultivar tolerance to nicosulfuron

Eleven sweet corn cultivars were evaluated to identify cultivar sensitivity to nicosulfuron in three field studies, conducted over a 2-yr period. Response to nicosulfuron varied, depending on cultivar and application dose. DelMonte 2038 was highly sensitive to nicosulfuron, resulting in very severe injury and in most cases the death of all plants at both locations each year. At Exeter in 1997 and 1998, injury was slight, with no yield reductions on other cultivars. At Simcoe in 1998, five cultivars showed severe visual injury, especially at 50 g ha−1 of nicosulfuron; however, this did not always result in a significant yield reduction. Cultivars with a yield reduction were Elite, GH 1703 and Calico Belle. The cultivars Bonus Bt, Reveille, Krispy-King, GSS 7831 and GH 2690 were classified as fully tolerant to field applications of nicosulfuron showing injury of 5% or less at 25 g ha−1 and with no yield reduction. Key words: Sensitivity, herbicide injury, cultivars, nicosulfuron, Zea mays

Sweet Corn (Zea mays) Cultivar Sensitivity to RPA 2017721

Abstract: Field studies were conducted in 1998 and 1999 at Simcoe and Exeter, ON, to evaluate the tolerance of nine sweet corn cultivars, representing a range of genotypes, to RPA 201772 applied preemergence at 105 and 210 g ai/ha. The location × year interaction was significant for visible plant injury, plant height, and yield. All cultivars showed significant injury at Simcoe in 1999, especially at 210 g/ha. Calico Belle was the most sensitive cultivar, with RPA 201772 resulting in severe injury at Simcoe in 1999. Increased injury in 1999 was due to significant rainfall (48.5 mm) within 10 d of RPA 201772 application at Simcoe. Calico Belle also showed injury at Exeter in 1999 and at Simcoe in 1998. Plant height of all cultivars was reduced at the Simcoe location in 1999. Yield of five cultivars was also reduced at Simcoe in 1999. Sensitivity to RPA 201772 increased as application rate increased. Plant height and yield was not reduced at Exeter. Nomenclature: RPA 201772 (proposed common name, isoxaflutole), 5-cyclopropyl-isoxazol-4-yl 2-mesyl-4-trifluoromethyl phenyl ketone; sweet corn, Zea mays L. Additional index words: Plant height, crop injury, preemergence, benzoly isoxazole. Abbreviations: DAT, days after treatment; OM, organic matter; PRE, preemergence.

Sweet Corn (Zea mays) Cultivar Sensitivity to AE F1303601

Eight sweet corn cultivars were evaluated for tolerance to AE F130360 in five field experiments conducted over 2 yr in Ontario. AE F130360 was applied postemergence at 70 and 140 g ai/ha, the latter rate representing a spray overlap in the field. Response to AE F130360 varied with respect to sweet corn cultivar and herbicide rate. Minimal crop injury was observed in seven of the eight cultivars. One cultivar, ‘DelMonte 2038’, was extremely sensitive, showing 94% or more injury for all site-years. Plant height of most cultivars was not negatively affected by AE F130360 treatments, with the exception of DelMonte 2038, which sustained height reductions of 78% or greater compared with the untreated control. The crop injury and height reductions that were observed in DelMonte 2038 were reflected in the marketable yields, which were reduced by 92% or more as a result of the AE F130360 treatments. Marketable yields also tended to be reduced in ‘Calico Belle’ and ‘Rival’. On the basis of marketable yields, it was concluded that ‘CNS 710’, ‘GG 222’, ‘GG 246’, ‘GH 2684’, and ‘Reveille’ have full tolerance to AE F130360, Calico Belle and Rival tend to have moderate tolerance, and DelMonte 2038 has zero tolerance to AE F130360. Nomenclature: AE F130360 (proposed common name, foramsulfuron), N,N-dimethyl-2-[3-(4,6-dimethoxypyrimidin-2-yl)ureidosulfonyl]-4-formylaminobenzamide; sweet corn, Zea mays L. Additional index words: Cultivar, herbicide injury, sensitivity, sulfonylurea. Abbreviations: DAT, days after treatment; POST, postemergence; SAS, Statistical Analysis Systems; SU, sulfonylurea.

Sweet Corn (Zea mays) Cultivar Sensitivity to CGA 152005 Postemergence1

Abstract: Field studies were conducted in 1997 and 1998 to evaluate tolerance of nine sweet corn cultivars to CGA 152005 postemergence at 10 and 20 g ai/ha. There was a cultivar by herbicide interaction for visible plant injury, plant height, ear weight, and yield. Sweet corn injury from CGA 152005 increased as rate increased. CGA 152005 at both rates killed ‘DelMonte 2038’. ‘Eliminator’, ‘Reward’, ‘Delectable’, and ‘Reveille’ were injured (10 to 12% plant height reduction), and the remaining cultivars (‘Challenger’, ‘Krispy King’, ‘CNS 710’, and ‘GH 2690’) were tolerant to CGA 152005 at both rates. Nomenclature: CGA 152005 (proposed common name, prosulfuron), 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)-phenylsulfonyl]-urea; sweet corn, Zea mays L. Additional index words: Plant height, crop injury, sulfonylurea. Abbreviations: DAP, days after planting; DAT, days after treatment; OM, organic matter; PRE, preemergence; POST, postemergence; SU, sulfonylurea.

Sweet Corn Cultivar Sensitivity to Bentazon

Five sweet corn cultivars were evaluated for tolerance to bentazon in five field experiments conducted during 2 yr in Ontario. Bentazon was applied postemergence (POST) at 1.08 and 2.16 kg ai/ha, the highest registered rate and twice the highest registered rate, respectively, used in sweet corn in Ontario. When bentazon was applied POST at 1.08 and 2.16 kg/ha to sweet corn cultivar ‘DelMonte 2038’, injury included plant stunting and leaf damage ranging from 6 to 69% and 15 to 90%, respectively. Plant height was reduced to 48 and 100% of the untreated check when treated with bentazon at 1.08 and 2.16 kg/ha, respectively. The visual injury and height reductions were reflected in the marketable yields, which were reduced to 94% when treated with bentazon. Significant reductions in height and marketable yield were not observed in the other four cultivars tested. No correlation was observed between bentazon sensitivity and endosperm genotype. Based on visual injury ratings, sweet corn height, and marketable yield, it was concluded that ‘Calico Belle’, ‘GH 2684’, ‘Reveille’, and ‘Rival’ are tolerant to POST application of bentazon. Nomenclature: Bentazon; sweet corn, Zea mays L. ‘Calico Belle’, ‘DelMonte 2038’, ‘GH 2684’, ‘Reveille’, ‘Rival’. Additional index words: Cultivar tolerance, herbicide injury, photosystem II–inhibiting herbicide. Abbreviations: DAT, days after treatment; POST, postemergence.

Crop Response to Carryover of Mesotrione Residues in the Field

Abstract Two field residue studies were conducted from 2005 to 2007 in Simcoe, Ontario, Canada, to evaluate the effects of mesotrione soil residues on injury, plant dry weight, and yield of sugar beet, cucumber, pea, green bean, and soybean and to verify the potential of reducing a 2-yr field-residue study (conventional residue carryover) to a 1-yr field study (simulated residue-carryover study) by growing these crops in soil treated with reduced rates of mesotrione applied in the same year. There was a significant difference in mesotrione carryover between 2006 and 2007 and differences between years can be explained by differences in soil pH and soil moisture. The conventional and the simulated residue-carryover studies successfully measured mesotrione persistence and rotational crop sensitivity. Both studies showed that sugar beet was the most-sensitive crop with injury, plant dry weight reduction, and yield loss because of mesotrione residues as high as 100%. Green bean was the next most-sensitive crop to mesotrione residues followed by pea, cucumber, and soybean. The simulated residue-carryover study provided a more-rigorous test of rotational crop sensitivity to mesotrione residues than the conventional residue-carryover study, especially at higher rates for the more-sensitive crops. For the other crops, responses to mesotrione residues were similar between the conventional and simulated residue-carryover studies. Nomenclature: Mesotrione; cucumber, Cucumis sativus L.; green bean, Phaseolus vulgaris L; pea, Pisum sativum L.; soybean, Glycine max (L.) Merr.; sugar beet, Beta vulgaris L. Resumen Se realizaron dos estudios de residualidad en campo desde 2005 a 2007 en Simcoe, Ontario, Canadá, para evaluar los efectos de los residuos de mesotrione en el suelo sobre el daño, el peso seco de planta y el rendimiento de la remolacha azucarera, el pepino, el guisante, la vainica y la soya, y para verificar el potencial de reducir un estudio de residualidad de 2 años bajo condiciones de campo (residualidad convencional) a un estudio de campo de 1 año (estudio de residualidad simulada) al crecer estos cultivos en suelo tratado con dosis reducidas de mesotrione aplicado en el mismo año. Hubo una diferencia significativa en la residualidad de mesotrione entre 2006 y 2007 y las diferencias entre años pueden ser explicadas por diferencias en el pH y la humedad del suelo. Los estudios de residualidad convencional y simulada midieron exitosamente la persistencia de mesotrione y la sensibilidad de los cultivos de rotación. Ambos estudios mostraron que la remolacha azucarera fue el cultivo más sensible a los residuos de mesotrione con daño, reducción de peso seco de planta y pérdida de rendimiento de hasta 100%. La vainica fue el siguiente cultivo más sensible a los residuos de mesotrione, seguida por el guisante, el pepino y la soya. El estudio de residualidad simulada brindó una prueba más rigurosa de la sensibilidad a los residuos de mesotrione de los cultivos de rotación que el estudio de residualidad convencional, especialmente a las dosis más altas para los cultivos más sensibles. Para el resto de cultivos, las respuestas a los residuos de mesotrione fueron similares entre los estudios de residualidad convencional y simulada.

Stale-Seedbed as a Weed Management Alternative for Machine-Harvested Cucumbers (Cucumis sativus)1

The objective of this 2-yr study was to determine the optimal length of time between stale-seedbed preparation and planting that maximized weed control along with growth, development, and yield of cucumbers, compared with conventional seedbeds. Stale-seedbeds were prepared 40, 30, 20, and 10 d before planting (DBP), with an additional treatment of 40-DBP seedbed that received an application of glyphosate at 0.9 kg ae/ha, 20 DBP (40 and 20 DBP). The control (0 DBP) was prepared at planting. Glyphosate plus glufosinate ammonium at 1.26 and 0.042 kg ae/ha were applied after cucumber seeding to kill any emerged weeds. The experiment was a split-plot design in which one half of the main plots were treated with a preemergence application of clomazone at 0.42 kg ai/ha after cucumber seeding. Management of the stale-seedbed influenced the level of weed control and final crop yield. Generally, the 40-DBP seedbed had the highest weed biomass at planting and the lowest at harvest. Cucumber density, leaf number, and vine length were reduced in this treatment, and flowering was delayed because of the high weed biomass present during seedling emergence. All stale-seedbeds, with the exception of the 40-DBP stale-seedbed, had greater yields compared with the control (0 DBP) seedbed. The optimal timing of stale-seedbed preparation was 20 to 30 DBP. Seedbed preparation could be expanded to 40 DBP; however, an application of glyphosate at 20 DBP would be required to optimize yield. The stale-seedbed in combination with herbicides was a superior integrated weed management tool compared with conventional weed management practices. Nomenclature: Clomazone; glufosinate ammonium; glyphosate; cucumber, Cucumis sativus. Additional index words: Conservation tillage, weed biomass, weed density, Secale cereale L. Abbreviations: DBP, days before planting.