High availability of alachlor affects the roots and general growth of sunflower seedlings

Ceronio

2007

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Occasionally a herbicide that is considered safe to use at prescribed rates causes damage to crop plants at those same rates. Alachlor (Lasso EC®)is registered for use on sunflower at a rate of 1.5 to 1.92 kg ai ha-1 . Occasional injury to sunflower plants at these rates is usually caused by incorrect application or unsuitable weather conditions, but sometimes no explanation can be found. In many crops it has been shown that genetic differences can make specific cultivars more susceptible to alachlor injury. The objective of this study was to screen 22 of the available sunflower cultivars for sensitivity to alachlor in a glasshouse trial. Planting took place in pots filled with a sandy loam soil (20% clay). Five rates of alachlor (0,0.96,1.92,3.84 and 7.68 kg ai ha-1 ) were applied and leached into the soil with 100 ml of water. Pots were laid out in an air-conditioned glasshouse set to 28/18°C day/night in a randomised block design with three replicates. Plants were harvested 38 days after planting, at which stage plant height and mass were determined. The results indicated that cultivar differences with respect to alachlor tolerance were present. Plant height appeared to be the best predictor of alachlor activity in sunflower. Cultivars were divided into three classes (tolerant, intermediate and sensitive) based on their reaction to the herbicide.

Section: Dry Masssupporting

confidence: 80%

Section: Resultsmentioning

confidence: 99%

Screening of South African sunflower (Helianthus annuusL.) cultivars for alachlor sensitivity

Ceronio

2007

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“…This concurs with the findings of Allemann and Reinhardt (1995) regarding the effect of alachlor, a related herbicide, on sunflower. The degree of thickening occurring in the seedlings could affect the dry mass of seedlings, so affecting the order of reaction to the herbicide as measured by dry mass.…”

Section: Dry Masssupporting

confidence: 80%

Screening of some South African maize (Zea maysL.) cultivars for acetochlor tolerance

Mphundi

2010

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Acetochlor containing a safener is registered for pre-emergence use on maize to control mainly annual grasses. It is applied at rates of between 0.49 and 1.89 kg ai ha -1 on soils with a clay content from <10% to 55%. Some cases of acetochlor injury to maize have occurred in the field despite the correct application rates being used. A randomised complete block design trial was conducted in a glasshouse set at 28/18°C day/night to screen 21 maize cultivars for their tolerance to acetochlor (WENNER 700 S EC ® ). Maize was planted in pots containing a sandy loam soil (15% clay). Five acetochlor rates (0, 0.74, 1.47, 2.94 and 5.88 kg ai ha -1 ) were applied the next day and leached into the soil. Characteristic symptoms of acetochlor phytotoxicity occurred, particularly at higher application rates. Most cultivars showed significant decreases in both plant height and dry mass at the recommended application rate. Significant differences were noted between cultivars, with slight variations in results for seedling height and dry mass. Cultivars were grouped into tolerant, intermediate and sensitive classes based on their reaction to the herbicide. Most cultivars were rated as intermediate, although both tolerant and sensitive cultivars were found, so proving the existence of cultivar differences with respect to acetochlor tolerance.

“…Previous research has indicated that both plant height and the dry mass of plants gives a fairly good indication of alachlor activity (Reinhardt, 1985;Van Rensburg & Van Dyk, 1986;Winarsih & Moenandir, 1986;Allemann & Ceronio, 2007). As alachlor inhibits both cell division and cell enlargement (Deal & Hess, 1980), plant height would appear to be the parameter that is most sensitive to alachlor treatment, a finding that was substantiated by Allemann and Reinhardt (1995).…”

Section: Resultssupporting

confidence: 49%

“…These results concur with field observations of alachlor treated sunflower grown on light textured soils, which showed that growth of seedlings was inhibited following heavy rainfall during germination or shortly after seedling emergence (Meissner et al, 1987). As sunflower has been shown to absorb alachlor through its roots (Allemann & Reinhardt, 1995) it follows that greater activity would be attained on the sand soil where greater leaching of the herbicide can take place (Reinhardt & Nel, 1982, 1984Weber & Peter, 1982), so carrying it into the root zone of the crop. Availability of alachlor has also been shown to increase with decreasing clay content in soils (Reinhardt & Nel, 1982).…”

Section: Seedling Survivalmentioning

confidence: 99%

Effect of microencapsulated alachlor on South African sunflower (Helianthus annuusL.) cultivars

Ceronio

2009

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The microencapsulated formulation of alachlor is becoming increasingly popular for use on sunflower in South Africa, where it is registered for use at a rate of 1.54 to 1.92 kg ai ha -1. Some injury symptoms, apparently herbicide induced, have been observed on sunflower where this herbicide has been applied in the field. The response of 22 commercially available sunflower cultivars was tested in a glasshouse experiment using both a sand (10% clay, 0.24% C) and a sandy loam soil (20% clay, 0.52% C). Five rates of alachlor (0, 0.5, 1, 2 and 4 times the recommended application rate for each of these soils) were applied and leached into the soil after planting. At harvest plant height, above-ground biomass and seedling survival rate were determined. Results indicated that cultivars differed with respect to alachlor tolerance, but that behaviour was modified by soil type. All effects were far more pronounced on the sandy soil, despite a lower recommended application rate. Plant height was affected by increasing application rate to a far greater degree than dry mass. Although the application rate for this herbicide was lower on the sandy soil, plant growth was significantly reduced at the recommended rate of application for this soil (1.536 kg ai ha -1 ). Seedling survival rates were reduced at the recommended application rate on both soils, although the effect was far more pronounced on the sand soil. The results indicated that despite the lower recommended application rate of microencapsulated alachlor on sandy soils a far greater degree of herbicide damage to sunflower can be expected on these soils due to increased availability to crop roots. These findings in part explain some of the problems found on sunflower where this formulation of alachlor has been applied.