ABSTRACT
Planting bioenergy crops on land previously used for citrus production may offer an alternative source of revenue for growers looking for alternative-to-citrus crops. However, residual herbicides used in citrus production may adversely affect alternative crops. This study evaluated effects of three herbicides (bromacil, norflurazon, and simazine) commonly used in citrus production on the bioenergy crop Sorghum bicolor 'Topper 76-6'. Plants were exposed to herbicides in soil for 1-5 weeks and observations of effects on photosynthetic quantum yield, leaf greenness, height, and biomass were made. Results indicate that concentrations of bromacil and norflurazon greater than 0.09 and 0.07 mg/kg and simazine >0.46 mg/kg will impair growth and development in similar soils. Concentrations below these may also be toxic.
Subject(s)
Biofuels/supply & distribution , Bromouracil/analogs & derivatives , Crops, Agricultural/drug effects , Crops, Agricultural/growth & development , Herbicides/toxicity , Pyridazines/toxicity , Simazine/toxicity , Sorghum/drug effects , Sorghum/growth & development , Bromouracil/toxicity , Soil Pollutants/toxicityABSTRACT
Practical resistance to sterol demethylation inhibitor (DMI) fungicides among populations of Blumeriella jaapii, the cherry leaf spot (CLS) pathogen, was documented in 2005. In the present study, strategies to reduce selection for DMI-resistant strains of B. jaapii and adapt to possible restrictions on the use of chlorothalonil are described. Ten field trials were conducted on the sour cherry cultivars Balaton and Montmorency to test the efficacy of integrating respiration-inhibitor and copper-based fungicides into spray programs. Programs that included up to three sprays of copper-based fungicides were among the most effective for controlling CLS, although leaf phy-totoxicity was sometimes observed. Under high disease pressure, eliminating chlorothalonil compromised CLS control. 'Balaton' and 'Montmorency' did not differ in the percentage of leaves with CLS or defoliation resulting from CLS. The physical modes of action of representative DMI, QoI, and copper-based fungicides were evaluated in a leaf disk assay. Trifloxystrobin, a QoI fungicide, provided the best protection against infection by B. jaapii. All fungicides were more effective than water when applied 46 h postinfection, although differences were not statistically significant in one of two trials. Tebuconazole, a DMI, was the only fungicide that was more effective than water in preventing resporulation from existing lesions in both trials. Isolates of B. jaapii, which varied in DMI-sensitivity, all were sensitive to copper in vitro.
