| Florida citrus growers must combine horticultural and ecological considerations to produce citrus in an environmentally friendly and economically viable manner while controlling weeds and production costs. Studies were conducted over a two-year period using seven preemergence herbicides to assess their safety toward citrus seedlings, herbicide mobility in soil and, in field studies, the herbicide's effectiveness for controlling weeds and the effect that weed control had on the growth of young citrus trees. Herbicides evaluated were bromacil, diuron, norflurazon, oryzalin, oxyfluorfen, simazine, and thiazopyr.; High rates of herbicides, especially bromacil, can reduce shoot and root growth of citrus seedlings. If only mild phytoxicity symptoms appear on seedlings and additional applications at damaging rates are not applied, the seedlings should not suffer long-term damage. Differences between Carrizo and Swingle were noted in their tolerances to herbicide applications with Carrizo being more sensitive to herbicide application than was Swingle.; The seven herbicides were studied under various simulated rainfall rates. The herbicides can be divided into low, moderate, or high soil mobility based upon their movement in the soil column studies. Low mobility herbicides were oryzalin, thiazopyr, oxyfluorfen, and diuron. Moderately mobile herbicides were norflurazon and simazine. The highly mobile herbicide was bromacil. Bromacil moved to a greater depth than all other herbicides at various simulated rainfall rates.; Field studies indicated all preemergence herbicide treatments provided significantly greater weed control that was true for controls. Treatment rankings based on overall mean weed control showed that treatments that included norflurazon or bromacil provided the highest level of control. Weed control was generally highest in the Ridge citrus production region (Lake Garfield) and poorest in the Flatwoods growing region (Arcadia), with intermediate control in the Indian River region (Indiantown). Seasonal variations in weed control were observed with frequency and time of herbicide application.; Weeds compete with the citrus trees for moisture, nutrients, and light. Where weed competition is reduced or inputs are not limiting, tree growth is not significantly affected by weed growth. |
