Sandbur control and white specks on magnolia leaves

Q. I have an infestation of sandburs. Is there anything that I can use in my lawn to get rid of this weed?

A. Sandbur or sandspur is a warm season (summer) annual grass. As such, it comes up from seed during spring. In the seedling stage it blends in with the lawn grass. Later in spring and summer, it produces the stickers (burs/spurs), which contain seed. The parent plants die as a result of the first killing frost or freeze. The seed remain dormant throughout winter and germinate the following spring to start the cycle over again. Because sandbur is a true grass, there are few to no effective and safe postemergence choices for controlling this weed in a lawn. So, you’ll need to apply a preemergence herbicide. Look for preemergence lawn herbicides that contain benefin, bensulide, dimethenamid-P, oryzalin, oxadiazon, pendimethalin, prodiamine, or triflualin and apply the product during February 15 to March 1. This provides a very narrow window to achieve control. Timing is extremely important when using a preemergence herbicide. You may need to apply a second application six to nine weeks after the initial application to achieve season-long control. Always follow the label directions and precautions when using any pesticide, including herbicides. For more information on growing a Florida lawn, including weed control, visit http://hort.ifas.ufl.edu/yourfloridalawn.

Q. My magnolia tree leaves have white specks on them. What is this and will it damage my trees?

A. More than likely this is a scale insect, probably false oleander scale, sometimes called magnolia white scale. If the tree is otherwise healthy, the scale will not cause permanent harm. But scale insects may be more prevalent on trees that have been weakened by other factors such as construction damage (adding or removing soil around the roots, paving over the roots, soil compaction, etc.), storm damage or herbicide damage, including damage from weed and feed applications in nearby lawn areas. You can spray the infested leaves with one of the horticultural oil sprays designed to be used on evergreen type plants. But good coverage of infested leaves is important. Make sure it is summer oil, not dormant oil. If the tree is too large to spray, you may get some control with a systemic insecticide containing imidacloprid. If the tree is otherwise healthy, the scale should not be a problem for the tree. It’s not uncommon to find this scale on native magnolia trees out in the wild. For more information on scale insects and their control, visit the below links.

http://entnemdept.ufl.edu/creatures/orn/scales/false_oleander_scale.htm

http://edis.ifas.ufl.edu/pdffiles/ST/ST37100.pdf

Larry Williams is the Extension horticulture agent with the Okaloosa County Cooperative Extension Service, University of Florida. Contact Larry at 689-5850 or email lwilliams@co.okaloosa.fl.us.