SPRAYING IN THE RAINY SEASON: How can we use MSMA for postemergence grassy weed control in our bermudagrass ball fields? We try to make 2-4 repeat applications, at 7-10 day intervals, but in the summer it usually rains within the 24-48 hours uptake period. Dade County

ANSWER: The suggested uptake period is conservative. According to Dr. B. J. Johnson, Professor of Weed Science (University of Georgia, Griffin), you can usually get sufficient (8 hours) uptake by applying MSMA the first thing in the morning, anticipating late afternoon rains. Depending on the target weeds, there are alternatives to your present approach. With some exceptions, these approaches pertain to bermudagrass athletic fields as well as fairways.

Single-application control of crabgrass in bermudagrass can be accomplished by tank-mixing 1/8 to 1/4 pound a.i./acre dithiopyr (e.g., Dimension) with the MSMA. Johnson says "try a small area first." You should get 10 weeks crabgrass control. To be consistent with the label, the dithiopyr would be applied for preemergence control of crabgrass.

Rain or shine, if goosegrass is the target, MSMA by itself will give poor control. The solution for goosegrass is to tank-mix metribuzin (e.g., Sencor) with a reduced rate of MSMA. The yellowing which occurs from MSMA will be more severe with metribuzin. Furthermore, severe metribuzin injury can occur under conditions of close mowing (don't apply to tees or greens!), high temperature, and dry conditions. Iron can be tank-mixed with the MSMA/metribuzin combination to lessen the discoloration, but you should still be cautious in applying any herbicide to stressed turf. Golf superintendent Mr. Mike Bailey (Adios Golf Club, Coconut Creek) says it would be better to err on the side of lighter, more frequent applications. Be ready to reapply MSMA at the beginning of the 7 to 10 day interval. In that way, if rain is impending on day 7, then you can delay treatment until rain is less likely.

A less severe alternative, labeled only for golf courses, is diclofop (e.g., Illoxan) applied by itself. Repeat at 4-6 weeks to control goosegrass seedlings. Crowfootgrass as well as goosegrass are controlled. Unlike metribuzin, diclofop can be used on greens. Based on research by Dr. Bert McCarty, Johnson advises, don't tank-mix diclofop, or you will loose the effectiveness of the MSMA.

Mike Bailey describes a vicious cycle involving weak, traffic-compacted areas (e.g., the ends of the cart paths) which become thin and infested with goosegrass. Compaction is also a common theme on the 50-yard line, the baseball infield, and the entrance to the dugout area. Although bermudagrass normally recovers quickly from wear injury, its roots cannot tolerate compacted, poorly aerated soil. The manager is incorrectly encouraged to over-irrigate those areas to try to bring back the lush green turf. Then when it rains, the soil becomes saturated and compacts even worse from subsequent traffic. Bailey suggests that in the rainy season, keep the area a little dry, leaving some soil macropores empty for anticipated rain. Although weeds are killed with herbicide, they are controlled by growing a healthy turf.