Integrated Weed Management Program, Multiple Methods of Control a Must

“Grass,” “grasses,” or specific grass species are common answers to the problematic weed question that appears in the UF-IFAS End of the Blueberry Season questionnaire that is distributed by Doug Phillips. The grass botanical family, Poaceae, is a broad family that can be difficult to control because there is a species for every situation. Perennial and Annual. Summer annual and Winter annual. Wet and Dry. Propagation through seeds, stolons, and rhizomes. Multiple control methods are required to control such a broad species.

Identification

Correct identification of grasses is the important first step for control. Grass weeds are often confused with members of the Cyperaceae or sedge family because both species have long linear leaves. Grass species will have cylindrical stems with nodes above the soil surface and leaves will be on either side of the stem. Sedges will have solid triangular stems, remember “Sedges of edges”; the triangular stem will cause the leaves to encircle the stem. Mechanical and chemical control between grasses and sedges is significantly different and this article will include grass control only. Correctly identifying the grass species will impact the type and timing of the control measure.

Prevention

Prevention is also an important step toward control. Mowing when the grass seed is immature will reduce the number of seeds that are in the soil seed bank. Grass seeds can blow in the wind so mow the edges of the field, canal ditches, and fence lines. If the grass is producing seed then blow the clippings into the row middles and not under the bushes. Clean equipment after fields with significant grass infestations. If you are hand pulling or hoeing rhizomes or stolons then remove those plant parts from the field. Field selection for newly planted bushes can have a significant impact for the next five to seven years, species such as cogon grass require intense control methods that are only available preplant.

Cultural practices for weed management are a delicate balance between grass control and blueberry bush health. Apply fertilizers under the bushes and not the row middles to prevent the grasses from spreading as aggressively. Reapply bark mulch in a timely manner and if older mulch is being raked or moved to the bed top then reduce the amount of soil disturbance where the grass seed is present. Grass species that prefer wet environments will have reduced seed emergence if the frequency or quantity of irrigation water is reduced.

Pre-emergence herbicides should be applied in the fall and early spring to control annual species. Preemergence herbicides that provide grass control are diuron (Direx® 4L, Diuron 4L) napropomide (Devrinol® DF-XT), simazine (Princep® L, Simazine 4L) sulfentrazone (Spartan® 4F, Zeus® XC). These herbicides control root or shoot growth at seed germination so these herbicides will not control underground parts of perennial grass species.

Selective postemergence herbicides which only control grass can be used in situations where grass species are most problematic and you don’t want to reach the maximum amount allowed per year of nonselective postemergence herbicides. These selective herbicides include clethodim, fusillade, and sethoxydim. Large grass weeds or perennial grasses will require multiple applications and consult the label for the maximum number of allowed applications per year.

Choosing a nonselective postemergence herbicide is dependent on species. Glyphosate should be applied in situations with perennial grasses because the glyphosate will translocate to underground structures and improve weed control. Annual grasses can be controlled with diquat, glufosinate, glyphosate, or paraquat. OMRI approved herbicides should be applied when the grass weeds are small and have not produced a thick cuticle layer on the leaf.

Grass weeds can be some of the most problematic weeds for blueberry because they have adapted to many climates. An integrated weed management program that includes many methods of control is necessary.

CREDIT
PETER DITTMAR, UF associate professor, horticultural sciences