Agricultural pest management
Special Weed Problems
(Reviewed 9/09, updated 9/09)
ANNUAL BLUEGRASS. Annual bluegrass is a cool season grass that germinates when soil temperatures are less than 70°F. It is especially prevalent in wet areas. Several preemergent herbicides will control annual bluegrass including bensulide, DCPA, dithiopyr, oryzalin, oxadiazon, pendimethalin, and prodiamine. Ethofumesate also will control annual bluegrass after emergence, but it must be applied to very young seedlings. Bispyribac, foramsulfuron, and sulfosulfuron also have postemergent activity but application sites are limited. Seed production by this weed can be suppressed with a plant growth regulator, such as paclobutrazol or mefluidide.
BERMUDAGRASS. Although bermudagrass is used as a turfgrass, its rapid growth by stolons into other turfgrass areas makes it a weed in those situations. Bermudagrass is a perennial that is commonly found throughout California. It spreads by seed and by stem sections (rhizomes and stolons). The rhizomes and stolons are many jointed and root at the nodes. Avoid spreading stem sections of bermudagrass with mowers and other turf maintenance equipment to uninfested areas. Bermudagrass does not grow well in the shade. Fall and winter fertilization and high mowing heights (greater than 1.5 inches) will reduce bermudagrass invasion into cool season turf. Preemergent herbicides (pendimethalin, siduron) will aid in the control of germinating bermudagrass seedlings. Postemergent herbicides (fluazifop, quinclorac, and triclopyr) suppress bermudagrass invasion in cool season tall fescue, but repeated applications are needed.
CALIFORNIA BURCLOVER AND BLACK MEDIC. California burclover and black medic are annual or short-lived perennial broadleaf weeds that infest turf. Invasion by these two species is encouraged by low nitrogen fertility. Herbicides that control these annual species include clopyralid, dicamba, fluroxypyr, mecoprop, quinclorac, or triclopyr.
CRABGRASS. Two species of crabgrass that commonly infest turf in California are smooth crabgrass and large crabgrass. Both species are annuals that spread primarily by seed, and to a lesser extent, by rooting at swollen nodes of stems. Crabgrass is frequently a problem in overirrigated turf. Frequent, shallow irrigation encourages the establishment of crabgrass. Preemergent applications of products containing bensulide, DCPA, dithiopyr, napropamide, oryzalin, oxadiazon, pendimethalin, and prodiamine control crabgrass. Siduron can give some control when cool season grasses are planted in spring. Postemergent applications of products containing MSMA will aid in the control of crabgrass.
Crabgrass is a common, warm season, annual grass weed in California turf. In warmer parts of the state (southern CA) it may germinate throughout the year. In cooler parts of the state (northern CA) it has a shorter germination period and growing season. In most areas of California, the major germination period starts from late January to mid-March, depending on the weather, and seeds continue to germinate throughout the spring and summer. While germination is early in warm winter areas, growth is slow during spring months until the weather warms. In June and July the plants produce tillers, shoots, and flowers in late July and August. Crabgrass may overwinter in warm areas and produce new growth and a second crop of seed in spring or early summer. For best control, apply preemergent herbicides 2 to 3 weeks before expected germination. In general this occurs before the end of January in warm winter areas of southern California, by mid-February in the Central Valley and Central Coast, and from mid-February to March 1 for northern California and the North Coast area. The optimum application period for postemergent herbicides is before flowering when the weed is actively growing.
CREEPING WOODSORREL (Oxalis). Creeping woodsorrel is a perennial broadleaf weed that is often found in well maintained turf areas. Creeping woodsorrel grows year round in California and has leaves similar to those of clover. It spreads by seed and by creeping stems that root at the nodes. It is a difficult weed to control once established. There are no cultural controls available for this weed. Preemergent herbicides containing dithiopyr, isoxaben, pendimethalin, or prodiamine will limit emergence. In cool season turf, postemergent treatments with triclopyr controls creeping woodsorrel. This weed is not controlled by 2,4-D. In warm season turfgrasses, combinations of 2,4-D, MCPP, and dicamba plus MSMA or carfentrazone are fairly effective, just be sure to use mixtures developed for warm season turfgrasses. Applications with fluroxypyr are also effective, just be sure to follow label rates. Applications of both pre- and postemergent herbicides are generally needed to provide satisfactory control of creeping woodsorrel for several months in both cool and warm season turfgrasses.
DALLISGRASS. Dallisgrass seed germinates in spring and summer and it becomes a perennial plant with the formation of short rhizomes. It has a clumpy growth habit that gives turf an irregular surface unsuitable for most sports activities. Repeated postemergent treatment with MSMA or nonselective spot treatment with glyphosate can reduce dallisgrass infestations. Foramsulfuron suppresses dallisgrass in bermudagrass and zoysiagrass. To control seedlings use a preemergent herbicide such as those listed for crabgrass.
DANDELION. Dandelion is a perennial broadleaf weed with a persistent, fibrous-fleshy taproot. Removal of the leaves and 1 to 2 inches of taproot will not control dandelion because it regenerates from the remaining portion of the taproot. Poorly maintained open turf areas allow the establishment of dandelion. Frequent mowing to remove the flowers will reduce the spread of viable seeds. Seedlings can be controlled with DCPA, isoxaben, or napropamide before they emerge. Postemergent treatment with 2,4-D, fluroxypyr, and triclopyr will control dandelion; products containing MCPA, MCPP, and quinclorac also work but are less effective. Dicamba is not effective for controlling this weed.
ENGLISH DAISY. English daisy is a perennial broadleaf weed that is most common in cool coastal climates, especially in some golf courses. It has smooth, succulent-like leaves and thick fleshy rhizomes, which become woody under close mowing. Regrowth from rhizomes is common as is spread by seed. Plants are easier to control with herbicides at higher rather than lower mowing heights.
GOOSEGRASS (Silver Crabgrass, Wiregrass). Goosegrass seedlings are often confused with crabgrass, but goosegrass germinates later in spring, is darker green, grows in tufts, and has a white or silvery color near the flattened stem bases. This annual weed is normally found on compacted soils or areas of heavy wear. Crabgrass preemergent herbicides have been successful in the control of goosegrass.
GREEN KYLLINGA. This small perennial sedge is a prolific seed producer that also spreads by rhizomes. It has been found in the southern coastal counties, the Sacramento region, and the Fresno area. It is becoming more widespread and is often found in areas that are frequently irrigated, have standing water, or where soil remains wet. Repeated applications of MSMA, halosulfuron, or sulfosulfuron work well, but combinations of halosulfuron or sulfosulfuron plus MSMA seem to be the best control.
KIKUYUGRASS. Like bermudagrass, kikuyugrass is a perennial weed that is found in south and central coastal counties and in parts of the Sacramento and San Joaquin valleys. Frequently, kikuyugrass is mistaken for St. Augustinegrass. A quick way to tell them apart is to examine their leaves: kikuyugrass has pointed leaves with hairy stems, St. Augustinegrass has short, blunt leaves with no hairs. Most cultural practices will not reduce kikuyugrass invasion. Repeated postemergent applications of MSMA will reduce kikuyugrass in warm season turf. Repeated triclopyr or triclopyr plus MSMA applications have controlled kikuyugrass invasions into cool season turf. Repeated applications of quinclorac alone or in combination with MSMA have limited kikuyugrass spread in warm season turfgrass.
NUTSEDGE. Yellow and purple nutsedge, sometimes called nutgrass, are serious perennial weeds in turf. Both produce an extensive system of underground tubers from which they can regenerate. Nutsedge, especially purple, is very difficult to control once it is established in turf. When establishing turf, try to plant in seedbeds that are free of nutsedge. Small localized infestations of nutsedge can be controlled with nonselective materials such as glyphosate applied in repeated applications. Purple and yellow nutsedge can be reduced in turf with multiple postemergent applications of products containing halosulfuron, sulfosulfuron, and trifloxysulfuron or multiple applications of MSMA. Bentazon is effective on yellow but not purple nutsedge. To minimize nutsedge invasion maintain a uniform, competitive turf and avoid overly wet soil.
PLANTAIN. Both broadleaf and narrowleaf (buckhorn) plantains are found as weeds in turf. Buckhorn plantain can act as an annual, biennial, or perennial weed, whereas broadleaf plantain is a perennial. Poorly maintained open areas in turf encourage the establishment of plantain. Postemergent treatment with broadleaf weed killers containing 2,4-D, MCPP, dicamba, or quinclorac in two or three way combinations or applications with products containing fluroxypyr or triclopyr will control these weeds. Buckhorn plantain is more tolerant of drought but less tolerant of compaction than is broadleaf plantain.
SMUTGRASS. This perennial grass spreads by seed and quickly becomes established. Control at first indication with spot treatments of glyphosate or fluazifop. Germinating seeds can be controlled with preemergent herbicides used for crabgrass control.
SPOTTED (PROSTRATE) SPURGE. Spurge is an annual broadleaf weed that germinates in open spaces from March through October. It can be a problem in closely mowed turf that has open areas. Preemergent applications of products containing DCPA, dithiopyr, isoxaben, oryzalin, oryzalin plus benefin, pendimethalin, or prodiamine are very helpful in limiting the establishment of spurge. Postemergent applications of products containing bromoxynil or triclopyr have been helpful in the control of spurge. Two or three way combinations of postemergent broadleaf weed killers in combination with carfentrazone or quinclorac are also successful in the control of spurge. In addition, raising the mowing height and increasing fertility helps make the turf more competitive against this weed.
WHITE CLOVER. White clover is a low-growing perennial broadleaf that roots at nodes along its stems. It produces white flowers that attract bees to turf areas. It develops readily in turf that is low in nitrogen, so to make the turfgrass more competitive apply nitrogen fertilizer in spring and fall for cool season turf and in summer months for warm season turfgrasses. Postemergent application of clopyralid, dicamba, mecoprop, quinclorac, or triclopyr will control white clover.
UC IPM Pest Management Guidelines: Turfgrass
C. A. Wilen, UC IPM Program, UC Cooperative Extension, San Diego County
Acknowledgment for contributions to Weeds:C. L. Elmore, Vegetable Crops/Weed Science, UC Davis
D. W. Cudney, Botany and Plant Sciences, UC Riverside
V. A. Gibeault, Botany and Plant Sciences, UC Riverside