Tuesday, March 17, 2015

Weed of the month for February 2015 is Dandelion

Dandelion  

Biology: Dandelion (Taraxacum offinianale), is a broadleaf perennial weed that can be found in lawns, nursery crops, and landscapes throughout the United States. It has the ability to survive many different soil types, environmental conditions, and management practices; thus, it is a commonly found weed in lawns throughout the northern half of the U.S.

Identification: Dandelion is one of the most identifiable broadleaf weeds. It is a perennial broadleaf that is a member of the composite or daisy family. It prefers full sun and grows best in moist soils; however, it can survive in multiple environmental conditions (shade and heat) and management practices (fertility, drought, low mowing practices). Dandelions generally appear in early spring as they regrow from a few overwintering leaves and their taproot. Leaves have distinct wavy margins that form into the irregular ‘toothed’ appearance that makes the plant easily identifiable. The ends of the ‘teeth’ tend to point downward towards the base of the rosette.

Dandelion produces a strong taproot and the plant has the capability to regenerate from surviving taproot segments (so hoeing a dandelion from your garden may not actually kill the plant). The survivability of this taproot helps to make dandelion a very prevalent and ‘difficult to completely control’ weed in lawns in Indiana, even following herbicide applications.

Dandelions typically flower from late April to mid-May in Indiana. Yellow flowers consisting of sunflower-like petals, are produced at the ends of long, leafless, erect stalks. Dandelions typically flower in their second year of growth after germination from seed. Yellow-brown fruit (flowers) are formed into a conspicuous, globe-like, white seedhead with light, feathery ends capable of easy dispersal by the wind. Each seedhead is capable of producing 140 to 190 individual viable seed, which helps to contribute to the vast populations of dandelion located in lawns throughout the Midwestern United States. Dandelion seeds germinate in emerge from late spring (after flowering and seed dispersal) to early autumn.

Dandelion may often be mistaken for chicory since both form toothed leaves that form from a basal rosette. However, the basal leaves of chicory tend to be rough to the touch with distinct, coarse hairs. Additionally, the toothed lobes of chicory are often alternately arranged on the leaf and point both backwards and forward, while the toothed margins of dandelion are located opposite of each other on the leaf and predominantly point backwards. The most distinct difference between the two plants is that dandelion produces yellow flowers while the flowers of chicory are purplish-blue in color. 









I am not sure who created this .gif movie of dandelion flowering, but it is amazing.










Cultural control: None known specifically for dandelion. Digging up as much of the taproot as possible will improve control. Dandelion knives and other similar tools are available for removing individual plants with very little disturbance to the soil. These tools, however, are only effective when all the taproot is removed. Adjusting fertilization practices to minimize the about of potassium (K) or potash (K2O) may help to reduce dandelion populations, but this process is very slow to generate results (many years). Management practices such as increased mowing heights, fertility, and irrigation may help to produce a dense vigorous turf capable of outcompeting germinating dandelion plants.

Biological control: The fungus Sclerotinia minor can selectively remove dandelions from cool-season lawns. In Canada it is formulated and sold as Sarritor, a new biological weed control product. This product has yet to be released in the US as of 2015.

Chemical control: Many herbicides effectively control dandelions, especially those that contain 2,4-D. Fall is the best time to control perennial broadleaves like dandelion, and both amine or ester formulations of 2,4-D provide optimum dandelion control in the fall. If dandelions are problematic in the spring, dandelion control can be optimized in the cooler months (April) by using ester formulations of broadleaf herbicides, or by using florasulam (Defendor). However, even ester formulations can be ineffective if applied too early. As spring progresses and temperatures warm, turf managers should switch from ester formulations of broadleaf herbicides to amine formulations because (1) their efficacy improves during warmer temperatures in May and early summer and (2) they are safer than ester formulations to use around landscape plantings, gardens, and other sensitive plants. For more information about using amines or esters, see “Should I use an amine or ester formulation for postemergence broadleaf weed control?” in" Turfgrass Weed Control for Professionals."


For more information on weed control, search this blog and check out our Turfgrass Weed Control for Professionals Publication.

For archives of past weed of the month postings, visit our Weed of the Month Archive.

To become a true dandelion aficionado, check out this publication from the Canadian Weed Science Society: click here

Aaron Patton, Turfgrass Extension Specialist, Purdue University
Leslie Beck, Weed Extension Specialist, New Mexico State University

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