Green Industry Resources
Hort Update- Seasonal Information for the Green Industry
Weed Control- Dandelion, Ground Ivy and Wild Violets
Dandelion, Taraxacum officinale, is probably the most widely recognized turfgrass weed.It is a weed that was imported as an ornamental plant from Europe. Dandelion seed was available to the pioneers for ornamental plantings and were sometimes used on the roofs of sod houses to make them stand out on the prairie.
It is a simple perennial, having a thick, fleshy taproot that can penetrate into the soil 2 feet or more. The above ground portion consists of a rosette of leaves arising from the crown of the plant. The leaves are long and deeply notched, with the lobes pointing back toward the crown. Flower stalks arise from the crown area and are long, hollow and hairy. Both the leaves and the flower stalk contain a white, milky sap. The flowers produced on the stalks are bright yellow round, flat-topped clusters of many tiny individual flowers. The seed head is a familiar white puffball full of seeds that are blown by the wind to disperse when mature. It is one of the first plants to emerge each spring, and new seedlings continue to appear throughout the growing season.
Dandelions can be controlled by hand pulling or digging when small numbers are present. Use a dandelion digger to cut the taproot off 4-5 inches below the crown of the plant to prevent regrowth.
Herbicide applications are another common way to control dandelions. If only a few weeds are present in a lawn or landscaping bed, then apply a spot treatment. Spot treatment involves spraying each individual weed, and not broadcasting herbicide over the entire lawn. Spot treating can result in a significant amount of money saved, due to the reduced amount of herbicide used. Use a 2,4-D based broadleaf herbicide in turf areas; this will not damage the underlying grass. In landscaping beds, 2,4-D can again be used but will damage surrounding shrubs and other ornamental plantings if accidentally sprayed, or if spray mist drifts to them. So use it cautiously! Be certain you read all the label instructions and follow them carefully including the use of all necessary personal protective equipment.
Post-emergent herbicides for dandelion control are commonly applied in combination with fertilizer applications. Make these applications after irrigation, or early in the morning when the grass is still damp so that the herbicide will stick on the dandelions leaves and have a chance to become absorbed. Again, read and follow all directions on the herbicide label.
Creeping Charlie, creeping Jenny or ground ivy are all common names for a very common lawn and garden weed, known botanically as Glecoma hederacea. Ground ivy is a cool season, perennial weed that grows best during spring and fall. Ground ivy thrives in cool, moist, shaded areas of the landscape but can also be found growing in full sun.
Ground ivy is a member of the mint family, having the characteristic square stems and minty scent when damaged. It grounds low to the ground, twining through a lawn or landscaped area, by rapidly creeping stems that are capable of rooting down at the nodes. Its opposite leaves are round, with scalloped or toothed edges and arise from the stems on petioles. The leaves resemble those of the common annual geranium, although much smaller. Light blue to bluish-purple, or very rarely white, flowers on 2-3 inch spikes appear in early spring.
If you catch it early, you may be able to control ground ivy by pulling it out. If it becomes thick, you can use a special tool called a de-thatching rake. This helps to comb through the grass, pulling much of the vining weed out. It doesn't eliminate it, but may keep it in check. (Some grass will be pulled up in the process.) Using this tool is more physically demanding than fall leaf raking however. It provides a strenuous workout, and may be more laborious than you wish to undertake. This operation de-thatches the lawn and cuts into the soil. Afterwards, youcan work in some shade-tolerant grass seed to replace the ground ivy. The best time to do this for most cool season lawns is between mid-August and mid-September. Choose a time when the weather is beginning to feel cooler.
Ground ivy can be controlled with a 2,4-D based herbicide. The herbicide will damage or possibly kill any woody or broad-leafed vegetation that comes in contact with the spray, so it must be used with caution. The best time to spray is in autumn, once temperatures have cooled to the 60's or 70's, with no rain forecast for 48 hours. This spray program may be repeated every ten to fourteen days as long as the weather is cooperative. Do not spray during hot or windy weather, to avoid herbicide drift onto desirable plants. Always follow the label directions carefully.
This weed can also be controlled with Borax. Borax contains boron, which is an essential nutrient needed in very tiny amounts for healthy plant growth. Amounts even slightly over what is needed are toxic to plants. Borax can be used against creeping Charlie because the weed is more sensitive to boron than is grass. Small amounts can kill creeping Charlie without permanently harming the lawn. (Grass may brown a bit, but it will grow out of it.)
The problem is, boron does not dissipate or break down like standard weed-killers. If it's applied repeatedly or at too strong a rate, you will end up with an area where you can't grow anything until the boron leaches out. That may take years. At most, you should only treat your lawn with borax once each spring for two years. Here's the formula: dissolve eight ounces of a product like Twenty Mule Team Borax into four ounces of warm water, then dilute it in 2 1/2 gallons of water. This should be sprayed evenly over 1,000 square feet of lawn, no more, no less.
Once the weed is gone, try to maintain a weed-free lawn through regular and proper mowing, watering, fertilizing, and reducing shade when possible in excessively shady areas. These cultural steps will greatly contribute to a more weed-free lawn by encouraging thicker grass.
Wild violet, Viola pratincola, is a cool season, perennial, broadleaf weed. It is one of the first plants to flower in spring, growing well during cool parts of the growing season, and is usually found in shaded, moist areas. Violets range in height from 2-12 inches and have a dense, fibrous root system. The heart-shaped leaves have scalloped edges and originate from the crown of the plant atop long petiole stems. Leaf shape among wild violets is highly variable due to the frequent hybridizing that occurs among several violet species, resulting in leaves that range from entire (whole with a continuous margin) to strongly dissected. All violet leaves have a waxy coating.
Violets produce two different types of flowers: chasmogamous and cleistogamous. Chasmogamous flowers are borne on long stalks and range in color from light blue to deep purple. These flowers are the familiar, showy flowers normally associated with violets, however, in some species they are sterile and do not produce viable seed. The second type, cleistogamous flowers, do produce viable seed but are self-fertilized without opening. These flowers have no petals and are not showy. They are held underneath the foliage and sometimes slightly beneath the top layers of soil or mulch. Homeowners, who often wonder why their wild violet problem keeps getting worse when they never see any flowers producing seed, seldom notice cleistogamous flowers!
Established colonies of wild violets are very drought tolerant, due to fleshy underground stems called rhizomes that store water and allow the plants to survive dry conditions. The rhizomes also allow the plants to spread, forming colonies. These extensive perennial root systems are one reason the weeds can be so difficult to control.
Controlling wild violets in a lawn or landscape can be a difficult challenge, and will certainly require more than one herbicide application before it is accomplished. Violets should be targeted for control in fall as they are preparing to go into winter. Plants take in herbicides most readily during this time. Very poor control is the usual result of attempts to control violets during the summer. Dicamba and triclopyr are two herbicides often included in products providing control of violets. Read the product labels carefully, making sure that violets are listed on the label, before buying any herbicide product.
The waxy coating on violet leaves causes liquid herbicides to quickly run off the leaf after application, with little chemical being taken in by the plant. For this reason, herbicide applications targeted at violets should include a spreader-sticker. This product helps the chemical “stick” on the weed leaves better, resulting in better herbicide absorption and thus giving better control.
As with any lawn weed, the best control practice is to promote a dense and healthy turf through proper mowing, fertilizing and irrigation.