Perennial broadleaf weeds die back to ground level in fall but send up new growth in spring. These weed species have leaves that are wider and often have a major vein running down the center of the leaf with secondary veins branching off of it. They are typically botanically classified as eudicots (dicots). Perennial weeds reproduce by seeds or may spread by creeping above or below ground stems or by spreading root systems. Examples of perennial broadleaf weeds include dandelion, thistle, pokeweed, plantain, violet, and creeping Charlie.
Keeping ahead of weeds and controlling them when they are small is essential for good weed management. This requires persistence throughout the entire growing season to remove weeds as they emerge.
In small areas, some weeds can be controlled by pulling and digging. This method is best accomplished after a soaking rain or deep watering. Unfortunately, pulling and digging is often ineffective on deep-rooted weeds. Pull or dig weeds when they are young before they become established.
Mulches control weeds by preventing the germination of weed seeds. They can be effective at preventing new perennial weeds from germinating, but are less effective on those weeds that are already established and can spread by rhizomes and stolons. Established weeds should be destroyed prior to the application of the mulch. Grass clippings, shredded leaves, coco hulls and weed-free straw are excellent mulches for vegetable gardens and annual flower beds. Apply several inches of these materials in early June after the soil has warmed sufficiently. Wood chips and shredded bark are excellent mulches for perennial beds and areas around trees and shrubs. Apply 2 to 4 inches of material around landscape plantings. These materials decay slowly and should last several years. However, it will be necessary to apply additional material periodically to maintain the desired depth.
In many situations, herbicides are the only practical and efficient method of weed control. Broadleaf selective herbicides kill broadleaf plants but do not harm grassy plants. Use these herbicides with care as many desirable garden and vegetable plants are also broadleaf plants and would be killed by a selective herbicide. Broadleaf herbicides include 2,4-D, MCPP, MCPA, dicamba, triclopyr, and others. Non-selective herbicides kill any green plant material they contact. Non-selective herbicides, like glyphosate, can be applied as a spot treatment to only those plants you wish to kill.
Herbicides must be carefully applied as they have a high potential to harm both weeds and desirable plants. Always apply herbicides when winds are calm and temperatures are cool to prevent drift and damage to desirable plants. Protect garden plants with barriers like buckets or boxes to further reduce problems with drift. They can also be applied with a sponge and wiped onto the leaves of the weed to prevent collateral damage to nearby plants.
For best control, apply herbicides in spring or fall. Since herbicides are more effective on small plants, spring applications are beneficial for killing weeds before they become large or flower and set seed. Most herbicides are absorbed and translocated throughout the stems, leaves, and root system to completely kill the weed. In fall, plants naturally move carbohydrates from stems and leaves to the roots. Often a more complete kill of the plant is observed with fall applications of herbicides because it takes advantage of this natural movement in the plant.
Herbicides must be used according to label instructions on the package. Failure to follow directions may kill desirable plants or prevent other plants from being grown in the area.
In small areas, some weeds can be controlled by pulling and digging. This method is best accomplished after a soaking rain or deep watering. Unfortunately, pulling and digging is often ineffective on deep-rooted weeds.
In many situations, herbicides are the only practical method of weed control. Effective broadleaf herbicides include 2,4-D, MCPP, MCPA, dicamba, triclopyr, and others. The most effective broadleaf herbicide products contain a mixture of 2 or 3 herbicides as no single compound will control all broadleaf weeds. Fall (mid-September to early November) is the best time to apply broadleaf herbicides to the lawn in Iowa. Broadleaf herbicides can be applied as liquids or granules.