1. Turfgrass Pest Management (Category 3A)

Weeds of Turfgrass

Chapter 7

2. A weed is any plant that grows where it is not wanted. Whether o not a plant is considered a wee depends more upon where the weed is growing than its species.
3. Standard tall fescue is drought tolerant and pest resistant. It makes a fine utility turf, but is considered a clumping weed when growing with fine-textured bluegrass.
4. Weeds ruin the visual and physical uniformity of turf stands. Weeds compete with turf for growing space, water, nutrients, and sunlight.
5. Some weeds thrive in poor turf growing conditions. Some examples include:

• Deep shade (ground ivy, common chickweed)
• Compacted soil (prostrate knotweed, goosegrass, annual bluegrass)

1. - Wet spots (yellow nutsedge, white clover, annual bluegrass)

• Heavy wear (yarrow)

1. It is not surprising that weeds commonly overrun turf in poor sites. Weeds are not a cause of poor turfgrass performance; weeds are a result of poor turfgrass performance.
2. The success of weed management depends upon choosing tactics based on the biology of the specific weed. Learn the following descriptions of weed characteristics and growth habits to help in weed identification and management.
3. Basic differences divide weed plants into two groups: monocotyledons and dicotyledons.

Monocots, or "narrowleaf" plants, have leaf veins in a parallel pattern. The growing points of most monocots are at or below ground level. Only non-woody, herbaceous monocots are found in termperate regions like Michigan.

Dicot, or "broadleaf’, weeeds have a netted pattern of leaf veins. All broadleaf plants have above-ground growing points, and some species also have underground growing points. Both herbaceous and woody dicots grow in Michigan.

4. Monocots include weeds in the grass (crabgrass, foxtail), sedge (yellow nutsedge), and lily (wild garlic) families.
5. There are many families of dicot weeds:

Composite (thistles, dandelions)

Mustard (sheperdspurse)

Carrot (wild carrot)

Morning glory (field bindweed)

6. After the seeds germinate, all plants have four stages of development:

1. Seedling Stage – the newly emerged, immature plant. Seedlings are tender and vulnerable to all stresses.
2. Vegetative Stage – the plant rapidly produces stems, roots, and foliage. There is great uptake of water and nutrients during this period of growth.
3. Seed Production – the plant’s energy is directed towards the production of seed. Uptake of water and nutrients is relatively slow and is directed mainly to flower, fruit, or seed structures.
4. Maturity Stage – the plant has little or no movement of water and nutrients or energy production.

1. The developmental stage of a weed affects how it responds to your management tactics. For example, a seedling is not yet established and is easily eliminated by any method. A plant in the vegetative stage will take up herbicide more quickly than a mature plant.
2. There are distinctive types of weeds based on the number of years required to complete their life cycle. Annual weeds live for only one year.

Summer annuals (prostrate knotweed, foxtail, crabgrass) germinate from seed in the spring, mature, set seed and die by winter.

Winter annuals (chickweed, sheperdspurse) germinate from seed in late summer, overwinter, then produce seed the following spring.

All biennial weeds are broadleaf plants with a two-year life cycle. Biennial wees (Queen Anne’s lace, bull thistle) germinate in the spring and develop a thick root and compacted cluster of leaves (rosette) the first summer. During the second year, biennials mature, produce seed and die.

Perennial weeds live for three or more years and are the most difficult weeds to manage. Initially, seed is usually produced during the second year of growth. Most perennials have specialized structures, called propagules, at or below the soil surface with the capacity to produce new plants. Rhizomes, stolons, bulbs, and tubers are all propagules. To successfully manage perennial weeds, you must destroy the underground plant parts.

3. Weeds are also divided into cool- or warm-season plant categories. Cool-season plants grow best during the cool periods of spring and fall. They mature or go dormant during mid-summer. Winter annuals and some perennials are cool-season weeds. Summer annuals are warm-season weeds, and remain dormant or do not germinate until May or June. Warm-season perennial grasses such as nimblewill, are considered weeds because they remain dormant and brown in the spring, weeks after Kentucky bluegrass greens-up.
4. Some weeds, especially grasses and sedges, look alike. However, this does no necessarily mean they require the some control measures. As with any pest, it is important you correctly identify weeds to successfully manage them. Comparing as unknown weed to a picture is the easiest way to identify its species. Obtain good references and consult other turf managers or MSU Extension to help correctly identify weeds.
5. Injury from insects and diseases, misuse of fertilizer and pesticides, or excessive wear weakens turf and allows weeds to become established. Prevention and immediate repairs of thinned turf are important weed management tactics.
6. Coordinating weed control activities with the susceptible stages of problem weeds can be difficult, but is vital to successful weed management. Keep records and regularly monitor the activity of weed problems in the turf you manage.
7. There are five strategies used to manage weeds of turfgrass. Keep in mind that most weed problems require the coordinated use of more than one strategy.

1. Maintain vigorous turf stands. A vigorous, dense turf stand is the most important step in weed management. If proper species selection, installation and turf care practices are followed, then only rarely will weeds be a problem.
2. Prevent seed production. Weed plants produce a great number of seeds capable of sprouting for decades. Eliminate weeds before the seed production stage. Whenever possible, destroy sources of weed seed in areas adjacent to valuable turf stands. Beware of introducing seed-infested compost, mulch, top-soil, or grass seed.
3. Prevent seed germination. Most seeds require sunlight to germinate. Turf mowed 2" or higher shades the soil and deters germination. Thick, rapidly-growing turfgrass crowds out weeds beginning to grow in thinned areas. Take care not to bring dormant weed seeds in the soil to the surface where they can germinate. Germinating weeds can be suppressed with preemergence herbicide.

1. 4. Eliminate weed seedlings. Small plants with immature root systems are easily

destroyed with mechanical controls. Seedlings are also more easily injured by

chemicals. In addition, rapid growth of seedlings means herbicide is more

effectively absorbed and moved within the plant. The bar graph here clearly

shows that annual weeds are most susceptible to herbicide when developing.

1. Target susceptible stages of developed weed plants. Controlling mature weeds is

weakened or have depleted food reserves. Perennials are weakest during the bud-

to-bloom stage. You can create stress in second-year biennial and perennial

weeds by repeatedly removing their tops.

1. Ideally, you will manage most turf weeds by encouraging vigorous turfgrass. Realized that without herbicides a turf stand is not likely to be weed-free. Also realize only turf that has great visual importance or requires uniformity for its use needs to be weed-free. There are many herbicides for use on turf, with many characteristics to consider.

23. Biological and physical properties of weed influence herbicidal action:

• Growing point that are sheathed or located below the soil surface will not be affected by contact herbicide sprays.
• Leaf shape. Herbicide tend to bounce or runoff narrow, upright leaves; broad, flat leaves tend to hold the herbicide.
• Wax and cuticle prevent foliar sprays from coming in contact with the leave.
• Leaf hairs, when dense, hold herbicide droplets away from the leaf surface. Conversely, a thin layer of hairs allows for more absorption by holding the chemical onto the leaf surface.
• Deactivation. Certain plants can deativate herbicides and are therfore less susceptible to chemical injury.
• Life cycle stage. Seedlings are vulnerable to most management practices. Vegetative and early bud stages are susceptible to systemic herbicides. Mature plants are affected the least by herbicides.

25. Avoid unintentional herbicide injury, and get full benefit of the product by carefully reading and following label recommendations.