An Explanation Of Common Weeds In Lawn Care

Why is dormancy important to the persistence of annual weed species? 

  • Annual weed species can be controlled using dormancy. For instance, environmental dormancy can be used to control certain species, such as crabgrass. Crabgrass requires sufficient light, so if the control method reduces light the seeds will remain dormant and will not germinate.51-2 White clover flower Environmental dormancy occurs when the seed does not have sufficient resources to germinate. Another type of dormancy is inherent dormancy, which occurs when the seed has all the environmental requirements it needs, but will not germinate until the seed has been broken by stratification (moistened seed), scarification (scratched seed) or by the maturation of the embryo. The factors involved in seed dormancy are impermeability of the seed coat, presence of germination inhibitors, or a immature embryo.

Which type of perennial is more difficult to control?

  • There are two types of perennials, simple and creeping. Simple perennials produce new plants by seed. Simple perennials have a fleshy root. If the root has been cut, they will produce a new aboveground growth. A dandelion is an example of a simple perennial.3-1 Black medick circular whorlCreeping perennials are more difficult to control, because they reproduce by seed and vegetatively. The best time to control this type of weed is when the plants are at the 3-4 leaf stage. During active growth, site preparation is most effective in early spring or in fall before crop emergence. Between the bud and flowering stages are optimal for in crop treatments for most perennial broadleaf weeds.

What are winter annuals?

  • Two weeds that are examples of winter annuals are, chickweed and henbit. As long as soil temperatures are above 7-10 degrees celsius winter annuals will germinate late in the summer and throughout early fall. Winter annuals will flower and set seed in late spring and die off in the summer. Their entire life cycle is completed within a 12 month period.

The four vegetative reproductive structures weeds possess.  What must be done to ensure these structures are killed during site preparation?

  • There are four vegetative structures weeds possess to reproduce, rhizomes, creeping roots, tubers, and stolons. Rhizomes grow horizontally below or just above the ground. Plants can multiply very quickly using rhizomes because of their many growing points that are produced at the nodes. These growing points are called buds, which allow for new lateral growth. Creeping roots are storage systems for reproduction. These organs are deep within the soil and are very resistant to control measures because they penetrate deeper than most vegetative structures. Stolons are able to propagate easily because of their growth pattern. Their special stems grow on the ground, developing roots when they touch the soil. A tuber is a stem structure that grows below the ground. The accumulation of food material causes a swelling near the tip of a rhizome. A tuber is a storage and propagative organ. A tuber is produced in one season, and dormancy is involved before sprouting will occur.32-1 Moss close up The best way to kill off weeds that reproduce vegetatively is during site preparation. A method called cultivation is a practice that involves turning the soil using sharp discs. This will spread the soil and lead to the death of the vegetative parts of the plants and destroy their food reserves. It takes a healthy and competitive turf to ensure these types of weeds cannot penetrate an area.

Many weed species are able to adapt to a wide range of conditions, however, certain weeds are notable because of their response to specific environmental conditions.  Here are some of the specific conditions that actually encourage the following weeds:

Yellow nut sedge grows best in wet areas than dry.

Prostrate knotweed grows best in severely compacted soils.

Black medic grows best in dry, nitrogen poor soils.

Crabgrass grows best in sandy soils that are exposed to light.

Annual bluegrass grows best in well irrigated areas.

Mosses grows best in acidic soils

White clover grows best in soils high in potassium.

The effects of mowing too low, why bentgrass can be mowed lower than most other cool-season turfgrass species, and removing too much grass at any one mowing can damage your lawn:

  • Properly mowing turf is an essential practice for reducing weed invasions. At any time no more than ⅓ of the grass plant should be removed. This will ensure the plant remains healthy and stress free. Removing excessive amounts of the turf, will cause stress to the lawn and make it easier for weeds to penetrate the area. Cutting the lawn too short will allow too much light into the soil, resulting in the germination of crabgrass seeds. Only certain turfgrass species can be cut short, like bentgrass or annual bluegrass. This is because they have an extremely low growing point. Removing the clippings from the ground is also a good idea to ensure a healthy turf. Thatch is a layer of dead and living organic matter, and too much thatch can cause problems in the lawn. To make sure the lawn doesn’t build up a layer of thatch the clippings should be removed from the lawn when feasible.

 When is it important to add phosphorus to turf and why?

  • It is important to add phosphorus to the turf when establishing an area. Phosphorus will help develop the root system which will lead to a healthy turf. It is also a good idea to add phosphorus before a dormancy period. This will allow the turf to develop the root system one last time before a long stretch of little growth.

Why is high pH not normally a problem in lawns?  What is the appropriate pH range for creeping bentgrass, and what can be added to raise soil pH?

  • Most fertilizers lower the pH in lawns, so it is unlikely to find a situation where the soil pH is too high. Creeping bentgrass can tolerate a pH level between 5.8 and 6.5. Lime can be added to increase a soils pH.

How much water does turf require through the summer months on a weekly basis?  Which weed species do you encourage when you do not water enough, or water too heavily?  Why is crabgrass likely to become a problem on creeping bentgrass greens?

  • Turf requires one inch of water on a weekly basis to encourage deep root growth. If irrigation is done too infrequently the lawn will become stressed and weed species with deep roots like, quackgrass, field binweed, or white clover will invade. If irrigation is done too frequently most turfgrass will suffer, and weed species such as yellow nutsedge and annual bluegrass will invade because they prefer wet soils.

What weed species are associated with thin turf stands caused by snow mold?

  • Early germinating weeds will invade thin turf stands caused by snow mold. Weed species like, annual bluegrass and knotweed are the most commonly found.

What is the primary difference between a simple and a creeping perennial?  Why are creeping perennials so much more difficult to kill than simple perennials?

  • The primary difference between a simple perennial and a creeping perennial are their root systems. A simple perennial has a long fleshy tap root, and creeping perennial has an expansive root system. Creeping perennials are more difficult to kill because their root systems are more complex. Their roots develop deep in the soil and are able to store resources which makes them more difficult to control. Simple perennials have one main root which can be often removed mechanically. Some examples of simple perennials are dandelions, plantain, and curled dock. Some examples of creeping perennials are quackgrass, ground-ivy, and yellow nutsedge.