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Weed Biology Part 1 Monocot Vs. Dicot

Monocot vs Dicot: What’s the difference and why does it matter?

Weed management can be a difficult task for turf and ornamental managers. Sometimes our mechanical or cultural controls like mowing or mulching fail to control the weeds and our client isn’t happy. It’s important that turf and ornamental managers have a working knowledge of the weeds common to their region. Over the next several weeks we’re going to take a look at weed biology. Our first installment: monocots vs dicots.

What is a cotyledon?

A cotyledon is an embryonic leaf in seed-bearing plants. There are usually one or two cotyledons for most weeds and the cotyledons either contain or have access to stored food the seedling will need before it can produce its first true leaves. Plants with one cotyledon are called monocots and plants with two cotyledons are called dicots. In most cases the cotyledon in monocots, for example corn, will stay at or below ground level. When corn is planted, the kernel of corn doesn’t come up out of the ground, it stays below the soil surface. The cotyledon transfers the energy stores in the endosperm of the seed to the growing plant. Conversely, the cotyledons in dicots, a green bean for example, not only serve as energy stores for the new plant but will push up out of the ground and photosynthesize before the first true leaves emerge.

Monocot vs Dicot

The difference in the number of cotyledons is only the beginning of the differences between these two types of plants. Differences include venation patterns, vascular bundle arrangements, roots systems and flower anatomy.

In monocots like grass, corn, or daffodils, the veins in the leaves run parallel to each other along the length of the leaf or stem. The vascular bundles are usually arranged in a complex pattern and the root system is pretty fibrous. The flower structures in monocots are arranged in multiples of three.

In dicots like green beans, woodsorrel, and most woody trees and plants, the veins in the leaves form a complex, netlike system. Instead of running from one end of the leaf to the other, the veins will branch off one central vein to form a network. The vascular bundles in dicots will usually be arranged in a ring. These rings are most easily seen in trunks of trees. The root systems in dicots will usually have a primary taproot. Of course plants adapt as well as they can to the site they’re planted in, so dicots planted in extremely compacted soil may not have a well developed taproot. Lastly, the flower structures in dicots are arranged in multiples of four or five.

Growing Points

The last obvious difference between monocots and dicots is the location of the growing points. In monocots, the growing point is at or just below the soil surface and is often protected by a sheath. In dicots, there are multiple growing points which are located at the end of every stem.

The different locations in growing points is what allows turf weeds to be managed by consistent mowing. The growing point in turf is at the soil surface and is not damaged by consistent mowing. However, the growing points on weeds like bittercress or wood sorrel are above the soil surface. Consistent mowing means consistent removal of growing points for the weed.

Pesticide Use

Understanding the difference between monocots and dicots is also important when selecting a pesticide as part of an integrated pest management program. Non-selective herbicides aren’t usually the best choice when managing weeds in a turf stand, unless of course the intent is to wipe out all things green and begin again. Turf managers who need to manage broadleaved weeds (dicots) within their turf stand will want to apply a selective herbicide. 2,4-D is a great example of a selective herbicide. While applied to all vegetation in a turf stand, grasses inactivate 2,4-D while broadleaf dicots do not, thus killing the dicots while leaving the turf unharmed (when applied within label rates).

However, landscape managers will want to avoid spraying 2,4-D on planting beds as the herbicide will harm the desired plant. Landscape managers will want to select an herbicide that will kill the monocot weed (usually grass) such as sethoxydim to control grasses that are invading the planting area.

Want to know more?

Choose your state from the drop down below and check out the following courses for more information on managing weeds in both turf and ornamental areas.

Common Turfgrass Weeds

Common Ornamental Plant Pests

Home Lawn and Landscape Management

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