control whitetop

At first glance, whitetops present themselves as pretty white flowers that you could bundle up in a bouquet and present to a loved one. And why not? They have a unique appearance and would improve your yard, making you the envy of the neighborhood. But before you go about plucking these delightful flowers, there is something you need to know – that outgrowth is not a flower, it’s a weed. And you need to act fast if you wish to see the last of it. In this article we will talk about how to control Whitetop (Hoary Cress) in your yard.

History of whitetop

Whitetop is a plant native to southwestern Asia. According to reports, it found its way to the United States in the form of contaminated alfalfa seeds from Turkistan. This introduction took place over four to five decades in different shipments, before the plant’s first sighting in California back in 1876.

It currently falls under the classification of noxious weeds, and there has been a lot of research regarding its eradication. Given that one plant can result in as many as four hundred shoots in one year, nipping this weed in the bud would go a long way in preventing its spread.

In this guide, we will cover its identification, impact on the environment, and ways to control whitetop. In doing so, you will have an easy time dealing with this weed, should the need arise for the same. Let’s get started!

Whitetop description

When dealing with any weed, it helps to understand what it is and what contributes to its growth. Whitetop also goes by the name whiteweed, hoary cardaria, peppergrass, and heart-podded hoary cress. This non-native plant can grow as high as two feet.

For this article, whitetop will refer to the three species: globe-podded hoary cress and lens-podded hoary cress, alongside heart-podded hoary cress. The former refers to hairy whitetop, whose scientific name is C. pubescens. All these hoary cresses belong to the mustard family (Brassicaceae), and the reason behind their grouping lies in their similarities in appearance, invasion methods, and difficulty of control.

You can, however, differentiate the three by studying their fruits, which vary in shapes. The heart-podded hoary cress has pods with heart shapes, which feature prominent veins when dry. The lens-podded hoary cress has oval pods that lack prominent veins while the globe-podded hoary cress has globe-like pods with a purple hue.

flowering Hoary Cress

Flowering Hoary Cress

How to Identify whitetop

As mentioned above, this guide will cover the whitetop as if it were one species, but keep in mind that there are variations within the three. They, however, have some similarities which you can use when weeding them out from the rest of the crops.

For one, these perennial plants grow to heights of about sixteen to twenty inches and have broad leaves. Their tap root system is well-developed and can creep extensively to reach water tables while storing carbohydrates.

Are you wondering why the globe-podded hoary cress also goes by the name hairy whitetop? Well, it might help you to note that these plants have soft hairy appearances. Towards the ground level, they are hairier, and the hairs reduce as you travel up the plant. Their leaves are equally hairy, with short and white hairs covering the surface. Their stems can grow either way: upright or along the ground. However, they do not root at the nodes.

whitetop flowers

Whitetop flowers

As you move up the plant, the number of leaves increases as does the branches. The leaves change as they grow. When young, they appear tapered, and as they age, they take up long and slender appearances with toothed margins.

Have you seen a plant around your home that meets all of the following descriptions? You could be dealing with whitetop. And if this is the case, read on to see how this can affect the plants and animals around your home.

whitetop plant

Whitetop plant

Why is whitetop invasive?

You need to take action if you have whitetop growing in your yard, more so if you wish to have native plants in your yard. Do you remember the part where we covered their extensive root system? Well, these roots are so well-developed and so strong that they can make their way to pasture areas, gardens, lawns, and roadways, you name it.

As they do this, the plants take up a lot of water and nutrients and develop thick canopies that are hard to penetrate. At this stage, they not only deprive native plants of nutrients and water, but they also keep shorter plants from getting access to sunlight.

Whitetop plants can grow as high as two feet, so you can imagine the kind of havoc they would wreak in a vegetable garden. Let’s say you’ve spotted them in your yard. All it takes is some pulling here and there to get rid of them, isn’t that right? Well, no, it’s not that easy. Given their extensive root system, you will need more than that, and that’s why they fall into the noxious weeds category.

Since their introduction, they have infested millions of acres across the globe. They are not only a threat to the ecological system, but agricultural sustenance and the economy as well. Landowners are using millions of dollars each year in the hope of eradicating these weeds, which are taking up more land cover by the day.

And that’s not all. If you have cattle, you have more reasons to be afraid of these plants. Whitetop species contain glucosinolates, and if your cattle consume these plants, they could die.

With all these adverse effects, it is not hard to see why governments would classify these species as noxious weeds and declare war against them.

Where does it grow?

Whitetop species can thrive in different soil types, and as they grow, they form dense monocultures. Not all sites are at a threat of invasion, as some are more conducive to their growth than others. Generally, these plants do well in areas with rainfall of about twelve to sixteen inches each year. Though they do best in alkaline soils that are wet towards the end of spring, it is not a pre-requisite.

They also do well in open areas with lots of access to sunlight. You will find these plants in roadsides, waste areas, and irrigated rangeland, as well as regions with similar conditions. If you live in arid rangeland, you are in luck. These species will avoid you with the same effort you would use to get rid of them.

For people with croplands, these species can be a bother as they will compete with sugar beets, peas, onions, and other such crops. Productivity goes down, and the land begins to lose its value. It can be a real headache for the farmer.

whitetop US

Reports of whitetop in the US

How does whitetop spread?

These species populate in areas with adequate access to water, such as irrigated areas. Dispersion by water is therefore common. They also spread during cultivation where machinery picks them up before they get transported to a new site by vehicles. One plant can produce as many as 4,800 seeds in a year, seeds that can remain viable for up to three years. What’s worse, the seeds are so hardy that they do well in salt-stressed areas.

When a seed is in ideal conditions, it takes root and can grow up to twelve feet wide in its first year. From this point, it grows by at least two feet each year. It can grow faster than this, where it lacks competition over nutrients and water.

In the early stages, the plant has one main taproot with supporting lateral roots. As it thrives, the lateral roots also face down and move further into the ground. In most cases, the lateral roots can become much longer than the main root.

It is essential to control whitetop plants from the moment you see them as their root system is hard to beat. Think about it like this. By the second growing season, the root system could be up to nine meters deep into the ground, so much so that it reaches the water table. Can you imagine how hard it would be to deal with such an extensive system?

It gets worse. Both the main root and the developing lateral roots can produce buds, which later become shoots, accelerating the spread of the plant. Where the lateral root faces down, a shoot grows. Think of how many shoots can come of this. Studies show that one plant can result in as many as four hundred shoots in a year where it lacks competition over nutrients. Unbelievable? Well, believe it!

How to control whitetop

At this point, it is clear that these plants do more harm than good, and eliminating them is the way to protect our biodiversity. How can you do this?

One, we have to admit that dealing with these species would be an uphill task owing to their extensive root system. Thus, you require to take many steps to control whitetop. You need to contain the current infestations while combining different means to combat their growth. Getting them to a tolerable level would be a good start.


While this option may not be available to everyone, it would help if people prevented the growth of these weeds from the early stages. One way to do so would be to monitor the plants around you and check if there are any infestations.

Using Machinery

A whitetop plant results from seed, and preventing the spread of seeds would significantly reduce the number of these species. Where an area is full of whitetop plants, avoid using vehicles and machines in the area. If you have to, make sure that you wash the car before leaving the area.

Grazing livestock

Keep livestock from infested areas. Where they have already consumed the seeds, keep them in a confined space where they can pass the seeds. It should take about fourteen weeks, and after this, you can clean the area and let them graze. When grazing livestock, it helps to have a rotation plan as this allows for native plants to recover before the next grazing season.


Where you have a field of crop and part of it has an infestation, avoid nearing the area during harvesting as the produce could get contaminated. You should also check the irrigation water for traces of whitetop seeds. If you use contaminated water, you will spread the weeds throughout the entire field.

Mechanical control

In this strategy, you would use manual labor. While some people argue that this is costly and time-consuming, it has proven to be an effective method to control whitetop species. However, you should combine it with another method to get the most out of it.


Where infestation is on a small scale, you can deal with the plants by removing them by hand. At this stage, the plant root systems would not be extensive, and you can get to the root of the problem, get it? Pun intended.

This method works for young plants as well as species along riparian lands. Ensure that you get the whole plant out before burning the debris in a pile. If burning does not appeal to you, bagging the remains and depositing them in a landfill is another alternative that would work.

physical invasive plant removal

Physical invasive plant removal is labor-intensive

Using machinery

You can use a machine where the infestation is at a high level. Where this is the case, you should clean the machine after use to avoid spreading fragments of the roots, as well as seeds.


While this method is not as labor-intensive as hand removal, it has its downsides. For one, it contributes to the spread of fragments and seeds to non-infested areas. However, you can use it in flat ground areas as long as you follow up with the application of herbicides.

Start by mowing the whitetop plants when the growing season starts. At this point, the plants will be at flower bud stages. Wait for the plants to re-sprout and reach the flower bud stage before applying herbicides on them.

What is the essence of this? Well, when you mow the plants, the whitetops produce larger leaves that lie perpendicular to the ground surface. In this way, you will have an easier time covering most of the plants with the herbicide of your choice.

Alternatively, you could do away with the waiting and opt to spray the plants towards the end of summer. You could also do it when fall starts before following up with mowing during spring when there will be new shoots. Whatever method you choose, you should note that herbicide applications will be continuous. It is only in this way that you can control the growth of these plants.


Another common method to control whitetop is tillage. It works best where the weeds are in their early stages and are yet to spread their extensive root system. Start by tilling plants to the point that is underneath the tap and the lateral roots. Having done this, follow up with cultivation as soon as you notice new shoots.

Continue doing this every two weeks for the eight weeks of the growing season. As time goes by, the frequency of the same will reduce. This method relies on consistency, and you should do this for at least two years to control the growth of the whitetops. You can get even better results with herbicide applications in play.

Fire- yay or nay?

With other weeds, you may find that the use of fire is an effective means of eradication. But with whitetops, this is sadly not the case. You see, these plants depend on their extensive root systems, and 75% of their biomass lies beneath the ground surface.

Thus, if you set fire to what is above the ground, which is the stem, leaves, branches, fruits, flowers, and seeds, there is another massive part that remains unburned. In a few weeks, the weeds would be back. Remember the part where the roots form up to four hundred shoots in one year? Yes, that is what you are up against.

As much as you can rely on fire to get rid of remaining debris from hand pulling, this method cannot get to the root of the problem, get it?


Rather than baptism by fire, which has proven not to work, you can rely on water. For this to work, you will need to flood the affected areas with at least six inches of water for two months. That means you might have to hit pause on farming unless you are dealing with water-loving plants such as rice.

Biological Control

Is it possible to control whitetop using natural means? Let’s find out:


On the downside, goats and sheep have not taken a liking to these plants to the extent of over-feeding on them.

In most cases, they will graze on these weeds till the early flowering stage before they move on to more palatable plants. Though it may seem like a drop in the ocean, it has proven to be effective in dealing with small quantities of the whitetop plants. Cattle should not feed on whitetop plants as they contain chemicals that can harm cows when consumed in large quantities.

At this point, grazing is the only known biological method to control whitetop plants. Research into these plants is yet to yield a biological agent to help in the same.

Chemical Control

The thing with whitetop plants is that they grow in most soil conditions. Thus, choosing what would work for them without affecting the desirable plants is often a problem. While you could find a chemical that could wipe out these noxious weeds, using it might kill the crops in your land. Worse yet, the chemical could hinder the subsequent growth of other plants in the land. Is that a risk you would be willing to take?

Most people find themselves in this situation, but all is not lost. As long as you choose a chemical suited to the elimination of whitetop plants and use it as required, your problem should be a thing of the past. If you are using a chemical in or near water, use one that has approval for the same. If you live in a hot area, get something that works for your land.

Reading instructions is essential as it ensures that the weeds do not develop resistance. If they do, you will have a hard time eliminating them. So where you are in doubt, always refer to the guidelines or contact an expert.

The application process

Remember that the use of the herbicides will depend on what the guidelines state. However, in most cases, you will find that the application should take place in early spring or in the fall before winter dormancy.

Aim the herbicide at the leaves and stems for several minutes, such that it drips off the plant. If you use the chemicals near or in water, wicking is a good option as it avoids the spread of the herbicides over a large area.

Herbicides used to control mustards work well on whitetop. Chlorsulfuron or metsulfuron methyl provide effective whitetop control in noncropland areas. Glyphosate, imazapic, or imazapyr formulations are acceptable for use in areas near water.

Once you succeed in removing whitetop plants from an area, limit disturbances as these could encourage the re-establishment of the weeds. That said, all the best on this journey!