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Garden Help Desk: Identifying and handling white top on your lawn

By USU Extension - | May 27, 2023

Courtesy photo

White top is a tough, spreading weed that can be difficult to control. Control efforts should begin as soon as the weeds are noticed.

I have a plant that is growing on my property that I am trying to get rid of. We have tried pulling it multiple times and it continues to regrow. Can you please identify the plant in the pictures and recommend what do to remove it.

This looks like white top, also known as Hoary Cress. It can be a very stubborn perennial weed. The plants being to appear in early to mid-spring but often go unnoticed until they flower in late spring. If white top is ignored, the clusters of white flowers can drop mature seeds during the summer. The top growth on white top dies back once frosty fall weather returns.

White top is a spreading perennial. It spreads in landscapes, waysides, and pastures by way of rhizomes (underground “runners”) and by seed. In landscapes this weed can crowd out lawn grasses and low-growing ornamental perennials. In pastures large quantities of white top may be toxic to cattle.

There are a few things you can try for white top control, but a combination of methods will be most successful.

Hand-pulling can be helpful, especially if you get it done before the plants can drop seeds. Water the area a day or two before and gently loosen the soil so that it’s easier to remove as many rhizomes as you can along with the plants. The more rhizomes you can remove, the fewer there will be to resprout.

Courtesy photo

The immature pollen cones on spruce trees add bright color to the springtime landscape. As they mature, they will lose their bright color.

Gardeners often try to just remove the plants in flowerbeds or pastures with a hoe or till them under. If the plants are young seedlings this can be effective, but if the plants are mature, they’ll be chopping up roots and rhizomes that can sprout, producing many more white top than they had before.

Hand-pulling, hoeing, or tilling aren’t practical options for white top in lawns. Control white top in your lawn with post-emergent herbicides beginning in the spring as soon as you notice the plants. You can use this method up until the time daytime temperatures begin to exceed 85 degrees, but not later.

As you work to get your white top under control, use regular mowing to reduce seed production. A white top plant can produce thousands of seeds during a season. Every flower cluster you remove in the spring is hundreds of new plants you won’t have to deal with in the future.

It will probably take more than one year of diligent effort to get rid of the white top but stick with it and you’ll succeed.

I planted this tree and two others 5 years ago. They weren’t supposed to have pinecones. One tree had a few cones at the top last year. The nursery told me my tree was probably a male. Now the other 2 trees are covered in what appears to be little red pinecones. Is there any way to get rid of them?

Courtesy photo

Most female spruce cones are borne in the upper part of the tree where they are less likely to be pollinated with pollen from the same tree.

By now you’ve probably realized that these magenta-colored cones on your spruce trees were immature pollen (male) cones. My own Oriental Spruce has these beautiful pollen cones in the spring and last year a couple of female cones matured near the top of the tree. The female cones were unexpected because my tree is isolated from other spruce trees and spruces seldom self-pollinate.

Female cones are usually found only in the upper part of the tree. Pollen cones occupy the lower part of the tree. Spruce, pine, and fir trees are wind pollinated. Having the female cones at the top of the tree reduces the chances that pollen from its own male cones will reach the female cones. Instead, the pollen will travel on breezes, gradually traveling higher until it reaches the tops of other trees. This strategy for preventing most self-pollination improves the genetic diversity and vigor of the following generation.

Spruce trees have both male and female cones on the same tree, so there aren’t separate male or female trees. There are products available for reducing the fruit set on some kinds of trees, but there isn’t a product that will prevent cone development on conifers.

Spruce pollen cones are found on the lower part of the tree. When they're mature, breezes will carry pollen from these male cones to the female cones on other trees.


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