Heat has summer weeds flourishing

My landscape and garden are in a mess. The hot, dry conditions kept me from putting in as much time as I would like pulling weeds and taking care of the plants, and now I have a jungle.

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There are certain weeds that take over when these conditions occur, including niruri and lespedeza.

One of the harder weeds to control in landscapes is niruri, also known as chamberbitter, phyllanthus, gripeweed, little mimosa and leaf-flower. This weed comes in two types. One has smaller leaflets than the other. Also, the seeds form on the bottom of the branch. On one type, the seeds are attached directly to the branch, and on the other the seeds are on a long stalk attached to the bottom of the leaf.

These weeds look like little mimosa trees with compound leaves and lots of little leaflets.

This weed is small but hard to control. The seeds require light to germinate, and they usually germinate later than most other weeds.

Several control measures can be used to reduce their numbers.

The first is to keep a thick layer of mulch around your plants so the seed will not come up. This will prevent sunlight from reaching the seeds. These seeds can remain in the soil for years, so if the seed is exposed to sunlight, the plants will germinate.

If the niruri is still coming up in mulched beds, make sure the mulch is evenly spread and is 2 to 4 inches deep.

The weed can also be pulled up by hand. This works best when the soil is moist.

The third option is a herbicide. In an ornamental bed, this can be tricky. A pre-emergence herbicide is best. There are several on the market that can be used in ornamental beds and in turf and will give good to excellent control. Two that are readily available for homeowners are isoxaben and oryzalin.

Isoxaben can be found in products such as Snapshot. Oryzalin can be found in Surflan or in conjunction with another herbicide (benefin) in Amaze.

Two post-emergent herbicides -- glufosinate (Finale) and glyphosate (Roundup) -- can be used to control niruri in ornamental beds.

However, they have to be sprayed directly on the weeds. If the herbicide gets on the ornamentals, they will be damaged or killed.

In turf, a healthy grass is the best way to keep this weed under control. The thick grass will block the sunlight from reaching the seeds.

This is accomplished by proper fertilization, irrigation and mowing.

However, if weeds are present, they can be controlled with the application of a post-emergent herbicide. In centipede and St. Augustine, atrazine can be used. In zoysia and Bermuda grass, products that contain 2,4-D are the only option.

These products are rated at about 70 percent control, so it's best to put out a pre-emergence herbicide in the spring. Atrazine is the herbicide of choice. It should be applied in mid-February and again 45 days later.

The latter application will be important in late-season weed control. Atrazine can be used on Bermuda grass only if the grass is dormant.

Lespedeza, a low-growing weed that has three leaflets and a woody stem, is also hard to control. It will flower in late summer, with single flowers that are pink to purple.

This weed is mostly found in centipede lawns. That's because lespedeza is a legume. Legumes produce their own nitrogen from bacteria that grow in nodules on their roots, so they like to grow in areas that get little fertilization, and centipede lawns are the least fertilized of all the lawn grasses.

One control option is to increase the amount of nitrogen the centipede receives. Most centipede lawns will receive one pound of nitrogen per 1,000 square feet per year. Increasing the application to two pounds of nitrogen per 1,000 square feet will help control this weed. The increase in nitrogen will shut down the production of nitrogen by the bacteria, and the weed will die.

Other control options are chemical. In centipede, atrazine can be used as a pre-emergence herbicide. It is best to follow the same application schedule that is used for niruri.

A few more herbicides can be used to control this weed post emergent, including atrazine, which can be used either as a pre- or post-herbicide. Another option is one of the three-way products that contain 2,4-D. These products can only be used at a half rate on centipede and St. Augustine. If used at full rate, these grasses can be damaged.

Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at cphillipshort@comcast.net.