Part 2 bluegrass rhizomes and pre-m

[lawrence stone]

Jim writes:

>That leaves rhizome growth in KGB. The rhizome is basically a horizontal underground stem, that can send up new grass plants from nodes. KBG rhizomes start to grow well in the fall, and continue growth, even when the grass looks dormant, until the ground freezes. I have seen KBG rhizomes grow up to 18" in mild winters here. But again, pre-ems affect roots, and they would not hinder rhizome growth.

We can agree on the chemical will not hinder rhizome growth underneath the barrier of the pre-M.

But what does the barrier do to the shoots of KYB the emerge from the terminal nodes of the rhizome?

With the exception of Taperstan (sp?)how does the chemical distinguish between a KYB shoot and a shoot of an undesirable species of weed that has just germinated from a seed?

[GroundKprs]

reply

Most of the pre-ems we use today are root inhibitors. They keep the newly germinated weeds seeds from forming roots, and they can hinder new root growth from crowns of existing grass plants. <i>Tupersan</i> (a.i.= siduron) selectively controls crabgrass and some other grassy weeds; <i>Ronstar</i> (a.i.= oxadiazon), NOT LABELLED for residential turf, acts by interrupting activity in meristematic areas. (Meristem is plant growth area, usually at end of a root or stem, where special plant cells divide and multiply to cause plant growth.)

So any of your root inhibitors will not hurt any plant already living in the treated soil and growing upward; only effect is on the roots. While I have not specifically tracked rhizome growth and shoot formation in treated and untreated turf, I have never noticed a problem in that area.

Now <i>Ronstar</i> may be a different story, but not many contractors use that in their programs for turf pre-em. I have never seen any data on the idea, but I am guessing that new shoots growing up into the layer of oxadiazon could be stressed.

That is why I stated that rhizome growth is not stressed in pre-em apps. The rhizome grows laterally, usually under the pre-em barrier. If the rhizome is growing into a pre-em, I don't think (note: I'm just thinking - haven't seen studies on this, although it probably has been studied) that it would be stressed because the pre-em only affects roots, not stems.

[lawrence stone]

reply

We seam to have two contradicting points of view on the nature of pre-m.

Penn State says :

"Summer annual grass weeds are usually controlled with preemergence herbicides. These herbicides act by forming a chemical barrier in the soil prior to seed germination or emergence. The barrier prevents grass seedlings from emerging and developing normally"

http://www.agronomy.psu.edu/Extension/Turf/WeedMgmtd.html#ChemicalControl

In the weed management courses that I have attended that were presented by Dr. Landschoot and his associates they presented the mode of action of a pre-M as a sort of strangulation of the seedling at point of soil break.

Now if this scenario holds true why would not a sprout from a rhizome be subjected to the same mode of action and final outcome as a seed sprouted from an undesirable weed species?

[GroundKprs]

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That quote is a very general statement about the mode of action of preemergents. Most of our turf grassy weed pre-ems are root inhibitors, as I stated above. I am not certain of the mode of action of siduron; it may be a selective root inhibitor, or some other action.

Check http://rvm.cas.psu.edu/Publications/Selective_in_Non-Crop.pdf , on page 18, for more information on the modes of action of various herbicides. If anyone wishes to know the exact mode of action of various pre-ems, not dealt with in that document, I would suggest you make a list, then call or email your state extension turfgrass specialist for that information.

The common discussions, over the years in various turf seminars, of the root inhibiting effect of pre-ems is what led me to look closer at how they impacted the turf areas I manage.

[lawrence stone]

reply

From:
http://www.turffiles.ncsu.edu/pubs/weeds/ln&lnd.html

Understand the Herbicide

Understanding how the various preemergence herbicides work is necessary if optimum weed control is to be obtained. One of the most commonly used family of preemergence herbicides is the dinitroanilines (sometimes referred to as DNAs). Individual herbicides in this family include Barricade, Team, pendimethalin (various trade names including Pendulum, Pre-M, and Weedgrass Control), Surflan, and Balan. Dimension herbicide does not belong to the DNA family although its mechanism of action is very similar. These herbicides are widely used for preemergence annual grass control in established turfgrasses. Generally, they provide good weed control if applied correctly. By understanding how this family of herbicides provide weed control, it becomes more clear as to how they should be utilized.
First of all, DNAs do not prevent weed seed germination. As the seedling germinates, the herbicide is absorbed by young roots and emerging shoots and cell division is inhibited causing plant death in susceptible species. Therefore, for optimum control, it is necessary to apply these herbicides prior to expected weed germination. After application, these herbicides need rainfall/irrigation for activation. This causes a chemical herbicide barrier at the soil surface. As weeds begin to germinate, they encounter this herbicide barrier, absorb the herbicide and fail to emerge. Because this family of herbicides is not very water soluble and readily binds to soil particles, they tend to remain near the soil surface and do not leach through the soil profile. Therefore, this chemical barrier remains intact until soil microorganisms and other factors degrade the herbicide over time.

Another herbicide used for preemergence control of annual grasses in many turfgrass species is Ronstar (oxadiazon). Ronstar is not registered for use in home lawns but can be used in commercial turf by professional applicators. Ronstar does not belong to the DNAs and the mechanism of action is completely different. Ronstar is absorbed by shoots of the young weed species as the emerge through the herbicide treated zone and plant death in sensitive species occurs soon thereafter. Little to no root absorption occurs; therefore rooting of the turfgrass is not adversely affected. The timing of Ronstar application should be 10 to 14 days prior to expected weed germination followed by irrigation/rainfall. Ronstar will not control most emerged weeds.

Improper timing (application after weed emergence) is a major cause of poor control with these herbicides. While very small crabgrass plants (generally in the one-leaf stage for some of the DNAs and two to three leaf stage for Dimension) can be controlled with these products, much better control is obtained when application and irrigation/rainfall occurs prior to germination. For lawn care/grounds care operators, it is important to prioritize your preemergence application for customers. This should be based on several factors. Soil temperatures can vary even in a particular neighborhood. South facing slopes that receive full sun in the spring warm-up more quickly. Coarse-textured soils (sandy soils) also warm more quickly than fine-textured soils. Either of these areas should receive a priority for a preemergence application for control of summer annual grasses such as crabgrass, goosegrass, etc. Another important aspect of establishing a priority is whether or not the site can be irrigated. Remember, establishing a chemical barrier is necessary for proper control. If a customer does not utilize irrigation and must depend on rainfall, it would be wise to apply these products well in advance of expected germination whereas a site with irrigation can establish the chemical barrier immediately after application.

Applying these products well in advance of expected germination is acceptable. Many lawn care operators express concern over the herbicide degrading more quickly (therefore a breakdown in control) if they are applied several weeks prior to expected germination. Because these herbicides are primarily degraded by soil microbes, and because soil microbes are less active in cooler soils, degradation does not proceed at the same rate when the soil temperature is 45 degrees versus 70 degrees.

It is also important that these herbicides be properly applied and at the correct rate to prevent turfgrass injury. Remember, these herbicides are absorbed by roots and inhibit root growth. Therefore, improperly calibrated applicators, excessive overlap, etc can cause significant harm to the turfgrass.

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As the seedling germinates, the herbicide is absorbed by young roots and emerging shoots and cell division is inhibited causing plant death in susceptible species.

The question is:

Is KYB a susceptible species?

[GroundKprs]

reply

ALL GRASSES are susceptable. Therefore you are stressing the roots of all grasses. You kill germinating grasses because they cannot form roots. The crowns of any grass plants above the pre-em barrier cannot grow new roots very well.

And the work quoted above does seem to indicate that oxadiazon would harm shoots from rhizomes. The root inhibiting pre-ems would also retard the new rooting of these shoots.

[lawrence stone]

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Like you Jim I have not applied any pre-m at all over the last three years.

When combined with my superior cultural practices of core aeration, tine raking, using the "right" fertilizer at the right time, at the right amount, and applying grub and sodwebworm control measures I have produced some the the finest KYB stands on the planet.

Now that the turf in not hindered by Pre-m the amount of plants per square foot in unbelievable.

But I must weight the consequences of doing the "right" thing by not applying pre-m or suffer some crabgrass breakouts. Now I can post M the crabs but the dead spiders are not aesthetically acceptable. I don't want to tine rake during the summer to try and remove the dead crabs for this will just stir up more undesirable seed germination.

Now you understand the reason why I am tine raking four times a year and have issues with the dead crabs is that my customers only view the quality of my product by aesthetics and playability. These factors unfortunately with aesthetics being the number one measure of my performance when it comes time to renew my contract for next season.

So I am left with having to apply some type of pre-m in the late May/early June time-frame on a carrier of low N/medP/highK fert to help the KYB stay somewhat presentable on non irrigated sites during the upcoming 10 weeks or so of grass death (summer).

Now with Ronstar (applied on sports fields)I only get a single whammy and it will leave my roots alone to be able to get down deep to find water. But the problem is that ronstar .95% on 5-10-17 is downright cost prohibitive at $3.18/1k sqft.

So I am stuck with using Dimension .15% with 5-10-17. I can apply this product at a reduced rate of 1.91 lbs/1k sqft using program one on high cut Northern turf. To get the bag rate of the fert I would need to apply at 2.75 lbs/1k sqft but I am happy with the reduced ratio and the cost is about equal to a 25-5-10w/40%SCU applied at 1lb of N/1k sqft. At these rates there is no post emergent effect but I am doing this in a spot fashion anyway.

Since I have given the turf the entire spring to grow without pre M I will have some good long existing roots to gather water.

My only consideration is that I will be shutting down the rhizome sprouts but I don't see why rhizome production will be shut down. Once the pre-m degrades by Mid September rhizome shoot production should start up and continue until the ground freezes.

Here is an interesting statement from the following website:
http://aggie-horticulture.tamu.edu/plantanswers/turf/publications/bluegrass.html

"Rhizomes of Kentucky bluegrass develop most frequently in early summer as leaf growth begins to decline. During this season, high nitrogen fertilization and close mowing retard the development of rhizomes. Factors which favor photosynthesis such as long days, high temperatures and high light intensities promote rhizome development. Likewise, factors that promote leaf growth such as high nitrogen fertilization retard rhizome development in Kentucky bluegrass."

[GroundKprs]

reply

OK. But I wouldn't go to TX for info on bluegrass. Don't think they grow it anywhere in TX, LOL.