Poa in zoysia

Are you aware of any post-emergent herbicide selective for Poa annua that could be used on Zoysiagrass while dormant or while actively growing? — via the Internet

Considering that Poa annua is essentially a winter annual (at least in most of the warmer climates where zoysia is more prevalent) you might try a non-selective herbicide while the zoysiagrass is dormant. You'll want to be sure that the zoysia is completely dormant, of course. But as long as it is, a non-selective product, such as glyphosate or glufosinate, should provide good control with little or no harm to the turf. Contact herbicides will certainly give you some burndown, but because some Poa annua plants are actually perennial, some systemic action would be beneficial. This might be the best approach if the Poa annua infestation is fairly light and could be treated with spot spraying.

For heavier infestations or large areas, consider a pre-emergent in late summer, which should prevent much of the fall germination of Poa annua. A follow-up application might be necessary, as Poa annua can germinate throughout winter. Most turf pre-emergents include registration for zoysiagrass, but be sure to read the label before you apply.

Try some nitrogen

My overseeded perennial rye has been yellowing this winter. I've been hitting it with iron but it just isn't doing the trick. Any suggestions? Could it be the frosty (upper 20s) temperatures we've had? — California

Cool temperature is not likely to be the cause of yellowing in perennial ryegrass. The number one reason that turf (or almost any plant) yellows (or becomes chlorotic, to use the proper term) is inadequate nitrogen. Give the turf an application of fertilizer that includes at least part of its nitrogen in quick-release form. If you don't see results soon, then you'll have to look for another reason for the chlorosis.

If the nitrogen didn't work, iron would probably be the next factor to consider, though you've already tried that approach and it apparently isn't the problem in your case.

With just about any suspected nutritional problem, a small foliar test application is a quick and cheap way to confirm your suspicions. If a deficiency really is the problem, turf generally responds quickly. One caveat: High pH can make it difficult for roots to take up iron, so a foliar application might show results, while a granular application might not.

Repair or replace?

How do I justify replacing equipment, vs. repairing it? I have to come up with a policy for my company and don't know what formulas people use. — via the Internet

It's not that people don't occasionally use some numerical formula for this decision, but too many factors affect the repair-or-replace equation to boil it down to simple math that applies broadly. In general terms, it comes down to determining when the cost of the breakdowns exceeds the cost of the new equipment. But many operators fail to account for just how expensive — in terms of lost productivity — the downtime is.

Gilbert Peña, marketing manager of commercial mowing for John Deere, deals with this question frequently, and thinks that most operators wait too long to replace old equipment. As Pena tells it, people think that, “If your machine is down for a major repair, that's when the decision needs to take place. But you need to decide not only what it's going to take to repair, but also what the downtime is costing you. Considering that, you have to ask, ‘Shouldn't this be taken care of during the off-season?’”

The answer, of course, is yes. But then comes the task of deciding — in the off season, before that major breakdown occurs during the peak time — whether the equipment has another season of dependable service left in it. According to Peña, that is a matter of experience and knowing the history of equipment you've used. For example, if a zero-turn mower typically gives you three to four years of service and your current unit is three years old, chances are good you'll be money ahead to buy the new mower now, before the fourth season begins, rather than waiting until a major breakdown. Not only will you enter the season with dependable equipment, you'll get more for the old equipment when you sell it or trade it in. According to Peña, operators who “drive it 'til it dies” usually keep the old unit as salvage, rather than trade it in.

As for the actual average life span of equipment, that just depends. Peña says, “When someone asks me how long a walk-behind mower lasts, and I say, ‘3 to 5 years,’ they ask ‘What does that mean?’ I tell them it means just that. It all depends on how you use the equipment.” For example, equipment in the North lasts longer than equipment in the South, which has to run all year. And owner-operators often get more life out of their equipment than someone who runs large crews, who may not use the same degree of care with the equipment.

Peña says that he encourages customers to buy their new equipment during the off season for another reason: you tend to get better deals. Dealers often provide their best prices and most attractive financing packages during the off season. If you wait until the peak season, “You're in line with all the other guys, you're in a hurry, you'll take what may not be the best possible price, or a brand you didn't really want, just because you need a new unit right away,” says Peña.

According to Peña, because the cost of ownership entails not only purchase price, but also repair costs and downtime, some operators have started thinking, “What if we only used equipment that was under warranty?” In other words, just leasing equipment, for example, and trading it in before the warranties expire. “They look at it as, ‘What does it cost me to operate the machine per month,’ not just what it costs to purchase the equipment. Sometimes, its cheaper to lease if you look at that way,” says Peña, who feels that institutional operations and golf courses are well ahead of commercial operators when it comes to taking that kind of approach.

Eric Liskey has a bachelor's degree in ornamental horticulture and a master's degree in botany. He has been licensed for pesticide advising and applications in California and Missouri, and has more than 10 years combined professional experience in landscape installation and maintenance, nursery retailing, pest management and botany.

If you have a question about landscape or turf management, write to “Researching Maintenance,” Grounds Maintenance, P.O. Box 12901, Overland Park, KS 66282-2901, or send you question by e-mail to

Questions are selected on the basis of current general interest. Unfortunately, we are unable to guarantee a response to individual letters.

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