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The 2010 All Horticulture Field Day was held yesterday at the Iowa State University Horticulture Research Station. The weather was beautiful and there was plenty to see ranging from cultivar trials, sports turf seeding rate studies, fertility, disease, and herbicide trials. This has been a great year to evaluate products for their effectiveness against crabgrass will all the weed pressure we’ve experienced. Our crabgrass trial featured a new herbicide from Bayer called Specticle.

Specticle is a preemergence herbicide with some post control and offers promise in controlling crabgrass and Poa annua. Specticle just recently received federal registration and will now be available in the turf market. The active ingredient in Specticle is indaziflam.

One of the highlights of the day was watching Gary Twedt, CGCS, receive the 2010 Distinguished Service to Iowa Horticulture Award. Congratulations Gary on this achievement and all that you do for Horticulture in Iowa. Check out some pictures from the event!

I had a chance to speak about my bentgrass spaced plant trial investigating lateral spread among 24 bentgrass cultivars.

Dr. Christians speaks to a group about different bentgrass cultivars.

Dr. Minner demonstrated various methods to control moles.

Gary Twedt received the 2010 Distinguished Service to Iowa Horticulture Award.

A key to the successful control of annual grasses (such as crabgrass) in established turf is the correct application timing of preemergence herbicides. Preemergence herbicides should be applied by May 1^st in central Iowa. Dr. Christians has noticed that this date does not vary much from year to year, after monitoring germination dates for the last 34 years.

In addition to timing: application uniformity, using recommended product rates, and the requirement of (1/2 inch) irrigation within 3-5 days of application can play a vital role in crabgrass control. 

Several products are available for effective annual grass emergence control. These products vary slightly in mode of action, length of control, specific weed efficacy, desired turfgrass seed inhibition, and early postemergence control. Benefin, benefin + trifluralin,bensulide, oxadiazon, siduron, pendimethalin, mesotrione, prodiamine, isoxaben, and dithiopyr are preemergence products available in the market today. 

Please note that some products are not labeled for certain turfgrass species. For example, oxadiazon is not recommended for use in fine fescue; however, oxadiazon provides   excellent goosegrass control in Kentucky bluegrass. Always read thoroughly and follow the label directions. Remember, the label is the law.

Dithiopyr and prodiamine have the longest window of effectiveness and can control weeds for up to 16 weeks. Dithiopyr and mesotrione offer early postemergence control when applications are made following weed emergence. Siduron and mesotrione have a unique property that allows herbicide application to seeded areas. Siduron selectively controls weedy annual grasses such as crabgrass, foxtail, and barnyardgrass, while allowing the desired turfgrasses to grow.  Mesotrione is only labeled for preemergent use on newly seeded Kentucky bluegrass lawns. All of the other preemergent herbicides kill the seeds of the cool-season grasses and cannot be used at the time of seeding.

Fertilizer-herbicide combinations are sold at most retail stores. This allows homeowners to combine the two operations into one application. A disadvantage of the combination is that the proper time for weed control often does not coincide with the optimum time to fertilize. Combinations with preemergence herbicides are generally effective in controlling annual grass weeds as long as applications are made at the appropriate time and recommended amount.

In addition to annual grassy weeds, a spring application of a preemergence herbicide will control annual broadleaf weeds, such as prostrate knotweed and spurge. A second application at a reduced rate may be necessary for season-long control.

Paying attention to herbicide timing, application uniformity, product and rate, and ensuring (1/2 inch) irrigation within 3-5 days of application will help prevent annual grass (crabgrass) invasion. Below you will see two pictures of crabgrass in an early leaf-stages.

The last picture is a general guide of preemergence application dates via Quali-Pro's Prodiamine label:

It is May 2 and we have a snow storm going on in Ames.  Normally, when people ask me for a date by which they should have their preemergence herbicide applied for crabgrass control, my standard answer is to have it down by May 1.  The question that I have received most often in the last two days, is whether this cold weather will delay germination. 

The expected answer would be that the cold weather will delay germination,  however, I have been watching crabgrass germination dates for 34 years here in central Iowa.  What I have observed is that the germination date does not vary much from year to year.  When we have a warm spring and you would expect early germination, the crabgrass still germinates about the same time (around May 1).  When we have a cold spring, like this one, the crabgrass still seems to germinate about the same time.  It may be a few days early or late, but not a few weeks.

I am still expecting crabgrass to germinate soon.  If you do not have your preemerge down, I would recommend applying it as soon after the snow melts as possible.  I put mine on last week.
 

On July 3, I put up a post about Windmill grass (Chloris verticilatta) and on August 2 a post on Bermudagrass (Cynodon dactylon).  You will also find several posts on crabgrass (Digitaria spp) over the last two years.

Right now is early August, the seedheads from each of these species are visible in lawns.  I thought it would be a good time to get some pictures of the three species to help with identification.

Here is the seedhead of Windmill grass.  This warm-season grass has been moving into central Iowa and north for the past few years and there is quite a bit of it in Ames this yeas.  It branches off in all directions and rolls like a tumble weed when it breaks lose from the stem.  It is a little larger than most crabgrass seed heads.

Windmill grass forms a tight-knit mass of slolons in the lawn and at this time of year it is covered by seedheads.  (See picture 2)

Here is bermudagrass.  It also has a branching seedhead, but notice how each branch arises from the same point.   It is quite rare in central Iowa, although it looks like it may be expanding in this region.

This is crabgrass.   It is one of the most common weeds in Iowa.  Unlike the other two which are perennials, this one is an annual and has to come back from seed each year.  It is similar to bermudagrass, but notice how it branches off from varying areas along the stem.

We have had three mornings with frost on April 10, 11, and 12. I took a walk on campus on the afternoon of the 12th to see what the impact of the frost had been on the crabgrass that I observed on April 2 (see earlier post). Crabgrass is very susceptible to cold damage, particularly in the seedling stage. I expected the crabgrass to be dead, but to my surprise, it appears to be doing fine. The crabgrass is in a somewhat protected area around the horticulture building, but it is an area that did have some frost.

I am still not seeing much germination of crabgrass in more exposed areas on campus and we have not seen any emergence at the horticulture research station as of April 12. It did get down to 20 F at the research station on the morning of the 11th. If any crabgrass was beginning to peak through, I would expect it to be dead. I'll continue to monitor the early germinating crabgrass over the next few weeks and let you know what is happening.

The trial in which we are applying Baricade and Dimension on April 1, 15 and May 1 to separate plots is continuing. As soon as I have some results from that work, I will put up a post.

Figures 1 and 2. Crabgrass by the horticulture building on the afternoon of April 12 after three mornings with frost.