Fall Broadleaf Weed Control

Dr. Kevin W. Frank
Assoc. Professor & Extension Turf Specialist

The summer of 2013 was one of the best in recent memory for growing turf and unfortunately also one of the best for growing broadleaf weeds.  The turf thrived with favorable temperatures and timely precipitation throughout much of the summer and so did broadleaf weeds.  Summer herbicide applications likely burned down the top-growth of many perennial broadleaf weeds but recently weeds such as white clover, dandelion, ground ivy, and black medic have magically reappeared.  

White clover in turf.

The challenge with the summer herbicide applications is that they are very effective at burning down top-growth but in some cases they are not effective at killing the entire plant.  In contrast, fall is the ideal time to control weeds because unlike the summer when weeds are focusing on top-growth, in the fall weeds are storing energy in their root system and are more susceptible to herbicide applications.  So if your turf has been overtaken by a bevy of broadleaf weeds, applying a herbicide in late September or early October will make a difference in what you battle next year.  Apply the herbicides on a sunny day when rain is not in the forecast for 24 hours.  We want the herbicides to dry on the leaf surfaces and not be immediately washed off.  There are many different herbicides that could be used including the most common three-way broadleaf weed control mixtures.  As with any pesticide application always make sure to wear the appropriate safety attire and follow all label recommendations.  As many have lamented over the years, the only shortcoming of fall broadleaf weed control is that you really don’t get to watch them die.  You generally won’t see the twisting, shriveling, and discoloration that often accompany herbicide applications but next spring the weeds will be gone or at least their numbers will be significantly reduced.

With fall herbicide applications we often miss the site of weeds dying.

Nematodes in Michigan?

Fred Warner
Nematologist
MSU Diagnostic Services

I once read a statement that some golf courses/country clubs spend up to $50,000 per year on fungicides. Obviously that figure implies there are some serious diseases of turf caused by fungi. But, what about nematodes? They too can cause serious problems but are often ignored. I’m often fond of saying, “Ignoring a problem won’t make it go away.” Nematodes are probably the cause of some symptoms observed on turf and are going undiagnosed. I base this assessment on the fact that until the past two or three years we typically received fewer than a dozen commercial turf samples per year in Diagnostic Services for nematode analyses. Things have changed as I think some superintendents now have me on speed dial.

Over the past few years, nematode problems appear to have become more prevalent on golf course greens in our region. The cause for this phenomenon is unknown but if I am to think out loud, I wonder if it has to do with a movement away from traditional insecticides used to control cutworms and other insects in turf to materials of different chemistries. Nematologists have observed this in corn as many growers have stopped using traditional insecticides for corn rootworm control in lieu of genetically modified, stacked, seed-treated corn hybrids. The organophosphates and carbamates used in the past probably helped to keep nematode numbers in check but with their discontinued use, nematode populations have had the opportunity to increase in densities. Could this be occurring in turf? Roughly 75% of all golf course samples processed in Diagnostic Services this year have contained high to severe numbers of plant-parasitic nematodes. At these levels, infected turf will exhibit symptoms that many superintendents say mimic those caused by summer patch. And if summer patch is suspected, my guess is nematode control is not objective number one.

Nematode feeding damage on a fairway in Michigan.

Cool-season turfgrass species are hosts to at least 10 genera of plant-parasitic nematodes. Typically, samples collected from greens and tees on golf courses contain at least three genera. In general, it appears, our turfgrasses tolerate nematode feeding fairly well. However, there have been situations in Michigan and our neighboring states where nematode feeding has resulted in serious symptoms. I’ve visited some greens where the turf has been thinned so severely that only sand exists especially after top dressing. One thing to keep in mind about the impact of nematodes is their feeding does not result in the production of any characteristic above-ground (secondary) symptoms. In controlled studies at MSU, the only quantitative effects nematodes had on the above-ground growth of creeping bentgrass were reductions in the numbers of tillers and leaves produced. The distribution of symptoms often gives a clue as to whether nematodes are involved. Nematodes tend to be aggregated in their distributions (especially cyst and root-knot nematodes), so the symptoms appear as patches. However, other soil-borne plant pathogens, especially fungi, can and often do have similar distributions.

The only way to properly diagnose nematode problems is to collect soil and plant tissue samples and send them to a nematode lab for analyses. To avoid problems, this should be done preferably in the spring. Roots of cool-season turf grasses grow most vigorously when soil temperatures are cool and due to this phenomenon, nematode numbers tend to rise as more feeding sites are available. To avoid problems, control tactics must be implemented at action threshold levels before nematodes reach damage thresholds. This is an important principle of pest control but is better understood for insects than nematodes. The key strategy is to keep population densities of pathogens and pests below levels where they are expected to cause damage.

One significant issue when learning of a plant-parasitic nematode problem in turf is the lack of chemical control options. Nemacur was an effective nematicide for use on creeping bentgrass greens but is no longer available. Other products exist but have not been evaluated in Michigan. Any organophosphates or carbamates should provide some control of nematodes but those marketed as insecticides will not be extremely effective. For example, nematode populations have been shown to rebound very quickly on greens where chlorpyrifos had been applied.

Typically, nematode control is not necessary on new greens and tees because sand mixes are used for their establishment and these materials should ideally be free (or nearly so) from nematodes. But, this is not always the case as some superintendents have experienced severe symptoms due to nematode feeding on newly established greens from contaminated sources. Usually, however, nematode numbers increase over time as they migrate from aprons, collars and fairways, from deeper in the soil or are transported on plugs from core cultivators.  New greens and tees should be sampled for nematodes roughly five years after establishment. Plant-parasitic nematodes are much easier to manage, or to alleviate symptoms of their feeding, if control tactics are implemented when their numbers are low. Early detection is important, remedies are limited.

Nematode damage on a fairway.

If you suspect you have a nematode problem, in addition to collecting a sample for a nematode analysis, I also suggest you also collect soil and grass clippings for nutritional analyses. Because chemical control options are limited, cultural controls are the first tactics to consider. If nematodes are recovered at levels below damage thresholds, then the evidence indicates they are not the causal organisms if symptoms are present. However, if high population densities are recovered, action should be taken to reduce their population densities or alleviate the symptoms they cause. What approach to take? Well, the soil and tissue samples will help to determine the course of action. If the soil and tissue results indicate less than adequate levels of nutrients, especially potassium, obviously an additional fertilizer application(s) is necessary. However, if the soil results indicate nutrients are above critical levels but tissue tests suggest otherwise, these results indicate root dysfunction. The nutrients are available in the soil based on the test result(s) but the roots are not capturing them, therefore the plants are growing poorly. What pathogens reduce root volumes and weights? Nematodes. Additional steps now need to be taken to improve plant health and this may involve reducing the population densities of plant-parasitic nematodes. However, proper fertilization, using synthetic or non-synthetic fertilizers, using a different watering program and aeration should go a long way toward alleviating the symptoms caused by nematode feeding. If nematodes are present, the most important concern is the health of the turf roots. Reducing nematode numbers may not be necessary. Implement any cultural tactics that improve root health. After all, is the owner or member of a country club going to be more interested in the numbers of plant-parasitic nematodes in the soil or that the greens appear healthy and look good? 

5 Tips for Seeding Lawns

Dr. Kevin W. Frank

Assoc. Professor & Extension Turf Specialist

September is the ideal time for seeding turf in Michigan.  Reduced weed competition from summer annuals such as crabgrass, cooler temperatures, and shorter day length that results in less time for soil drying all facilitate turf establishment.  In many cases home lawns don’t need complete reestablishment but only reseeding of small areas or interseeding into a thin lawn to increase density.  The following are 5 tips for fall seeding success.   

1. Is Seeding Necessary?

The first question to answer is if seeding is even necessary.  If the turf is thin or there are small patches of dead grass about the size of baseballs, a fertilizer application and cool temperatures should help the existing turfgrass to recover and spread into the bare spots.  If the bare areas are the size of soccer balls or larger, or if the area only has sporadic green patches of turf, then interseeding is necessary to restore the area to turf.  Another consideration is to assess weed pressure.  If the turf is covered in crabgrass it’s going to be difficult to have new seedlings compete with crabgrass.  If weed competition is severe make sure to kill the weeds before seeding.   

This lawn would benefit from interseeding into the existing stand.

2. Seed to Soil Contact

A successful seeding starts with good seed to soil contact.  Broadcasting seed onto an area without incorporating the seed into holes, slits, or covering with soil will feed birds but not be effective for growing new turfgrass.  Equipment such as core aerifiers, power rakes, slit seeders, or even hand raking small areas will get the job done.  For established areas that may just need an interseeding to improve density, core aerification is a viable option.  It’ll also give you the benefit of improving soil aeration that is critical for many sites that have compacted soils or high clay content soils.  The best method for incorporating seed is to use a slit seeder.  Slit seeders create a slice in the soil that the seed falls directly into and ensures good seed to soil contact.  To improve establishment and turf spread, slit seed in at least two directions perpendicular to each other.  Many lawn care companies offer this service or if you’re a do it yourselfer core aerators and slit seeders might be available at a local rental store.

Core aeration followed by seeding can be effective.

3. Species and Rates

Making sure you have the correct species and cultivar, especially if you are interseeding an existing lawn, is a critical step to ensure satisfaction.  One common frustration some homeowners have after interseeding is that the newly seeded turf has a different color/appearance than the existing turf stand.  To avoid this problem do your homework to try and find out the turfgrass species that was originally established.  In most areas of Michigan if you’re not sure of the turfgrass species on the lawn, odds are its Kentucky bluegrass so select Kentucky bluegrass cultivars to reseed the turf.  If however you are completely renovating an area and are looking for something a little different that might be able to withstand dry conditions better, consider tall fescue.  Look for key words on the seed bag such as Turf type, Improved, or Dwarf when selecting tall fescue cultivars.  I would avoid the standard Kentucky 31 (K-31) tall fescue for use in home lawns due to its wide leaf blade. Turf type tall fescue is now being mixed with Kentucky bluegrass and is more widely available to consumers than it was just a few years ago.  

Follow the recommended seeding rates on the bag and avoid the temptation to seed at higher rates.  Higher rates do not result in shorter time to establishment.  High rates can result in increased competition among the turfgrass seedlings and a weaker turf stand.

4. Mulch, Fertilizer, and Irrigation

One of the advantages of interseeding into an existing stand is that the existing turf acts like a mulch cover to help retain soil moisture.  At seeding, apply a starter fertilizer at a rate of 1 lb. N/1000 sq. ft. to help the seedlings establish.   A starter fertilizer is a fertilizer with a N:P₂O₅ ratio similar to 1:1 or 1:1.5.  Under the Michigan phosphorus restriction that is in place, starter fertilizer is still allowed for turfgrass establishment.  The maximum amount of phosphorus that can be applied in a single application is 1.5 lbs. P₂O₅/1000 ft.² with a yearly maximum of 2.5 lbs. P₂O₅/1000 ft.².  If you have the time to take a soil test, follow the soil test recommendations for establishment.  Homeowners can purchase a soil testing kit from the MSUE bookstore (http://www.bookstore.msue.msu.edu/product/soil-test-kit-selfmailer-1116.cfm).  More information on soil testing can be found at www.msusoiltest.com. 
Make sure to keep the seeded area moist throughout establishment.  This may require watering several times a day.  Water lightly when irrigating, there is no need to see water puddling or running off the site.

5. Mowing

Finally, don’t be afraid to mow the new turf.  Don’t wait until the turf is so tall it’s falling over.  If you interseeded into an existing thin lawn then keep on your normal mowing schedule.  Mowing turf helps it spread laterally and fill the area.