Pythium in turf. 31

There are several Pythium sp that cause Pythium in turf. This turfgrass blog discusses pythium fungus in grass, what this is, and how to identify and control it. Pythium in turfgrass are often called Pythium blight, root rot, root dysfunction, and damping off.  

Symptoms can be seen as irregular patches of discoloured, dead, or wilted turf. They are particularly prevalent warm, wet conditions.

Their effective management involves the use of cultural practices and fungicides. Cultural options include:

• Moisture management.
• Drainage.
• Reducing thatch. 

In Australia laboratories tests only tend to diagnose the Pythium in grass as “Pythium sp” when in fact you could be dealing with root rot, Pythium blight, root dysfunction, or damping off.

The diagnosis as Pythium sp is oversimplifying the management of this disease. To make the correct pythium fungicide choice¹Hampy, H.D., Van Ryzin, B.J., Butler, E.L., Kerns, J.P., Etiology and management of Pythium root rot in golf course putting greens, Int Turfgrass Soc Res J.2022;14:851–860 it is important to know which species is present.

There are two key reasons for this:

• Not all Pythium fungicides and turf-registered fungicides work equally well against all species of pythium in turf. This is the case in both the home garden and professional turf markets.
• Incorrect disease identification is a waste of both your time and your money.

Pythium spp.

Damping off.

Damping off is a Pythium disease in turf that occurs when grass is at the seedling stage of sports turf seed. If conditions such as too much moisture, the right temperature, and poor light levels are present, damping off becomes more likely.

Pythium Root Rot (PRR).

A further complication in the diagnosis of root rot is that there are actually two different root diseases.

Root Rot (PRR) and Root dysfunction (PRD) are both seen in the roots. There are distinct differences between these that impact their management.

• They tend to occur in wet soils.
• Root rot affects all turf varieties.
• They are more common in high organic matter content or poorly draining soils.
• These are commonly seen in close mown, intensively managed turf.

Root death and a rotting smell are symptoms of this fungus in grass.

The fact that temperature impacts the organisms that cause this disease explains why you can get such variable results when you carry out chemical control.

Conditions That Favour Root Rot.

• Root rot tends to develop on cool-season golf greens. Often you see it in the Summer when the soils are warm and wet.
• On warm-season turf, this disease is most severe under low light conditions. This is typically in the Autumn, Winter, and the Spring.
• PRR tends to occur where water pools. However, it can also affect high areas after rain.
• Greens in shade with little air movement are the most susceptible to this. It is a key reason why many clubs use turf fans to improve air circulation, and promote surface drying.
• You can continue to see the symptoms as new spots or areas that continue to expand, as long as the soils are warm and wet.
• It tends to increase when sting or root-knot nematodes are present²Gu, M., Bermudagrass root rot complexes associated with plant parasitic nematodes and pythium species on golf courses in Florida, May 2019, Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy.

Cultural Control of Pythium Root Rot.

• Reduce plant stress.
• Improve light penetration and air movement.
• Don’t over fertilise with N.
• Improve the soil drainage and carry out regular soil aeration.
• Increase the height of cut where appropriate.
• Regularly topdress. This helps water move away from the surface.

Chemical Control of Pythium Root Rot

• Cyazofamid provides the best control of this Pythium in turfgrass;
• Other options are: Fosetyl-Aluminium, Mefonaxam, and Propamocarb;
• Etridiazole is effective³Kerns, J.P., Pythium in golf course putting greens, Golf Dom, November 23, 2021, but you only get a residual of three to four days after use.
• Make sure to rotate your actives.
• For cool-season golf greens in the Spring. Monitor the temperature, and once it reaches 18°C at a 50mm depth for four to five consecutive days start to use Cyazofamid at 2.5 L/Ha.
• A rotation of Cyazofamid, Solitaire, and Shrapnel on a two-week cycle works well with in a PRR program. You must make sure you water these in with 3 mm of water.
• Preventative foliars of Grenadier also work well.

Pythium in Turf

Pythium Root Dysfunction (PRD).

This is a very different pythium fungus in grass in comparison to root rot. You only see Root Dysfunction on bent golf greens. Its symptoms don’t include root death which means it is much more difficult to identify.

Because the causal pathogen, P. volutum, is a root-rotting pathogen, it affects the ability of the creeping bent grass to take up water. This means the turf looks wilted when the soil and surface temperatures are high.

Traditional Pythium fungicides do not control Root Dysfunction. Instead you should focus on the use of the QoIs (azoxystrobin, pyraclostrobin) and Cyazofamid as these are the most effective.

A standalone Pyraclostrobin isn’t yet registered in Australia, so your best option is Lexicon Intrinsic fungicide. Make preventative applications of Root Dysfunction fungicides in the Autumn and the Spring before any symptoms occur.

Symptoms of Pythium Root Dysfunction.

• The disease only occurs on creeping bent. It tends to be is at its worst on new golf greens, and especially those with root zones of > 85 % sand⁴Kerns, J.P., Soika, M.D., and Tredway, L.P., 2009. Preventative control of Pythium root dysfunction in creeping bentgrass putting greens and sensitivity of Pythium volutum to fungicides. Plant Disease. 93(12): p. 1275-1280. or more;
• Root Dysfunction is more common on well-drained young bent grass greens that are less than 5 years old.
• Roots become short, have a lack of root hairs, and bulbous root tips.
• As they have no root hairs, sand does not stick to roots. When you shake a soil plug most of the sand will easily fall off the roots.
• Roots are only slightly more tan or buff than normal roots.
• Symptoms start to develop on exposed golf greens that suffer from drought stress.
• The disease develops in high areas first. It look like hot spots or drought stress. Even after you hand water these areas they will not improve.
• You often see the symptoms in the Summer months. However, it also develops in the Autumn, Winter, and Spring in warm, windy, and/or dry spells.

Cultural Control of Pythium Root Dysfunction.

• Use more resistant cultivars of bentgrass⁵Kerns, J.P., Biology and management of Pythium root dysfunction in North Carolina.   North Carolina State University ProQuest Dissertations Publishing,  2008. 3329206.to reduce chemical use for this pythium fungus in grass.
• Improve the drainage and aerate regularly to reduce any soil compaction.
• Reduce thatch levels.
• Increase the height of cut above 3mm. Maintain the turf at this height of cut until the turf recovers.
• Ideally use a walk-behind mower.
• Reduce how often you mow.
• Irrigate based on what the turf needs rather than a schedule. Aim to hand water badly affected areas, and use soil wetting agents to improve water movement away from the surface.
• Don’t mow when the turf is wet. This will reduce any mechanical damage;
• Supply the turf with enough N. High N encourages this disease, while too little N will slow recovery;
• Overseed as soon as you can after an outbreak.

Pythium Blight.

The final Pythium in turfgrass often has white, fluffy mycelium that grow from infected turf grass. These mycelium are often mistaken for dollar spot and brown patch but it is in fact Pythium blight.

This disease can kill turf in 24 to 48 hours and the key to its control is prevention. Different species cause blights at low or high temperatures.

It needs high humidity or leaf wetness for the disease to develop⁶https://www.golfcourseindustry.com/news/turftip-050415-golembiewski-pythium-expert/.

• Temperatures around 32°C are ideal for the disease to develop. You don’t tend to see damage at temperatures below 20°C.
• High temperatures plus periods of high humidity or wet weather favour this disease.

Cultural Control of Pythium Blight.

• Aim to water early in the day to allow the grass blades to dry. This reduces the chances of leaves remaining wet overnight. Any practice that reduces leaf wetness helps in the control of this disease.
• Ensure the site is drains well.
• Reduce thatch levels.
• Do not over fertilise with N. This is especially important in the hot Summer months.
• Avoid any deficiency in soil Ca.
• Maintain an acidic soil pH.
• Promote good airflow across golf greens⁷Koh, K.J., et al. “Shade and airflow restriction effects on creeping bentgrass golf greens.” Crop Science, vol. 43, no. 6, Nov.-Dec. 2003, pp. 2182.
• Reduce shade.
• Don’t mow wet areas when the temperature is > 21°C.
• Wash mowers before they enter unaffected areas.
• Aerate to encourage root growth.
• Delay any over seeding with cool season turfgrass for as long as you can. You should aim to do this in the late Summer or the early Autumn when the night temperatures are < 18°C.

Chemical Control of Pythium Blight.

Pythium blight is the most common pythium fungus in grass. You can often see it along drain lines andwhen air movement is restricted in shade areas.

The best way to manage Pythium blight is with a preventative program.

• Base a program on Fosetyl and/or Cyazofamid.
• If it does appear, Fosetyl doesn’t work as a curative.
• Cyazofamid is the best option.
• Metalaxyl is less expensive. However, turf recovery takes longer and you can see scars for several days after you use it.
• Curative applications only protect plants that aren’t already infected.
• These fungicide chemical groups work against Pythium blight: M3, Group 4, Group 14, Group 11, Group 21,Group 28, and Group 33.

The repeat use of some Pythium fungicides, like metalaxyl (phenylamides), may select for resistant populations of P. aphanidermatum.

This means that it is important to rotate this with chemicals from other groups. If you alternate between systemic and contact fungicides it may also delay the development of any resistance to pythium in turf.