Bulletin 46

Summer…...the turf manager's busiest, most challenging, but also often most satisfying season. It can bring long hours, high temperatures, drought, excessive growth, and too many golfers to fit in the day, but also the satisfaction of presenting your course at its best! Summer also brings with it one of the biggest challenges for turf managers, that is controlling summer diseases. One in particular is Anthracnose (Colletotrichum cereal) affecting mostly cool season turfgrass with Poa annua being very susceptible.

Anthracnose affects turfgrass in two forms:

• Basal rot, which affects the lower parts of the turfgrass plant, crowns, stem bases, and roots.
• Foliar blight is the second and leads to a yellowing of leaves and shoots having a similar appearance to drought stress in appearance.

Whichever form it is, it’s important to note that Anthracnose is very much a stress-related disease.

There are numerous Best Management Practices which can be employed to reduce Anthracnose incidence. Key to this is to understand the conditions conducive for infection to be successful ‘know your enemy’!  Identify the conditions which lead to infection and then influence these factors to minimize the challenge. While Cultural practices such as programs combining regular light weight rolling, sequential topdressing, raising height of cut and judicious use of irrigation inputs can be very effective in suppressing disease levels, the use of targeted nutritional programs is key in significantly reducing Anthracnose in turfgrass. 

A balanced nutritional program, tailored to the specific needs of the sports surface and the nutritional status of the rootzone is a key factor in successful turfgrass management.

However, apart from supplying essential nutrition, many nutritional inputs also have added benefits and can significantly suppress Anthracnose incidence in turfgrass!

Here are some examples:

• Nitrogen, applied regularly during periods of high Anthracnose pressure has been proven to reduce disease levels.
• Potassium levels maintained at a minimum 35 ppm is essential in reducing Anthracnose pressure.
• Copper and Sulphur have been used as fungicides for centuries and can be very effective, especially when combined in a program with other elements.
• Silica, when applied as a foliar treatment, can strengthen plant cell walls, reducing pathogen ingression.
• Phosphite has much data to support its efficacy in reducing numerous turfgrass diseases - including Anthracnose.
• Manganese and Zinc activate key enzymes vital for turfgrass defense responses.
• Salicylic acid is the most important signaling compound for initiation of Systemic Acquired Resistance in turfgrasses.

All the above will have some effect on Anthracnose, but it’s only when you start combining them together in a nutritional program that you will see very significant disease suppression results. 

Research in the USA and Ireland confirms this, with conclusive evidence showing that combining the above elements will not only significantly suppress Anthracnose but also lead to enhanced turfgrass quality when compared to untreated controls.

Results from trials carried out in Ireland during the summer of 2018, clearly show the positive effects of nutritional inputs on levels of Anthracnose in Poa annua greens surfaces.

The treatment program comprised of Plant Food Company, Inc. products, listed below in Table 1, which were applied bi-weekly from July to September 2018. The program provided carefully calculated nutrient inputs, and, as well as spoon-feeding Nitrogen and Potassium, included elements important for disease suppression listed above - Calcium, Sulphur, Copper, Manganese, Zinc, Polyphosphite, and Salicylic acid.  

Plant Food Green-T^® 29-0-0 is a high nitrogen formula containing four different sources of N -ammonium nitrate, urea, ammonium thiosulfate and triazone nitrogen, which apart from spoon-feeding Nitrogen, provided Calcium, Sulphur, Copper, Manganese and Zinc, all key to plant defense responses and Anthracnose control.

Healthy Start 8-27-5, provided necessary NPK in the form of ammonium polyphosphate with polyphosphite. The potassium component stimulates rooting, and increased cell wall structures, thickness, and turgidity. Polyphosphite is proven to stimulate the plant’s natural defense mechanisms and directly inhibit Anthracnose.  The phosphate, which is important for ATP (plant energy) is in the ortho and polyphosphate form.  This is a “quick and slow-release” phosphate source that is plant available while minimizing phosphate lockup in the soil.

Green-T Impulse^® is an amino acid and sucrose combination which increases potassium and calcium levels within plant cell walls, expels sodium within the plant, and improves stress tolerances. It also contains glycine betaine & proline which helps moderate excessive Hydrogen Peroxide levels produced as part of the Hypersensitive Response when turfgrass is under biotic stress. It also provides Salicylic acid which stimulates the induction of Systemic Acquired Resistance.

PolyPhosphite 30^®, 0-0-27 provided a long-chain polyphosphite which has proven to not only directly inhibit the growth of fungal pathogens but will prime turfgrass defense responses prior to infection. The systemic potassium source ensures uptake throughout the turf plant.

Hydration A-Plus^®, is a surfactant which was included in the program, and this enabled better water infiltration and consistency of moisture within the rootzone, allowing for reduced drought stress (less stress = less Anthracnose). It also contains Mineral Acid Technology which is an acid-based formulation which solubilized locked-up nutrients for an extended period of time including Calcium. Calcium plays a vital role in early defense responses in infected turfgrass as part of the Ion Flux, and ensuring a readily available calcium source is crucial.

Figure 1. Treatment effect on percent Anthracnose incidence on trial plots (n=6). Mean values from 6^th August to 21^st September 2018. Bars indicate 95% confidence intervals; letters indicate statistical differences as determined by Tukey post hoc analyses at a significance level of p = 0.05.

This program reduced Anthracnose disease incidence to 3%, statistically identical to the fungicide treatment of BannerMaxx (Propiconazole). It was successful because it supplied adequate and balanced nutrition, primed and enhanced the plants natural defenses, stimulated systemic acquired resistance, and reduced drought stress.

The program in a nutshell produced:

• Less stress = less Anthracnose.
• Availability of elements proven to reduce disease incidence.
• Primed and enhanced plant defense responses.

An important secondary result from the trial showed that the combination of Green-T^® 29-0-0, Healthy Start 8-27-5, Green-T Impulse^®, PolyPhosphite 30^®, and Hydration A-Plus^® produced a higher quality of turf, compared to not only untreated controls but the fungicide treated plots. So as well as suppressing Anthracnose to the same level as a bi-weekly fungicide program the nutrient program provided a significantly better turfgrass quality.

Figure 2 Treatment effect on mean levels of turfgrass quality (n=6). Data are mean values from August to September 2018. Bars indicate 95% confidence intervals; letters indicate statistical differences as determined by Tukey post hoc analyses at a significance level of p = 0.05.

So the key points to consider in order to control Anthracnose:

• Know your enemy!
• Influence as many factors that contribute to conducive conditions for this disease.
• Employ cultural practices which will enhance your turfgrasses ability to withstand pathogen challenge.
• Employ a balanced nutritional program and include the elements and compounds above which have been shown to have suppressive properties.
• If available or desirable, include a fungicide program suitable for Anthracnose but remember to use best management practices to avoid possible resistance buildup.
• Fungicides are most effective when combined with cultural and nutritional practices that reduce plant stress and prime them to withstand challenge!