The basic cultural practice of irrigation is generally considered to be a no-brainer in golf course management. Irrigation is a core undertaking in terms of keeping the proper moisture content in the root zone for the function of the site. When an inadequate or excessive amount is provided, turf roots fail to grow and function normally.
In addition to the reduced capacity for turf plants to operate in a healthy manner due to water application, improper volumes and frequencies often cause turf roots and shoots to be compromised in their tolerance to infection from fungal diseases. Knowing the causal factors for these interactions is helpful in overall management and plant health care.
Whenever irrigation is mentioned, it’s important to keep track of natural rainfall in the overall context of rooting, plant health and the need for supplemental irrigation. Mother Nature’s provisions are a good baseline to use in the overall context of plant need for a certain time period. On-course weather stations, tensiometers and moisture sensors are helpful tools in this regard.
As supplemental water is applied to bring the root zone up to an optimal amount, knowing the starting point is essential. As much as is practical, keeping track as the season rolls along provides both an in-season and historical record of moisture received, creating helpful records for management.
“Requires free moisture on the leaf surface” is a common phrase used to describe the conditions that are favorable for the development of foliar diseases such as dollar spot and brown patch.
Another is “extend the period of natural wetness,” which refers to the application of water past the point in the day when sunlight would be drying grass blades sufficiently to discourage disease spore germination. Both of these phrases are related to a characteristic length of time that is required for good disease development – not that this is a good thing, just that it’s important to know what does and doesn’t facilitate disease activity, so that it can be avoided. In terms of foliar diseases, in general, the drier the leaf the better.
With the concept of the benefit of dry leaves in mind, it’s helpful to adjust irrigation practices accordingly. However, doing so should be conducted with other practices and control procedures in mind.
For example, if exceedingly hot and dry weather conditions are being experienced, it may be helpful to “spritz” the turf to cool the blades temporarily, reducing overall stress. If practical, these light applications of water should be made in the late morning or early afternoon so that sufficient time remains in the day for the foliage to dry before the onset of dew in the early or late evening.
When foliar disease pressure is high, it may be necessary to apply preventive fungicides. These applications should be made with irrigation frequency and volume in mind.
The complicating factors to consider with regards to efficacy of these products are timing, possible dilution or removal of the product and residual activity. Generally, applications are best made to turfs that are in good vigor and growing in moist soils.
Making a fungicide application soon after or before an irrigation cycle tends to run counter to obtaining the maximum effectiveness from the effort. Overall, the general idea is to spray the control product on the blades and allow it to fully dry to keep it there as long as possible.
Keeping in mind that daily irrigation is required to produce high-quality golf turf, coordination of applications and irrigation is necessary. Consideration of delay or omission of an irrigation cycle or two may be necessary in some cases to increase the potential for disease control.
Weak and blighted grass blades are one thing, but rotten roots are quite another. Sure, lesion-covered leaves don’t function well in terms of photosynthesis and other essential plant processes, but in many cases they will recover when the season changes or following a judicious topical fungicide application.
Pathogens that primarily affect the root system are usually more serious, in that they kill the parts of the plant that draw water and nutrients from the soil. The effects from root diseases usually cause the turf plants to die rather than just struggle.
Managing root diseases such as summer patch and Pythium root dysfunction is difficult but can be accomplished through the use of several tools. The first is frequent monitoring of sites prone to injury. Early detection is key to the control of these pathogens.
Second, the use of historical data and notes on infections in previous years, sometimes referred to as disease mapping, can be very helpful in predicting where and when diseases may occur, as many root diseases infect earlier in the season and symptoms show up later.
The third is the use of preventive fungicides that prevent damage, particularly on susceptible sites of high value turf. Because these pathogens are active in the root system, it’s important that they be watered in soon after application.
Fortunately, the irrigation system can be relied on to move the product off the leaf blade and into the root zone for root protections. Fungicide labels usually provide helpful information about the specific time required for this important step.
Over and under
Over and under irrigation can weaken the plant and leave it susceptible to infection from various plant diseases.
Roots that have been damaged from overly frequent runs of the system or excessively large volumes of water are not capable of absorbing systemic fungicides that are designed to be moved throughout the plant. Likewise, roots that are withered from drought or under irrigation are similarly affected and incapable of absorption.
Extremes of irrigation cycling affect foliar diseases as well, in that when leaves are curled due to low turgor pressure the surface area is not fully exposed to spray applications that are designed to cover the entire leaf blade.
Ideally, all grass blades would be flat and arranged such that maximum coverage is achieved.
When a fungicide application is called for, knowing how the product works best is crucial to the effectiveness of the application.
Many options for learning this information are available. Product manufacturers and representatives are good sources of specific details and can explain the specifics of how products are to be applied, follow-up actions to take and protective gear to wear during the applications.
Reading the label yourself is always an important part of fungicide usage especially when it comes to interactions with irrigation, spritzing and other applications of water to the course.
COVER AND PHOTOS: JOHN C. FECH, UNL