Over-irrigation can lead to a plethora of turf diseases.
When one thinks of irrigation, the often quoted and proverbial part of the Rime of the Ancient Mariner may come to mind:
“Water, water, every where,
And all the boards did shrink;
Water, water, every where,
Nor any drop to drink.”
The provision of water to the turf and ornamentals on the golf course plays a monumentally large role in its overall performance and playing conditions. In addition to simply meeting the water needs of the plants, there are interactions with various pests – abiotic and biotic diseases, insects and vertebrates – that should be considered as well.
Diseases that love water
What is over-irrigation? Is it watering too much or too often … or both? There are several ways to look at it, but perhaps the one that makes the most sense is to categorize by overly wet foliage and overly wet roots/soil. There are certainly problems associated with both regimes.
Foliage that is frequently wetted by rainfall events and sprinkler systems can fall victim to several fungal diseases, especially if it is not allowed to dry out on occasion. Any of the foliar diseases of turf will be favored by frequent irrigation. Those commonly encountered with this are Bipolaris or any of the Helminthosporium leaf spots and melting out diseases, brown patch and dollar spot.
Optimum temperature ranges for each disease will regulate when they occur, but all will be favored by frequent irrigation. While brown patch is a disease most commonly observed in tall fescues, it will also occur in bluegrass if conditions are favorable. All of these diseases will be a problem on bentgrass greens and fairways. Dollar spot prefers slightly cooler temperatures than brown patch, and most commonly affects bluegrass and bentgrass varieties.
Another problem associated with extremely wet conditions is Pythium root infections (dysfunction) and Pythium blight. Pythium is a water mold and will be most active in areas with pooling water or saturated soil profiles. Look for a greasy feel to the blighted leaf tissue if pooling water has occurred, followed by disease development with blighted turf.
Timing is everything. Although it seems counterintuitive, irrigation applied in the early morning will actually wash off the heavy dew layer and result in the foliage drying more rapidly. If your situation requires frequent irrigation, make sure you do this in the early morning hours of the day.
Diseases that don’t like water
The most common observed disease in dry spots in the golfscape is Ascochyta leaf blight. This disease is clearly associated with dry spots and will quickly be alleviated with the addition of water; generally, fungicide applications are not needed. Ascochyta results in individual leaves dying from the tip back and shriveling to form a needlepoint appearance. As soon as the turf is properly watered this disease typically goes away.
Along with proper fertilization, periodic aeration, mowing practices and pest control, the health and vigor of the turf stand is encouraged by keeping the roots evenly moist. Mother Nature can help out quite a bit with this goal, as she tends to distribute the same amount of water across the entire turf surface. Of course, it is the rare situation when supplemental irrigation is not required, so consideration of the interaction of applied water and diseases is important.
Though tremendous advances in sprinkler technology have been made since their introduction, they remain mechanical systems that have flaws with parts that break. Because of this, the amount of water that is delivered to various parts of the fairway, tee or green are certainly different. When this occurs, certain parts of the turf receive more water than others. Because the turf is healthiest when uniformly moist, the tendency is to “water until all the turf is green” or “water for the dry spots.”
Unfortunately, when the areas that receive less than the desired amount (the dry spots) are watered until they turn from dry to moist, or brown to green, the accompanying outcome is that the other areas receive too much water, which magnifies the problem.
Let’s take a quick peek at how this plays out. If a certain area within a zone receives .25 inch of water and other areas within that same zone receive 1/8 inch during each run time because of inefficiency and the entire zone is routinely run until all the turf is green, then the spots that receive more will be overwatered. This overwatering results in overly wet foliage and overly wet roots.
Inefficiencies in sprinkler system performance exist because of a variety of causes, including:
- clogged nozzles;
- differences in pipe sizing;
- tree roots that grow around underground pipe and reduce flow;
- risers that do not clear the turf adequately;
- bent risers that do not rise perpendicular to the turf;
- heads that don’t turn; and
- parts that don’t function as intended due to wear or abuse from golfers.
Diseases can be easier to manage and a significant water savings can be realized through auditing the sprinkler system. Audits are a step-by-step process:
Turn on the system and watch it run. Obviously, it’s best if you have help with this task, considering the size of the area to be observed.
Fix the obvious flaws that were detected.
Audit the sprinkler output of the zones with catch cans. These can be purchased from sprinkler suppliers and are well worth the cost. Be sure to use enough to collect the water from adjacent zones, as water drift patterns can account for variances in the total amount collected.
Make changes in run time and adjustments in equipment based on the output from various heads during the audit.
Retest to see if the fixes worked, or if other issues remain. In some cases, small problems go unnoticed because the focus is on the larger problems. Once the second step fixes and third step adjustments have been implemented, the less obvious flaws will stand out.
Fine-tune to see if other water savings can be achieved. Once the big problems have been addressed, it’s possible to implement “trims,” or small reductions in run time to achieve water savings and improve efficiency.
If taken seriously, and the efficiency can be improved from an average of 65 percent to 85 percent, lots of water can be saved, and the effects of overly wet shoots and roots will be greatly reduced.
Ornamental diseases that like water
Just as overly wet or overly dry foliage and soils can dramatically affect the disease potential of turfgrasses, the same is true for ornamental plants. Foliage that remains wet for extended periods of time because of being sprayed too frequently from overhead irrigation can lead to diseases such as iris leaf spot, anthracnose of sycamores and black spot on roses.
These effects can be because of either the run time being too long or overspray from turf heads. Considering the desirable leaf wetness of the ornamentals on your course, it’s wise to check with university extension faculty in your area to gain a sense of whether certain plants prefer to have dry, moderately moist or moist leaves. For disease management, dry leaves are preferable in most cases.
One of the most common adjustments for ornamental spray heads is to ensure that the risers deliver water in a manner that clears the entire mass of leaves. As plants grow to maturity, they often become taller and wider, thereby causing the spray output from the riser to be blocked. This leads to inefficiency and uneven water distribution. When this happens, consider the use of drip irrigation.
In general, to avoid overly wet foliage, consider spray heads that wet the foliage of shrubs, flowers and ground covers minimally, or deliver water to the base of the plants rather than the aboveground parts. Overly wet roots and soil can result from running an irrigation system too long, regardless of type.