How to treat lawn diseases (brown patch, leaf spot, melting) without fungicides?

Question

Google tells me "stress your lawn", meaning cut the water for some time.

But wouldn't that hurt it even more, given we are in mid summer?

I live in Calgary, AB - Canada. Fungicides are a no-go here.

Answer 1

Information from Google is essentially worthless, unless you've discovered a reputable source. For lawn questions, I like to use The Lawn Institute, a science-based organization committed to providing information on lawns and lawncare. Here's a link to their Lawn Diseases page. Note that there is information about cultural control (which is what you're asking about) and chemical control for each disease listed. For example, for brown patch the Institute says:

Over fertilization can increase the severity of brown patch. In general, cool-season turfgrasses should not receive more than 1 lb nitrogen/1,000 square feet at any one time. Do not apply more than 0.5 lb nitrogen/1,000 square feet when conditions favor disease development. If applications are kept at or below 0.5 lb nitrogen/1,000 square feet during this time, they will not increase brown patch severity. As always, be sure adequate amount of phosphorous, potassium, and other nutrients are applied based on soil test results.

Reducing leaf wetness periods will greatly reduce brown patch severity. Leaves can become wet from irrigation, rain, dew, or guttation (water exuded from turfgrass leaves during the night). Do not irrigate daily. Instead, irrigation should be applied based on weather conditions and the water requirements of the turf. The time of day that irrigation is applied is also critical; it is best to irrigate early in the morning, just before sunrise. This removes large droplets of dew and water from the leaves and speeds drying of the foliage after sunrise. Avoid watering after sunrise or in the late afternoon or evening, as this will increase the duration of leaf wetness.

Proper landscape design and site preparation can help to minimize brown patch. Turf surrounded by trees, shrubs, buildings, or other barriers will remain wet for extended periods of time due to reduced air movement and sunlight. Removal or pruning of trees and other barriers will help minimize leaf wetness and discourage brown patch development.

But the site does not have information on leaf spot/melting, possibly because it is a disease of bentgrass and is getting less common due to improved resistance in cultivars. Do you have bentgrass in Alberta? If not, then what you see is not melting. When I find a case where there's missing information, though, I turn to a US University Extension. In this case, the University of Massachusetts, which effectively restates the "lawn basics" as the cultural control of all diseases listed on its site:

• Raise mowing heights and reduce mowing frequency when conditions are conducive to disease development.
• Avoid mowing infested turf when it is wet
• Water deeply and as infrequently as possible without causing moisture stress;avoid late afternoon or evening irrigation. Irrigate in the morning to reduce the duration of leaf wetness which favors disease spread.
• Avoid excessive levels of nitrogen, while maintaining adequate potassium and phosphorous fertility. Correct fertility is important to the turf's recovery and disease resistance.
• Aerate compacted soils. Soil compaction reduces water and nutrient infiltration and contributes to excess moisture in the plant canopy.
• Reduce thatch if it accumulates to more than 0.5 in. Pathogens survive in plant debris such as thatch therefore its reduction is a key component of cultural control. Selectively prune trees and shrubs to improve air circulation and light penetration.
• Reseed with improved cultivars with disease resistance or tolerance.
• Avoid applying herbicides or installing new sod during or just before an extended period of hot, humid weather