ISSUE 11 July 15, 2004
LAWN AERATION AND POWER-RAKING
Resist the temptation to aerate or power rake lawns during mid-summer. These are highly stressful procedures, and the grass needs cool weather to be able to recover adequately from these procedures. Spring or Fall are good times for these procedures to take place. Of the two procedures, aeration is probably the most beneficial. Aeration is the technique that actually pulls plugs of earth, in the shape of small tubes, right out of the ground. The tiny holes that are left behind help loosen the soil and allow oxygen to reach compacted roots. Aeration is especially helpful if your lawn is compacted or is established in heavy clay soil, or if the lawn’s thatch layer is greater than ˝" thick. If your lawn is aerated once every year or two, it has a better chance of staying healthy. Sometimes, aeration is followed by over-seeding, especially if a lawn is thin. One method to over-seed involves broadcasting seed over holes formed from the aeration process, and then applying a thin layer of sand or very light soil to cover the seed.
FEATURED LAWN DISEASE: "MELTING-OUT"
Cool, wet weather favors "melting-out" disease of Kentucky bluegrass lawns. Melting-out during cool weather is caused by the fungus Drechslera poae. Initially, black to purple spots can be seen on the leaf blades, and later, the spots appear on leaf sheaths. Crowns and roots are then affected. The affected lawn appears yellow if the lawn was deficient in nitrogen during infection, or blackish-brown if nitrogen levels were high. The disease can cause the lawn to thin and brown and appear wilted. An entire Kentucky bluegrass lawn can be lost within weeks. During warm weather, the grass may begin to recover and fill in, but the amount of recovery depends on infection severity, grass variety, nitrogen level, and irrigation practices.
Management of ‘Melting-Out’:
Raise mowing height (best is between 2-3 inches);
Apply moderate nitrogen during cool weather (spring or fall);
Apply about 0.10 inch irrigation daily, at midday.
When combined, the above management techniques can often eliminate the need to apply a fungicide. However, in the case of severe or prolonged disease, fungicide applications may be needed. If a significant amount of grass has died, over-seeding with a variety of grass that is tolerant to melting-out is recommended. Keep in mind that seed from Kentucky bluegrass varieties take longer to germinate than other types of grass. Re-seeding or over-seeding in cooler temperatures is recommended (rather than in mid summer), because it is usually easier to keep the seed bed uniformly moist, to ensure even germination.
Plant Pest Diagnostician