Rust and water

By John Fulton

[July 07, 2009]  As grass growth slows, rust will be one of the lawn fungi we are dealing with. Rust appears as an orange or yellowish-orange powder (spores) on grass leaf blades, especially in late summer to early fall when the weather is dry. Rust typically develops on lawns growing very slowly. Overall, the turf may assume a yellow, red or brown appearance. Close examination will reveal the pustules, which easily rub off on your hand. Rust spores can easily be tracked into homes.

Low fertility (nitrogen, in particular) and low water availability slow down turf growth, allowing rust to develop. Seasons with excess rain may have rust outbreaks due to loss of available nitrogen. Frequent, light rainfall and cool nights with heavy dew add to the ideal conditions for rust to develop. Warm, cloudy, humid weather followed by hot, sunny weather also favors rust development on lawns. Kentucky bluegrass, perennial ryegrass and tall fescue are all affected, depending on cultivars. Rust spreads through air, water, shoes, equipment and sod. Rust may weaken turfgrasses and make them more susceptible to other problems.

Control rust through sound turf management. Begin by choosing a quality blend of turfgrass seed. Resistance to rust can vary according to the race of the disease present. Maintain lawns through sound watering, mowing and fertilizing. If you are watering, water early in the day so the grass dries quickly. Manage problem thatch. Increase vigor with an early fall nitrogen application, but don't overdo it. Check soil phosphorus and potassium levels through soil testing. Also assure good airflow and light penetration over the site by pruning trees and shrubs in the area near the lawn.

When rust occurs at this time, improved growth conditions of early fall often get lawns growing more vigorously and the rust fades away. Early September is a key time for fertilization. If conditions are dry, irrigation is also needed to increase the growth rate of the lawn.

Fungicides are rarely suggested for rust control on home lawns. Focus on the listed culturing practices described above.

Excessive water injury

This year has again seen rainfall exceed the norm. Saturated soils can wreak havoc on trees and other plants. The main reason injury occurs is related to oxygen availability in the soil. In flooded or waterlogged soils, oxygen diffuses slowly and reduces in concentration to a few percent or zero. As oxygen is excluded from roots, there is decreased aerobic root respiration, root growth, transpiration and translocation. This results in less growth, yellow leaves, leaf drop, less fruit and possible plant death.

Although survival is directly related to species' tolerance of waterlogged soils, other factors are important -- including the soil type; the time, duration and depth of the water; the state of the floodwater; and the age and size of woody plants.

Tolerant species, such as baldcypress, littleleaf linden, red-twig dogwood, mulberry, silver maple and willow, can live on sites where the soil is saturated for indefinite periods during the growing season.

Moderately tolerant species, such as green ash, hawthorns, honey locust, pin oak, red maple, river birch, sweet gum and sycamore, can stand saturated soil for a few weeks to several months during the growing season, but these species die if waterlogging persists or reoccurs for several consecutive years.

Weakly tolerant species, such as American holly, balsam fir, black walnut, bur oak, catalpa, hackberry, Douglas fir, eastern cottonwood and red oak can stand relatively short periods of soil saturation -- a few days to a few weeks -- during the growing season, but they die if waterlogging persists for longer periods.

Intolerant species, such as American beech, black locust, crab apples, eastern hemlock, flowering dogwood, paper birch, pines, redbud, spruces, sugar maple, tulip tree, white oak and yews, die if they are subjected to short periods of one or two weeks of soil saturation during the growing season. White pines and burning bushes are among the most sensitive, with saturation for as little as two days causing root death, followed by plant death.

Unfortunately, little can be done to prevent damage to plants growing in waterlogged soils. If a woody plant shows injury symptoms, such as leaf drop, do not immediately replace it. Some plants will show initial injury symptoms and then recover. Many woody and herbaceous plants, including turf areas, will not recover. Be patient. Whether your plants are simply waterlogged or actually growing in flood areas, it will take a while to see the full extent of plant damage.

[By JOHN FULTON, University of Illinois Extension, Logan County]