Late Summer Heat and Drought Tough on Cool-Season Grasses

Late Summer Heat and Drought Tough on Cool-Season Grasses

In spite of a relatively cool summer, the extended heat and drought over the next week or more may take a toll on cool-season grasses. These grasses are at their weakest point in the year with their lowest energy reserves, and thus their lowest tolerance to stresses like heat, drought, and pests. Minor disease infection with summer patch in Kentucky bluegrass or gray leaf spot in perennial ryegrass, minimal grub feeding in almost all grasses, or traffic in excess or at the hottest part of the day can cause significant damage. The good news is that day lengths are becoming shorter and the heat should not extend for too long into September.

Considerations for turf health in late August heat:

•  On greens, consider skipping a day of mowing leaning instead to rolling. This maintains maximum photosynthetic area without sacrificing green speed.
• Hold off on any fertilization until temperatures cool in September.
• If the roots are very shallow, irrigate frequently and wet the soil only to the depth of rooting. This flies in the face of the “deep and infrequent” irrigation we normally recommend, but we may be soon be into damage control rather than sound turf management
• Water early in the morning on other turf areas to limit disease pressure as much as possible
• Syringe Poa annua in the afternoon to cool it slightly and increase its chances for survival
• Preventative fungicide applications are recommended for high value areas, especially with high Poa annua or perennial ryegrass populations. Brown patch, pythium and gray leaf spot are the primary target disease right now.
• White grub applications should already be applied but rescue applications with Dylox™ may be needed.
• Though crabgrass and yellow nutsedge are flourishing, they are at the end of their life cycle and applications are not needed. Almost any herbicide can cause phytotoxicity once temperatures are >85F so avoid applications.
• Limit topdressing, grooming, verticutting, dethatching or aerification until the weather moderates. If aerification is needed on greens, consider narrow, solid tines.
• Minimize and restrict traffic where possible and change traffic patterns frequently.
• If areas were seeded in the last two weeks, fungicides targeted for pythium/rhizoctonia should be applied to help protect the seedlings.

Zac Reicher, Professor of Turfgrass Science, zreicher2@unl.edu

Extension is a Division of the Institute of Agriculture and Natural Resources at the University of Nebraska-Lincoln cooperating with the Counties and the United States Department of Agriculture.
University of Nebraska-Lincoln Extension education programs abide with the nondiscrimination policies of the University of Nebraska-Lincoln and the United States Department of Agriculture.

Easing Turf Stress

In response to the latest round of hot and dry weather, we will occasionally roll greens in the place of mowing.

Nebraska Turfgrass Association Tournament

The Nebraska Turfgrass Assocation's annual fundraiser will be at Firethorn Golf Club in Lincoln.  Check out this year’s new 4-person scramble format and fast play 2-putt rule.  Join us on Monday, September 23rd, with an 11 a.m. shotgun start, for a fun day of golf on a great course.

To register for the event, please click here.

Yellowing of Kentucky Bluegrass

Yellowing of Kentucky bluegrass

Similar to previous summers with adequate rainfall, Kentucky bluegrass has turned an off-color yellow in the last few weeks (Figs. 1 and 2).

Figure 1. Irrigated Kentucky bluegrass lawn showing severe yellowing on Aug. 6, 2011. Darker green areas are patches of tall fescue or different cultivars of Kentucky bluegrass.

Figure 2. Irrigated Kentucky bluegrass baseball field showing severe yellowing on Aug. 6, 2011. Darker green areas are patches of perennial ryegrass or different cultivars of Kentucky bluegrass. Rectangle of obvious yellow is a sod replaced in the last year.

We are still unsure of what could be causing this. What we do know:

•  Only the young leaves are yellow (Figs. 3 and 4), so it is probably not related to nitrogen or other nutrients mobile in the plant. However, iron deficiency could explain the symptoms because Fe is relatively immobile in the plant.
• There are no obvious lesions present so it is not mediated by above-ground diseases.
• We do not see it in tall fescue, perennial ryegrass, and some cultivars of Kentucky bluegrass (Figs. 1 and 2).
• We see it when soil temperatures are at their seasonal highs.
• We see it almost exclusively on irrigated turf and most frequently during wet summers.

Figure 3. Close-up picture showing the lower, older leaves of Kentucky bluegrass farther down in the canopy are retaining their color while the new leaves are chlorotic.

Figure 4. Close-up picture showing the lower, older leaves of Kentucky bluegrass retaining most of their color.

We know from past experience that this a visual effect and long-term health of the plant is not an issue. Therefore, immediate action is probably not needed other than to improve aesthetics. Reducing irrigation in the short should help. Increasing drainage and reducing compaction with more frequent aerification should also help in the long-term. We would not recommend a fungicide, insecticide, or > 0.5 lbs N/1000 sq ft (avoid almost any N in August except on greens or sports turf in use). We often see symptoms similar to this in the spring, but those are usually attributed to denitrification and Fe applications do not help then. However, a low rate of iron may be effective now. Since most the chlorotic leaves are the youngest and higher in the canopy, mowing should remove much of the yellowing.

Zac Reicher, Professor of Turfgrass Science, zreicher2@unl.edu

Extension is a Division of the Institute of Agriculture and Natural Resources at the University of Nebraska-Lincoln cooperating with the Counties and the United States Department of Agriculture.
University of Nebraska-Lincoln Extension education programs abide with the nondiscrimination policies
of the University of Nebraska-Lincoln and the United States Department of Agriculture.

Fall Tree Planting

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Tree Care After Planting

By Kelly Feehan, UNL Extension Educator

Many trees are planted each spring. Once the right tree is selected for the location and planted at the correct depth, the next steps are correct watering, mulching and staking. Practices to avoid at planting and usually for the first year after planting are fertilizing with nitrogen and pruning.

Watering
Water is critical to root establishment. Even so, more young trees die from too much water than from not enough. This is especially common in denser clay soils or in over-irrigated lawns. Too much water suffocates roots because they require oxygen as much as they need water.

As a rule, maintain a consistently moist soil about eight to 12 inches deep and be sure to moisten the soil outside of the root ball. This will promote root growth outward into surrounding soil. The amount of water and frequency of watering needed to do this depends on the type of nursery stock selected, the soils texture, tree species planted, and weather conditions.

There really is no standard answer such as water once a week with a certain amount of water. This might be too much on a clay soil or for a red oak tree, but too little on a sandy soil or for a river birch.

As a general recommendation, the Nebraska Forest Service recommends watering trees immediately after planting and again the next day. Then water three days later and once again three days after that.
From then on, the key is to monitor the soil around the tree and irrigate as needed. During dry summer spells, balled and burlapped (B&B) trees should be watered about once every seven to ten days if planted in clay soils and about once a week if planted in sandy soils.

Sprinkler systems may provide sufficient water up until summer heat arrives. During the hottest, driest parts of summer, a newly planted tree is likely to require additional water. Container-grown trees will dry out faster than B&B trees. Monitor trees and soil moisture closely.

Mulch Mulch protects tree roots from extreme temperatures, eliminates weed and grass competition, conserves soil moisture, and keeps lawn equipment away from tree trunks. However, too much mulch can trap moisture at the base of the trunk and negatively impact root growth. If there is too deep of a mulch layer, roots will grow into the mulch. These roots tend to dry out and die during the heat of summer and are killed by cold winter temperatures. This adds additional stress to young trees trying to recover from transplant shock. When mulching, use organic mulch like shredded wood. Mulch the tree at least out to the trees drip-line (ends of the branches). Next to the trunk, keep the mulch only one inch thick. Outward, towards the edge of the root ball or at the trees drip-line, mulch can be up to four inches deep but no deeper. Staking Staking should be done on trees that are tall and leggy and planted in high wind areas. Keep in mind trees are staked to anchor the root ball, not to eliminate movement of the stem or tree canopy (branches and leaves). The goal is to prevent the root ball from rocking and tearing new roots. When staking, use materials that will not rub against the trunk and create wounds. Do not stake too high on the tree and only stake a tree for one year after planting. If large trees are moved with a tree spade, they may require staking for two years. Source: Nebraska Forest Service

Excess mulch application negatively impacts tree health.

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Ball Marks

                                    
The course had nearly 800 rounds of golf played over a two-day span last weekend. The picture quality isn't the best, but we counted almost 100 ball marks in a 15'x15' area on #3 Red Feather green. Please don't misunderstand me, we absolutely love the patronage (without it we don't exist), but it definitely takes a toll on the greens.

As badly as we want to keep the greens lean and fast, we also need to keep the turf growing to promote recovery, which is a tricky balance. You can help out in a couple ways. Next time you are on a green, fix your ball mark and another one that someone left behind. If you are playing with someone who doesn't understand the importance of ball mark repair, take a couple of moments to educate them.