All eyes on the fall lawn

Armyworms have been trying to conquer lawns mainly on the outer edges of Wichita, while walnut caterpillars are thick in pecan and walnut trees. Extension agent Bob Neier checked on a catalpa tree this week that was being chewed up, and the culprit turned out to be the catalpa worm.

It must be a good worm year.

The good news is that if your lawn or tree was healthy before it was invaded, it should make it through the onslaught. If it was dried out or weak, the worms could deal a finishing blow.

Armyworms can invade any lawn in town, but it’s mainly been the outer-lying areas of Wichita that have been afflicted this year, Neier says. The infestation so far is not matching that of the year 2000. And Bermuda lawns are unscathed by the worms, he says. “They really like fescue.”

If you’ve been keeping the grass watered in dry times, even if the worms chew the grass blades, the crowns of the grass plants should be living and will send out new grass, Neier says.

“Armyworm damage can resemble drought damage, but close inspection of the turf will reveal the larvae,” Ward Upham of K-State writes this week in the Horticulture 2014 newsletter.

“Look for active feeding during early morning or evening hours or on cloudy days. Larvae feed on foliage, and the resulting dehydration causes turf to quickly brown.”

If you want to go after the worms, you can use spinosad (Conserve; Borer, Bagworm, Leafminer & Tent Caterpillar Spray; Captain Jack’s Dead Bug Brew), carbaryl (Sevin), cyhalothrin (Spectracide Triazicide and Bonide Caterpillar Killer), or Dylox. K-State is finding that pyrethroid-based insecticides may not work as well as the others.

“Treat in late afternoon, when the caterpillars are likely to begin feeding,” Upham says. “Do not mow for three days after treatment.”

The Extension has been getting calls from people whose neighbors are treating for armyworms, and they wonder if they should treat, too, even if their lawn doesn’t have the worms. But the chemicals are not preventative and only should be used if you see the worms, Neier says.

The invasion of the armyworms is coinciding with the best time of year to fertilize and overseed fescue lawns. If you had a thick lawn before armyworms attacked, you shouldn’t need to overseed. But do fertilize, Neier says.

If you had a thin lawn before or without armyworms, it’s time to overseed. The deadline for putting down fescue seed is Oct. 15, but the earlier in the season you can get it done, the more time the new grass will have to develop before cold weather sets in.

Your trees

If you’re seeing the second generation of walnut caterpillars in your walnut or pecan tree – and they occasionally show up in some other trees – the tree may be defoliated, but it should leaf back out as long as the tree was healthy to begin with, Neier says.

“If they’re already thin, this can really damage trees and send them downhill,” he says. The same chemicals that are used on armyworms can be used on the walnut caterpillars, he says.

Fertilizing fescue

When fertilizing fescue (it’s too late to fertilize warm-season lawns of Bermuda, zoysia and buffalo), apply 1 to 1.5 pounds of actual nitrogen per 1,000 square feet.

“The settings recommended on lawn fertilizer bags usually result in about 1 pound of nitrogen per 1,000 square feet,” Upham says. “We recommend a quick-release source of nitrogen at this time. Most fertilizers sold in garden centers and department stores contain either quick-release nitrogen or a mixture of quick- and slow-release. Usually only lawn fertilizers recommended for summer use contain slow-release nitrogen. Any of the others should be quick-release.”

If you can’t find a setting for your particular spreader on the back of the fertilizer bag, master gardener Everett Price suggests using the lowest spreader setting and going in a crossing pattern with the spreader until you use up the amount of fertilizer that you’ve calculated for the size of your lawn.

“The second most important fertilization of cool-season grasses also occurs during the fall,” Upham says. “A November fertilizer application will help the grass green up earlier next spring and provide the nutrients needed until summer. It also should be quick-release applied at the rate of 1 pound actual nitrogen per 1,000 square feet.”

Overseeding

When putting in a new fescue lawn by seed or overseeding a thin fescue lawn, be sure to buy Kansas Premium Blend Seed that has been tested to do well here, extension agent Rebecca McMahon says. It also does not contain the weed seeds that other seed mixes could have; check the label for the percentage of noxious or other weed seed. Ideally, it will be zero.

The more you can do to prepare the soil for the seed the better, McMahon says. The top inch or 2 of soil should be loose when it receives the seed. Core aeration is good; cultivating/raking is better; and tilling is best, McMahon says. If there is thick dead grass, it should be removed so that the seed can make contact with the soil.

Core-aeration removes cores of soil, thereby relieving compaction, hastening thatch decomposition, and improving water, nutrient, and oxygen movement into the soil, Upham says.

Core-aerate when the soil is just moist enough so that it crumbles easily when worked between the fingers. Enough passes should be made so that the holes are spaced about 2 to 3 inches apart. Ideally, the holes should penetrate 2.5 to 3 inches deep. The cores can be left on the lawn to decompose naturally, which takes two to three weeks.

If you are overseeding, apply a starter fertilizer after core aerating (or the nutrients that the results of a soil test) and then the seed, McMahon says.

You can also put down sod rather than seeding, and that can be done later into the season.

This story was originally published September 4, 2014 at 10:59 PM with the headline "All eyes on the fall lawn."