Hort Update for October 3, 2022

1. Twig girdler vs. twig prunerTwo insects cause small dead terminal twigs; variety of trees affected

Every summer, an unusual type of insect makes an appearance in many landscapes. Actually, there is a small group of insects, called twig girdler or twig pruners, that cause similar damage in a variety of trees. But fortunately, these insects are not a serious problem and their activity doesn't have serious consequences for the trees. But their presence can be seen as small twigs at branch tips turn brown and die.

In eastern Nebraska, oaks are the main host, but these insects can also potentially be found in persimmon, pecan, elm, hickory, honeylocust, hackberry, poplar, linden, redbud, basswood, dogwood and various fruit trees.

Twig girdler causes clusters of terminal leaves to turn brown; a symptom called 'flagging'. It also causes a small amount of twig dieback. The girdler is a long-horned beetle that emerges in late summer. As part of egg laying, the female girdles the twig to kill it because the larvae cannot develop in healthy wood. The dead tip may fall to the ground or hang in the tree until wind knocks it out. While damage is obvious, it is rarely severe, and there is usually no need for control. Larvae overwinter inside twigs. Pick up and discard dead twig sections that fall to the ground to reduce this insect. Squirrels clipping tree twigs can be confused with girdler damage.

Twig Girdler - severed twig end has a small ragged center section, surrounded by smooth convex outer edges

In eastern Nebraska, the most common twig girdler is Oncideres cingulata. This group of insects are known as longhorn beetles due to the length of the adult insects' antennae. They have one generation per year, and at maturity are grayish-brown, stout-bodied beetles, about 3/4" long. Adults appear in late summer from mid-August through early October.

The female beetle prepares to lay eggs by chewing through the bark of a small twig, in a grooved channel that goes all the way around the twig, girdling it. She lays an egg in the girdled twig section, which quickly wilts, turns brown and dies. Larvae, which are creamy white, grub-like borers, cannot survive in healthy wood, but do fine in the dead twig even after it falls from the tree. When twigs fall from the tree, a close inspection of the twig's cut end looks a lot like beaver damage, in miniature.

Twig Girdler, Kansas State University Research and Extension

Images:

• Above left - adult twig girdler, Oncideres cingulata, Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org. 
• Above right - small stems clipped by twig girdler, Gerald J. Lenhard, Louisiana State University, Bugwood.org. 

Twig Pruner - severed twig end has ragged outer edges but a smooth concave innner surface. 

This is another group of insects causing similar damage symptoms in trees.

* Oak twig pruner, Anelaphus parallelus, is found primarily in oaks.

* Twig pruner, Anelaphus villosus, has a wide host range including most deciduous trees and woody shrubs, except oak and ash.

Twig pruners also have one generation per year, but requires two years to complete its lifecycle. Adults are a longhorn beetle, reddish-brown with light tan markings, about ½ to 3/4 inches long. In spring adults emerge and females lay eggs in and around bud clusters near the tips of small twigs and branches. Larvae hatch within a few days and tunnel into the twig. Young insects feed within the twig’s wood. In fall they tunnel toward the base of the twig where they overwinter.

In the second year, larvae continue to feed until late summer when they begin making concentric cuts in the wood of the twig, spiraling outward until they almost reach the outer bark. The larvae then retreats into the outer portion of the twig. The larvae overwinters inside the twig, pupating and emerging as an adult the following spring. On close inspection, twigs severed by the twig pruner will have ragged outer edges but a smooth concave inner surface. Tunneling will also be evident. Affected twigs may range in diameter from one-half inch to two inches.

Twig Girdler and Twig Pruner, University of Missouri Extension

Images:

• Above left - twig pruner, Anelaphus villosus, James Solomon, USDA Forest Service, Bugwood.org. 
• Above right - Anelaphus parallelus larva tunnel down a twig, Trish Hanson, Vermont Forestry Divisionl, Bugwood.org. 
• Left - Oak twig girdler adult. By xpda - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=67705015

Control
Twigs girdled by either of these insects may stay attached to the main branch for several weeks, or be broken out of the tree by wind at any time during fall or winter. Tunneling may or may not be evident in twigs, depending on which insect is present. Homeowners are usually first aware of these insects, due to the many dead twigs that appear at branch tips in late summer. Heavily infested mature trees can look a little ragged, but the damage is not a serious health problem so chemical control is not recommended or practical. The best way to minimize insect activity is to remove, and burn or discard twigs in fall and spring that contain the developing larvae.

Top

2. October 2nd growing degree days (GDD)

Top

3. Mulching leaf litter into lawnsGround tree leaves will not increase thatch

Mulch mowing reduces yard waste and returns complex organic matter and nutrients to soil. It is easier and less time consuming than bagging, but can require more frequent mowing. According to Kansas State Extension, research has shown if done properly six inches or more of fallen leaves can be chopped by the mower and returned to the soil without causing damage. However, mow each time a thin layer, an inch or so of leaves cover the turf until six inches has been returned. Do not wait until six inches has piled up and then mow. This process of frequent mowing can continue as long as the shredded leaves do not start to pile up on top of the turf and shade out grass.

Ground tree leaves will not increase thatch, which is mainly a layer of dead roots and rhizomes. Tree leaves can fall fast and quickly pile over the lawn. If needed, rake and bag leaves, then compost them or use as garden mulch. Do not blow leaves into the street or onto other concrete surfaces. Leaves can leach nutrients that pollute waterways; or be carried to surface water through storm drains where they release nutrients leading to algal problems. 

Mulch Mowing Fall Leaves, K-State University Research & Extension

Top

4. Fall drought concernsWatering into fall and early winter very important

Nebraska's current drought conditions range from abnormally dry to exceptional drought with the majority of the state in extreme drought. For more detail, refer to the Nebraska Drought Monitor map, U.S Drought Monitor map. Fall/winter watering remain extremely important. Along with an increased risk of winter dessication and cold temperature injury, drought stressed trees and shrubs are more susceptible to attack by harmful pests like borers, canker disease and Verticillium wilt. Plant owners often believe their landscape plants survived a drought year, but then dieback shows up three to five years after a drought.

Woody plants - While most plants benefit from fall watering, the priority should be evergreens, newly planted trees and shrubs and younger woody plants. Winter watering may be needed in the absence of rain/snowfall. Water can be applied early in the day when soils are not frozen and air temperatures are above 40 to 45 degrees Fahrenheit. Soil needs to be kept moist to an 8" to 12" depth from the trunk/stems out to at least the dripline of trees and preferably well beyond.

If plants are not mulched, a 3" to 4" deep layer of organic mulch, like wood chips, should be applied in at least a 4' to 6' diameter ring around plants to conserve soil moisture. Be sure mulch is not piled against tree trunks and avoid continuously saturated soils.

 The main purpose of winter watering is to avoid soil cracks and ensure moisture is available when tree roots can take it up.

Turf - While some fall drought stress can help induce deeper winter dormancy, too much drought stress can make turf more susceptible to winterkill. Apply enough irrigation to prevent visible drought stress but don't overdo it. Let your eyes be your guide. Also, remember that aboveground irrigation components (such as a backflow preventer) should be turned off and drained before a hard frost or freeze. In-ground systems should be drained or blown out before winter.

Top

5. Fall landscape sanitationGarden sanitation an important cultural tool to manage plant diseases & insects

This is one of our tools for managing plant diseases and harmful insects that overwinter on plant residue.

For vegetables and annual flower gardens, remove or till under plants once harvesting is over or a freeze has killed the plants. Avoid tilling too much as this can break down soil structure. Rake and remove, then recycle the leaves of trees and shrubs as they drop. Don't overlook picking up fallen fruit around fruit trees, and weed management in or near gardens. Some pests overwinter on or in nearby weedy areas. Wash to remove plant debris and soil from garden tools and equipment, then sanitize these items with a 10% bleach solution.

For herbaceous perennials and ornamental grasses, wait to cut back stems and leaves until after a hard freeze or wait until next spring. Whether to cut plants back in late fall or spring is up to the homeowner and may depend on the ecosystem value and/or winter interest of a plant. Plant stems provide nesting sites for some solitary bees which are important pollinators.

Seeds of some dried flowers, like Rudbeckia and coneflowers, are a food source for birds. The plumes of ornamental grasses provide winter interest.

Note: Tall ornamental grasses can be a fire hazard, especially if grown next to a house and left-over winter. If plants are cut back in late fall, leave 8" to 15" of stems to help conserve nesting pollinators.

Nesting and Overwintering Habitat: For Pollinators and Other Beneficial Insects, Xerces Society

Top

6. Pesticide storageRead and follow label directions for safe storage

Store pesticides correctly and securely. Storage information can be found on pesticide labels. Read and follow label directions for safety and to keep pesticides effectiveness from degrading.

In general, pesticides need to be stored in a secure, well ventilated location that can be locked. The location needs to be away from children, pets and food items as well as anything that might be contaminated in case of a leak or accidental spill.

Do not store pesticides near heat, sparks, or open flames; and check that containers are tightly closed. Always store pesticides in their original containers. A mistake made is pouring a pesticide into a container other than the original. This is against pesticide label law and has led to accidental poisonings.

A common question about winter storage is if a pesticide is still effective after it freezes. Most pesticides are safely stored between 40 to 100 degrees Fahrenheit, but it is best to check the label for storage temperature requirements and any warnings against freezing. If a liquid pesticide does freeze, it might be less effective in controlling pests.

Pesticides contain active and inactive ingredients. The active ingredient is what kills the pest. Inactive ingredients include solvents, carriers, or emulsifiers that make the pesticide more efficient. Due to some inactive ingredients, the freezing point of some liquid pesticides could be lower than 32 degrees F. Read the label for temperature storage requirements and what to do if a pesticide does freeze.

Pesticides formulated as wettable powders or granules are not affected by low temperatures. However, moisture can cause caking that may reduce effectiveness so follow label directions for correct storage recommendations. If you have products formulated in water-soluble packets, these should not be frozen as they tend to become brittle and then break open.

Safe Transport, Storage and Disposal of Pesticides, Nebraska Extension

Top

7. Evergreen natural needle dropUniform browning of interior evergreen needles

Evergreen conifers do not keep their needles forever. Older needles on the interior of trees are shed each fall after they turn yellow, brown or reddish tan in color. This natural process is usually subtle and goes unnoticed, but some years it is very evident, especially in white pine. However, natural needle drop is a natural process and is not harmful to trees. The fallen needles will also not make the soil too acid.

• Pine trees hold needles for 2-5 or more years, depending on the species.
• Spruce trees generally hold needles longer than pine trees, approximately 5-7 years, which serves to hide the browning needles.
• Firs and Douglas-fir needles last 3-4 years.
• Japanese Yew needles last about 3 years and tend to yellow and drop in spring rather than fall.
• Branchlets of Arborvitae turn brown and drop off, rather than individual needles. The brown branchlets remain on the tree for some time before falling.

Natural Needle Drop, Nebraska Extension

Top

8. Turf seeding follow-upToo late to seed now, sod instead. Concerns with fall seedings - what should it look like?

The optimum time to seed cool-season turfgrasses in Nebraska is between August 15 and September 15. Adjust these dates a week or two earlier for northern Nebraska or the Dakotas and a week or two later for southern Nebraska. We are well past that time now, so no further seeding should be done. Seed germination in cool soils will be very slow and survival of seedlings low.

Don't expect perfection now, even with successful seedings done during the ideal time frame. Seedlings will still be young and thin, not completely mature or filled-out until next spring. Weeds are usually still be a problem, since the new turf plants are not big enough yet to crowd them out. Keep mowing as long as the grass continues to grow. Mowing encourages turf crowns to mature and develop additional tillers, causing the plants to fill out. Mowing also keeps weeds short and minimizes their competition with the grass seedlings. Ignore annual weeds, they will die off naturally in a few weeks and can be controlled next year with preemergent herbicide. Use caution when controlling perennial weeds, being sure to choose herbicides labeled for use on young seedings, such as quinclorac and carfentrazone. As always, read and follow herbicide label directions to avoid turf damage.

If bare turf areas need coverage now, turf can be sodded almost any time soils are not frozen. Sodding in fall or winter can be done as long as winter irrigation is available to minimize winter desiccation on exposed sites. Soil preparation is just as important as for other times of the year and the soil must be moist when sod is laid. Watering after installation is a priority, even in the cooler temperatures of fall and winter. The goal is to keep the crowns moist to prevent winter desiccation and sod death.

Establishing Lawns From Sod, Nebraska Extension Turf iNfo

Top

9. Complete fall turf fertilizer applications by 10/30Updated guidelines for fall turf fertilization

Early to mid-September is an imporant fertilizer application for cool season lawns, but are any additional applications needed later in the season? 

For the last several years, our turf specialist's recommendation has been to eliminate the "winterizer" fertilizer application on healthy established lawns with good color and vigor. On new lawns, those on poor soils or turf with poor color make a final light fertilizer application before Halloween. This application bolsters root growth heading into winter. The best indicator as to timing for late season fertilization is the growth rate of the turf plants. Make the application after the majority of leaf expansion has ceased for the year, which usually by mid-October.

A light rate application means 0.25 - 0.3 lbs of N per 1,000 sq. ft. with a quickly soluble N source such as ammonium sulfate, ammonium nitrate or urea. Water the product off the blades into the soil soon after application.

Cool Season Lawn Calendar - Eastern Nebraska, Nebraska Extension

Top

10. Prepare for dormant seedingPrepare site now; good seed-soil contact important for dormant seeding success

Dormant seeding is defined as such because seed lies dormant until soil temperatures warm in April or May. It can be done as early as Thanksgiving or as late as March in most Nebraska locations. The key is to seed after the soil is cold enough that germination will not occur until after soils warm in spring. The benefit of dormant seeding is as soil heaves and cracks during winter, crevices are created for seed to fall into, providing ideal germination conditions in spring. Dormant seeding may be easier to schedule than spring seeding, because spring rains can make it difficult to do final soil preparation and seed after March.

However, there are risks with dormant seeding. It is most effective if weather remains cold enough to delay germination until spring. Occasionally, extended warm periods in winter could allow seed to germinate, and seedlings may then be killed by ensuing cold weather.

As with any seeding, soil preparation needs to be done prior to seeding. For dormant seeding, this would be in fall before the soil freezes or during dry winter periods when the soil is not frozen. If using dormant seeding, monitor the area in mid spring for the need to do additional over-seeding.

On new sites, use a rototiller or other tillage equipment to work the soil six inches deep. To improve a clay or sandy soil, spread about one inch of compost over the area just before tilling. Do not incorporate sand to improve clay soil. It will likely become even more compacted. Do not till wet soil or soil clods will form. Avoid over-tilling any soil as this destroys soil structure.

To overseed a thin lawn, core aerate the lawn a number of times to create holes for seed to fall into. If needed, compost can be spread over the turf and the area raked to work compost into aeration holes.

Next, buy quality seed from a reputable dealer. Blue tag certified seed is recommended to ensure a high germination percentage and fewer weed issues. Avoid buying seed from bulk bins.

Seeding is best done using a drop spreader. The easiest way to apply seed uniformly to a small area is to calculate and weigh out the amount of seed needed for an area. Set the spreader adjustment very low, sow seed in one direction and then sow at a right angle to the first. Repeat until the seed is gone.

The amount of seed recommended is two to three pounds per 1000 square feet for Kentucky bluegrass and six to eight pounds per 1000 square feet for tall fescue. It is not recommended to dormant seed perennial ryegrass.

Top

11. Fall is the season of tiny bitersNuisance insects - lace bugs and minute pirate bugs

Working outdoors brings with it several potential insects which can cause uncomfortable itchy bites. The most common culprits include mosquitoes, chiggers and biting flies. Below are two additional insects occasionally causing problems, especially in late summer.    

Lace Bugs
There are many species of lace bugs, all so named because of the delicate lacy wings adults hold flat over their back and not to be confused with lacewings. Adult insects are small, only about 3/16 inches long. Birch, hackberry, hawthorn, elm, oak, sycamore and walnut lace bugs are common species, each attracted by specific host trees. They are all plant-feeding insects, usually found on the undersides of leaves.

Each species has 2-3 generations per year, overwintering as adults in protected locations near their preferred tree. Small groups of eggs are inserted into leaf veins in spring, followed by several nymphal stages as the insects develop.

Both adults and nymphs have a piercing-sucking, straw-like mouth used to suck juices from leaves. In fall, adults and/or the even smaller nymphs can fall out of trees and land on your skin. Immature nymphs, which are black, may look like a tiny black speck of pepper. As their mouth pierces skin, you may feel a tiny prick. These insects don’t feel on people or blood, they are strictly a nuisance pest.

Lace Bugs, The Ohio State University

Minute Pirate Bugs
These tiny bugs, 1/8-inch long, can cause painful bites that seem out of proportion with their size. They are oval to triangular in shape, flattened and black with whitish markings on the back. Normally, they are predators and feed on insect eggs and small insects. They feed by impaling their prey with their short blunt beak and sucking the juices.

Minute pirate bugs are found throughout the summer in fields, woodlands, gardens and landscapes. In the late summer, they begin the unpleasant behavior of biting humans. They do not feed on blood or inject a venom or saliva.

People differ in their response to pirate bug bites. Some people have no reaction to the bite, but others have bites that swell like a mosquito bite or turn red. Because the bite is noticeable and the pirate bug doesn't fly quickly, the victim is usually able to successfully smash the offending insect.

Preventing lace bugs and minute pirate bugs from biting you is not easy. Repellents are generally not effective, although some people have found applying baby oil or suntan oil liberally to the skin may prevent some bites by coating the bugs with oil.

Minute Pirate Bugs: Little Bugs, Big Bite, Nebraska Extension

What’s Biting You?, Nebraska Extension

Top

Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by Nebraska Extension is implied. Use of commercial and trade names does not imply approval or constitute endorsement by Nebraska Extension. Nor does it imply discrimination against other similar products.