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Hort Update for September 7, 2021

Hort Update for September 7, 2021, Nebraska Extension,
Fall armyworm caterpillar. Image from Frank Peairs, Colorado State University,
Serious ConcernsMajor Symptom
1. Fall armyworms Very high numbers may cause turf damage in the next few weeks.
2. September growing degree days (GGD) Lincoln Airport 9/6/21 GGD -  3299,  Understanding Growing Degree Days
3. Timing of turf weed control Fall best time to control perennial, biennial and winter annual weeds.
4. Weed control on new grass seedlings Use herbicides carefully to avoid seedling damage.
5. Kermes oak scale Infested trees show twig/branch dieback; dripping sap.
Minor Issues
6. Lilac cercospora leaf spot Severe leaf browning caused by fungal leaf spot disease.
7. Kentucky bluegrass rust Orange-red fungal pustules on leaves; often due to low nitrogen levels.
Timely Topics
8. Fall tree planting Root starters not needed.
9. Fall tree watering Prevent winter desiccation damage; maintain tree health.

1. Fall armywormsVery high numbers many cause turf damage in the next few weeks

Some insects only sporadically cause problems in lawns and landscapes. They are there, every year, but usually in such low numbers they can easily be overlooked. Fall armyworm is one such insect, but it appears they will not go unnoticed this year. Turf managers in states south of Nebraska are reporting devastating numbers and high levels of turf damage. 

There are actually several species of armyworm, including common and yellowstriped, but the dominant species this year is fall armyworm, Spodoptera frugiperda. Armyworms get their common name from their tendency to move in large groups, or armies, of caterpillars.  

What are they?
Fall armyworm is the caterpillar larva of a moth. It’s a tropical species, seldom surviving winter in the United States, even in the Gulf coast states. But the adult moths are good flyers and migrate north every year from their overwintering sites in the extreme southern tips of Texas and Florida, as well as Mexico and Central America, often establishing themselves as far north as New England by early summer.  

Adult moths are similar to cutworm moths, having dark gray forewings mottled with lighter and darker patches. Their wingspan is about 1.5 inches and they have a whitish patch near the wing tip. 

Caterpillars range in color from light tan to green, or nearly black. They have light and dark stripes running the length of their body and an inverted white Y on the head, which distinguishes them from other armyworm species and cutworms.  

Adult moths cause no damage, but in the next few weeks may be seen feeding on flower nectar. Clients may report larger than normal numbers of moths in and around their homes, along with unusual egg masses. Females lay eggs in masses, several hundred eggs each, on flat surfaces like tree leaves, light posts or fence rails. They are attracted to lights at night, resulting in higher amounts of eggs laid nearby. They prefer to lay eggs near favored grasses, especially actively growing turf that has been recently fertilized. Egg masses are light gray and covered with grayish fuzz.  

During the last week of August, Nebraska Extension entomologists began receiving reports of high numbers of flying adults and egg laying in eastern parts of the state. Jody Green, Nebraska Extension entomologist, reports egg masses (40 in one yard) found in Lincoln. That means this week feeding may begin from the newly hatched young caterpillars.   

Armyworm caterpillars feed primarily on grasses, including tall fescue, fine-leaf fescues, Kentucky bluegrass, perennial ryegrass and bentgrass. They can also be found on sweet corn, beans, other vegetables, flowers and fruit trees. In sweet corn, larvae tunnel into ears from the tip or sides causing damage similar to corn earworm. They are common in soybean or corn fields and will move into turf when their food supply is gone.  

In turfgrass, caterpillars devour entire leaves resulting in rapidly spreading brown patches. Close inspection easily shows the caterpillars’ presence. Severe leaf loss exposes turfgrass crowns to direct sunlight and high temperatures making them susceptible to desiccation and death, so it’s important to control the insects before total leaf loss occurs.   

Armyworms can be controlled by homeowners with contact insecticide spray applications using products such as those below.  

  • Azadirachtin - Azaguard Botanical Insecticide and others   
  • Bacillus thuringiensis – Dipel, Thuricide 
  • Bifenthrin - Ortho Bug B-Gon Lawn Insect Killer  
  • Deltamethrin – Hi-Yield Turf Ranger Insect Control 
  • Gamma-cyhalothrin – Spectracide Triazicide Insect Killer 
  • Imidacloprid + cyfluthrin – Bioadvanced Complete Insect Killer 
  • Permethrin – Hi-Yield 38 Plus Turf, Termite and Ornamental 
  • Spinosad - Captain Jack’s Dead Bug Brew, Fertilome Borer, Bagworm, Tent Caterpillar and Leafminer Spray 
  • Trichlorfon – Bayer Advanced 24 Hour Grub Killer Plus 

Professional turfgrass managers can use a pyrethroid, but may get better results with chlorantraniliprole (e.g. Acelepryn) or tetraniliprole (e.g. Tetrino). Used at their lowest rate both provide excellent caterpillar control. Or use a combination product containing a pyrethroid and neonicotinoid, such as Aloft (clothianidin+bifenthrin) or Alucion (dinotefuran+bifenthrin). 

Mow the turf before treating, to shorten the turf height and make coverage easier. Mowing also removes weed flower heads that may attract pollinators, which would be killed by an insecticide application. Spray early or late in the day when insects are most active. On thick, well-established turf use a minimum of 1 gallon of water per 1000 square feet to be sprayed. Follow product label direction on chemical use rates.   

Professional turf managers are reporting good control from chlorantraniliprole, the active ingredient in Scott’s GrubX. So homeowners who applied this product in spring, may not see problems in their turf.  

Lawn Recovery
To prevent grass crown desiccation, keep damaged areas watered until new leaf blades begin to appear. Apply a fall fertilizer in early September to help grass recover. Overseed heavily damaged areas that do not recover on their own.  

More information.
Fall Armyworms March Across Ohio, The Ohio State University
Controlling Fall Armyworms on Lawns and Turf, Alabama A& M and Auburn University Extension


3. Timing of turf weed controlFall best time to control perennial, biennial and winter annual weeds

While fall is the preferred time for herbicide control of perennial broadleaf weeds, it is not a good time to control many weeds. Identification of weeds, and knowing if they are annual or perennial, warm season or cool season, is key to knowing when and how to effectively manage weeds. Below is the preferred timing to apply labeled herbicides for some of our more common turf weeds in lawns. Be sure to alternate herbicides with different modes of action to help reduce herbicide resistance in weeds.

  • Perennial broadleaf weeds, i.e. dandelion, ground ivy, violet: September into October
  • Winter annual broadleaf weeds, i.e. henbit, chickweed, speedwell: preemergence herbicides applied in September
  • Warm season annual weeds, i.e. crabgrass, spurge, purslane: preemergence herbicides applied in spring; post emergence herbicides applied when plants are young if necessary
  • Warm season perennial grasses, i.e. tumble windmill grass, nimblewill: summer beginning when plants are fairly small. Repeat applications are needed. 
  • Cool season perennial grasses, i.e. tall fescue, orchardgrass, roughstalk bluegrass: dig out or apply glyphosate at a time when the area can be reseeded/sodded fairly soon.

Turfgrass Weed Control for Professionals publication to purchase, Purdue University 

Perennial Weedy Grass Control, Nebraska Extension

Broadleaf Weed Control in Home Lawns, Nebraska Extension


4. Weed control on new grass seedlingsUse herbicides carefully to avoid seedling damage

New grass seedlings can be damaged by broadleaf herbicide applications. Choose products carefully and follow label directions to avoid seedling damage. Traditional products like 2,4-D and dicamba should not be applied until the grass is "well established" or after the 2nd or 3rd mowing. 
summary of safety on newly established turf


5. Kermes oak scaleInfested trees show twig/branch dieback; dripping sap

Pale brown, hemispherical scales appear as growths attached to leaf midribs and twigs. Mature scales are tough and gall-like. Leaves become stressed, yellow, or withered, and honeydew secretions are evident. Infested trees can suffer branch dieback, but infestations are usually isolated to specific trees and are rarely widespread. Hosts affected have been red, pin, and bur oaks, but a wide range of oaks can be infested.

This scale produces a profuse amount of honeydew that covers leaves and becomes blackened by sooty mold. Ants and many other insects feed on the honeydew, and there are a number of natural enemies that help restrain populations.

There is one generation per season, with females reaching maturity in June. Crawlers emerge in September then migrate to buds being formed for the following year where they spend the winter.  A dormant-season spray oil from March through mid-April is an opportunity to treat. Crawlers are also susceptible to control in September with a topical insecticidal spray.

Kermes Oak Scale, Kansas State Research and Extension


6. Lilac cercospora leaf spotSevere leaf browning caused by fungal leaf spot disease

Fungal leaf spots can defoliate lilacs by this time of the season. Cercospora leaf spot, caused by a fungus in the Pseudocercospora genus,  is common during wet and/or humid years. Although lilac shrubs can look quite bad, loss of leaves this late in the season will not harm otherwise healthy shrubs.  As a rule, fungicides do not need to be applied for this foliar leaf disease. If a client chooses to manage the disease, during spring just as shrubs are leafing out and during rainy periods is a key time for fungicide applications. Sanitation will help now. Advise homeowners to rake and remove fallen leaves from around lilacs. If lilac stems are dying, check the plant for signs of lilac-ash borer or oystershell scale.

Lilac Pseudocercospora Leaf Spot, Iowa State University Extension


7. Kentucky bluegrass rustOrange-red fungal pustules on leaves; often due to low nitrogen levels

Stem rust is a fungal disease that develops late in the season on lawns with older bluegrass varieties and slow growth due to low nitrogen. The obvious symptom is rust colored "powder" (fungal spores) on grass blades, shoes and lawn mower. Heavily infected turf may show some yellowing of grass blades. Fungicide controls are rarely recommended or needed for home lawns. Fall lawn care, especially correct nitrogen fertilization, along with cooler fall weather promotes turfgrass growth and rust disappears.

Note for Sports Turf - If stem rust occurs on low maintenance athletic fields, the fungal spores can cause problems for allergy/asthma sufferers. Control of stem rust is recommended on sports turfs using a combination of wise turf management and timely fungicide applications.

Rust Diseases in Turf, Purdue Extension


8. Fall tree plantingRoot starters not needed

Fall is a great time to plant trees, shrubs and perennial herbaceous ornamentals. According to Professor Ed Gilman, University of Florida School of Forest Resources and Environmental Horticulture, tree establishment is determined by many factors. Fertilization and the addition of root stimulant products have little or no effect on how quickly a plant re-establishes on the new site.

Practices that encourage growth

  • loose soil (dig a wide, not deep planting hole), proper irrigation
  • mulch ring 6 - 8 feet in diameter or more around planting hole; not piled against trunk
  • root flare slightly above soil surface after planting (planting hole not dug too deep)
  • leaving crown of tree intact (no pruning at planting except for dead or broken branches)

Practices that limit growth

  • compacted soil
  • little or no irrigation
  • grass and weeds close to trunk
  • planting too deep
  • pruning at planting

Practices that have little or no effect

  • peat or organic matter addition as backfill
  • root stimulant products
  • fertilizing at planting
  • adding mycorrhizae
  • adding water absorbing gel crystals


9. Fall tree wateringPrevent winter desiccation damage; maintain tree health & vigor

Homeowners may comment that tree decline tree cannot be due to a lack of water because they have automatic irrigation systems. However, irrigation systems are set for turfgrass which have shallower roots than trees. During dry periods or drought, turf irrigation alone may not be enough to fully benefit trees and they can become drought stressed. Relying on turf irrigation alone can also promote shallower tree roots more prone to water stress. Another potential issue are systems that are left on automatic all season.  In this case, the upper layer of soil may remain too wet which can limit oxygen exchange between air and soil. Roots need soil oxygen as much as they need moisture and this can become a stress factor. 

In the absence of rainfall, summer and fall watering is critical to reducing the risk of winter desiccation. Encourage clients to keep the soil of young trees and evergreens uniformly moist, not wet, up until the soil begins to freeze. Moisten the soil 12 to 18 inches deep for trees. Using a 2 to 4 inch deep layer of mulch also helps conserve soil moisture. For tree and turf health, and water conservation, encourage homeowners to use irrigation systems manually. Only turn them on when turfgrass shows signs of needing irrigation.

Improve Tree, Shrub Health Through Fall Watering, Nebraska Extension


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.