Hort Update for June 14, 2019

Hort Update for June 14, 2019, Nebraska Extension, http://communityenvironment.unl.edu/update6142019
Serious ConcernsMajor Symptom:
1. Yellow nutsedge Apple-green, grass-like plant with waxy blades and a triangular-shaped stem
2. Crabgrass control Time for second preemergence application
3. Bagworms Apply insecticides when insects reach 1/4 to 1/2" long
Minor IssuesMajor points:
4. Insects of garden ornamentals Watch for these common insects damaging garden ornamentals now
5. Vegetable gardens insects Watch for these common insects in vegetable gardens now
6. Turf diseases appearing now These common turf diseases are appearing now
7. Chlorosis in trees Abnormal yellowing of tree leaves or needles while veins remain darker green, often caused by iron deficiency
Timely TopicsMajor points:
8. May/June beetles High numbers of May/June beetles (Phyllophaga spp.) are being reported around the state
9. Maple seedlings Mow, hoe or hand-pull seedling while still small



1. Yellow nutsedge apple-green, grass-like plant with waxy blades and a triangular-shaped stem

Yellow nutsedge grows rapidly in summer, becoming quite noticeable in mid to late June through the end of summer. However, early June to just past mid-June is the time to apply herbicides for effective control. When herbicides are applied after June 21, the plant may be killed but it will have already produced many small underground tubers that will regrow this year or in future years.

According to the May 29, 2019 University of Nebraska-LincolnTurf Info titled “Yellow Nutsedge, it’s Time to Treat” - to be successful, yellow nutsedge herbicide control programs must be implemented early in the season and in consecutive years. Late applications and/or not sticking to a multi-year strategy often results in no net gain against this troublesome perennial weed.

How early? As early as it is visible – in most of Nebraska this is early June. At this point, newly formed tubers are immature and stopping above ground growth will significantly impair their maturation and emergence. Products which contain sulfentrazone, such as Dismiss or Solitare may also provide preemergence with postemergence control; only Echelon (prodiamine + sulfentrazone) is specifically labeled for preemergence control. Other products may also control or suppress tuber formation indirectly by shutting down top growth and limiting photosynthesis and eventual carbohydrate formation in the tubers. When nutsedge is young with less leaf area, coverage is improved and systemic herbicides are more readily translocated to roots, rhizomes and tubers.

Sequential applications are also recommended. Sequential applications work better than single application for most herbicides. Make a second application 3 or 6 weeks after the initial application. To limit the potential for development of herbicide resistance consider rotating modes of action. For example, Dismiss and Sedgehammer have different modes of action and provide good to excellent control when sequentially applied, especially if Sedgehammer is applied first.

Recently, a relatively new herbicide, imazosulfuron (Celero, NuFarm) was tested with good results after a single application when compared to single application of sulfentrazone (Dismiss). Testing of imazosulfuron to provide additional data and information will continue.

Yellow Nutsedge, It’s Time to Treat, Nebraska Extension

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2. Crabgrass controltime for second preemergence application

Premergence herbicides (PREs) applied in April, especially early April or earlier, will be nearing the end of the products control window and a second application may be needed. With cooler soil temperatures this spring, some crabgrass seed germination was delayed and a late April into early May PRE application would have been close to ideal. Crabgrass will continue to germinate through June and into July. Look at when the first application of PRE was made and consider a second application if needed. General management of crabgrass includes correct lawn care practices to encourage a dense turf that shades out crabgrass seeds/seedlings. Use a mowing height of 3.5 inches.  

Premergence Herbicide Failure, Nebraska Turfgrass iNfoCrabgrass Control in Home LawnsNebraska Extension

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3. Bagwormsapply insecticides when insects reach 1/4 to 1/2" long

Populations remain high on evergreen trees. Eggs are hatching and now, while bagworms are small (1/4 to ½” long), is the time to apply insecticides to prevent significant damage to evergreens that can kill trees. Monitor spruce, Juniper, Arborvitae and pine for bagworms. While larvae are small is the time products like Bacillus thuringiensis, as well as other insecticides, are most effective.

After hatching, larvae spin protective cases or “bags” around themselves. Bags are constructed of silk and fragments of needles or leaves. Bags are initially one-eighth inch long. As larvae feed and grow, they enlarge the bag. By summers end, bags are up to two inches long.

Bagworms move around trees feeding on needles until early September. Early signs of damage are brown or stressed needles at branch tips caused by tiny, first-stage caterpillars etching needle surfaces as they feed. Heavy infestations of older bagworms can defoliate an evergreen tree or shrub. Less severe injury will slow growth and stunt plants. Bagworms are especially damaging to conifers because destroyed foliage is not regenerated.

Insecticides are most effective when applied from mid to late June targeting young caterpillars. Insecticidal spray applications require thorough coverage to penetrate the tree canopy. It’s best to use ground equipment capable of delivering higher spray volumes and pressure. Aerial applications may not provide thorough coverage. Insecticides containing Bacillus thuringiensis (Bt), spinosad, or neem oil (azadirachtin) and insecticidal soaps are effective against young larvae, but may require repeat applications. These products generally have minimal impact on beneficial insects.

Other insecticide options for bagworm control on conifers includes acephate, bifenthrin, chlorantraniliprole, carbaryl, cyfluthrin, dimethoate, esfenvalerate, fluvalinate, lambda-cyhalothrin, malathion, permethrin, and tebufenozide. When making an application, be certain the product is specifically labeled for both the target pest and plant species.

 Bagworms, Nebraska Extension

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4. Insects of garden ornamentalsWatch for these common insects damaging garden ornamentals now

Aphids in the Home & Garden, University of Minnesota Extension
Leafcutter Bees (important native insect), Colorado State University
Phlox Plant Bug, Missouri Botanical Garden
Rose Chafers, University of Minnesota Extension 
Roseslug, University of Maryland Extension

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5. Vegetable garden insectsWatch for these common insects in vegetable gardens now

Asparagus Beetles, University of Minnesota Extension
Bean Leaf Beetles, University of Minnesota Extension
Flea Beetles, University of Minnesota Extension

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6. Turf diseases appearing now these common turf diseases Are appearing now

Brown Patch Disease of Turfgrass, Nebraska Extension
Dollar Spot Disease in Turgrass, Nebraska Extension 
Leaf Spot and Melting Out of Turf, Nebraska Extension

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7. Chlorosis in treesAbnormal yellowing of leaves or needles while veins remain darker green, often caused by an iron deficiency

Chlorosis describes any condition in which leaves or needles develop an abnormally light green or yellow color. The most common cause of chlorosis in trees is a deficiency of iron in the tissues. Other causes of chlorosis include over-watering, over-fertilizing, damage to roots, and deficiencies in manganese or other micronutrients.

Chlorosis of Trees in Eastern Nebraska, Nebraska Forest Service
Chlorosis of Trees in Central and Western Nebraska, Nebraska Forest Service

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8. May/June beetlesHigh numbers of May/June beetles (Phyllophaga spp.) are being reported around the state

Numbers so high that in one case beetles were shoveled away from a building and were odiferous. Likely, environmental conditions last season and over winter allowed for a high population survival. To keep beetles from congregating, shut off outdoors lights or replace them with LED bulbs that are less attractive.

Do high beetle populations mean white grubs will cause more damage to lawns this season? Not necessarily. The white grub that generally causes the most damage to turfgrass in Nebraska is the annual white grub whose adult is a masked chafer (Cyclocephala spp.). June beetles are a 3 year grub, meaning it requires 3 seasons for them to complete their life cycle from egg to adult.

If a lawn had serious grub damage last season, preventive grub products could be applied by early July. If a lawn did not have confirmed white grub damage last season, monitor the lawn from mid-August into September for grub populations. Several animals, especially skunks and raccoons, are attracted to turf insect infestations and signs of their foraging in an area are indications of white grub activity. Flocks of birds, particularly starlings, feeding in the turf provide additional evidence of a possible infestation.

If 8 to 10 masked chafer or Japanese beetle grubs can be found per square feet in August, or 3 to 5 June beetle grubs per square foot; then an application of Dylox or carbaryl (Sevin) is justified at that time.

White Grub Management, Nebraska 

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9. Maple seedlingsMow, hoe or hand-pull seedling while still small

A heavy maple seed crop combined with frequent rainfall translates into many maple tree seedlings growing as weeds in lawns and landscape beds. In landscape beds, maple seedlings are extremely easy to hand-pull if you do not wait too long and allow them to establish a deeper root. If you wait too long, they will need to be dug out with a spade or killed with careful spot treatment of glyphosate (Roundup).

In lawns, regular mowing will kill maple seedlings and herbicide control will not be needed. If you have a newly seeded lawn, don’t wait too long to begin mowing. As soon as the new grass reaches three inches or close to three inches, begin to mow. This will also control maple seedling as well as encourage growth and maturation of the new grass.

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