Hort Update for June 22, 2018

Hort Update for June 22, 2018

Nebraska Extension Hort Update for June 22, 2018, http://communityenvironment.unl.edu/update06222018
Newly hatched bagworm caterpillars creating protective bags out of the juniper on which they are feeding. At this stage they are less than 1/2 inch long. Image from the Nebraska Forest Service.
Serious ConcernsMajor Symptom:
1. Bagworms Insects have hatched and are feeding; look for very small new bags on susceptible evergreens or those with a history of infestation
2. Japanese beetles Adult beetles are beginning to emerge in Omaha and Lincoln
3. Fire blight Save pruning for dormant season, unless conditions below exist
4. Storm damaged trees Nebraska Forest Service resources helpful in managing damaged trees
5. Summer herbicide applications & spray drift Hot temperatures, low humidity and high winds create "perfect storm" for herbicide drift
Minor IssuesMajor Symptom:
6. White grub control Time to apply preventive grub control products
7. Heat and water stress Common symptoms of heat & dry conditions on turf, ornamentals and woody plants
8. Strawberry root weevils Occasional home invader; chemical control not necessary
Timely topics
9. Correct use of mulch Avoid common problems with mulch application
Product UpdateNotes:
10. Mesotrione update Over application will cause grass seedlings and existing turf leaves to turn white
Research UpdateVideo:
11. Phosphorus, nitrogen, algae Nitrogen effects on phosphorus deficiency expression


1. BagwormsInsects have hatched and are feeding; look for very small new bags on susceptible evergreens or those with a history of infestation

Feeding on conifer trees and shrubs justify control. Large populations are capable of seriously damaging or killing evergreens. Monitor spruce, Juniper, Arborvitae and pine for bagworms. Eggs hatch from mid-May through early June. Larvae are still fairly small and this is the time products like Bacillus thuringiensis, as well as other insecticides, are most effective. Controlling young larvae reduces plant damage.

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. At this time of year, bagworms are between one-fourth and one-half long. 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 a 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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2. Japanese beetlesAdult beetles are beginning to emerge in Omaha and Lincoln

Japanese beetles have been reported feeding in Omaha and Lincoln in spotty locations. Unlike most insect pests, both adults and grubs cause plant damage. As beetles, they feed on leaves, flowers and fruits of more than 300 plant species. Linden trees, roses, grapes and soybeans are a few favorite foods. The beetles feed over a 4 to 6 week period beginning in late June. They eat green tissue between leaf veins causing leaves to appear lacy. Severe defoliation can stress trees and reduce yields in orchards and crops. 

As grubs, they feed on turf roots starting in July/early August and continue through summer. If grub populations are high enough, the turf may turn brown and can easily be rolled up like carpet. Note: Treating for the grubs will not prevent beetle damage since new beetles fly in.

Reduced risk beetle control consists of collecting beetles (7 PM at night seems to be a good time) and placing them in a bucket of soapy water or using plant covers to exclude them where feasible. Fine mesh nets can be placed over roses. Two organic sprays, Neem and Pyola, can protect plants but usually not beyond 3-7 days.

Chemically, adults can be controlled with pyrethroid products like Tempo and Bayer Advanced Lawn & Garden Multi-Insect Killer (cyfluthrin) or Ortho Bug B Gone (bifenthrin). Sevin (carbaryl) is another option. These all provide about 2 weeks of protection for foliage and flowers after thorough treatment. 

Because insecticides affect pollinators, try to spray in the evening only and after trees have finished blooming. Follow label instructions explicitly to avoid harming pollinators and damaging plants.

The grub stage are often kept in check by natural enemies like ants, parasitoid wasps, and disease. If they become a problem, insecticides, applied at the right time of year, can be helpful in controlling them. GrubEx (active ingredient: chlorantraniliprole; Scott’s Turf) applied in mid-June to mid-July can decrease populations of young white grubs. If dealing with an advanced infestation later in the season, products like Bayer Advanced Complete Insect Killer for Soil and Turf (active ingredient: imidacloprid; Bayer) can control > 50% of the grubs. 

Japanese Beetles, Nebraska Extension
Dealing with Japanese Beetles, Nebraska Extension

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3. Fire blightSave pruning for dormant season, unless conditions below exist

This bacterial disease that can kill branches and entire plants. The bacteria commonly overwinters in branch cankers. It is spread by insects, windblown rain or on pruning tools during spring. It attacks plants in the rose family including pears, apples, crabapple, quince, and cotoneaster. Symptoms include dead branches, water-soaked blossoms, light brown to blackened leaves, discolored and sunken bark, black "shepherd's crook" twigs and branch ends, and dried fruits.

Fire blight is difficult to control. It is best to avoid fire blight by planting resistant cultivars. Management includes using cultural practices that promote healthy plants, pruning to remove cankered branches, and preventive chemical sprays beginning in spring.

Pruning is best done during the dormant season when the bacteria is not active. Only remove fire blight infected branches in summer if the following situations apply. 

  • fire blight canker infections in young vigorous trees that may girdle the main stem or branches
  • infections are in trees with dwarfing rootstocks that are highly susceptible to infection, such as M.9 or M.26
  • older trees with limited infections that can easily be removed
  • it is a dry, sunny day when there is no chance of rain for 48 hours

When pruning always cut 8 to 12 inches below a canker, if possible; and clean pruning equipment between each cut to avoid spreading infections throughout the tree. Dip tools in a 10% bleach solution or ethyl alcohol. All pruned branches and twigs should be removed from the site.

Chemical controls are best applied during blooming. Copper-based products and bactericides (e.g. Streptomycin) can provide control when applied when 25 percent of flowers are open and temperatures are between 60 and 75 degrees F. Applications are repeated at 4-5 day intervals until petal drop if temperatures remain warm and moist. A minimum of two applications is needed.

Fire Blight, University of Missouri Extension  

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4. Storm damaged treesNebraska Forest Service resources helpful in managing damaged trees

Refer to the Nebraska Forest Service series for help in dealing with storm damaged trees. This series contains 10 short publications with the following titles:

  • Immediate Care for Storm-Damaged Trees
  • How to Select an Arborist or Tree Service
  • Pruning Storm Damaged Trees
  • Large Tree Pruning & Care
  • Don’t Top Trees
  • Recognizing & Correcting Tree Hazards
  • Tree Selection & Placement
  • Tree Planting
  • Care of Newly Planted Trees
  • Storm Damage Resources

 Nebraska Forest Service Storm Damage Series  

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5. Spring herbicide applications & spray drift

early hot temperatures, low humidity and high winds create "perfect storm" for herbicide drift

Drift occurs in two ways, particle or vapor. Particle drift occurs when small spray droplets travel long distances during periods of high wind and blow droplets from the targeted site. To avoid this, use larger spray droplets with low pressure, and apply herbicides only when wind speed is low.

Vapor drift occurs when products volatilize or evaporate and move off the application site. The volatility of some products increases as temperatures rise into the upper 80s and 90s. The product label will provide information on when it's not safe to apply the product based on certain temperatures. The highest potential for drift is when it's hot and dry.

5 Things to Know to Avoid Herbicide Drift, Nebraska Extension

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6. White grub controlTime to apply preventive grub control products

Effective white grub control depends on proper timing of the application and moving the insecticide down to the root zone where grubs are feeding. Most of the preventively-applied insecticides including chlorantraniliprole (Acelepryn), clothianidin (Arena), imidacloprid (Merit), and thiamethoxam (Meridian) are systemic in nature and will be taken up by the plant and translocated to the root zone where the grubs are active. These products are typically applied from late May up until July 1, before egg hatch. Curative insecticides such as carbaryl (Sevin) or trichlorfon (Dylox) are applied after egg hatch, typically sometime from mid-August to mid-September. These products must be watered in for acceptable control. Moving the insecticide into the root zone involves applying ½ inch of water immediately after application.

White Grub Management, Turf iNfo from Nebraska Extension

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7. Heat and water stressCommon symptoms of heat & dry conditions on turf, ornamentals, woody plants

According to a June 1 report from Al Dutcher, Associate Nebraska State Climatologist, Nebraska experienced the second coldest April on record dating back to 1895. But conditions changed in May with temperatures poised to rank in the top 10 warmest years on record. May average temperatures haven't been so warm since 2012. In addition, precipitation was significantly below normal from mid April through June 1 across most of east central, south central and southeast Nebraska, with concern building for potential worsening of drought conditions this summer. Fortunately many locations through the state have received rain during the week of June 18-22nd, which will help moderate dry conditions for a while. But as of June 21, our state's southeast corner is still listed as either abnormally dry or moderate drought conditions. 

In turf, landscapes and gardens common affects of heat and/or dry conditions include those below. 

  • leaf scorch on ornamentals, especially shade plants getting too much sun
  • blossom drop/flower abortion in vegetable gardens caused by poor pollination due to high temperatures, low humidity or plant stress; home gardeners experience poor fruit set during summer periods when daytime temperatures are above 90°F
  • extended drought will result in Kentucky bluegrass turning brown as it goes dormant; even in the dormant state 1/4 inch of water every 4-5 weeks is required to keep the grass from dying
  • severe drought conditions may cause tall fescue lawns to begin browning indicating the plants are dying; tall fescue does not have the ability to go dormant like Kentucky bluegrass

Drought stress is often slower to appear in woody plants, but can have long-term consequences. Drought stressed trees are more susceptible to secondary attack by insect pests and disease problems, such as borers and canker diseases, which can cause tree death.

One common symptom of drought stress in woody plants is leaf scorch - a uniform yellowing or browning of leaf edges on broadleaf plants or the tips of evergreen needles. However, even trees that don't exhibit leaf scorch can be experiencing drought stress, and once a tree is stressed it takes 3-5 years of normal moisture conditions before the tree recovers its full vigor. Healthy trees, receiving adequate water, are much more resistant to pest problems.

For more information on watering, refer to last month's Hort Update - Dry spring & watering recommendations. 

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8. Strawberry root weevilsOccasional home invader; Chemical control not necessary

Weevils are pear-shaped beetles with a conspicous snout. Strawberry root weevils (SRW) are about 1/4 inch long, black or dark brown, six legs and do not fly. Immature, grub-like larvae feed on the roots of strawberries, evergreens (Arborvitae, spruce, yew), brambles (raspberry, blackberry), grapes and other plants. Adult beetles may find their way indoors in search of water from the end of June through August. Homeowners often find them in sinks, bathtubs, or similar places. 

Exclusion is the best control. Caulk foundation cracks, seal gaps around doors and windows. Chemical control is not necessary. 

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9. Correct use of mulch

avoid common problems with mulch application

The use of organic mulch, like wood chips, in perennial flower beds, shrub borders and around trees is an excellent maintenance practice, but often overdone.

Using too deep of a mulch layer or piling mulch against plant stems are common mistakes. Both can harm landscape plants. If too deep, some roots grow in mulch instead of soil and die from drying or heat. Deep mulch layers reduce oxygen levels in soil which weakens or kills roots. Plant roots need soil oxygen as much as soil water.

Mulch piled against plant stems holds moisture against stems and leads to rot or decay. It provides a haven for insects or small rodents to feed on plants.

During spring planting, the mulch in many beds and trees is replenished. When doing so, use it correctly. Mulch, like wood chips, is used correctly if placed on moist soil, kept to a depth of about three inches, and not piled against plant stems. Also monitor mulch for matting. Some mulches, like heavily shredded mulch, will mat down and act like roof thatch, repelling moisture and oxygen. Rake to fluff mulch as needed.

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10. Mesotrione updateOverapplication will cause grass seedlings and existing turf leaves to turn white 

In the April 2018 Hort Update, we discussed mesotrione most commonly sold as Tenacity by Syngenta and available to homeowners as  Scotts Turf Builder Starter Food for New Grass. It's a newer herbicide that can be used on cool season grass and buffalograss lawns to control both broadleaf and grassy weeds. 

Mesotrione is a group 27 herbicide, killing weeds by disrupting pigment development.  It's mode of action is through the inhibition of the HPPD enzyme (p-hydroxyphenylpyruvate dioxygenase) which is involved in carotenoid pigment synthesis. These pigments protect chlorophyll from decomposition by sunlight. A sign mesotrione is working following application, is seen when affected weeds lose their green color, created in plants through the presence of chlorophyll, turn white and die. 

Overapplication of mesotrione causes these same symptoms to appear in desirable turfgrasses. Turfgrasses will recover and turn green again, but this is an important reminder to use the proper herbicide rate to avoid cosmetic damage and concern by homeowners. Tenacity is applied at very low rates of product per acre, so take care to measure and apply the product accurately. Homeowners using granular products many cause overapplication symptoms to appear if they hand-apply Scotts Turf Builder Starter Food for New Grass and exceed the amount of herbicide specified by the label rate.

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11. Phosphorus, nitrogen, algaeNitrogen effects on phosphorus deficiency expression

Phosphorus deficiency is fairly rare in turf unless soil test levels are extremely low. This research project compared nitrogen effects on phosphorus deficiency symptoms.

Read research findings

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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.

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