OSU Extension Greene County

The following articles were compiled during the last 7 days by members of the Extension, Nursery, Landscape, Turf (ENLT) team to benefit those who are managing a commercial nursery, garden center, or landscape business or someone who just wants to keep their yard looking good all summer.  Access the BYGL website for additional information on other seasonal topics at: http://bygl.osu.edu

For more pictures and information, click on the article titles.  To contact the authors, click on their names.

Be Alert for Boxwood Leafminer

Authors Joe Boggs

Published on April 12, 2019

Boxwoods with yellow to brown leaves are common this spring throughout Ohio.  Boxwoods with yellow to brown leaves are common this spring throughout Ohio.  Some of the leaf discoloration is due to winter injury with foliage at the tips of branches or on the windward side of plants most heavily affected.

Some discoloration was caused by salt damage either directly with “ice melt” or rock salt inadvertently thrown onto foliage, or indirectly with “salt spray” carried onto foliage from nearby roadways.  Salt damage is sometimes, but not always, concentrated on one side of the plant.

However, a close examination may also reveal the telltale blister-like leaf symptoms caused by the boxwood leafminer (Monarthropalpus flavus).  Leafmines may be found throughout the plants although the highest concentration often occurs on foliage at branch tips.

Gently separating the upper and lower leaf surfaces (the leafminer had already done most of the work!) will reveal the bright yellow leafmining larvae (maggots) of this midge fly wiggling around in their blister mines.  The larvae will complete their development in a few weeks and pupate.  The pupae are also bright yellow at first, but turn orangish-yellow as this stage nears completion.

This non-native midge fly was accidentally introduced into North America from Europe in the early 1900s and is now common throughout Ohio.  Adults emerge at around the same time red horsechestnuts (Aesculus × carnea) and doublefile viburnums (Viburnum plicatum) are in full bloom (440 GDD).  Except for their bright orange abdomens, the adults superficially resemble miniature mosquitoes.

Females use their needle-like ovipositors to insert eggs between the upper and lower leaf surfaces of boxwood leaves.  Each leaf may contain multiple oviposition sites with several eggs per site.  These sites will become individual leafmines producing the blister-like leaf symptoms.

Eggs hatch in early-summer and the resulting larvae spend the remainder of the season consume interior leaf tissue as they develop through the 1st and 2nd instar stages.  Winter is spent as 3rd instar larvae inside the leafmines.  The larvae resume feeding in the spring and develop through a 4th instar stage.

Much of the leaf damage occurs in early spring with the ravenous larvae rapidly expanding their leafmines.  Multiple leafmines in individual leaves may coalesce causing the upper and lower leaf surfaces to delaminate over the entire leaf.  Individual mines may turn reddish-green at this time of the year with heavily mined leaves turning from yellow to orangish-brown causing the leafmining damage to be mistaken for winter injury.

A close examination of the leafmines at this time of the year may reveal small translucent “windowpanes” created by the larvae in the lower leaf surface.  The pupae will wiggle through these weak points to ease the emergence of fragile adults.

This pupal activity is responsible for one of the most unusual features of this midge fly:  reports of hissing, crackling, or rustling sounds coming from heavily infested boxwoods.  I’ve reported on this strange phenomenon in past BYGLs.  So, reports from gardeners or landscapers that they’ve heard boxwoods going snap, crackle, and pop should be taken seriously as the odd sounds are an indicator of a heavy boxwood leafminer infestation.

Damaging boxwood leafminer infestations can be suppressed through applications of neonicotinoids such as imidacloprid (e.g. Merit, Marathon, and generics) or dinotefuran (e.g. Safari or Zylam).  However, applications should be delayed until AFTER boxwoods bloom to protect pollinators.

Boxwood blooms attract a wide range of pollinators; blooming plants can literally buzz with their activity.  Delaying applications until blooms drop will result in some minor miner damage, particularly with the imidacloprid that is taken-up more slowly compared to dinotefuran.  However, this is a small price to pay for protecting pollinators.

You may find recommendations for topical applications of pyrethroid insecticides such as bifenthrin (e.g. Talstar) to target adult leafminer females before they lay eggs.  However, adults typically emerge in Greater Cincinnati while boxwoods are in full bloom, so I no longer recommend this application.

Plant selection provides a more long term solution to the depredations of boxwood leafminer by removing insecticides from the management equation.  A helpful research-based listing of the relative susceptibility of boxwoods to the leafminer was published in 2014 by the American Boxwood Society in their “The Boxwood Bulletin” [see More Information below].

More Information

American Boxwood Society, Boxwood Leafminer Evaluation

http://www.boxwoodsociety.org/uploads/54_1_2014_Summer.pdf#page=9

How To Hire An Arborist

Authors Amy Stone

Published on April 12, 2019

Ohio State University Extension’s Home Yard and Garden FactSheet HYG-1032 has been update and is available online. The OSU FactSheet includes tips for selecting an arborist and resources available to help find local arborists.

An arborist, by definition, is an individual trained in the art and science of planting, caring for, and maintaining individual trees. Arborists are knowledgeable about the needs of trees and are trained and equipped to provide proper tree care. Hiring an arborist is a decision that should not be taken lightly. Proper tree care is an investment that can lead to substantial returns. Well-cared-for trees are attractive and can add considerable value to your property. Poorly maintained trees can be a significant liability. Pruning or removing trees, especially large trees, can be dangerous work. Tree work should be done only by those trained and equipped to work safely in trees (ISA, 2018).

A huge thank you to Cindy Meyer with Warren County Soil and Water Conservation District for her work as a co-author and the photo used in this alert.

More Information

OSU Extension Home Yard and Garden 1032

https://ohioline.osu.edu/factsheet/hyg-1032

Green Tigers Prowling Forest Trails

Authors Joe Boggs

Published on April 10, 2019

I spotted one of my favorite forest dwellers during a walk in the woods yesterday:  six-spotted tiger beetles (Cicindela sexguttata).  The beetles have a curious affinity for hanging out on woodland trails and they can certainly liven up a hike.

The beetles are well-named because these tiny “tigers” hunt, kill, and eat other insects.  The overall color of these shiny beetles varies from deep emerald green to slightly bluish-green depending on the angle of the light.  Six white spots are arranged along the trailing edge of the wing covers, three spots per side.  The spots are small and sometimes obscured by light bouncing off their highly reflective shiny bodies.

The beetles have bulging black eyes (the better to see you with, my dear!) that makes them look like they’re wearing goggles.  The beetles are agile flyers and their excellent eyesight coupled with long legs which gives them swift speed can make getting a close look difficult.

However, a close examination of this ferocious predator will reveal powerful sickle-shaped mandibles that are used to grab and dispatch luckless arthropod prey; a trait that is shared with other tiger beetles (family Carabidae (Ground Beetles); subfamily Cicindelinae (Tiger Beetles)).  A word of caution:  these carnivores can also use their impressive mandibles to deliver a painful bite to the hand of the overly curious.

Even the larvae of this tiny tiger are predators.  However, instead of actively hunting their prey, they conceal themselves in vertical burrows in the soil to await hapless victims.  When a meat item such as insects or spiders walks past, the tiger larva springs forth like a jack-in-the-box to grab dinner with their powerful mandibles.

The bottom line is that six-spotted tiger beetles are highly effective and important predators throughout their life cycle.  So, keep your eyes peeled for and hands away from these tiny tigers prowling our woodland trails … and don’t kill them since they are good guys!

Magnificent Magnolias

Authors Thomas deHaas

Published on April 9, 2019

Magnolias come in a range of flower colors and sizes.

The two most common in the landscape are Star Magnolia Magnolia stellata, which has a white flower, and Saucer Magnolia Magnolia soulangiana, which has a pale purple flower.

Many more cultivated varieties exist which include a yellow, Butterflies Magnolia Magnolia x. ‘Butterflies”, Magnolia x. loebneri ‘Leonard Messel’,

Magnolias can grow as a single stem tree form, which can reach 30 feet, or a small specimen tree that can be kept at 10 feet through pruning. Magnolias also come in a multi-stemmed small tree or shrub form.

The magnolias as a group are free from cultural problems except for an occasional outbreak of magnolia scale.

The one drawback as a group is because they flower so early; they can occasionally be burned by a frost, which will damage the flowers. But the solution is look to the ‘girl’ hybrids which bloom later:

By using varieties that bloom later, they tend be less susceptible to frost damage.

Take a look……………Magnolias are ‘MAGNIFICENT’

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