Plant and Insect Diagnostic Clinic Update – May 10, 2019

It's plant sale time — we were all looking forward to it! As you shop for plants remember “an ounce of prevention is worth a pound of cure.” Select the right plants for the location and carefully inspect plants for disease or pests prior to purchase. For more tips to get a good start to the garden season, see this 2-page publication: Integrated Pest Management for Home Gardens and Landscapes

Boxwood

We received several inquiries that show boxwood affected by winter injury. Yews are a phenomenal alternative for boxwood in Iowa. To learn about common boxwood problems, see this article discussing boxwood blight look-alikes article. If you have boxwood in your garden, remember it's essential to check them for boxwood blight, as the fungal pathogen has been moving to neighboring states, and last holiday season it moved on holiday wreaths.

If you are seeing, defoliation in boxwood, and suspect boxwood blight may be involved, consider sending our clinic a sample, we will perform a yes or no assessment free of charge.

Junipers

If your junipers are looking unsightly, there may be several causes, including winter injury, various fungi causing blight, different fungi causing cankers on the wood, or pathogens causing roots rots.

A picture illustrating the symptoms of blight in Juniper branches
A picture illustrating the symptoms of Kabatina blight in Juniper branches.

We recommend you observe the damage (compare with the description on the table below) and monitor new growth and keep note if it improves or worsens. If you are considering pruning them, consider the pruning recommendations in the publication Pruning Trees: Shade, Flowering and conifers. For more information see the publication Juniper Diseases.

Table 1. Timing, symptoms, and management of juniper diseases

Disease Characteristics

Kabatina Tip Blight

Phomopsis Tip Blight

Cercospora Needle Blight

Cedar Rusts

Botryosphaeria Canker

Seiridium Canker

Symptoms

February-May; tip dieback; gray lesion at base of shoot

May-September; tip dieback, gray lesions at base of shoot

August-May; inner needles die and drop; fuzzy black fruiting structures on needles

Active orange, gelatinous galls in April and May

Symptoms all year; branch cankers and dieback; tree mortality

Symptoms all year; branch cankers and dieback; tree mortality

Infection Period

September-November

May-September

June-July

July-September

May-June

Unknown

Cultural Control

Prune out dead tips; provide good air movement by proper plant spacing

Prune out dead tips; provide good air movement by proper plant spacing

Avoid planting Rocky Mountain Juniper; promote good air circulation

Remove galls; eradicate rosaceous hosts; resistant cultivars

Remove diseased branches; avoid planting Rocky Mountain Juniper

Remove diseased branches; more common on arborvitae

Spruce

If concerned with needle casts on spruce, see our articles Rhizosphaera Needle Cast and Stigmina Needle Cast with management recommendations.

Lawns 

In this cool and wet spring, most gardeners are concerned about moss on their lawns. See the current article Removing Moss from Lawns.

We have received photos and samples of tall fescues patches in lawns. Consider the article Tall Fescue: A Low-Maintenance Alternative to Kentucky Bluegrass.

 

A picture illustrating the appearance of tall fescue samples
A picture illustrating the appearance of tall fescue samples

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Lina Rodriguez Salamanca Extension Plant Pathologist and Diagnostician

Dr. Lina Rodriguez-Salamanca is an extension plant pathologist and diagnostician with the Iowa State University Plant and Insect Diagnostic Clinic  (clinic.ipm.iastate.edu), a member of the National Plant Diagnostic Network (NPDN,&nbsp...

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 10, 2019. The information contained within may not be the most current and accurate depending on when it is accessed.