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Plant health sherrie Smith r issue 5, April 6, 2016 icky Corder

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Department of Plant Pathology


Sherrie Smith

Issue 5, April 6, 2016

icky Corder CLINIC NEWS

This bulletin from the Cooperative Extension Plant Health Clinic (Plant Disease Clinic) is an electronic update about diseases and other problems observed in our lab each month. Input from everybody interested in plants is welcome and appreciated.

Rose Rosette Virus (RRV) kills roses and can spread from rose to rose in the landscape. This virus is passed to roses by the the Wooly Rose mite, Phyllocoptes fructiphilus. These tiny mites are only ¼ the size of spider mites. Twenty of them can fit on the head of a pin. They are easily carrried by wind to roses in the garden. Symptoms are thickened, succulent stems, often with abnormal red color of foliage and stems. An affected shoot may elongate rapidly. Other symptoms are shortened internodes, stems with an abnormal amount of pliable thorns, distorted or dwarfed leaves, deformed buds and flowers, abnormal flower color, reduced winter hardiness, spiral cane growth, and witch’s broom. When a rose is diagnosed with this disease, it should be removed from the planting immediately. It is a good idea to try to kill the mites before removing the rose to prevent shaking them off onto nearby roses. Unlike spider mites, many common insecticides kill these tiny mites. Virus is not curable.

Wooly Rose Mite-Phyllocoptes fructiphilus

Photograph courtesy of USDA Agricultural Research Services

Rose Rosette Virus-(RRV)

Sarah Witaker University of Arkansas Cooperative Extension

Rose Rosette Virus-(RRV)

Sarah Witaker University of Arkansas Cooperative Extension

Yucca Brown spot- Coniothyrium concentricum
rown spot of Yucca is a fungal disease caused by the fungus Coniothyrium concentricum. Brown spot occurs most often after periods of prolonged wet, humid weather. Symptoms begin as tiny, clear spots on older leaves. The spots enlarge, turn yellow, and then brown with a purple to black border. Old lesions can appear nearly black. The lesions are oval to elliptical with black pimples (fruiting bodies of the fungus) in the center of the lesion. Lesions may grow together to blight large sections of the leaves. Control consists of cleaning up diseased foliage, avoiding overhead irrigation, and the use of fungicides. Copper based fungicides and Mancozeb are effective when combined with good cultural control.

Sherrie Smith University of Arkansas Cooperative Extension

Yucca Brown spot- Coniothyrium concentricum

Sherrie Smith University of Arkansas Cooperative Extension

The most common disease of hollyhock is rust, caused by the fungus Puccinia malvacearum. All Malva and hollyhock species are susceptible, with the common Malva weed, Malva rotundifolia serving as a reservoir for the disease. Symptoms are numerous yellow to orange spots on the upper surface of the leaves. The undersides of the leaves become dramatically covered with large orange to brown pustules. Heavily infected plants may also have the pustules on stems and green flower parts. Most of the leaves can be killed when infections are severe. Good sanitation is important in controlling Hollyhock rust. Infected leaves should be removed immediately. In the fall plants should be cut to the ground and burned or otherwise disposed of, along with any leaves left on the ground. Fungicides should be applied early in the spring at new growth. Products containing chlorothalonil such as Daconil, or Mancozeb, or myclobutanil should be applied through early July.

Hollyhock Rust- Puccinia malvacearum

Sherrie Smith University of Arkansas Cooperative Extension

Request for help from Dr. Robbins:
Root knot nematode populations are needed for our Arkansas species study. I am a nematologist in the department of Plant Pathology in Fayetteville. My student and I are trying to amass populations of as many species of Root knot nematode (Meloidogyne sp.) as possible for species identification using molecular techniques. At present no root knot species in Arkansas have been identified using molecular technology. We are interested in receiving populations from home gardens, shrubs, flowers, trees and grasses. For samples we need about a pint of soil and feeder roots in a sealed plastic bag that is plainly identified by plant host, location (City County, physical address, collector and date of collection). Please send samples to us at the follow address:
Dr. Robert Robbins

Cralley-Warren Research Center

2601 N. Young Ave

Fayetteville, AR 72701

Phone 479-575-2555

Fax 479-575-3348


The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, national origin, religion, gender, age, disability, marital or veteran status, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.

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