Rose Rosette Disease

Rose rosette disease is an untreatable rose disease caused by the Rose rosette virus (RRV), and is spread and introduced into the rose during feeding by the rose leaf curl mite (Phyllocoptes fructiplilus). This extremely small eriophyid mite feeds on cell sap of the tender stems and leaf petioles. The rose leaf curl mite alone causes little damage while feeding, but if it is a carrier of RRV, symptoms begin to appear in the rose typically within one to three months.

Roses exhibit reddened terminal growth on infected branches, and the stems become thicker and more succulent than those on unaffected parts of the plant. These stems exhibit an abnormally high number of pliable thorns, which may be either green or red. Rose leaves that develop on infected branches are smaller than normal and may be deformed similarly to herbicide injury by 2,4-D. Lateral branches may grow excessively from main stems and create a witch’s broom symptom quite like glyphosate (Roundup™) injury on roses. Flowering is reduced, and the petals may be distorted and fewer in number.

Rose with Rose Rosette Disease showing symptoms of  reddened new growth, thicker stem, excessive thorns, and smaller leaves.
Meg Williamson, Plant Problem Clinic, Clemson University

These symptoms generally become evident in the late spring to early summer and progress during the growing season. Once the rose becomes infected, RRV moves throughout the plant and the entire plant is infectious. By the time symptoms are evident in a rose, it already may have spread to adjacent plants by the movement of the eriophyid mites. Infected plants typically die within a couple of years.

Prevention & Treatment: The wild multiflora rose is very susceptible to the rose rosette disease, so any nearby wild plants should be removed and promptly disposed. Any infected, cultivated roses should be immediately removed, then burned or bagged. Also remove any roots, which might re-sprout later. Do not leave an uprooted infected plant in the garden, as the mites may leave this rose for other nearby plants. Always space rose plants so they do not touch.

Because RRV is systemic within the infected rose plants, grafting asymptomatic stems onto other rose plants will transmit the virus. Pruners used on diseased plants must be disinfested with rubbing alcohol or a dilute bleach solution before being used on uninfected plants, as sap on the pruners is contaminated with the virus.

To reduce the spread of the eriophyid mites from the site of an infected rose, nearby roses can be treated with a bifenthrin spray every two weeks between April and September. This may prevent additional plants from becoming diseased. Examples of products containing bifenthrin are Hi-Yield Bug Blaster Bifenthrin 2.4 Concentrate or Ready-to-Spray, Hi-Yield Bug Blaster II Turf Termite & Ornamental Insect Control Concentrate, and Ortho Bug-B-Gon Max Lawn & Garden Insect Killer Concentrate. Check product labels for the correct active ingredient. Follow label directions for use.

Gardening Talk: Soil Preparation

Begin soil preparation by removing old plant supports, plastic mulches, excessive vegetative residues and other debris from the garden area several weeks before planting to allow the soil to dry out. The amount of plant residue that may be turned under depends on how large the pieces are, how the garden will be turned and how long before the area will be worked.

If there’s no already-prepared-for-planting soil in your backyard, then you should do it yourself. If you know nothing about its quality, you have two options: buying a home testing kit, or sending a sample to your local agricultural extension office. You will get all the necessary data about the soil for low cost, and you’ll get detailed information about the nutrients that the soil needs.

Long cucumber or tomato vines, for example, may be spaded or plowed under but may tangle on the tines of a rototiller. Cover crops and thick mulch or crop residue should be turned under six weeks or more before planting. This will promote decay and reduce nutritional and insect and disease problems in the garden. Adding three pounds of ammonium nitrate per 1000 square feet of soil surface before turning organic materials under will speed decay considerably.
Turning under significant amounts (an inch or more) of plant materials such as compost, organic mulches, leaves or cover crops annually will gradually increase soil organic matter content and improve most garden soils. The moisture-holding capacity will improve, as will the soil structure and nutrient-holding capability. Root penetration will improve on clay soils and soil crusting will be reduced.
Garden soil should not be worked when it is too wet. Pick up a handful of soil and roll it into a ball. If the soil sticks together and does not crumble when dropped, it is too wet to work. Soil worked too wet forms large, hard clods which are difficult to break up and are completely unsuitable for a seedbed.

Soil should be worked to a depth of at least 6 or 7 inches and smoothed before planting. Seed should be planted only in moist, finely aggregated soil. Soils worked into a powdery condition are more likely to crust. Small seed planted in cloddy soil usually dry out and germinate poorly. Garden soil may be worked with farm equipment, a rototiller or spaded with a shovel.
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Pesticides and Vegetable Disease Control

Fungicides can be a great help in preventing diseases when properly applied to the plant foliage. Since fungicides are preventive, they should be applied before the disease occurs, or as soon as the first symptoms of disease appear.

Some vegetable diseases require specific fungicides for their control. An outline of diseases of specific vegetables, disease description, suggested cultural and chemical control and comments follows this section.

Fungicides are available primarily as wet-table powders, dry flowables and dusts, but a few are sold as emulsifiable concentrates, flowables and liquids. Wettable powders (WP) and dry flowable (DF) are formulated in such a manner as to be readily suspendable in water. Dusts (D) should not be mixed in water, but applied directly to the plant. Emulsifiable concentrate (EC) fungicides contain an emulsifying agent that makes them readily suspendable in water. Flowable (F) fungicides are finely ground wettable powders that are suspended in a liquid.

Some soil fungicides are available as granules and are applied in the furrow at planting. Dust and spray fungicides may also be used as in furrow treatments for seedling disease control.

Never attempt to use dust formulations of fungicides in spray solutions. Dusts will not suspend in the spray solution. Wettable powder formulations may appear similar to dusts, but they are formulated to be suspended in spray solutions. Foliar sprays will aid in controlling leaf spots, rusts, mildews, anthracnose and fruit rots. Foliar sprays are not effective against vascular wilts or root rots. Foliar sprays are protectants, because they form a protective layer of fungicide over the surface of the fruit and foliage. Disease agents (bacteria and fungi) that land on these fungicide-coated surfaces are killed or prevented from infecting the plant.

Most fungicides are not effective in inhibiting disease organisms once they have infected a plant. It is imperative that foliar fungicides be applied prior to infection of the plant. A spray schedule should be followed that maintains a protective fungicide layer on the foliage and fruit during favorable infection periods. By carefully monitoring their vegetables, some gardeners can usually delay the first fungicide application until the first sign of disease. Then a 7-14 day spray schedule should be followed. During rainy or humid weather, spray application intervals should be shortened.

Proper pesticide mixing and spraying plays a very important part in achieving disease control. Most home gardeners will find a 1-2 gallon compressed-air sprayer adequate for applying foliar sprays. A nozzle with a cone pattern will provide the most effective coverage of plant foliage. Keep the pressure up to insure small spray particle size and good coverage.

Sprayers should be cleaned and rinsed after each use. Hose-end sprayers are not very effective in applying fungicides to vegetables. Never use the same sprayer for fungicides and insecticides that has been used for herbicides. Residues of certain types of herbicides are very difficult to remove from sprayers. These residues may cause crop injury if a herbicide-contaminated sprayer is used in applying fungicides or insecticides.

Garden Problem Guide

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Symptoms	Possible Causes	Possible Cures
Drying Young Plants	Fertilizer burn	Mix fertilizer thoroughly with soil
	Disease (damping-off)	Treat seed; don't over-water
Stunted plants pale to yellow	Low soil fertility	Soil test for fertilizer recommendations.
	Low soil pH (too acid)	Soil test for lime recommendations.
	Poor soil drainage	Drain and add organic matter.
	Shallow or compacted Soil	Plow deeper.
	Insects or diseases	Identify and use control Measures
	Nematodes	Soil test for treatment recommendations.
Stunted plants  purplish color	Low temperature	Plant at recommended time.
	Lack of phosphorus	Add phosphorus fertilizer.
Holes in leaves	Insects	Identify and use control measures.
	Hail	Be thankful it was not worse.
Spots, molds, darkened areas on leaves and stems	Disease	Identify, spray or dust, use resistant varieties.
	Chemical burn	Use recommended chemical at recommended rate.
	Fertilizer burn	Keep fertilizer off plants.
Wilting plants	Dry soil	Irrigate if possible
	Excess water in soil	Drain.
	Nematodes	Soil test for treatment recommendations.
	Disease	Use resistant varieties if possible.
Weak, spindly plants	Too much shade	Remove shade or move plants to sunny spot.
	Too much water Plants too thick	Seed at recommended rate.
	Too much nitrogen	Avoid excess fertilization
Failure to set fruit	High temperature	Follow recommended planting time.
	Low temperature	Follow recommended planting time.
	Too much nitrogen	Avoid excess fertilization.
	Insects	Identify and use control measures.
Tomato leaf curl	Heavy pruning in hot weather	Don't
	Disease	Identify and use control measures.
Dry brown to black rot on blossom end of tomato	Low soil calcium	Add liming material.
	Extremely dry soil	Irrigate.
Misshapen tomatoes (catfacing)	Cool weather during Blooming	Plant at recommended time.
Abnormal leaves and growth	2, 4-D weed killer	Don't use sprayer that has previously applied 2, 4-D. Don't allow spray to drift to garden.
	Virus disease	Remove infected plants to prevent spreading. Control insects that transmit.