Zany for Zinnias

Classic old fashion garden favorite. Large beautiful long lasting flowers that attract all the butterflies and hummingbirds. Long lasting for cut flowers and flower arrangements

Zinnia Problems October 30, 2008

Zinnia Problems            

Unfortunately, in our quest for the perfect zinnia, we may face certain problems along the way.  Here is some pratical information on these basic problems.
 
Skinny, Spindly Seedlings Need More Light or Need Pinching
Zinnias need many hours of bright, direct sun to flourish. If they are at all shaded they are forced to stretch to reach the light, causing them to develop thin stems. If you are growing seedlings indoors under lights, adjust the fluorescent lights to remain only 3 or 4 inches above the seedlings as they grow taller. To encourage thick, sturdy stems and compact plant shape, pinch the growing tips off of zinnia seedlings at least twice before the buds begin to form. This causes them to branch and grow denser. Dwarf varieties have naturally denser shapes. See
Starting Plants From Seed and see Seed Starting Supplies and Equipment.

Foliage Curls, Puckers, Turns Yellow Due To Aphids
Aphids are about the size of a pinhead and have soft, pear-shaped bodies. They may be green, brown or pink. They tend to cluster on tender, new growth on zinnia stems and on the undersides of young leaves. They suck juices from plant cells, causing foliage to curl, pucker and turn yellow. Often the leaves and blossoms become stunted. Sometimes ants are visible, crawling along plant stems and foliage, attracted by the presence of the sticky honeydew secreted by aphids as they feed. If aphids are on plant tips, simply pinch them off and discard them in the trash. If they have infested a lot of the foliage, spray them with commercial insecticidal soap according to label instructions. Be sure the soap spray contacts the aphids directly.
Click here for more information on
Dealing with Aphids.

Leaves Spotted, Discolored May Mean Mites
Mites are about 1/50 inch long, barely visible to the unaided eye. Related to spiders, they have four pairs of legs, piercing-sucking mouthparts and very compact bodies. They may be yellow, green, red or brown. They suck juices from the leaf tissues, draining their chlorophyll and injecting them with toxins. Usually their damage is most visible on the upper leaf surfaces of the lowest leaves on the zinnia stem. They are stippled with small yellow dots or red spots. Leaves and adjacent stems are often distorted or swathed in fine webbing. Spray affected leaves in the late afternoon with insecticidal soap according to label instructions. Pull out and throw away any zinnias that are fully infested so that the mites do not spread to other plants. Take care not to transfer them to other plants on your hands or on tools. Click here for more information on Dealing with Mites.

Holes Are Chewed In Leaves And Flowers By Japanese Beetles
Adult Japanese beetles are 1/2 inch long. They have distinctive shiny metallic green and copper-brown wing covers. As larvae (grubs) they are inch long, plump, grayish-white worms with brown heads which lie curled just below the surface of the soil over the winter. They emerge in mid summer as voraciously hungry beetles and cluster on plant foliage. In no time they can skeletonize a leaf so that only its veins remain.

Begin to handpick any beetles as soon as you spot them. Drop them into a jar of soapy water. If they are overwhelming your zinnia planting, spray the beetles, leaves and stems with a pyrethrin/pyrethrum insecticide product as directed on its label. For long term control of chronic Japanese beetle problems, spray your lawn (where they lay their eggs) with a predatory nematode product as directed. These microscopic roundworms are packaged as a powder to be mixed with water. They ride the moisture into the soil and seek out grubs to lay their eggs in, killing them before they mature into beetles.
Click here for more information on Dealing with Japanese Beetles

Leaves And Roots Are Chewed By Various Beetles
Asiatic garden beetle larvae sometimes feed on zinnia leaves and flowers. Adults are velvety chestnut-brown, nearly 1/2 inch long, resembling Japanese beetles. They lay their eggs in the soil at the base of the plants, where the newly hatched grubs eat their roots. Black blister beetles also may attack zinnias. They are cinnamon brown and 1/2 inch long and their larvae also attack plant roots. Control these beetles the same way you deal with Japanese beetles. Be sure to wear gloves if handpicking blister beetles because they can cause blisters on bare skin. There are, as yet, no traps for these beetles. They are less likely to congregate in the numbers that Japanese beetles do.

Pale Spots On Foliage Signal Leafhoppers
Redbanded leafhopper and six-spotted leafhopper may attack zinnias. Leafhoppers are often strikingly colored green, brown or yellow, blunt-profiled bugs. About 1/4 to 1/3 inches long, they are wedge-shaped, holding their wings in a rooflike position above their bodies. They’re very active and move sideways or hop suddenly when disturbed. Nymphs and adults suck juices from leaves, buds, and stems. Some species may spread virus diseases such as aster yellows. Affected leaves are finely mottled with white or yellow spots. They eventually dry up, shrivel and drop off. Plants are weakened. Honeydew from the insects’ feeding may give foliage a glazed appearance and foster growth of sooty mold. Spray insects with insecticidal soap or a pyrethrin/pyrethrum insecticide product as directed on the product label.

White Powder Coating Leaves Is Powdery Mildew
Later in the summer zinnia foliage and flowers are likely to develop an ashy gray coating. This is a fungus disease which develops in hot humid weather. Typically it shows first on the lower leaves, especially in situations where plants grow close together so air circulation is reduced and humidity builds. Many yardeners simply ignore it, as it does not harm the plant. It just looks unattractive. Control the spread of the mildew by spraying unaffected leaves with garden sulfur fungicide according to label directions. Look for mildew resistant varieties such as ‘Rose Pinwheel’ and plant zinnia seedlings farther apart. Click here for more information on Dealing with Fungal Disease.

Brown Spots, Sores on Flowers Is Caused By Stem Blight
Blight is caused by a fungus that causes small reddish brown spots with gray centers to form on zinnia flowers. Sometimes dark brown cankers form on their stems. Cut off affected flowers and discard them in the trash. Keep the area around the plant clear of weeds and dead plant debris. If blight proves to be a chronic problem in the area, spray healthy zinnias plant surfaces with a garden sulfur fungicide as directed on the label.

Spindly Shoots; Foliage Are Yellowed, Curled By Virus Diseases
Various diseases caused by viruses occasionally attack zinnias. They are usually spread by insects. The plants may show curled, distorted, mottled foliage, they may be stunted or deformed, wilting, turning yellow and then dying. Sometimes flowers are a sickly yellow green or fail to develop at all. There is no cure for plant viruses. However, by controlling insect pests like leafhoppers, transmission of these diseases is reduced. Dig up infected plants and put them in the trash. Do not compost them. Keep the garden area clear of weeds and debris that may harbor infection. To avoid spreading the disease disinfect garden tools by dipping them into a solution of 1 part household bleach to 3 parts hot water.

 
 

 

Zinnia Diseases

Zinnia Diseases

This page will give images and information on some of the diseases that may afflect your zinnias.

wvu.edu

Alteraria leaf blight:

DESCRIPTION: Alternaria is a fungus which causes leaf spotting. Leaf spots progress from older leaves to newer. Spots are circular, target-shaped, and often surrounded by a slight yellow area.  Entire leaves may die and drop from the plant. They may also be found around stem ends on fruits and on stem.

LIFE CYCLE: Alternaria survives in plant debris and may be spread by insects or wind, and by rain/irrigation. Spores germinate in several hours during high humidity conditions. Infection occurs through natural plant openings if water remains on plant tissue for more than a couple of hours. After 2-3 days, first symptoms appear. Optimum temperatures for infection are 60-75° F, high humidity, and low fertility.

Cultural Control: This disease is spread by splashing water and by walking through plants when wet. Keep water off leaves. Water with soaker hoses or drip irrigation. Use 3 – 4 year rotations between susceptible crops. Maintain adequate nitrogen levels. Remove and destroy infected leaves.

Chemical Control: Sulfur and copper can be sprayed when temperatures are between 55 and 85° F and weather is wet, to protect leaves from infection. These “least toxic” options are less effective when overhead irrigation is applied. Missoula County Extension Service

Bacterial Leaf Spot

General Recommendations: Bacteria that cause leaf and flower spots, blights and fruit rots are ever-present in the environment. They survive in diseased plant debris from one year to the next and are transferred to new plants by wind, splashing rain, flowing water, contaminated soil and insects. Since bacteria typically require a wound through which to enter and infect a plant part, anything that can cause injury to plants, including abrasion by blowing sand, hail, pruning cuts and other tools, are commonly associated with bacterial infections. In some cases, natural openings in the leaves (stomata and hydrathodes), flowers (nectaries), and stems (lenticils) can serve as entry points for bacteria. Symptoms of bacterial infections vary with the host. A general symptom that indicates that bacterium is involved is the presence of a yellow halo surrounding a tan to dark brown lesion. This symptom is not always present when bacterial spots and blights occur, but it is a positive indication when present. Systemic infection can also occur when roots are damaged and bacteria enter, traveling up the stem in the water- or nutrient- conducting tissue. Leaf spots and blights result from a more localized infection. Rots occur when fleshy tissue is broken down by the action of rapid bacterial development. The progressive deterioration of rotting tissue typically leads to offensive odors which are also diagnostic of a bacterial infection.

Control of Bacterial Spots, Blights and Rots:

1. Clean up diseased debris. With a few exceptions, bacterial plant pathogens survive from year to year because they are protected in plant debris, including leaves, stem and roots that they infest. Since the ability of bacterial pathogens to move from place to place is limited, eliminating diseased debris is a primary factor in reducing the incidence of disease. This debris should be removed from the garden and buried or discarded. In addition, turning the soil over to bury any debris that cannot be picked up is also an important step in reducing the chance of disease spread. Buried debris will eventually decompose and decrease the viable population of bacteria. Composting infested plant material is not advised.

2. Remove infested plant parts. Bacterial infections, discovered during the growing season, should be removed from the plant. Use clean tools as the use of contaminated tools can exacerbate disease spread. Disinfect tools between cuts by dipping them in rubbing alcohol or a solution of 1 part bleach to 4 parts water. When finished, clean the tools and wipe with an oiled rag to lubricate the parts and discourage rust. Avoid extensive pruning during wet or humid weather when the bacteria can be easily transmitted to and enter wounds. When seeking to reduce the spread of bacterial diseases, such as fireblight, Mid summer or fall pruning is preferred to spring pruning. An occasional affected branch on an otherwise clean plant can be pruned almost anytime. Prune 6 -12 inches behind the affected area.

3. Mulch. Since infested debris must be exposed to splashing rain in order for bacteria to be moved to a new infection site covering the soil around the plant with a layer of leaf mold or compost which buries the debris will help to prevent the spread of bacteria to new plants. Mulch also buffers the soil from extreme moisture loss, reducing the amount of stress during drought conditions.

4. Avoid overhead watering. Splashing rain or water is the primary vehicle that transfers bacterial pathogens around a plant or to a new host plant. Reducing the amount of overhead watering lessens the chances that the bacterial inoculum will be spread both from plant part to plant part and from the soil, where infested debris may reside, to the plant.

5. Rotate crops. Since bacteria populations tend to build up on diseased debris if the same plants are grown in the identical location year after year rotate unrelated vegetable and flowers in and out of a garden planting site each year.

6. Apply a bactericide. Except for copper and streptomycin sprays, which can not be used on all plants, there are few materials available that are effective in controlling bacterial diseases. And, even these bactericides provide limited insurance when a plant has open wounds and are ineffective after infection has occurred. Consequently, disease prevention is the most important initial step.

7. Use clean seed. Some bacterial pathogens can be introduced via seed where they reside either as contaminants on the outside of the seed coat or in wounds. Discard shriveled and discolored seed. Seed treatments have limited value.

8. Select resistant cultivars. Resistance to bacterial diseases is a common goal of vegetable and herbaceous plant breeders. Always select resistant cultivars when they are available, especially when growing plants in humid environments.

Kemper Center

Powdery mildew

Powdery mildew is one of the most widespread and easily recognized plant diseases. Powdery mildews are most severe when the weather is warm and dry, and they affect virtually all kinds of plants: cereals and grasses, vegetables, flowers, weeds, shrubs, fruit trees, and broad-leaved shade and forest trees. Many plants have been developed to be resistant to or tolerant of powdery mildew. Succulent tissue is the most susceptible to infection.

Description:

Even though there are several types of powdery mildew fungi, they all produce similar symptoms on plants. Powdery mildews are characterized by spots or patches of white to grayish, talcum powder-like growth. Tiny, pinhead-sized, spherical fruiting structures–first white, then yellow-brown and finally black–may be present singly or in a group. These are the cleistothecia or overwintering bodies of the fungus. The disease is most commonly observed on the upper side of the leaves. It also affects the bottom sides of leaves, young stems, buds, flowers and young fruit. Infected leaves may become distorted, turn yellow with small patches of green, and fall prematurely. Infected buds may fail to open.

Damage:

The severity of the disease depends on many factors: variety of the host plant, age and condition of the plant and weather conditions during the growing season. Powdery mildews are severe in warm, dry weather because, unlike most fungi, powdery mildew require a wet leaf surface for infection to occur. However, the relative humidity of the air does need to be high for spore germination. Therefore, the disease is common in crowded plantings where air circulation is poor and in damp, shaded areas. Incidence of infection increases as relative humidity rises to 90 percent, but it does not occur when leaf surfaces are wet (e.g., in a rain shower). Young, succulent growth is usually more susceptible than older plant tissues. Powdery mildew can seriously impact yield on flowering crops such as squash, pumpkins, cyclamen and reiger begonia, but on other plants such as lilac and oak, the mildew is unsightly but does not severely harm the plant.

Life Cycle:

Powdery mildews are host specific: they cannot survive without the proper host plant. For example, the species Uncinula necator, which causes powdery mildew on grape and linden, does not attack lilac. Similarly, Microsphaea alni affects elm, catalpa, lilac and oak but not turfgrass.

Powdery mildews produce mycelium (fungal threads) that grow only on the surface of the plant. They never invade the tissues themselves. The fungi feed by sending haustoria, or root-like structures, into the epidermal (top) cells of the plant. The fungi overwinter on plant debris as cleistothecia or mycelium. In the spring, the cleistothecia produce spores that are moved to susceptible host tissue by splashing raindrops, wind or insects.

Control:

Several practices will reduce or prevent powdery mildews. Many plants, such as roses, vegetables and Kentucky bluegrass, are developed to be resistant or tolerant to powdery mildew. Use resistant varieties whenever possible.

Once the disease becomes a problem:

•  Avoid late-summer applications of nitrogen fertilizer to limit the production of succulent tissue (which is more susceptible to infection).
• Avoid overhead watering to help reduce the relative humidity or water in the early morning to let the tissue dry as soon as possible.
• Remove and destroy all infected plant parts (leaves, etc.). For infected vegetables and other annuals, remove as much of the plant and its debris in the fall. This decreases the ability of the fungus to survive the winter. Do not compost infected plant debris. Temperatures often are not hot enough to kill the fungus.
• Selectively prune overcrowded plant material to help increase air circulation. This helps reduce relative humidity and infection.
• An alternative nontoxic control for mildew is baking soda combined with a lightweight horticultural oil. Researchers at the University of Rhode Island have confirmed that a combination of 1 tablespoon baking soda plus 2.5 tablespoons oil in 1 gallon of water is effective against powdery mildew on roses. Use of this combination on other crops is still experimental.

 

 

uri.edu

 

Zinnias – Part Three

Zinnias – Part Three

Zinnias are good for edgings, massed in borders or beds, or the taller varieties as background plants. Many varieties make excellent cut flowers and the smaller varieties are suitable for container plantings. Most varieties begin to bloom when still very small and continue until frost. Zinnia flowers are also attractive to many species of butterflies.

Zinnias can be started from seed, either indoors 4 to 6 weeks before the last frost, or directly in the garden when the soil has warmed sufficiently. You can also purchase zinnias as bedding plants, although you may not have as many choices of cultivars. Plant zinnia seedlings outdoors only after the danger of frost is past as young plants are susceptible to chilling cold. They will not grow substantially until temperatures are above 50 degrees. 

Zinnias are one of the easier annuals to start from seeds. Germination takes 5-7 days. I’ve been very successful in growing plants when seeded individually in cells of seed-starting trays or when transplanted from a group of seedlings in a single cell – despite warnings in many publications that zinnias resent being disturbed and should only be seeded in place or grown in peat pots. When transplanting, wait until the first true leaf is emerging. Separate the roots as carefully as possible and place the seedlings into their new cells as deep as possible, up to the first set of leaves. Select  appropriately sized tray cells depending on the predicted size of your cultivars. Tall varieties grow quickly and may outgrow their container before it’s time to plant outside!

Zinnias do best in full sun in fertile, well-drained soil, so amend your site first if necessary, and fertilize twice monthly for optimum bloom. When planting in the garden, space the plants 4 to 24 inches apart according to variety – whatever their height will be at maturity. For cut flowers, however, I crowd my plants in their raised bed in the cutting garden to encourage longer stems. To produce bushier plants, pinch the tops out of young plants when they are 4-6 inches high (but some varieties have been bred to be compact). Remove faded blossoms to keep them producing. Plants should be kept well-watered. 

Zinnias have few insect pests. Aphids can be controlled with sprays of insecticidal soap or synthetic insecticides, or by releasing predaceous green lacewing larvae. Naturally-occurring predators and parasitoids may also decimate aphid colonies. Feeding by four-lined plant bug causes small, round, brown sunken spots on the leaves. This insect generally only causes sporadic damage, and no good controls are available. Spider mites are generally only a problem in hot, dry weather. Their feeding causes the foliage to become bronzed or stippled. Insecticidal soap or miticides can be used to suppress their populations.

Powdery mildew is the most significant disease of zinnias that are not resistant to the fungus. It is particularly a problem late in the season when white to grayish powdery growth appears on the leaves. The fungus can be controlled with applications of fungicides (chlorothalonil or benomyl). Planting zinnias far enough apart to provide good air circulation will help reduce or delay development of disease. If you have persistent problems with powdery mildew, try to plant resistant varieties.

Other diseases include blight, or alternaria leaf spot, which starts as reddish brown spots with graying centers. Eventually dark brown cankers form on the stems and flowers become spotted or completely blighted.  Bacterial leaf spot also causes reddish brown spots, but these are angular and only on the leaves. This disease can cause plants to die out by mid-August.

Susan Mahr, Department of Horticulture, University of Wisconsin – Madison

Zinnias

Wisconsin EDU