Vinca leaves turning yellow

vinca.cora.deep.lavender.jpg

A basket of well drained vinca Cora Deep Lavender — what healthy vinca flowers should look like.

(Kurt Reynolds/Goldsmith Seeds)

Q: I planted 24 annual vinca flowers, and the leaves have turned yellow. The flowering is very sparse, if any at all. Do you think they rotted from the rain in early June? Some have more normal color with new growth and a few flower buds. Do you think these will be OK? For the ones looking bad, should I pull them and replant new vinca? Or is there a chance there’s a disease in the soil that will kill new vinca, too? In that case, is there something else I should plant that doesn’t get disease?

A: That could be yellowing and rotting from the cool start to spring – especially if the site got soggy at all during the dumpings we had in early June.

Vinca like it hot and dry. They don’t like to go out in the garden too early in spring, and they don’t even like it too cool under greenhouse conditions. I read once that vinca grown under too-cool greenhouse conditions never really do recover, even once out in the garden in hot, dry weather.

Wet soil also goes hand in hand with soil disease, though. And vinca are prone to at least three wet-soil-related fungal diseases – phytophthora, botrytis and rhizoctonia. They can also get aster yellows, which is manifested by the same kind of yellowing leaves that result from rotting in soggy soil and from cold weather.

My guess is that if we get some consistently warm and dry weather, your OK vinca might improve and go on to have a decent season – although not like they should.

The sad ones are likely goners. You might as well yank those. To be on the safe side, I’d assume there’s one of the vinca pathogens in the soil and avoid replanting with new vinca.

Most other annuals aren’t going to be affected. Options for sun include petunias, zinnias, marigolds, angelonia, dusty miller, euphorbia, geraniums and celosia.

It’s always a good idea to work compost into the soil before replanting anything. That way you’re constantly improving the soil, improving drainage and adding organic matter and nutrition that will help any annual thrive.

Some vinca varieties do better than others and are also more disease resistant. The Cora® series is touted as being the most disease resistant, and most colors of it have tested out well at Penn State’s flower trials.

The Titan® and ‘Nirvana’ series also have done very well in Penn State’s trials.

If you want to nail down whether you’ve really got a disease in your soil or whether it was just plain rotting from excess moisture, you can send off a few of your sad vincas to Penn State’s disease lab. The lab offers free disease testing and diagnosis for Pennsylvania homeowners.

Don’t Let Leaf Spot Spoil Your Vincas

Yan Chen and Allen Owings

Annual vinca, also referred to as periwinkle by many home gardeners and industry professionals, is one of the best-selling bedding plants in the Southeastern United States. It is adaptive to summer heat, sand and silt-based soils, acid soils and low rainfall. Once established in the landscape, vinca provides season-long color with nonstop bloom performance. A wide variety of colors and sizes is available for landscape use.

The vinca is not without its problems, however. During the spring months, vinca is susceptible to root and stem rot. Another major concern is a disease called Alternaria leaf spot. These leaf spots are prevalent in the late summer and fall months and can sometimes be observed in new plantings. Individual Alternaria leaf spots are tan to black, pinhead to penny-sized lesions. The spots develop on the leaves starting at bottom of the stems and progressing to the top. Infected leaves will turn yellow and fall off. A severe infection can strip the stems and render the planting unattractive. Heat and humidity in late summer provide ideal conditions for leaf spot infection. Effective control requires frequent fungicide applications that are expensive and may pose negative environmental impact. Other factors that may affect disease incidence include planting techniques and variety selections.
A field study conducted in 2005 and repeated in 2006 at the LSU AgCenter’s Hammond Research Station investigated how these factors would affect the development of Alternaria leaf spots. Four-inch pots of 6-week-old vinca plants were planted on April 1 and May 1 in a landscape bed mulched with pine bark and irrigated. Disease severity was assessed in June, July and August.
Disease-resistant Varieties
Vinca varieties can be categorized as open-pollinated upright, F1 hybrid upright, open-pollinated trailing, and cuttingpropagated. In the Hammond study, the scientists compared varieties Cooler Hot Rose (open-pollinated), Titan Rose (F1) and trailing vinca Mediterranean Lilac (open-pollinated) with Nirvana Rose and Nirvana Red, both of which are cuttingpropagated.
The open-pollinated Cooler Hot Rose had the least leaf spot infection. Both Nirvana varieties were as susceptible as the hybrid Titan Rose. The trailing Mediterranean Lilac was the most susceptible of all varieties grown. Because leaf spots are transmitted by raindrop splashes, trailing varieties are infected more easily than upright varieties. Based on these results, the classic open-pollinated vinca varieties are relatively resistant to Alternaria leaf spots.
Planting Late
As a warm-season plant, vinca has a wide window for planting and can be planted from April to June. Many landscapers like to plant in early April to get the color effect as soon as possible in the spring. Results indicated that planting late (May 1) significantly reduced the amount of Alternaria leaf spots over an April 1 planting date. Plants planted in May were still acceptable in August, while the plants planted in April needed to be removed. Because both planting times gave about 14 weeks of blooms, landscape professionals can choose planting date to meet their specific time frame for color display.
Fertilize Wisely
Though extremely adaptive to poor soil in their native habitat, newer vinca varieties will show nutrient deficiency symptoms when left unfertilized after planting. In the Hammond study, the trailing vinca Mediterranean Lilac performed better with less nitrogen than the other varieties. A complete formula controlled-release fertilizer such as 13-13-13 (N-P-K) at 0.5 pound nitrogen per 1,000 square feet is sufficient for trailing varieties for most soils. For upright varieties, the recommendation is 1 pound nitrogen per 1,000 square feet. Higher fertilizer rates (4 pounds of nitrogen per 1,000 square feet) did not improve plant quality but encouraged the development of disease with excessive lush growth.

We also evaluated the effects of Aliette T&O fungicide as a preventive spray applied 1) at planting, 2) at planting and after leaf spots were first observed, or 3) every four weeks over the season. Applying Aliette fungicide every four weeks only gave a slight improvement in plant quality, while applying it at planting or at disease observation did not make any difference in how much leaf spot occurred.
Based on these findings, leaf spot lesions can be reduced with the use of less susceptible open-pollinated and upright varieties combined with the proper level of fertilizer. A fertilizer rate of 1 pound nitrogen per 1,000 square feet should be sufficient for vinca planted in most landscape soils. Planting later in the spring (May 1) will delay disease development and delay the need to replace the planting into August.
(This article was published in the winter 2007 issue of Louisiana Agriculture.)

Why are some of my vincas dying, but not others?

While Kathy Huber is on vacation, we’re publishing online a question from the archives:

Q: I am having a problem with my deep-purple-pink-colored vincas. In May, I planted some white vincas along with the deep-purple-pink variety. Two weeks later, I noticed that the pink ones were drying up and had died, but the white ones in the same flower bed were fine.

I bought some more pink plants from a different garden shop and planted them the last week in May. Recently, these, too, are beginning to die, but the white ones are fine. Do you have any idea what could be causing this?

I planted the same plants at the other end of the flower bed and both pink and white varieties are doing fine. — K.W., Houston

A: Many have experienced your dilemma. Vincas, or periwinkles, can be infected with a fungal disease called aerial phytophthora. The disease spreads when the fungal spores in the soil are splashed on the plants when you water or when it rains. Some varieties seem more prone to this common fungus than others.

Symptoms of aerial phytophthora include dull, gray, shriveled foliage and deterioration of the upper stems. Symptoms develop quickly – especially during rainy weather. You may detect a brown, sunken lesion where the petioles are attached to the stems. When these spots develop, the stem collapses. If rains or overwatering continues, the fungus can spread to the base of the plant and it can die.

Pull and discard (not in the compost pile) infected plants. To discourage future outbreaks, wait until the soil temperature is fairly hot to plant, perhaps early June. Mulch to prevent splash. Water the soil rather than the plants. Drip irrigation is ideal.

Vincas also may fall victim to pythium root and stem rot, characterized by lesions on stems and roots. Symptoms develop quickly, and infected plants soon die.

Avoid overwatering.

Yellow Leaves on Vincas

Sometimes Vinca can suffer from bacterial diseases such as botrytis that are practically undetectable when they’re in packs at the garden center. Weakened, they stress easily when transplanted into the garden, and the yellowing leaves are a common symptom. However, if the weather is warm and dry, the plants can often grow right through it and hardly show any symptoms. (I’m guessing you’ve got warm weather there in Tennessee.) On the other hand, if the weather is cool and rainy, yellowing leaves on a disease-weakened Vinca is almost guaranteed.

If you think a disease and weather combination might be your problem, hope for a warm, drier spell. Water only when the soil is dry at least an inch below the mulch. Some of the yellowing plants will continue to decline and die; you may have to replace them. The only other possibility for yellowing leaves would be fertilizer burn, but that’s unlikely. You’d notice the yellowing and then browning at the leaf edges and tips first, not just an even yellowing over the whole leaf.

any idea why vinca flowers are turning yellow we have several locations that…

If too much water was causing the yellowing, I would expect that most of the planting would be affected. From the photo, the yellow leaves seem to be only on a few selected plants. Nitrogen is a mobile nutrient within the plant and if there is not enough available it will be moved from the older leaves (lower) to the newer leaves on the upper part of the plant. I see you have shredded hardwood mulch which can sometimes keep nitrogen from being available to the plants. So that is one possibility. Another might be dog urine – is it possible that folks are walking their dogs and they may be urinating on these plants?
I would recommend that you take a sample into the Loudoun County Master Gardeners for them to look at and diagnose for you – take an entire plant, roots and all. They are located in the Extension Office in the Wells Fargo Bank Building, 30 Catoctin Circle SE, Leesburg. They operate a Help Desk, Monday-Friday, 9 am – Noon (though you can drop off a sample anytime between 8 am – 5 pm) and their phone number is 703-771-5150.
Please let me know if I can be of further assistance.
Debbie

Problems With Vinca

vinca image by Alison Bowden from Fotolia.com

Vinca plants, also known as periwinkle and myrtle, are known for their multicolored flowers and glossy foliage. They are hardy plants that grow well with little care or attention, even in dry, hot areas. Vinca is usually used for ground cover edging, or as a border plant. While easy to grow, even for first-time gardeners, vinca can be prone to certain problems.

Leaf Spot

If black or brown spots appear on the leaves and shoots of your vinca plant, leaf spot is the likely culprit. Alternaria leaf spot causes light and dark rings of dead tissue with a bull’s eye appearance. The leaves turn yellow and defoliation, or leaf drop, begins at the base of the shoot. All but the newest leaves are lost. To put an end to this pesky fungus, apply a fungicide once every week to two weeks after you notice spots on the lower leaves. The fungi that causes leaf spot thrives in the cool, moist weather of the early growing season, so this is seldom a problem once the warm, dry weather arrives. Leaf spot can make your vinca to look unattractive but it rarely kills the plant.

Phytophthora Blight

Phytophthora blight is caused by phytophthora parasitica. It is a common disease of vinca and it can be particularly destructive to the plant. The early flagging of a single shoot and wilting are early symptoms of this disease, along with watery lesions at the base of the wilted shoots and sunken, reddish brown cankers along the entire main stem of the plant. If phytophthora becomes an infestation, root rot and plant death can occur within one to two weeks of the onset of symptoms. The key to preventing this ailment is to keep the area near the vinca free of old plant debris, and try to keep the foliage from becoming wet. Two to three treatments of a fungicide may be necessary. Always follow label directions when applying any fungicide.

Black Root Rot

Caused by the soil-borne fungus, Thielaviopsis basicola, this disease causes brown or black bands and bullet-shaped spores to form on the roots of the vinca, resulting in yellow foliage and poor growth. Prevent this problem by not under-watering or over-watering your plant. Further, be sure to clean and disinfect all work surfaces and tools used to cultivate vinca.

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