By: Bonnie L. Grant, Certified Urban Agriculturist
Wisteria is a showy climbing vine with clusters of scented dangling white to purple blooms. They provide impact to fences, trellises, walls and other areas where the thick woody vines can trail or scramble. Two main varieties are used: Chinese and Japanese. Both are fairly hardy vines but they are deciduous, and the lacy leaves turn color and defoliate in fall. A wisteria with yellow leaves may be due to this natural occurrence or there might be a pest, disease or cultural problem. Let’s investigate why do wisteria leaves turn yellow and find out what, if anything, to do about the issue.
A classic garden is almost incomplete without the lush vines and pendant blooms of a wisteria vine. The plant’s easy elegance and twining vines create a layer of texture and beauty that is unmatched by other vines. Wisteria leaf problems can stem from a number of conditions, but the plant is vigorous and relatively tolerant of minor conditions. My wisteria leaves turned yellow during October as a natural response to cold temperatures. If you find leaves on wisteria turning yellow out of season, then it’s time to do a soil test and look for pest activity.
Average seasonal foliar displays aside, why do wisteria leaves turn yellow in the growing season? One of the main reasons may be an iron deficiency in the soil. An easy to find soil kit can give you the answer. If iron is deficient, roots have trouble taking up nutrients. Wisteria enjoy neutral to slightly acidic soil. The lack of iron in soil will create a soil pH that is too alkaline. This is easy to amend with the addition of compost or peat.
Another possible issue is poor drainage. Overly boggy, soggy soil is not a condition that a wisteria will put up with and that excess moisture will manifest in limp, yellowing leaves that will start to fall off the plant. Check your drainage and stop watering until you can maintain proper porosity.
Wisteria are tolerant plants with few pest or disease issues. That said, wisteria can become prone to viruses and fungal diseases.
Tobacco mosaic virus is a common disease of ornamental plants. Aphids and other sucking insects transfer the disease and there is no cure. The leaves become streaked and mottled with yellow and may fall off. If the plant is healthy, the foliar disintegration will probably not kill it, but rampantly infected plants should be removed. Good cultural practices can help a stressed plant and improve its chances of survival.
Fungal diseases are the bane of many a gardener. Warm, wet regions are especially prone to fungal issues. Keep leaves dry by watering from under the plant with a soaker hose or drip system. Fungicides may have some effectiveness if applied at the beginning of the season, but if you wait until a wisteria with yellow leaves has been too badly affected, they are not terribly useful. Catch any issues early and baby the vine to enhance its endurance and vigor.
It takes some pretty serious infestations to bother a wisteria. Scale and aphids are sucking insects whose feeding behavior can cause faded, yellowing leaves and loss of plant health. In small numbers, they pose no serious threat to the plant but young plants or plants that are stressed may have reduced health.
Scales look like tiny bumps on stems and vines. Aphids are small flying insects which can be identified by the presence of honeydew, a sticky substance that is the insect’s waste. Honeydew creates a clear, sticky coating on leaves. Aphids can be rinsed off leaves or either pest can be controlled with insecticidal soap or neem oil.
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Which tank are the live plants in? How much, and what type, of light do you have? What ferts, CO2 supplementation is used?
Plants can yellow for many reasons. Is it new growth that is yellow? Do the veins stay green? Are there tiny pinholes in the affected leaves? Are the tips turning brown?
Sorry for all the questions, but this information might help to determine what is in shortage.
I believe low nitrates can also lead to yellowing leaves. Monitor your levels as these are heavy feeder plants. I'd also recommend adding root tabs near these plants as it may be able to help them overcome the shortage.
Good luck with your plants.
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Early symptoms of the disease include the wilting and yellowing of leaves and dieback of branches on seemingly healthy plants. An inspection of the wood below the bark reveals reddish-brown discolouration. Cankers often appear on the larger stems. Symptoms of inadequate watering include wilting and yellowing foliage that eventually starts to drop. As plants lose strength, they become more susceptible to secondary problems such as pathogenic infections and pest infestation. Aphids are soft-bodied pests that infest foliage undersides and other tender plant areas and suck plant sap. They cause distorted, curled and yellow leaves.
Vincas with yellowing leaves are often reacting to a lack of iron, which is a common problem in alkaline soil. A lack of nitrogen in the soil can also cause yellowing leaves. Use of a fertilizer containing nitrogen, iron and sulfur helps to replace the nutrients while balancing the pH. Apply a granular 12-10-10 product with iron added in early spring, using a 3 pounds of fertilizer for every 60 square feet of garden space. Read the label of the product for specifics, as products vary.
Vincas are drought-tolerant plants that don't grow well in soggy soil, and wet, humid conditions often promote diseases that cause yellowing of leaves. Various types of root rot and stem rot may cause yellow leaves, often followed by stunted growth, wilting and eventual plant death. Too much water can also contribute to fungal diseases that cause lesions on the leaves, followed by yellowing and leaf drop. Water vinca only when the top 1 to 2 inches of soil feel dry to the touch, and then water deeply enough to saturate the roots. Always allow the soil to dry before watering again.
MPPI. I know that D.odora suffers from a number of viral diseases . and some of these manifest themselves with yellowing of the leaves to some degree. although a better type of shrub has been bred to help overcome this.
My understanding is that once a viral infection has been caught by the daphne its outlook is extremely limited.
Lack of iron also causes yellowing in other plants. but the plant normally looks fairly healthy.
If not a virus MPPI, try using Camellia/Azaelea food on it. Mine picked up a treat after feeding it with this after I noticed it started to get yellow leaves.
A healthy tree is the best insurance against disease. Concentrated nitrogen applications like those listed above work well with fast results. A more natural but also slower method is to plant natural sources of nitrogen around the drip line of the peach tree. Peanuts, peas and other legume plants naturally fix nitrogen in the soil via their root systems. Alfalfa is another source of nitrogen. Adequate watering is essential to healthy fruit maturation. According to Rodale's methods, "if a dry spell should develop . watering every other day with 25 gallons per tree will help until the rains return."