Identifying Webs

Question: For the last two or three years, many of my boxwoods, hydrangeas and evergreens have been covered in webs in the summer. I have tried Neem Oil to get rid of them but it hasn't worked. The webs and whatever insects live in them appear to be causing portions of the plants and bushes and trees to burn out and die.

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied August 30, 2024, 12:40 PM EDT
response: The webs pictured are spider webs (probably from different species; Maryland is home to hundreds of spider species). Spider mite webbing would have a different look (it would tend to hug the branch or foliage more tightly, and we would see mite feeding damage to leaves, which we do not).  Spiders are beneficial in landscapes because they consume other insects, including biting flies, wasps, moths, and anything their webs can catch. They do not feed on plants, and can be ignored. If you won't like the look of webbing, you can try to break them apart with a stick or spray from a garden hose (just plain water), but the spiders may rebuild rather than moving elsewhere.  The dieback in any of the pictured plants is unrelated to the spiders, though use caution when try to treat a plant with horticultural oil (neem is one type of this kind of pesticide). The cause of plant damage should always be identified before a treatment is attempted, not only so you know if treatment is needed, but also so the right ingredient is used. Horticultural oil and many pesticide ingredients can "burn" plants if applied while temperatures are above 85 degrees, and oils can also strip the natural wax layer off of plants that gives some a more blue leaf color, like certain hostas, blue spruce, and others.  The Dwarf Alberta Spruce pictured looks to be in great shape...we don't see any damage, even though they can be vulnerable to spider mites, bagworms, and heat and drought stress, since spruces overall are not well-adapted to Maryland growing conditions.  The hydrangea has a typical amount of leaf spot infection, which is very, very common on hydrangeas by late summer, especially in years with wet weather or when irrigation gets the leaves wet repeatedly. (Leaf surfaces that stay wet for long periods are easier for many disease spores to infect.) Despite being an eyesore, it does not cause the plant any serious or long-term harm. While preventative treatment with certain fungicides might suppress infection in future years, it would require spraying much earlier in the season (around spring, well before symptoms appear), repeat applications, and its use might harm pollinators or other organisms. Plus, fungicide sprays don't always work and  sometimes leaf spot infections still occur. All of these reasons are why we usually don't recommend their use, especially when a disease doesn't threaten the life of a plant. When they hydrangea's leaves fall off later this fall, rake them out and dispose of them so they don't harbor spores to start an infection next year. This isn't foolproof, because spores can also be blown-in on the wind, but it helps to avoid a more immediate or severe repeat infection.  The boxwood is harder to diagnose since many factors can lead to leaf loss or bare branch sections/tips. You can explore our boxwood diagnostic page for common ailments to compare symptoms to. As a guess, and because it's very commonplace, the pictured bare area might have been a result of Volutella Blight. The shrub also looks heavily pruned, and regular shearing of boxwoods to create a dense layer of foliage can make them more vulnerable to disease and pest outbreaks. For the future, it's best not to prune them much, and to only trim what branches are needed to adjust plant shape, if a more manicured look is desired.  Miri

responder: The Question Asker Replied August 30, 2024, 1:43 PM EDT
response: Miri: Thanks so much!A few more questions (photos attached of my azaleas with holes and burnt out patches): What could be causing this? Could it just be due to the age of the azaleas? Are they in danger of dying, do you think?And last photo is of powdery mildew on one of my trees I can’t get rid of. Any suggestions? Many thanks!DanaOn Fri, Aug 30, 2024 at 12:40 PM Ask Extension <<personal data hidden>> wrote:

responder: The Question Asker Replied August 30, 2024, 1:48 PM EDT

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied August 30, 2024, 4:55 PM EDT
response: Root competition from the English Ivy below the azaleas may be a contributing factor (azaleas are comparatively shallow-rooted for a shrub, so some of the moisture they need is being taken by the ivy), and other environmental conditions are also probably playing a role in plant stress and dieback. Azaleas grow best in semi-shade (they are adapted to woodland or woods-edge habitats), in soil that is moist but drains well. Drought, full sun (or lots of direct afternoon sun), and heavy pruning can stress them and predispose them to opportunistic infections like Botryosphaeria canker. Branch dieback symptoms will greatly overlap from one cause to another, so it's hard to say that canker was the primary issue, but it can be common on a variety of shrubs and trees. The only recourse with a canker infection is to prune out the dead or dying branches.  Avoid shearing shrubs as the dense growth that promotes will make them more susceptible to pest and disease outbreaks, because it reduces the air circulation between the leaves. The dense outer leaf layer also shades the interior branches more, causing them to lose leaves earlier than they normally would, making the shrub interior bare, which of course becomes more noticeable when a branch dies out. If pruning is needed to manage plant size a bit, either trim individual branches that get too long, or occasionally do a more drastic pruning much lower into old wood and wait for the shrub to rejuvenate, which will take a few years.  Were the azaleas being monitored for watering needs this past summer (and last summer, when we also had a drought across much of the state)? If not, check the soil about five inches deep when the weather stays hot or dry, and if the soil feels somewhat dry to the touch at that depth, water thoroughly. (Shrubs this size would probably need at least 5-10 gallons of water per plant.) If the soil is damp to the touch at that depth when checked, watering can probably wait. As a very rough guideline, mature azaleas (especially in a sunny area) might need 1-2 soakings per week in a stretch of dry summer weather. Over-watering can also lead to branch dieback, but usually those symptoms would be more widespread and affecting more branches all at once, and the leaf color would turn a sickly yellowish-green before withering, which we don't see here.  There might be a bit of Azalea Bark Scale on one of the thicker branches in the image that includes the ivy, but it's hard to tell at that distance. You can use the information on our azalea diagnostic page to see if that, or any other common ailments, have symptoms that match what you're seeing.  Since the size of the azaleas suggests that they've been in that location for a while, you don't necessarily need to move them into more shade, but just be aware that summer sun can stress them in hot weather, and supplemental watering and monitoring for lace bug infestation (not visible here, but possible in these conditions) may be needed to catch problems before they cause too much damage. Transitioning away from shearing and into more selective pruning can also help to support their health over the long term.  The evergreen pictured looks like a 'Manhattan' Euonymus shrub, and powdery mildew can be quite common on this and a variety of other perennials, trees, and shrubs by late summer. It's not serious with regards to long-term plant health, but you can use the information on the linked page to try to suppress infection in future years. If some leaves shed in autumn, which can be normal for evergreens, try to rake them up and dispose of them so they don't harbor mildew spores for next year. It's not foolproof, as spores could blow in from elsewhere in a future year anyway, but it's a useful tactic to reduce the risk of reinfection.  Miri