Ask an expert: This azalea is toast. See these tips for growing strong, healthy azaleas next time

Winter weather has arrived and it’s time to dream of plans and future gardening. And while you dream you may have questions. For answers, turn to Ask an Expert, an online question-and-answer tool from Oregon State University’s Extension Service. OSU Extension faculty and Master Gardeners reply to queries within two business days, usually less. To ask a question, simply go to the OSU Extension website, type it in, and include the county where you live. Here are some questions asked by other gardeners. What’s yours?

Q: I have a serious infestation of azalea lace bugs. Damage has been done. I didn’t know what the problem was and throughout the spring/summer I was spraying with a fungicide, which obviously didn’t work.

More recently a neighbor told me about the azalea lace bugs, so I’ve been spraying neem oil weekly for the past month or so. I’m wondering if that is pointless this time of year. And should I be treating the ground with something to prevent problems next year.

I have others that aren’t as badly infested. I did look at the attached “Azalea Lace Bug” handout, but if you have more information on systemic controls, I would appreciate it.  Regarding spraying neem oil in the spring, is there a way to know when the nymphs are active?

Also, I’m wondering about watering guidelines.  I’ve been watering four times/week (7 minutes, let it soak in, and repeat with another 7 minutes).  Is that contributing to the problem? – Lane County

A: At this point, I recommended starting over with new plants. The damaged leaves won’t recover, and this high level of infestation may be very difficult to get ahead of with insecticides. 

Application timing and spray location of contact insecticides, like neem-based products, is very important. Neem is most effective against the nymphs. Nymphs are active in the spring and are on the undersides of the leaves. So, the neem or insecticidal soap must coat the underside of the leaves at just the right time in the season to kill it. Spraying earlier or later won’t be effective. 

There are some systemic insecticides that can be used. These are taken up by the plant and moved throughout the plant. When the azalea lace bug feeds, then it will die and the cycle stops.

When purchasing systemic insecticides look for one with an active ingredient of imidacloprid or clothianidin. These are usually applied to the soil. Follow the label for specific use and safety instructions. Note, these are harmful to bees and other pollinators that visit the flowers. So they should only be used if needed.

The nymphs become active depending on the temperatures. The general recommendation is to start looking for them in mid-May. But if we have a warm spring, I would start looking in early May. Look on the underside of the leaves. Figures 3 and 4 in the Extension Azalea Lacebug publication are good examples of what to look for. They are tiny and hard to see. You may need a magnifier.  

Stressed azaleas are more susceptible to damage. Grow in shade to part-shade (or at least protect from the late afternoon sun).

Azaleas have a shallow root system. Try digging to see how deep the water is getting into the soil. This might be something to do next year. Use a hand trowel or hori hori knife to make sure the water is penetrating several inches into the soil. Also, make sure to water around the edge of the shrub-not just next to the base. Most of the active roots are further out along the drip line of the shrub. 

If you do replant, consider using a resistant cultivar. Resistant azalea cultivars include: ‘Autumn Amethyst’, ‘Autumn Twist’, ‘Autumn Royalty’, ‘Autumn Sangria’, ‘Autumn Cheer’, and ‘Autumn Rouge’. In addition, some cultivars are moderately resistant: ‘Autumn Embers’, ‘Autumn Bravo’, ‘Autumn Starlite’, ‘Autumn Ruby’, and ‘Autumn Princess’.  – Brooke Edmunds, OSU Extension horticulturist

Q: I’m new to growing dahlias and need help with how best to protect them during the winter. In preparation, I’ve trimmed the stalks down the ground, ensuring that I do not have any ” hollow” stalks to try and prevent the tubers from rotting. I’ve covered each tuber with a bed of leaves to help with compost as well as a small amount of bone meal. What other steps should I be taking to protect the dahlias from the winter?

Also, I just received a new dahlia tuber from a neighbor and feel it is too late for planting. What is the best method of care and storage before planting in the Spring? – Clackamas County

A: Since a wet winter is often worse than a cold winter, keeping the tubers dry with a layer of leaves will help. You can also put black plastic over the bed or put an overturned pot over the tubers to direct the water away from them. You might also want to put some slug bait around while the weather is wet and warm to help diminish the population since they treat dahlias as candy in the spring.

As for your new tubers, the key is cold, dry, dark but frost-free. If they are going to be inside and a bit warmer, you will want to keep them moist in compost, wood chips or sand and check once a month to make sure they are not rotting or shriveling. A cool garage or basement is great, about 42-45 degrees. – Rhonda Frick-Wright, OSU Extension Master Gardener

Q: I recently transplanted a coffee plant that was experiencing root rot. I cut off the roots that were dead or unhealthy and gave it new soil with more drainage and vermiculite. It’s now looking more unhappy than ever and is very droopy. Soil is still moist from watering a week ago. Worried that it might be dying. Any tips for how to save it? – Washington County

A: Root rot is a very difficult disease to get rid of since the bacteria had invaded some of the roots that might not have looked dead yet. It sounds like you did everything you could do for the plant, and now it is up to the plant to see if it can recover. Make sure to keep up the same watering schedule you used to raise it to that healthy size and keep it in full light.

If the plant dies, be sure to sterilize the pot and put the soil outside somewhere it won’t affect other plants before you try again. Sorry the news isn’t better, — Rhonda Frick-Wright, OSU Extension Master Gardener