This time of year here in NJ we are ramping up with the heat and humidity, and some of our plants are starting to feel it. One of our most frequently asked questions here in the nursery is: "can you tell me what's going on with my plant?!"
We've compiled a list of our most frequently seen ailments and how you can treat each!
If you're noticing the foliage on your shrubs & perennials are starting to look like this:
You've got black spot. Black spot is a common fungal disease that attacks the foliage of many fleshy plants under the right conditions. It is spread by spores that can can be spread by air & wind or by water splashing up on the leaves. It can also overwinter on infected plant material, so it's important to discard any diseased foliage in the trash and not your compost! Black spot, while unsightly, is not usually fatal to the plant itself. It may look ragged but it should survive the winter and come back for you next year.
How to Treat: Trim back all affected foliage and dispose of properly. Treat plant with a horticultural oil or fungicide (follow the instructions provided). Sunlight and airflow will help kill off the spores and slow the rate of infection.
If you're noticing small leaves on your roses that look like this:
The culprit is likely the rose sawfly. Sawfly larvae can chomp up new growth on your roses at a rapid rate - telltale signs are whitish spots or small holes in the foliage.
How to Treat: Most sawfly damage will be done by the end of June or early July as the larvae grow up and move on. To treat early signs of larvae infestation, use a gentle insecticidal soap. Inspect the underside of your foliage regularly and address any larvae issues as they appear!
If you're noticing the foliage on your tender perennials are starting to look like this:
It's powdery mildew! This fungal disease gives foliage an appearance that makes it look like it was dusted in flour - hence the "powdery" in powdery mildew. Similarly to black spot, spores can travel into your garden from a variety of sources. Foliage will usually start off coated in the white fungus, then will curl to brown or yellow before falling off.
How to Treat: Once affected, powdery mildew is quite difficult to treat. The best way to treat is to isolate the plant so it does not spread to others in the garden. Prune and remove any infected foliage, flowers, or fruit and dispose of them properly (no compost!). Treat the plant with a good fungicide and ensure it has plenty of airflow in between the stems and leaves.
Always be sure to clean your clippers before and after trimming back infected foliage!