white sticks and brown bud tips on dahlias

Asked July 8, 2018, 12:16 PM EDT

My dahlias are developing brown apical leaves (usually much worse than show in the pics as I remove the leaves) -- and on the surface of the older leaves are these short white flattened sticks about 1 x 4 mm. They appear to be a plant fragment. What causes this? I do have what I think is a brown potato leaf hopper that I occasionally see on the leaves (last picture), and a large ornamental potato about 6 feet away. The Dahlias have slightly rumpled leaves but not the white mottling associated with viruses. I am wondering if the white sticks are a clue as to the cause of the browning and eaten leaves around the flower bud tips. If it is not caused by a bug, could it be caused by a Phytoplasma? (since it infects potatoes) -- and if it is this, does this disease infect the bulbs so all must be destroyed to get rid of the bacterium?

Lincoln County Oregon

5 Responses

Thank you for your questions. We apologize for the delay as it seems that yours was stuck in the queue for an excessively long time.

After this long wait, how have the plants done? How does the new foliage look now? Is it normal or more seriously damaged than previously?

It's difficult to see detail of the white stick-like objects. No legs or antennae are apparent so I wonder if they are debris from something nearby.That could be very likely if it was rather windy prior to their appearance.

If they are still present, consider taking them to the Lincoln County Master Gardener office for a first-hand look. (Contact information is here: https://extension.oregonstate.edu/lincoln.

The photo of the insect also lacks sufficient detail for identification. You might also take it to the Master Gardeners. That said, I doubt it is responsible for the damage to the new leaves.

I have not been successful locating sufficient clues about the poor color of the new foliage. However, during this period of excessive heat, also relatively high winds, I wonder if the cause is environmental instead of any sort of disease.

To help you resolve this issue, I'm reassigning your question to a plant disease specialist who may have some insights for you.

Not sure I can add much more. Agree the white sticks are nothing to be worried about. If leaf hoppers then they would be moving when disturbed. Since you are removing symptomatic leaves as they appear we can not help you with what it might be. It could be viral as the symptoms can be quite varied depending on the virus, the cultivar of dahlia and the environment.

The plant is still producing beautiful flowers -- so I won't destroy it. But note the damaged leaf to the left. I have included additional pics of the insects on the dahlia as well. One is the leaf hopper -- the other is a white spider that forms nest in the Dahlia leaves. Would like to know if they are damaging.

My plant again -- but showing the additional spider that I found -- in case it is important.

Spiders are generally not a problem unless they are of the small type called mites. Since you have large, lovely flowers and nice foliage I would stop worrying and enjoy the blooms.