By molly miller, master gardener trainee
Describe damage/problem:
- Problems on my two Japanese Hollies. Yellow leaves got my attention,
- Possibly found a caterpillar on a leaf with a spider (sample provided) on Holly #1. Is it a Leaftier (pronounced “tire”)?
- Hollies had Leaftier 2-3 years ago, treated with Cap Jack from Shonnards then—Holly #1 was the most affected; almost lost it.
- Discovered black dots like periods on underside of Holly #2 2 days ago; so think these are spider mites. I have been finding webs/whiffs of white on hollies—maybe spider mites?
- Holly #1 leads the way in damage from top to bottom, inside the tree is more yellow, and gray, crumbling leaves in center—a big patch.
- Holly #2 has most observable damage toward bottom of plant. Only some leaves above had damage, but underside showed spider mites.
- Other spiders (maybe beneficial?) seem to be active on Holly#1 (sample provided): seems to be a lot but they are almost not visible to naked eye.
- Observed with magnifying lens: black dots, and wisps of silk not visible from first inspection
Research
- Identify as Leaftier or something other (Leafminer?): https://catalog.extension.oregonstate.edu/em9294 has photo and info on Leaftier. Spiders often visit Leaftier sites. I have seen damage before for Leaf Tier on my plants. The damage is not something to live with. It traveled fast and Holly #1 was almost totally gray. I don’t see that kind of gray curling of leaves that was Lieftier.
Is it leaf Tier? It can affect a wide range of plants in PNW. Also, these hollies had it 2-3 years ago. Will it spread if that larvae (I think I found) is leaftier?
- Identify pest or pathogen, spider mites? Or other?
Diagnosing spider mites
Inspect stippled and distorted leaves to determine if mites are present. Similar symptoms can be caused by pests other than mites, including thrips, leafhoppers and lace bugs.
Many spider mites prefer to feed on the lower leaf surface, so examine the undersides of leaves first. A 10 ‑ 20 power hand lens or microscope is essential for clearly seeing the mites. The tiny mites will appear yellow, green, orange, purple, black or nearly transparent. Also visible on the leaf surface may be pale‑colored cast skins shed by developing mites, and the spherical, often translucent eggs.
- I inspected with lens. Definitely spider mites. Damage on plants match photos on below link.
This link has non-chemical and chemical controls listed. https://extension.oregonstate.edu/gardening/techniques/how-recognize-manage-spider-mites-home-garden
Other SM refs:
- http://pnwplants.wsu.edu/PlantDisplay.aspx?PlantID=728 says to beware of spider mites
- http://pnwplants.wsu.edu/PlantDisplay.aspx?PlantID=728
- Be alert to: Alkaline soil will cause the holly leaves to yellow https://plants.ces.ncsu.edu/plants/ilex-crenata/
- Went to Extension Office to Check Plant Samples on high powered microscope:
Examined possible caterpillar/spider sample listed as “b” under damage. There was a spider, and a web of caught insects. No confirmation of Leaf Tier. I think spiders are beneficial, eating spider mites. This sample also showed a big array of black dots, signs of spider mites.
Recommendation:
At this time, I think the problem is mostly spider mites. I may apply non-chemical controls, but think the damage is aggressive, especially on Holly #1. Chemical controls may be in order. Will want to be alert that resistance to chemicals in the mites can cause an increase in future populations, aka “Mite flare.” Also, don’t want to kill off beneficial insects, like the spiders that are there now.
At this time, I will “scout” over time for damage that looks different than spider mites. I don’t want to kill beneficial insects now that spider mites are here.
