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Plant Problem Show and Tell – Yellow Leaves on Ilex crenata

By molly miller, master gardener trainee

Describe damage/problem:

  1. Problems on my two Japanese Hollies. Yellow leaves got my attention,
  2. Possibly found a caterpillar on a leaf with a spider (sample provided) on Holly #1. Is it a Leaftier (pronounced “tire”)?
  3. Hollies had Leaftier  2-3 years ago, treated with Cap Jack from Shonnards then—Holly #1 was the most affected; almost lost it.
  4. 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?
  5. 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.
  6. Holly #2 has most observable damage toward bottom of plant. Only some leaves above had damage, but underside showed spider mites.
  7. 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.
  8. Observed with magnifying lens:   black dots, and wisps of silk not visible from first inspection

Research

  1. 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:

  • 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. 

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Lilacs with puny blossoms and leaf spots – Plant Problem Show and Tell from trainee Catherine W.

Here’s a description of the garden issue I found:


I have three lilac trees at least 6 years olds. I moved into the house three years ago. The trees are in the South part of the garden getting full sun. They are at least one foot apart.  They line the driveway to the garage. They get water regularly especially on hot days. They get fertilizer at least 1-2 times before blooming. They get compost dressing once a year and mulch in the late fall.  Last year and more this year, all three trees have few and puny blossoms which turn brown in a couple of days. About 60% of the leaves are brownish, curling or have spots. The branches are semi-bare except for leaves near the end. The tips of the many branches are black, almost burnt looking. 


I’m including photos that show the issue.
And here’s what I think is going on

My Lilacs have Lilac Bacterial blight

I conclude that it is blight based on the symptoms I described and on the pictures I posted compared to the resource:

  • -leaves look perfectly healthy and then a short time later they look as though someone has placed an open flame near them
  • -flowers will wilt and turn brown and unopened flower buds become blackened-disease starts as brown spots on stems and leaves of young shoots as they develop in early spring. A yellow halo may also be around the spot
  • -disease starts as brown spots on stems and leaves of young shoots as they develop in early spring. A yellow halo may also be around the spot. 
 Remedies

1. to take out and plant resistant cultivars or

2. to try to address first by cutting off all affected parts and spray with copper sulfate and not fertilize in late spring (which I did)

Update

I tried to cut off the affected parts over the last 2 days but realized most of the trees were infected, even the suckers. I contacted a tree service who will remove trees and roots and I will buy resistant cultivars. 

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TEST Practice Plant Clinic Desk Notes

This is a discussion spot for users of Practice Plant Clinic. Think of this as kind of like sticky notes attached to the keyboard at the office.

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Have a major question or concern? Have a big vision? Please reach out to Elizabeth Records, Program Staff: elizabeth.records@oregonstate.edu