Rhododendron : Leaves with black spots - Ask Extension
Noticing a few plants along the row of rhododendron having on top of the leaf some yellowing/brownish/blackish dots and on the underside brownish flec...
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Rhododendron : Leaves with black spots #781334
Asked February 05, 2022, 6:51 PM EST
Noticing a few plants along the row of rhododendron having on top of the leaf some yellowing/brownish/blackish dots and on the underside brownish flecks that actually came off on to the paper that I placed the leaf on to take the picture below. What could it be? thank you
Lane County Oregon
Expert Response
Hi, June,
Your Rhodies have azalea lace bug, which is increasingly common in this region.
OSU has published an article on Azalea Lace Bug (ALB) control in commercial nurseries and landscapes, and much of the information in that publication is directly relevant to home gardens, as well.See http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/40424/em9066.pdf to access the publication. The only part that you should disregard is the chemical control section ~ where specific product recommendations are made, as these are targeted to commercial growers who have pesticide license.
If you have the time and are diligent, a strong water spray can reduce populations. The key is to hit the undersides of as many leaves as possible, and do it numerous times throughout late spring and early summer, the season when the nymphs and adults are most active.
There are also several insecticidal sprays that are effective - again, they key is to hit the undersides of the leaves. Some, such as insecticidal soaps, are relatively non-toxic. Control will be best if you're able to knock back the first hatch of ALB. Monitor your plants, beginning in late April, as the eggs should hatch around that time through mid-May. When you see the signs and symptoms of the ALB nymphs, you can use an appropriate chemical control to knock them back.
Your Rhodies have azalea lace bug, which is increasingly common in this region.
OSU has published an article on Azalea Lace Bug (ALB) control in commercial nurseries and landscapes, and much of the information in that publication is directly relevant to home gardens, as well.See http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/40424/em9066.pdf to access the publication. The only part that you should disregard is the chemical control section ~ where specific product recommendations are made, as these are targeted to commercial growers who have pesticide license.
If you have the time and are diligent, a strong water spray can reduce populations. The key is to hit the undersides of as many leaves as possible, and do it numerous times throughout late spring and early summer, the season when the nymphs and adults are most active.
There are also several insecticidal sprays that are effective - again, they key is to hit the undersides of the leaves. Some, such as insecticidal soaps, are relatively non-toxic. Control will be best if you're able to knock back the first hatch of ALB. Monitor your plants, beginning in late April, as the eggs should hatch around that time through mid-May. When you see the signs and symptoms of the ALB nymphs, you can use an appropriate chemical control to knock them back.
