I have been bracing myself for the arrival of Japanese beetles, which for the last couple of years have ravaged my "William Baffin" rose. I was poking around the garden about 10 days ago when I noticed the arrival of another pest: the four-lined plant bug.
I've had these guys in the garden for years, and until recently I considered them only a nuisance. No more. I watched with growing alarm as the little yellow-and-black bugs attacked my mums, Russian sage, feverfew, rudbeckia, phlox and two newbies that had barely had time to get settled in the garden: a little cup plant and a wonderful perennial geranium.
You know you have four-lined plant bug when you see perfectly round gray or brown dots stippling plant leaves. It looks almost like someone burned the plant with a hot pencil lead.
This year, the bugs have attacked my garden so viciously that on some plants the dots merged until the leaves turned a crisp brown and began to curl. One of my mammoth mums looks beyond help.
You can't do much about four-lined plant bug using organic methods unless you catch them early and zap the red baby bugs with horticultural oil (if you can hit them – they tend to zip into hiding when you bend over a plant). I squished some of the bugs – there were so many that they were landing on my arms as I walked among the perennials – but I am loath to use stronger chemicals because they also harm bees and other beneficial insects.
Four-lined plant bug is usually around for about a month, so I figure we're a bit over halfway through their annual attack. I just can't justify using chemicals on these guys. so instead I'm planning an early attack on the babies with horticultural oil next year. Four-lined plant bug overwinters in the stems of some woody plants, so I will be careful about cleaning up the garden this fall and hope for the best next year.
What would you do? Is it worth using chemicals to protect plants that probably will bounce back from this sort of damage? They certainly won't flower as vigorously as they might have if these little devils hadn't shown up.
Can Japanese beetles be far behind? Ugh.
You can read more about four-lined plant bug here:
http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/e121plantbugs-fourlined.html