I have a large flowered yellow marigold in a big container by my steps.. the plant is huge and was beautiful, one of the prettiest marigold plants I’ve seen, up until a few days ago. I noticed the foliage had a dull, bronzed, “burnt” look– as if the plants were suffering from a serious lack of water. I’ve watered this plant regularly, so I knew it wasn’t lacking in that. I’ve also been diligent in deadheading, and in fertilizing it weekly. So I started looking a little closer at the plant itself, and noticed that each individual flower was completely covered with a fine webbing, like a thin, very tight spider web, stretched completely around each flower. These webs were also visible in spots throughout the undersides of the thick foliage. On closer inspection, I noticed literally -hundreds- of tiny little moving red dots. Spider mites. Yuck. In only three days time, my gorgeous big marigold has turned into a bronzed, burnt looking droopy mess. It looks like crap now.
After reading what I could find out about these pests on the internet, I don’t think these things are going to be easy to get rid of, and I think I may have caused it, or at least contributed to it. Right behind this plant, I have two hardy hibiscus plants, one on either side of my front steps. These large bushes suffer damage every year from some sort of small worm that eats holes in the leaves. This year, I was determined to get ahead of these pests, so I’ve dusted the hibiscus bushes with a pesticide dust two or three times in the past couple of months. I have no damage to the leaves of the hibiscus, and no sign of the worms, but now I have the spider mites. According to what I read, this dust kills the natural predators of these mites– ladybugs, lacewings, and beneficial mites.. so it seems that possibly my use of this dust, along with the hot weather and severe drought conditions in our area has caused the spider mite population to explode and thrive. On my marigold plants.
The possible controls for these pests include liquid rotenone/pyrethrin (edited to add: I found this product locally for only 7 dollars, less than half the online price), miticides, and insecticidal soaps. According to davesgarden.com, insecticidal soap is an organic mixture that is effective in destroying pests such as spider mites, aphids, thrips, mealybugs, and other soft bodied insects. This soap solution works by breaking down the coating that helps the adult or young insect retain moisture in its body. Once this coating is disrupted, the insect dehydrates and dies. If I can’t find this product locally, I may try this homemade version:
Recipe for an insecticidal soap:
1 Tablespoon Murphy’s oil soap
3 Tablespoons Cayenne pepper (Tabasco may also be used)
1 Quart warm water
Mix all together well and spray on plants.
Since a soap solution is supposedly only about 40-50% effective in controlling spider mites, I may just have to get rid of the marigold pot completely, before the mites spread to something else. I’m not sure of course, and maybe it was just a coincidence that after using the pesticide, the spider mites appeared… or it could be just the extremely hot weather conditions and the severe drought in my area for the past several months… I don’t know. I do know that I’ve never had these mites before.
Updated to add: I bought some pyrethrin and some insecticidal soap today. We’ll see what happens; in the meantime, I’ve moved the marigold pot out of the yard and far away from my flower beds.
Update: although the insecticidal soap didn’t work, the pyrethrin seems to have gotten rid of the pests. I cut the plants back, but am not sure they will recover.
Update, September 9: Although the pyrethrin did kill the spider mites in this particular container, the marigolds never fully recovered from the damage and had to be discarded. The spider mites also had spread to another large container nearby, this one with impatiens. I cut them back severely, laid the pot on it’s side and then sprayed the plants several times with a -strong- spray of water, making sure to spray the water onto the undersides of the foliage also. After the plants dried, I sprayed them lightly with the rotenone spray and waited a couple of days before moving the container back onto the porch. These plants did recover and are doing fine and have grown back to their original size with no further problems. I haven’t seen any more of the mites since. Next year, I’ll be more diligent in watching for these mites to start, and will spray the plants down with water at the first sign of the mites, and will use the rotenone spray. The mites can definitely do a lot of damage, and can absolutely ruin nice healthy plants.
All photos here are clickable for larger versions.