The Q&A Archives: Spider Mites Taking Over

Question: I live in sunny San Jose and have 10 window boxes on my deck which faces south. I have both regular and ivy geraniums in my boxes along with some lobella. My problem is yellow leaves, dried up leaves, and prolific spider webs. I have a drip water system which is nice but hard to regulate over a long distance such as the deck. I have regular geraniums from last year that are just now starting to come back. I have added new ones this year and their leaves are turning yellow. The older plants are not growing very well. I put fertilizer and water daily. What is the right level of watering? Also what can I do to get rid of the spiders? Last year I used a spray and it hurt the leaves. I spray in the evening but the deck gets very very hot. Thanks so much for you help

Answer: If your plants are developing yellow leaves and you find webbing in the plants, the likely cause is a tiny insect called a spider mite. These little pests love hot, dry conditions. They feed on the stems and undersides of the leaves and cause the leaves to yellow and eventually die. A really huge population will be difficult to control so if your plants are really in bad shape, you may want to toss them all and start over with healthy new plants. If you want to try and save the plants, there are insecticides in the garden section of your favorite nursery that you can use to spray your plants. Spider mites love hot, dry places so hosing your plants off every few days will help deter the pests. As for watering, it's difficult to predict. Containerized plants in full sunshine will require lots of water. If your drip system is inadequate, you may want to redesign it, splitting the system, or putting on a second system so the water pressure is high enough to water the planters at the far end of the deck. Or, you may want to hand water your plants, which will give you an opportunity to sprinkle the leaves and stems to ward off spider mites.

Best wishes with your planter boxes!

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