Marigolds, Tomatoes & Spider Mites

In the gardening world, some pest-control steps remove one problem while encouraging another. Though some varieties of marigolds (Tagetes spp.) Efficiently control root-knot nematodes, all of these attract spider mites. Should you plant marigolds around strawberries, then you might be aroused miniature interlopers that attack your plants and undermine their health. Managing these pesky creatures helps ensure healthy tomato plants which bear succulent fruit.


A gardening myth persists that marigolds’ pungent odor repels insects. Although research shows that French dwarf varieties control root-knot nematodes, these are not insects but worms which live in dirt and attack plant roots. To get marigolds to have maximum effectiveness against nematodes, they need to be sown set up or implanted before flowers open and permitted to grow thickly for a few months before being gunned to the soil. During those months, marigolds not just compete with tomato plants for nutrients and water, but they attract and fight spider mites.

Spider Mites

Spider mites are tiny arachnids that locate easy transport on air currents, which move them in marigolds to tomato plants. Though they are observable with the unaided eye, they are hard to see without close inspection. Many times, their presence is made known by delicate webbing they spin as defense mechanisms. Spider mites eat sap from piercing plant tissue and siphoning cells. They generally form colonies, with many spider mites clustered on undersides of leaves.


As a spider mite feeds on plant cell sap, the mesophyll tissue collapses. This leaves a tiny, chlorotic dot at each point where the mite’s hypodermic-like mouthpiece pierces plant tissue. As the mite moves across a leaf surface, yellow stippling follows. Large mite populations can cause whole leaves to turn yellow and infestations lead to leaf fall. If enough leaves autumn, plants are incapable of photosynthetic activity and they perish in the inability to make food to sustain themselves.


Since spider mites reproduce so quickly, ancient diagnosis is critical to efficiently treating them. All yellowing leaves are not symptomatic of spider mite damage, however, the presence of fragile webbing on plants with yellow leaves generally confirms their presence. Although insecticides will kill those insects, they also remove predators that manage their inhabitants naturally. For this reason, the University of Massachusetts Extension cautions that utilizing broad-spectrum insecticides frequently exacerbates the problem and causes outbreaks of spider mites. Alternatively, you can dislodge them with jets of water in your garden hose or use horticultural soap to spray plants to kill them. A natural control is rosemary oil, which deters spider mites but does not injure plants or beneficial predators.

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