Tomatoes & Weeds

Dodder

• Vine-like dodder grows as yellow, orange or red shoots that curl around, puncture and siphon nutrients from tomato-plant stems. Controlling dodder requires pulling out host tomato plants and throwing them in the trash. If the dodder on your tomatoes has flowered with its small, colorless blooms, burn the weed to kill its hardy seeds, which can survive several years in the ground. To prevent dodder infestations, apply a rimsulfuron-based herbicide spray such as Matrix or Resolve at the tomato-seedling stage. Dodder germinates between March and late May, so gardeners can also control dodder by planting tomatoes as late as possible in the growing season. The new vines will have no plants to feed from and may die as a result. Rotating every other year to corn, garlic and other crops that don't attract dodder can also reduce long-term proliferation of the weed.

Field Bindweed

• The perennial field bindweed is an intractable plant pest once established. Identify field bindweed through its bell-shaped leaves and trumpet-shaped white flowers, which open during the day and close at night. In addition to crowding tomato seedlings, field bindweed carries the virus that causes tomato spotted wilt. Established bindweed plants are nearly invulnerable to standard tomato-crop herbicides, so gardeners must dig out mature weeds by hand. However, herbicides containing trifluralin, such as Treflan, can work against bindweed seedlings. At the end of the growing season, use a garden cultivator to cut up bindweed rhizomes underground. It should take a year for the bindweed to grow back once cultivated.

Nightshade

• This weed belongs to the same plant family as the tomato, and it's home to pests and diseases that can quickly spread to nearby tomato plants. Most nightshade weeds have oval leaves, star-shaped white flowers and berries ranging in color from yellow to black. Nightshade is easiest to control with herbicides when it's less than 6 inches tall. Herbicides with rimsulfuron are the most effective, though Metribuzin may also work on nightshade seedlings. To prevent nightshade growth, treat garden soil with metam sodium before planting tomatoes. Because nightshade germinates within 1 inch to 2 inches of the soil's surface, deeply plowing the garden before planting can disrupt nightshade seed growth.

Nutsedge

• The tuberous nutsedge grows in clumps and looks like a thick grass. Nutsedge can grow to 3 feet and quickly overwhelm tomato plants. The weed grows long stems topped with purple or yellow flowers. Nutsedge won't grow if its tubers are buried deeper than 6 inches, so plowing garden soil under to a depth of 1 foot can suppress new colonies. Treating soil with metam sodium before planting tomatoes can also control nutsedge. Once the weed begins to grow, herbicides including Dual Magnum, which contains metolachlor, and Sandea, which contains halosulfuron, can keep expansion under control.

Other Tips

• A few basic gardening techniques can keep tomato-loving weeds in check. Apply a layer of mulch three weeks after tomato seedlings emerge. Dig up smaller weeds with a handheld hoe, but avoid damaging tomato plants' roots. Don't neglect weeds at the edges of your garden, because they can house as many harmful insects and viruses as weeds growing in the middle of your tomato crop. Avoid using the herbicide Arsenal, because it will kill your tomatoes along with the weeds. Finally, wash your harvested tomatoes thoroughly before eating to remove any herbicide residue.