The tomato is one of the easiest food-yielding plants to grow in your garden. Most varieties require little more than water to achieve a delicious, juicy crop. But any plant can fall prey to pests or disease. One of the universal issues for tomato plants is leaf curl The causes are usually — but not always — environmental.
It’s a response to hot and dry conditions
High temperatures and dry spells prompt tomato plants to conserve water. The leaves curl upward to reduce the surface area exposed to solar radiation. Tomatoes demand more water in late spring and early summer, during their active growing periods. Hot, dry conditions affect the lower leaves first. The condition persists throughout the season with some tomato varieties: plum and paste tomatoes are most prone to the issue.
The conditions are too cool and too wet
Sometimes, a tomato plant reacts to other conditions, such as cool, moist weather. Signs of this issue are similar to those caused by heat: the leaves curl upward. But instead of looking crumpled, the leaves take on a leathery appearance, which repels any additional moisture. This is a common condition for staked and pruned tomato plants.
It’s a sign of a viral infection
Hundreds of viruses can cause leaf curling. Whiteflies are a common pest tomato plants face. You can see the first signs of the infection they spread — yellowing or crumpled leaves — after about three weeks. Because the virus slows plant growth and the fruit flowers never develop, the tomato yield is significantly reduced. Insecticidal soaps help manage whiteflies, and some tomato varieties are bred to resist them.
Herbicide drift can lead to leaf curl
If you live close to cotton or cornfields and notice that your tomato plant leaves are curling, they may be victims of herbicide drift. Some farmers and gardeners spray large amounts of the chemicals to prevent and eliminate weeds, but a neighbor's use can affect your tomatoes as well. Wind carries and spreads the chemical beyond the intended targets, and tomato plants are super-sensitive to herbicides, reacting to even the smallest amounts, and this can impact the yield.
Residue in compost or mulch leads to leaf curling
Compost is usually a beneficial addition to a gardener’s arsenal. Not only does it help ensure healthier growing conditions, but it also discourages harmful weeds and destroys pathogens in the soil. However, some sellers collect hay or manure from fields that growers have sprayed with herbicides. Just like herbicide drift, when gardeners apply the compost, the chemical content can damage or even kill tomato plants. If you’re purchasing manure or hay compost, verify its source with the seller.
Wind damage can cause leaf curl
Blowing dust and low humidity levels combined with high winds can damage tomato plant leaves and stems. The edges of the leaves start to die before twisting and curling. In some cases, the wind is merely drying out the leaves at a rate faster than they can pull in soil moisture. Placing a fence around the tomatoes or surrounding them with wind-tolerant shrubs will protect them.
Broad mites damage leaves
Although you can’t see these tiny culprits, broad mites threaten the health of tomato, pepper, eggplant, potato, and citrus plants. They feed on the youngest leaves and blossoms, and, in the process, inject them with a toxin that leads to distorted, curled leaves. If broad mites are the issue, the leaves’ undersides will turn bronze or russet. Insecticidal soaps control mites, but growers must remove and destroy severely damaged plants.
Leaf curl is a reaction to uneven watering
Tomato plants don’t like stagnant water on their stems or leaves. When the plant recognizes the problem, its leaves curl inward. A regular watering schedule prevents the issue and encourages better oxygenation, which in turn impacts photosynthesis, and ensures healthy nutrient levels and steady plant growth. It also assists the plant in pulling carbon from the air and distributing it to its leaves, stems, and roots.
Over-fertilizing may cause leaf curl
Seedlings and young tomato plants experience leaf curl and spindly limbs when over-fertilized. Starting mixes usually have fertilizer in them, so gardeners need add only small amounts every couple of weeks. A high concentration of nitrogen in the soil can also damage the plant’s leaves and roots. Cut fertilizer amounts in half for young plants or seedlings.
Lack of pruning may lead to leaf curl
Tomato plants require regular and diligent pruning. Without it, the quick-growing leaves and foliage demand too many of the plant’s resources, leaving too little for fruit production. Tomato leaf curl is an early sign of a problem. Though tomato plants tend to be more forgiving when it comes to over-pruning, remove dead or diseased leaves and stems regularly to keep them healthy.
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