Brown spots on leaves on Plants

Symptoms

The spots you see can vary in form, from small discrete dots to raised areas. Some leaves carry small discrete raised dots on the surface. Others show irregular yellow or brownish patches that cover much of the leaf surface.

On drought-stressed plants, a yellow or brown area can begin between the leaf veins, mostly on the southwest side. Where mites are present, the foliage may show webbing or speckling. Sucking insects such as thrips, lace bugs, or plant bugs leave dark excrement on the leaves.

Leaf drop can follow when the infection is severe. The next section lists the causes that are named for brown spots. With leaf spot diseases, most infections can be tolerated because they do not cause long-term damage.

Look at where the yellow or brown area starts, because on drought-stressed plants it begins between the leaf veins. Then look for webbing, speckling, or dark excrement on the leaf surface. A leaf with raised dots looks different from one with irregular yellow or brownish patches, and both differ from one with a yellow or brown area between the veins.

Causes

Fungal pathogens are one cause of leaf spots. Similar spots can also come from bacterial pathogens, insects and mites, or abiotic factors on some plants. Abiotic factors are non-living ones. Air pollution, mineral deficiency or toxicity, and water deficiency are also named as causes.

Bacteria can cause blights, leaf spots, fruit rots, vascular wilts, and galls. Moisture that favors pathogen development is also a named cause. Pesticide injury is another, and it is commonly from herbicides. Sunburn on drought-stressed plants is a further cause.

Insects and mites are in the group, and sucking insects such as thrips, lace bugs, or plant bugs leave dark excrement on leaves. Mites may leave webbing or foliage speckling. Water appears on both sides of the list: water deficiency is a named cause, and so is moisture that favors pathogen development.

Fallen leaves and plant debris can be sources of reinfection by these pathogens. Similar spots can have different causes. The next section covers how to tell them apart.

Diagnosis

Begin by sorting what you see into the patterns the symptoms describe. Small discrete dots, raised areas, and irregular yellow or brownish patches are the spotting described for this problem. A yellow or brown area that begins between the veins is described for drought-stressed plants, mostly on the southwest side. Water deficiency and sunburn on drought-stressed plants are both named causes.

Webbing or speckling on the foliage is described where mites are present. Dark excrement on the leaves is described for sucking insects such as thrips, lace bugs, or plant bugs. Check the leaves for these signs before you assume a disease, because insects and mites can cause similar spots.

Fungal and bacterial pathogens are named causes, and so is moisture that favors their development. If the foliage has stayed wet, that moisture is the cause to weigh alongside the pathogens. Air pollution, mineral deficiency or toxicity, and pesticide injury are named as well. Ask whether an herbicide or other pesticide has been used on or near the plant, since pesticide injury is commonly from herbicides.

Treatments

Treatment for brown leaf spots is mostly about conditions around the plant, such as moisture and leftover debris, rather than about spraying. You can tolerate the infection rather than treating it, since in most cases it does not cause long-term damage. Spotted leaves that are still on the plant are not by themselves a reason to treat, since most infections can be tolerated. A severe infection can cause leaf drop, yet most infections do not cause long-term damage.

Remove fallen leaves and plant debris promptly to reduce the sources of reinfection. The cleanup advice is aimed at reinfection.

Avoid overhead sprinklers, and irrigate early in the day so the foliage dries more quickly. The reason given is that moisture favors the pathogens. Drier foliage is the aim of both the sprinkler advice and the early timing. The sprinkler and timing advice is aimed at moisture, which favors the pathogens.

The chemical entry on this page is a negative one: fungicide treatment is generally not warranted for leaf spot diseases. If you ever choose to apply any product, the product label is the legal instruction and must be followed for the crop and site being treated.

Prevention

Prevention comes down to the conditions around the plant. Letting the foliage dry quickly matters, since moisture favors the pathogens. Choose a watering method that does not wet the leaves from above, and irrigate early in the day.

Keep the planting free of fallen leaves and debris, since they are sources of reinfection. Moisture favoring pathogen development is a named cause, so the conditions that keep foliage wet are the ones to change.

Water deficiency is a named cause of leaf spots, and drought-stressed plants can also get sunburn. Herbicide use near the plant is worth watching, since pesticide injury is commonly from herbicides. Mineral deficiency or toxicity and air pollution are also named causes. Tolerating a mild infection is part of the approach as well, since in most cases it does not cause long-term damage.

Plants most often affected

No plant page in this build records this problem yet.