- Blue mold, caused by the Peronospora tabacina fungus, only occurs on tobacco plants. On tobacco, blue mold is very destructive and can ruin 100 percent of a tobacco crop. Blue mold is a colorful name, and it conjures up images of plants covered with fuzzy, blue growth, but this isn't necessarily the case. The most common symptoms of blue mold are leaf yellowing and distortion. As the problem progresses, the leaves turn brown and the plant starts to wilt and die. If you see symptoms of damage on philodendron leaves that look like blue mold, the most likely cause is insect infestation and not an actual fungal growth.
- Aphids feed on the nutrients inside of leaves, sucking them right out of foliage. As aphid feeding damages plants, the leaves begin to turn yellow. Distorted growth may occur. But aphids also create a secretion of honeydew, a silvery-grey substance on the leaves and stems. The honeydew may easily be mistaken for a type of mold, particularly as it often causes sooty mold. Aphids may be treated with insecticides.
- Mealybugs look like pieces of white cotton on leaves, but they are actually hungry insects. As mealybugs feed on philodendron, the foliage becomes stunted and distorted. Wilting and death may result. Like aphids, mealybugs may also secret a sooty mold-inducing honeydew substance. Insecticide and pesticides are effective in managing mealybug infestations.
- Thrips are tiny insects that feed heavily on philodendron leaves. As the pests eat the leaves, the foliage becomes curled or distorted around the edges. Silver-gray areas also appear where these feedings have occurred. The silvery-gray areas of damage may easily look like bluish mold, but no fungus is present. Thrips do transmit a viral disease known as tomato spotted wilt to plants, but it is not fungal or bacterial in nature.
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