PM does that. Some of my phlox this year have almost the whole stalk either bare, because they fell off, or almost all bare with just brown leaves left. Zinnias … To the naked eye, they look like tiny threads. Today I’ll break down all the reasons you might see brown tips or yellow leaf edges. This disease is worse in warm, wet or very humid weather. Some holes are on leaf edges, while others are in the centers of the leaves. Alternaria Leaf Spot: Small, round reddish brown spots with white to gray centers form on the upper surface of the leaves and along the midrib.The lesions may encircle the stems and cause wilt. THRIPS. While this is absolutely true, browning leaves are a sign that something is wrong. The pests feed by puncturing plants and sucking out the sap inside, creating the streaks. As mentioned, undernutrition isn’t the most common issue for houseplants. They seem to prefer hostas, but will attack virtually anything with leaves. In fact, too much sodium, potassium, magnesium, or other basic elements can cause problems. It can be hard to identify the cause because a lot of different things can cause similar symptoms. They don't start eating at the edge of the leaf, like caterpillars and sawflies, but go right for the middle. After all, this plant is supposed to retain its glossy green leaves for as long as it’s alive, right? After checking the link on leaf spot you included and my zinnias, I didn't see any brown/yellow spots, just holes. The most common zinnia ailment is zinnia blight (Alternaria zinniae), which initially causes small, red-brown spots to appear on the upper surfaces of leaves. When I grew the 'Profussion' zinias for several years, the bottom leaves always got it. 3. Avocado leaves with dry brown edges are usually due to dry air. Deficiencies or toxic buildups of macro-nutrients in the soil can turn leaves brown and are harder to diagnose. Root rot is basically a death sentence for your plant and will cause leaves to turn brown and die rapidly. If you notice that your peace lily’s leaves are beginning to turn brown, particularly at the tips and at the edges of the leaves, then you might be concerned. The plant is 30 inches (75 cm) tall and has only one main stem. Leaves have burnt tips, yellow tips, brown edges… These are some of the most common symptoms growers see on their cannabis plants. Attached are 2 closeups of affected zinnia leaves. Cheryl, my phlox get those brown leaves too. Why? CAUSE: Thrips are minute (less than 1/25 of an inch) insects that can be yellow, brown or black. Slug feeding damage presents as holes in leaves between a 1/4th to 1 inch in diameter. Heavily infected leaves turn brown and dry. The center of an older spot may drop out leaving a ragg ed hole. Either just the edges, or even the whole leaf. You can also just have brown leaf lips if you are not properly watering. Small, round, reddish brown spots with white to grayish white centers form on th e upper l eaf sur face. SYMPTOMS: Silver or bronze colored streaks on leaves, which eventually turn brown, dry and crumbly. Source: Question: I grew an avocado tree from seed this summer and now the edges of the leaves are turning brown. L ater, th e lesions become fairly large (up to 10 mm in diameter), irregular, dark reddish brown or purple, and dry (Figure 1). Environmental issues like excess light and heat can burn plants and turn leaves brown. Helena Answer: The avocado tree (Persea americana) rarely does… Often times, if you let your houseplant’s soil get bone dry, especially for extended periods, the lower leaves will typically turn brown and crispy. Don’t simply add more fertilizer if your plant looks poorly – overfertilization can burn sensitive roots and cause brown or rust spots on leaves and crisped edges. Common Disease Problems.