Lilac Disease or Pest PLEASE HELP

Asked September 30, 2015, 1:34 PM EDT

My small lilac bush, about 1/3rd of the plant, is showing signs of distress in the form of discolored leaves (Gray like in color) but the stems seem to be flexible, not yet dead when bent. They are all on the same side of the plant and located together at the base where the plant goes into the ground and root system. Once I noticed the leaf discoloration I inspected the plant and found that a white web (very fine and very thick almost like a cotton tee-shirt) had connected to every stem of the area of the plant with the discolored leaves. In the center of the web, there was a hole about the size of a quarter; this was also weaved very tight and thick, leading to the ground. I could not tell if the hole made entry into the ground as there was too much of the web as well as plant vegetation covering the base of the plant. I took a small stick and totally removed the entire web being careful not to damage the stems or leaves at that level of the plant body. I made certain to clear away all contact point the web had with every stem.

Several (3 or 4) days later I went back to inspect the area for any attempt of rebuilding the web I had removed. The web had not been rebuilt, however at the top of the plant strung between 2 healthy stems was the beginning of a new web, and this time I got a close look at the spider making the web I had just found. The difference was this time the web was at the top of the plant and not at its base. The spider was large as big as a nickel or a little bigger, and looked as if it could have gotten through the hole in the center of the first web. It was brown in color, with a large backside, that is all I can say as to the description of the spider, as I smashed it beyond recognition.

I would like to know if you have any data about the condition of my lilac problem. 1st the color of the leaves, gray like, and the web I found and destroyed, and the spider I killed. I realize that is not a lot of information but I would have to loose the plant as it has taken me 5 years to get it from the 6 inch sapling to the now 24 to 28 inch plant that flowered this year.

Leo Trimmer

501 E Street

Pawnee City NE 68420

(402) 852-2788

Pawnee County Nebraska

1 Response


First, all spiders are beneficial and should be conserved whenever possible. They eat the "bad bugs". No spider is harmful to plants. (Some spider mites can damage plants, but their webbing is so tiny you can barely see it without a magnifying glass). Based on the description of the web you provided, you definitely had a beneficial spider.

On the grayish leaves, your lilacs may have powdery mildew. This minor fungal disease is very common on lilacs and even more common this year with our cloudy conditions and increased rainfall. The disease appears as a grayish-white powdery-like substance on leaf surfaces, and it cannot be rubbed off. This disease will not kill a lilac; just make leaves appear grayish-white. Photosynthesis is somewhat reduced, but only on the leaves that are affected. While mildew does not need to be controlled, see the link below for information on managing it and for photos. If you do not think powdery mildew is the issue on your lilac, a photo would be helpful for identification. Thank-you!