Landowners learn to identify tree pests. [photo credit: UDFS Northeastern Area State and Private Forestry, www.na.fs.fed.us]
There are plenty of brochures to help landowners identify tree pests. I have a file folder full of publications pests like emerald ash borer. If you are like me, I see something that does not look quite right and want to know what’s going on. It may be nothing, but then maybe it is a real problem — time to figure out which.
Bring in the Experts
Fortunately, for those of us who live in Wisconsin, the UW Madison has experts whose job it is to diagnose tree problems for Wisconsin residents. The Plant Disease Diagnostics Clinic has an experienced plant pathologist who specializes in plant disease diagnostics. Additionally, the Wisconsin Insect Diagnostic Lab handles plant pests like insects, bugs, aphids, caterpillars. Questions or images can be sent to the Wisconsin bug guy, PJ Liesch: firstname.lastname@example.org.
Many of us prefer the do-it-yourself approach when dealing with tree pests. We want to know what we are seeing in the field without sending off samples and waiting for results. If you are like me, knowing for myself is better than having to depend on somebody else. I contact these folks for touch calls; they are great. I just do not want to load them down when I can figure the problem out for myself.
Do It Yourself
The Inventory Pest Evaluation and Detection (IPED) method provides an effective way to diagnose tree pest or disease problems. You can use this clear, simple and accurate way to detect and monitor pests wherever you live. The IPED Field Guide will help you identify the signs and symptoms of tree stress, insect pests, and diseases, letting you to make informed decisions. This guide is not intended to be used for diagnostic work, but rather as a resource guide to help you use the i-Tree Streets application at: http://www.itreetools.org/(link is external).
Most states have a plant diagnostic lab, frequently associated with the plant pathology department of a land grant university. If your state has one of those, make contact and find out their process for submitting samples for testing. There may be a reasonable charge. Other states use county extension agents to gather and send samples in for diagnosis.
Either way, the only way to know why you yucca plant has black spots and what you may be able to do about it is to have a qualified plant disease diagnostician test a sample from an actively growing plant with symptoms. That person can also tell you whether the spots are secondary to insect damage. Diseases and insect damage can be difficult to distinguish from one another.
If you have oak trees on your property, this is the time of year to cruise the woodlot and look for signs of oak wilt. Once a tree becomes infected, an entire stand can be affected because the disease moves across root grafts from one tree to the next. Oak wilt has been confirmed in 61 of Wisconsin’s 72 counties.
The Wisconsin DNR has a quick online Oak Wilt Guide that can help you assess your oak wilt risk. Now is the time to identify oak wilt if it exists on your land and make plans for dealing with it this coming winter.
According to the Wisconsin Department of Agriculture, Trade and Consumer Protection, oak wilt is transmitted by a beetle that is attracted to sap from open wounds. This beetle carries the oak wilt fungus (Ceratocystis fagacearum). That is why it is very important that landowners only prune oaks during the dormant season; late fall through mid-winter. Trees should not be pruned during April, May, or June or whenever the beetles are active.
There is no cure for infected trees. According to the US Forest Service, the only control action available is to isolate infected trees by cutting any root grafts between infected and uninfected trees. A trencher or vibrating plow set to 2-4 feet deep separates the root systems of adjacent oaks, preventing underground spread.
Infected trees should be cut down before April 1st; burned, chipped or covered with plastic for sixty days to prevent overhead spread of the beetles and fungus. New sprouts from infected roots need to be controlled with herbicide.
UW Extension has an informative Oak Wilt Bulletin that provides useful information about the pest; its diagnosis and control.For more information, contact the Wisconsin DNR Forest Health Staff.