Oak Wilt

submitted by Damon Waitt

A recent news story in the AAS raises the question whether Allandale residents should be concerned about oak wilt in our neighborhood. Unlike Lakeway and other areas in the Texas Hill Country, the Allandale urban forest is not characterized by dense stands of live oak with interconnected root systems that facilitate the spread of the oak wilt fungus. That’s the good news. However, oak wilt can also be transmitted by sap feeding beetles carrying spores from infected red oaks to improperly pruned or wounded live oaks. Following are some common question and answers about oak wilt if you are not familiar with this disease that is responsible for killing over a million oaks in central Texas.

What is oak wilt?

Oak wilt is an infectious disease caused by the fungus Ceratocystis fagacearum, which invades and disables the water-conducting system of certain oak trees.

Where is oak wilt a problem?

Oak wilt has been found in over 60 counties and in almost every city in Central Texas. It can be a problem wherever live oaks tend to be the predominate tree. It does not matter whether they are transplanted or naturally grown.

Which oaks get oak wilt?

White oaks are the least susceptible. They generally survive for a number of years with the disease. Common White Oaks include Post, Bur, Chinkapin, and Monterrey oak.

Red oaks are the most susceptible. They typically die within 2-4 weeks of symptom appearance. Common red oaks are Spanish, Texas, Shumard, Pin, and Blackjack oak.

Live oaks die in the greatest numbers, most often in expanding areas called Oak Wilt Centers.

How can I tell if my trees have oak wilt?

Live Oak trees die within 6-12 months. Adjacent trees begin to drop their leaves and die a few months later. Live Oaks also show veinal necrosis where the area around the leaf vein turns brown but the rest of leaf is still green.

Red Oak symptoms are less distinct. Leaves turn pale green then brown usually remaining attached for a period of time. This can begin on one branch and quickly engulf the entire tree. Trees generally die within 4-6 weeks.

How does oak wilt spread?

Oak wilt is spread by two methods, root transmission and by sap-feeding (Nitidulid) beetles. The fungus spreads from tree to tree through connected roots, either by root grafts or through a common root system. When oak wilt does infect a red oak species these trees under the right conditions can form what is called a fungal mat. The fungal mats form underneath the bark and produce millions of spores. Fungal mats have a very sweet smell like ripe fruit which attracts Nitidulid beetles. The beetles feed and breed on fungal mats and pick up spores of the oak wilt fungus on their bodies. If a contaminated beetle lands on a fresh wound on a healthy oak, that tree can become infected with oak wilt.

How can I prevent my trees from getting oak wilt?

New oak wilt centers are started when a contaminated beetle finds a fresh wound on a healthy oak tree. Insect populations in general increase during mild spring like weather and mild spring like weather is when fungal mats are most likely to form. So the most likely time a contaminated beetle will find your tree is when the weather is mild. The best time to prune is when a contaminated beetle is least likely to find your tree. The heat of summer and the cold of winter are when the beetle populations are the lowest and fungal mats are least likely to form. Therefore that is the best time to prune to prevent against an oak wilt infection.

The Texas Forest Service recommends that you always paint pruning cuts as soon as the cuts are made. When pruning cuts are made during the proper times of the year there still maybe a few contaminated Nitidulid beetles in the area. If the pruning cuts are painted with a pruning paint or latex paint this will prevent these sap feeding Nitidulid beetles from feeding and infecting your oak tree with the oak wilt fungus.

Adapted from Common Questions About Oak Wilt (Texas Forest Service). For more information about oak wilt, visit www.texasoakwilt.org.

Damon Waitt
Senior Botanist, Lyndon Baines Johnson Wildflower Center
Allandale Resident

Comments

[ERIC]

I believe the oak wilt show is being aired from 8am to 10am on Sunday.

[Victor]

There is an oak wilt symposium currently under way in Austin.

http://texasoakwilt.org/NOWS/conference.html

One of the KLBJ AM weekend garden shows this weekend will feature a Texas certified arborist Don Gardiner who will present a summary of the symposium and answer questions from callers. I believe it's one of John Dromgoole's shows, but I didn't note which one. If someone else knows, please share.