Dieback on Red Maples caused by Bot Canker

Summary

In recent years, Bot canker has caused an estimated loss of $500,000 to deciduous hardwood tree nurseries, particularly on red maples. The canker disease kills the branches resulting in extensive tree culling.

Situation

During 2018-2019, extensive damage to deciduous hardwood trees and tree seedlings, particularly red maples, grown in field and container nurseries attributed to Bot canker was observed across Georgia. In some nurseries, up to 80% of the affected trees were unmarketable or dead and had to be culled. Crop loss is estimated to be over $500,000 based on preliminary estimates. The true extent of the disease problem is unknown because the damage often goes unnoticed until the tree fail to leaf out in the spring. Extensive tree culling not only affects the current marketable tree crop, but also future sales of larger trees. Botryosphaeria ("Bot") canker is caused by several species of fungi, which are generally considered weak pathogens. There is limited information available on controlling the canker disease on deciduous trees, such as red maple.

Response

A field survey a tree nurseries in Georgia was conducted in 2019 to determine the extent of the canker disease and to collect samples to identify the pathogen causing the disease. Growers were also asked to provide the number of trees that were culled due to the disease to estimate their crop losses. Over 500 samples were collected and processed. County ANR extension agents with tree nurseries also toured nurseries with extension specialists in horticulture and plant pathology so they could see the disease in the field as well. Information on Bot canker disease was presented at over 15 county and industry meetings and in-service trainings to educate extension personnel.

Impact

Two species of Botryosphaeria were recovered from the red maple (Acer rubrum) tree disease samples. However, the vascular wilt fungal pathogen, Verticillium sp., was recovered from redbud (Cercis candadensis). The Verticillium pathogen causes Verticillium wilt, which is a disease that used to be rarely seen in Georgia. A preliminary fungicide control recommendation was provided to growers. The effectiveness of the fungicide applications will not be known until Spring 2020. A conservative estimate of crop loss is over $500,000 in 2019. The disease will continue to be monitored in 2020.

State Issue

Plant Production

Details

• Year: 2020
• Geographic Scope: State
• County: Clarke
• Location: College Station, Athens
• Program Areas:
  • Agriculture & Natural Resources