|Landscape flooding can create an environment for nearly all major plant pests. |
Photo from kimkollage.files.wordpress.com.
Storms and natural disasters are always difficult to prepare for and manage afterwards because they occur infrequently and everyone is usually physically, emotionally, and intellectually exhausted. Since there are not many reports on which plants grow well in production after flooding, the following is a compilation of ideas from specialists based on some research, reports in the landscape, experience, and intuition. These insights are for Hurricane Matthew (Oct. 2016) and may not apply to other storms or disasters that occur at other times of the growing season.
Containerized plants that were flooded with water containing silt or fine particles may result in decreased substrate air space and increased water holding capacity. Therefore, reevaluate irrigation scheduling to ensure that plants are not overwatered and that ample air is available to the plant roots to minimize potential root diseases.
At this time it is not necessary to apply a nursery wide preventative spray of permethrin (or similar pesticide) to prevent borers from attacking trees this fall. In general, borers are not active in the fall and insecticide applications will not remain effective through the spring when flight begins again. Therefore, monitor traps and wait until borers emerge in spring before beginning a spray program.
Additionally, follow Steve Frank on twitter (@ornapests) to learn when beetles emerge in spring 2017. Trapping at your location is the best way to know when insects are active. For nurseries spread over different properties or very large nurseries, deploying several traps can help identify “hot spots” and prioritize pesticide applications. Begin trapping for beetles at your nursery by using this guide: Granulate [Asian] Ambrosia Beetle Trapping.
Industry articles and publications about flooding and ambrosia beetles:
New Research to Help You Beat Ambrosia Beetles
Developing a Media Moisture Threshold for Nurseries to Reduce Tree Stress and Ambrosia Beetle Attacks
Other borers, for example clear-winged borers, are known to attack stressed trees up to 1-2 years after the stress has occurred. Follow this link to learn their life cycle and methods to scout and monitor for them: Peachtree Borer in the Landscape. Maintaining a current spray program next spring when those borers emerge would be ideal. Flatheaded appletree borers emerge later in spring and also attack previously stressed trees especially if some sort of wound is present. Trees may already be infested with borers from earlier this spring, so scouting is important. Their life cycle is here: Wood Boring Beetles in Trees.
A wide range of fungi incite canker diseases in both hardwood and conifer hosts by invading the bark, cambium, and outer sapwood of branches and stems weakened by mechanical injuries, insect feeding, water extremes, or other diseases. Branches and main trunks of trees submerged in flood waters or injured by floating debris will be prime targets for invasion by canker fungi. Some of the most common canker diseases include Nectria, Cytospora, Botryosphaeria, and Botryodiplodia.
Cankers appear as localized dead areas on branches or stems and are commonly associated with wounds or dead branch stubs. They often appear discolored or sunken, and the bark may or may not remain attached to the face of the canker. Some canker diseases such as Nectria produce zonate or target-like cankers in response to successive layers of callus tissue forming at the progressing edge of the canker. Cankers can girdle branches or small stems and result in wilting or dieback. Canker diseases are rarely fatal to their hosts unless large or multiple cankers girdle the main stem.
Because wounding and predisposition play a role in the development of canker diseases, the best approach to management is to minimize tree stress and injuries.
Species of Phytophthora and Pythium, commonly known as water-mold fungi, are ideally suited for waterlogged soil conditions. Plant roots stressed by reduced oxygen in waterlogged soils exude more amino acids and ethanol, which attract infective, swimming spores (zoospores) to root surfaces. Zoospores are dispersed in surface water such as flood, runoff and irrigation waters and therefore; an increase in root and collar rot diseases caused by species of Phytophthora and Pythium can be expected.
Symptoms include stunting, leaf chlorosis, reduced leaf size, basal stem cankers which often ooze sap, root and collar decay, crown dieback, wilting, and death. Pythium spp. cause damping-off and root rot on young seedlings in nurseries and can infect nearly all conifers and hardwoods. Phytophthora spp. incite root and collar rot diseases, as well as a number of foliar diseases, on a wide range of nursery and forest tree hosts including Rhododendron, Azalea, Kalmia, Abelia, Leucothoe, Viburnum, Pieris, Camellias.
Avoiding waterlogged or puddled areas is key to managing these pathogens. Removing plants from waterlogged areas as soon as possible will help limit disease. Additionally, there are several fungicide drenches and sprays available that will help reduce disease. See Relative Effectiveness of Various Chemicals for Disease Control of Ornamental Plants for products.