Ask a Master Gardener: Some trees more tolerant of flooding

Q: My tomatoes in my raised beds are looking terrible (see photo). I can't understand what happened. I got some manure from a farmer friend who told me it should be OK as it was well aged, two to three years.

A: The leaf puckering, leathering and cupping observed on the plants are consistent with symptoms of injury from a synthetic auxin herbicide. There are several herbicides such as picloram, 2, 4-D and dicamba in this group that can exhibit similar symptoms on sensitive plants like tomato. Given the recent introduction of manure, it is likely that former product (picloram or similar) which is in a popular in a pasture herbicide "Grazon" (but there are a number of others). Unfortunately, this active ingredient passes through to the manure and affects sensitive plants for many years later. Aging or composting might seem like an ideal way to break it down, but sunlight, not heat breaks it down. Thus, a big pile preserves the negative effects. The label of these herbicides clearly explain the risks, but too often, individuals don't read or heed the various warnings. To augment breaking down this material, plant cover crops from the grass family and till them in, repeat as much as possible prior to planting next year (e.g. sorghum this summer, oats in the fall and annual ryegrass in March). Sweet corn is tolerant of these products and cucurbits (melons, squash and cucumbers) are less sensitive. Keep tomatoes out of this area (if possible) for two years.

Q: I am concerned about those trees sitting in floodwater for such an extended time in the park area of North Jefferson City. How long does it take to damage trees? Are there other problems once the water recedes?

A: Fortunately for most trees, the prospect for survival and continued growth is good. Even flood-sensitive trees will escape injury if floodwaters recede in seven days or less. But, if floodwaters cover roots of sensitive trees for longer periods, injury symptoms such as leaf chlorosis (yellowing), downward curling of leaves, leaf drop and branch dieback may occur. And in a few extreme cases, entire trees may die.

Which trees are intolerant of flooding? Some of the more common species used in Iowa are sugar maple, white oak, yellow buckeye, tulip tree, black walnut, redbud, linden, red oak, and most pines and spruces. Researchers have found these species suffer severe injury or die if floodwaters persist over their roots for one month or less.

Moderately flood-tolerant species that have actually survived an entire growing season of flood conditions include hackberry, hawthorn, osage-orange, boxelder, river birch, American elm and sycamore. Species classified as being flood-tolerant, surviving as many as two growing seasons with their root systems under water include silver maple, sweetgum, red maple, green ash, honeylocust, eastern cottonwood and bald cypress.

Sand and silt deposition over the roots of the trees you mentioned may also be a concern. It doesn't take more than 1-3 inches of deposition to start causing root system issues for many tree species.

It may take a while before the full damage of the flood is realized on the garden's trees, so do warn the gardeners that the trees may look fine after the flood but could start to decline quite a while after the flood recedes. Root rots may start working on those fine feeder roots and eventually lead to tree death one, five and 10 years down the road.

Thanks to Robbie Doerhoff, forest entomologist with Missouri Department of Conservation on this question. For complete info, see: hortnews.extension.iastate.edu/1993/7-14-1993/flood.html

This observation came in from an individual involved in the question & discussion: In 1993, as the Missouri River floodwaters receded in North Jefferson City and also the Osage River in the Lower Osage Basin, the maples and oaks seemed to decline rather quickly. In some areas now, there are still only large sycamore and river birch surviving along with the new trees that have sprouted since 1993. There is a grove of trees nearby the airport, which had trees decline as described in this article (by type over time). It was sad to watch over the years, but maybe we should think positively that this is how the earth renews itself, and carry on.