Issue: April121, 2001

• Wood chips from treated stump?
• Watersprouts

Wood chips from treated stump?

Last year (April 2000) I had my China Berry trees cut down. The tree service sprayed a root killer on the exposed stumps. Now (in March) I had the stumps ground down. Can I use the mulch left over from the stumps or is it contaminated? Sam Romero Albuquerque

The answer to this question depends on which material was applied as a "root killer." Some materials that may be used in this manner cannot be absorbed by plants from the soil (or wood chips), others breakdown in sunlight or by microbial activity, and others are persistent and remain active in the soil for an extended period of time. If the product used was one of the first two mentioned (not absorbed from the wood chips or broken down by light or microbes), then after one year there should be no cause for concern. If it is the last class of materials that persist and remain active, then there will be a problem. In this last case, it would not be wise to use the wood chips for mulching or for composting.

Contact the tree service to determine what product they used and if it will be persistent and active. Ask also for its mode of decomposition in the environment. This should give you some idea regarding the probability of problems if you use the wood chips for mulching.

You can also conduct a "bioassay" by taking some of the wood chips, mixing them with soil or potting soil, and placing the mixture in flower pots. Plant some bean or radish (broadleaf plants) and some corn or grass seeds in the pots. Use five replications (different pots) for this bioassay. Plant an equal number in five pots of soil or potting soil without the wood chips as a control for comparison purposes.

If the chemical remains in the wood chips and causes one or both of the plant types (broadleaf or grass) to develop symptoms or die, then don't use the wood chips in the landscape. The control pots without wood chips in the soil should show no symptoms. If the control pots also show symptoms, then the problem is due to the conditions under which you are growing the plants (or the particular potting soil you used). Over-watering or under-watering is the most likely problem in the growing conditions. If both the control and the wood chip pots show symptoms of problems, rerun the bioassay with different potting soil and with more care to watering.

Watersprouts

My apple tree has some new stems that grew straight up from the branches last year. They don't look productive and have ruined the shape of the tree. Why did this happen and what should I do?

These are watersprouts which usually result from the tree's attempt to recover from heavy pruning. They can occur without pruning, but they are less common without heavy pruning. Watersprouts are usually non-productive for a few years but in time will become productive.

You can prune, removing them at the point at which they developed from the other branches, or you can cut them just above a bud (a foot or more above the point of origination in a location where they will not damage the form of the tree).

You can prune to keep the branch if it is in a good location where it doesn't rub on other branches or is not too shaded by other branches. In a couple of years it should develop blossoms and begin producing fruit.

It is too late for this type of pruning in most of New Mexico since leaf and flower growth has already begun. If essential, they can be pruned now; otherwise, wait until next fall when the tree is dormant.

If new watersprouts develop this year, remove them in the summer while they are still small, tender and green.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!