Stalk Borer

Every now and then (actually more frequently than I want to admit) I am totally stumped by a question. For example this morning I got a call from a gardener with a new garden spot (this was an important clue) whose tomatoes were dying one by one. She had done some good investigative work on her own and found a small larvae in the stem near the base of the plant. I asked Jim Jacobi, from our plant diagnostic lab and he was briefly stumped but came up with a possibility.

(PICTURE AT RIGHT FROM NCSU - IPM LINK BELOW)

After further investigation I agree with him that the likely culprit is the "Stalk Borer" (Papaipema nebris). As mentioned, the "new garden" comment was an important clue. Apparently this insect is mainly a pest in either "no-till" or recently tilled areas (previously in weeds or grass). According to the information linked above stalk borers tunnel in almost any large stemmed plant. Their host range encompasses at least 44 families and 176 species of plants. Some cultivated crops subject to infestation include corn, cotton, potato, tomato, alfalfa, rye, barley, pepper, spinach, beet, and sugarbeet. Although many weedy plants are infested, giant ragweed is preferred.

On the plus side this is not a serious pest on most garden sites. Tomatoes are not a favorite food source but happen to be the only thing nearby where they overwintered. Pesticides that could be used for control would be those that kill other larval species (check here for products) but I doubt this would be a serious recurring pest.

Arsenic and old ferns

Question: I have removed an old deck in an area where I want to plant a vegetable garden. I have been told there are unsafe materials that could have leached into the soil from the treated wood. What suggestions do you have to remedy this situation?

Answer: On February 12, 2002, the Environmental Protection Agency (EPA) announced a voluntary decision by the wood preserving industry to phase out the use of wood preservatives that contain arsenic for any wood products destined for consumer use. This affects virtually all residential uses of wood treated with chromated copper arsenate, also known as CCA, including wood used in play structures, decks, picnic tables, landscaping timbers, residential fencing, patios, and walkways. The EPA has not concluded that there is unreasonable risk to the public from CCA lumber, but believes that any reduction in exposure to arsenic is desirable.
Despite this assurance there is still some concern amongst vegetable gardeners and those who have small children who might play in (or eat) the soil that is contaminated. It can be very expensive to have soil tested by a private lab but Auburn University offers this service for a modest fee of $15 per sample. They can test for chromium, copper and arsenic if you request it on the soil test form available at any Extension office in the state. The normal soil test for plant nutrients cost only $7, so make certain you request this special test.
In a gardening situation, exposure to these elements can only occur if they move from the treated wood into soil or compost that is in contact with the wood, then are taken up by plants, and finally are ingested by humans who eat those plants. This is known as an “exposure pathway”. Low concentrations of arsenic, chromium, and copper occur naturally in water, soil, plants, and the human body. Copper and possibly chromium is essential for plant nutrition, and all three of these metals are essential for human and animal nutrition. That means humans must always have small amounts of these elements present in their diets. Although there are rare instances of dietary deficiencies of these elements, most normal diets supply adequate levels of each. Intake of excessive amounts, however, can have adverse effects on plants and humans.
Also on the positive side both copper and chromium are held very tightly to soil particles of clay and organic matter when the soil pH is maintained around 6.5 on the pH scale. This is also the best pH for vegetable growth. Unfortunately, arsenic is much more mobile within the soil and can be taken up into the plant roots and leaves. In general, most metals remain in the roots, with limited movement to edible portions above the ground. There are exceptions, of course: leafy green vegetables such as lettuce, spinach, and mustard greens tend to move arsenic from roots to leaves. In general, however, the greatest human consumption of metals results from eating root crops such as beets, turnips, carrots, and potatoes. In these crops, most of the metals remain in the surface skin and can be removed by peeling.
The ability of some plants to help take bad things out of the soil is called phytoremediation and a sun tolerant fern called brake fern has been found that has a remarkable ability to remove arsenic. The arsenic accumulates in the foliage and would require the gardener to remove the foliage and dispose of it off site or they are just recycling the arsenic. If you want to read the low down on this remarkable fern visit: http://www.malibuwater.com/Phyto.html and for further tips on gardening in contaminated soil visit: http://npic.orst.edu/ or call them at 1-800-858-7378. A company has a patented phytoremediating fern by the name of “edenfern” that you can purchase and find online with a simple web search.

Note: Photo from Stanford University photo collections

Ink Berry Holly

I recently talked with a Master Gardener trainee in North Alabama about her long row of Inkberry Holly that were dying one by one. She had brought a small sample of a dead stem for me to look at and I agreed it was dead. It is very hard to do a complete autopsy with a six inch sample of a large shrub. It is kind of like asking the CSI team to look at an ear and determine the cause of death of a person. I asked her to go home and dig up an entire plant so I could look at the root system.

Inkberry Holly (Ilex glabra) is native to the United States and is the only holly that spreads by underground runners. This bit of information would be helpful in the diagnosis. They are tall, multi-branched and evergreen. This holly can reach heights of 6 to 12 feet and widths of 8 to 10 feet. Inkberry holly is very adaptable to poor soils and is tolerant of extreme temperatures. It can often be found growing wild in the wetland areas of south Alabama although it is fairly drought tolerant. Inkberry holly is very pest resistant so I did not suspect an insect or disease. It is hardy in Zones 4 to 9. The leaves are a lustrous, dark green, and the fruit is typically black. This holly has many desirable features and makes a great screen plant which is the way it was being used in this case.

When she came back with a plant sample something jumped out (not literally) right away and I hope you can see it in the picture above. The plants were about 10 years old and had done fine until the year of the drought (2007). They started dying from the top of the hill and were making their way down (dying one by one). Even though the plants are fairly drought tolerant I suspected drought but I did not expect to see what I did. If you look closely you will see a layer of landscape fabric and a mass of roots above the fabric. This stolen producing plant had developed most of it's root system in the mulch layer that had increased year by year. The mulch had partially decayed creating a very good environment for roots (plenty of air and moisture) as long as moisture was plentiful. However, the extreme drought exposed the weakness of roots growing in mulch.

Mulch is great when used correctly and in moderation. If a landscape fabric is used the mulch must be removed when fresh mulch is added to avoid this problem. This same problem can develop without landscape fabric when mulch is used to excess (2-3 inches is plenty). When Dr. Jacobi at the Plant Diagnostic lab looked closely he saw few roots in the soil and almost all the roots above the fabric.

I thought this was very interesting and it may come up again after or during a dry year.

Slime Flux on Oak

Question: My oak tree is “weeping” awful smelling ooze down the trunk on one side. Insects and bees are constantly hovering around the ooze. What is it and will it harm my tree?

Answer: What you are describing is a fairly common occurrence on trees and it is called “wet wood” or, my favorite, “slime flux”. I am not sure who came up with a great name like “slime flux” but you have to admit it has a ring to it. It occurs in apple, birch, elm, hemlock, maple, mulberry, oak, poplar, willow and many other trees. Slime flux is very common in large, mature, landscape oaks, tulip poplar and elms.

Slime flux is a bacterial disease. The infected wood is frequently discolored or appears water soaked hence the name “wet wood”. Carbon dioxide gas is produced during fermentation by bacteria. The gas produces pressure in the wood. This pressure forces sap from the trunk through cracks in the trunk. This oozing of sap is termed fluxing. The flux is colorless to tan at first but darkens upon exposure to the air. As fluxing continues, large areas of the bark become soaked. Many different microorganisms grow in the flux producing a foul or alcoholic smell. As you mentioned, various types of insects are attracted to the slime flux. Did you notice if the bees and insects could fly in a straight line after feeding on the ooze?

Now I will address your original question about the health of your tree. If the fluxing continues for months on a branch rather than the main trunk, leaves on affected branches may be stunted and chlorotic. Grass may be killed where the flux runs down the trunk onto the grass. If as you described the ooze is from the main trunk the sap may continue to ooze for months, with no apparent damage to the tree. This slime flux may be triggered by heat, drought and other stress. Last years drought stress will likely cause a great increase in this problem this year and possibly next year.

There is no curative or preventive measures for slime flux except to maintain trees in a general good state of vigor and minimize wounds and injuries. In other words keep lawn mowers and weed eaters away from tree trunks. An insignificant nick in the trunk can lead to problems far down the road in terms of overall tree health. Treatment is not advised because more damage can be done to the tree in attempting to cure slime flux than the slime flux will do alone. It has been a common practice with slime flux to drill a hole in the trunk and insert a pipe, which does not cure the problem. Inserting a pipe only allows the sap to drip on the ground rather than run down the trunk. This practice is not recommended because it does not speed up the natural healing process. If there is loose or dead bark in the slime flux area, remove all of the loose bark and allow the area to dry. Do not apply a wound dressing.

The next time you are visiting with your neighbor across the backyard fence ask him if he has seen any slime flux lately. I am sure that will start an interesting conversation. For more information visit: http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/od8.html where much of the information for this article came.