Article and photos by Peg Smith -
I always give unknowns in my garden a chance to prove themselves before taking drastic action. For a couple of years, I have been cutting back what I finally decided had to be a perennial weed; in this case, I found that it was ‘pokeweed’ most likely deposited by seed from a bird.
I consulted Don Shor of Redwood Barn Nursery, and his information matched my experience with Pokeweed Phytolacca americana. Per Don, “This is one of the most commonly posted plants on plant identification groups on Facebook. It’s a pretty plant, and the seedlings always look vaguely familiar, so we leave them at first (I have them on my farm) and then the berries are very attractive to birds. One of those interesting plants that is both edible, if carefully prepared, and highly toxic. It has spread freely throughout California but is typically not highly invasive in any one place.”
Pokeweed Phytolacca americana is native to east of the Continental Divide. Plants have a large white taproot and can grow from three to nine feet. The blossoms are pale green to white along a spike producing mature purple/black berries.
Common pokeweed is poisonous to mammals and can be fatal to humans and livestock. All mature parts of the plant are toxic to humans. Only the very young leaves are possibly edible after a leaching process involving multiple cycles of boiling and draining to remove toxins. Not a risk I’m considering taking. I will definitely be digging out the taproot this year.
A fungus among us!
I am fascinated by the ecological power of fungus, an essential part to the breakdown of biological matter in the circle of our biosphere. These shaggy parasols have emerged in the garden in greater numbers this year, possibly because of the cooler, wetter spring and fewer days of extreme summer temperatures.
There are three closely related species that are commonly known as ‘shaggy parasols’ in the genus Chlorophylum. The newly emerged fungus has a cap that is oval. As it matures, it becomes flatter and has thick brown scales with protuberances on the fleshy white cap, which grows to almost eight inches in diameter.
‘Shaggy parasols’ are considered edible, but unfortunately, they look identical to the poisonous Chlorophylum molybdites. It is not recommended for inexperienced foraging mushroom hunters. Misidentification of the Chlorophylum molybdite mushroom is one of the most common causes of mushroom poisoning.
If you have an interest in learning more about fungi, the Field Guide to Mushrooms of Western North America1 is informative for both novice and experienced mushroom lovers.
Terminal tomato plants
There’s nothing more discouraging for a vegetable gardener than to have grown their own tomato seedlings, or planted the healthiest seedlings available, and after following all the advice on how to care for tomatoes, they find that as the summer heat intensifies that they appear to be slowly dying. As with most answers to plant problems, some detective work is required to identify the cause.
There can be several reasons for a tomato plant to ‘give up the ghost’ - poor care, disease, or pest. One of the most common reasons for tomatoes to wilt and die in summer heat is the presence of either or both of two fungi found commonly in soil. Verticillium and Fusarium fungi are endemic to our local soils, but which of these is the cause of the tomato plant's demise is hard to absolutely confirm without lab tests. However, there are some good guidelines to differentiate the effects of fungal disease from other possible causes.
The fungal disease is introduced into the plant through the roots and affects the water-conducting tissues. Plants can no longer take up enough water to survive, so leaves wilt and stems become brown. Both Verticillium and Fusarium can survive in the soil for many years, and there is no effective fungicide treatment.
Verticillium’s early symptoms are yellowing of older leaves, curling and limp leaves increase on the plants, eventually turning brown. Fruit may continue its development, which is usually small but edible. Verticillium has a wide host range, is more general, and affects both vegetables and ornamentals. Verticillium prefers moist soil and cooler soil temperatures (55° – 75°F).
Fusarium is more host specific with Fusarium oxysporum f.sp. lycopersici causes disease only in tomatoes. It can infect other non-tomato crops (melons, peppers, sunflowers) without causing any symptoms. Fusarium is hard to control as it persists in both tomato and non-tomato plant residue in the soil. Fusarium prefers warm soil temperatures (80°F). Symptoms often develop on one side of the plant or branch, showing bright yellow leaves; sometimes leaves will yellow on one side of the central vein. Older leaves are affected first, foliage yellows, wilts, and turns brown.
If you cut across one of the still green lower stems, the water conducting tissues will have turned brown and look stained. A healthy tomato’s tissue is light green to white.
If you have identified a possible wilt disease, remove the plant, including as much of the root matter and fallen leaves as you can. It is best to dispose of the plant in the green waste bin or garbage bin. Home compost will not reach the temperatures needed to kill the fungus.
Why is the fungus in my soil?
There are several ways for either Verticillium or Fusarium to be introduced into the garden. Most commonly through infected transplants, seeds, tubers, or spread by tools and equipment from one area to another. Wood chip mulch from an infected tree can also be a source. Verticillium and Fusarium can survive passage through the digestive system of horses and other animals. If an animal has consumed infected plant matter, their manure can be a source.
What can I do?
When a verticillium or fusarium infection is determined in one area of the garden, do not transplant plants from that area to another. A small amount of soil on the roots of plants can spread the fungi through the garden.
Disinfecting tools after their use in an infected area is very important. Wash or brush off soil from tools, then use a 70 – 100% solution of alcohol (isopropyl alcohol is readily available) to dip or wipe down tools.
There are both Verticillium and Fusarium-resistant tomatoes available, usually labelled clearly as V, F or VF resistant. Resistant does not mean immune, and if conditions are prime a resistant tomato may still show signs of infection, but will continue to produce, although the fruit will be smaller.
Heirloom tomatoes are not resistant to verticillium or fusarium and can be grown in disinfected containers with fresh potting soil or in areas of the garden where there has been no evidence of verticillium or fusarium disease.
Tomato seedlings can be grafted onto Verticillium and Fusarium-resistant rootstock. This requires some patience, but can be done by the home gardener. Grafted tomato seedlings are becoming more common in commercial outlets. For more information , see this article on Tomato Grafting from UC Master Gardeners of San Luis Obispo County
Rotating crops through an area that you have identified as having verticillium or fusarium present will help reduce the fungal population. Also check for specific varieties of peppers, eggplant, potatoes, broccoli, and squash that have resistance.
With our intensely hot summer weather, soil solarization can be a tool in controlling fungal soil populations. This requires the soil to be cleared of as much plant matter as possible, then a layer of clear UV-resistant plastic is laid over the soil with the edges tight to the soil layer. This will increase soil temperatures and reduce the fungal population. The plastic needs to remain in place for about six weeks. For more information, see UC IPM’s article Soil Solarization for Gardens & Landscapes.
It may be disheartening to see plants that you have grown wither, but with good garden hygiene, crop rotation, and careful selection of varieties, a bountiful harvest of tomatoes and vegetables is possible.
Reference
1Davis, R. M., Sommer, R., & Menge, J. A. (2012) Field Guide to Mushrooms of Western North America. University of California Press.