- Author: Help Desk Team
Do your tomato plants suffer from lack of vigor, yellowing leaves, and poor fruit production? These symptoms are associated with many different problems, including lack of soil nutrients, excess salts in the soil or irrigation water, poor drainage or waterlogged soil, or a variety of plant diseases.
Trying to figure out what has gone wrong in your garden may not sound like much fun, but it is a necessary and important part of gardening. The more information we have, the easier it is to diagnose the problem when our hopes for a bountiful garden turn to disappointment. A gardener may change how they care for ailing plants by applying more or less water, fertilizing, or even spraying with pesticides or fungicides. Often nothing they do makes a difference, the plants continue to fail, and many eventually wither and die.
If this describes your experience growing tomatoes, you may find that a wilt disease could be the culprit. Armed with the information in this article, you can determine whether a wilt disease is a problem in your garden.
What is a wilt disease?
Verticillium wilt and Fusarium wilt, also called vascular wilt diseases, are soil-borne fungal diseases that infect susceptible plants through the roots, growing into and plugging the water-conducting (vascular) tissues. This causes the plant to be unable to take up sufficient water needed for healthy growth. Verticillium and Fusarium cause similar symptoms in their hosts.
Once these pathogens are in the soil, they are difficult to manage as they can survive in the soil for many years and possibly decades without living host plants. There is nothing that can be done for plants that are already infected with either Verticillium or Fusarium wilt. There are no fungicides available for application to the plants that can be used to control these diseases.
Verticillium wilt is widespread and very destructive and is common in our area. It is estimated that over 300 plant species throughout the world are susceptible. The pathogen responsible for the disease in tomato plants is Verticillium dahliae. This fungus favors moist soil and relatively cool (55–75° F) soil temperatures.
Early symptoms include a progressive yellowing of older leaves and wilting of shoot tips at the top of the plant during the warm part of the day.
Later, leaf margins curl upward, and leaves often drop off. Any fruit produced is usually small. The wilting becomes progressively worse, and although plants may not die, their condition can be so poor that it is not worth the effort to try to keep them going. Verticillium wilt will also infect several other common garden plants.
The list is a long one, and includes many garden vegetables as well as shrubs, trees and ornamentals. Below are links to lists of plants that are susceptible to Verticillium and Fusarium wilt.
Fusarium wilt presents with symptoms that, while not identical, are quite similar to Verticillium wilt. Although it is not as widespread as Verticillium, Fusarium is also a common disease in tomatoes. It differs from Verticillium wilt in that the Fusarium oxysporum pathogen has several forms which are host-specific. This means that the specific Fusarium fungi, Fusarium oxysporum f.sp. lycopersici, only causes disease in tomato plants.
Unlike Verticillium wilt which has a very wide host range, the strain of Fusarium that infects tomatoes will not cause disease in other plant species. It can infect many different non-tomato crops, including melons, pepper, and sunflowers without causing any symptoms, and will persist in both tomato and non-tomato plant residue in soil. Infection and disease development in Fusarium wilt are favored by warm soil temperatures (80° F) and low soil moisture.
The symptoms of this disease are bright yellow leaves that commonly appear first on just one side or one branch of a plant. The leaf symptoms will also often appear as yellowing on just one side of a leaf, delineated by the central vein. These symptoms are distinctive and can be very helpful in making a diagnosis. The foliage yellows, wilts, then turns brown and dies. Older leaves are affected first, followed by death of the entire plant.
To confirm the diagnosis of a wilt disease, cut open one of the lower stems of the affected plant. If the vascular tissue inside the stem has turned brown or darkened (in contrast to the white or pale green color inside a healthy stem), it is a good indication that the plant has one or the other of these fungal diseases.
If you confirm the presence of the disease, you should remove the infected plant (including as much of the roots and plant debris as possible) and dispose of it in the garbage or your green waste bin. Don't compost it yourself since home compost piles rarely reach and maintain temperatures hot enough to kill the disease pathogens.
How did this disease get into my garden?
Both Fusarium and Verticillium fungi can be introduced on infected transplants, seeds, and tubers, or spread on equipment contaminated with infected soil. Wood chip mulch that comes from an infected tree can also spread the Verticillium fungi from one area to another. Because it can also survive in the digestive tract of horses and other animals who have consumed infected plant material, animal manures can sometimes be another source.
What steps can I take to keep these diseases from spreading throughout my garden?
- Do not transplant plants from one area to another. Moving soil, even a very small amount, can spread the disease.
- The fungi can also be transported on equipment such as shovels, trowels, etc. Thoroughly clean and disinfect tools used in the infected garden bed before using them in other areas of your yard or garden. First wash or brush off any soil or plant debris, then disinfect your tools with alcohol. You can either wipe or dip them in a solution that is 70–100% alcohol. Isopropyl alcohol is widely available and can easily be found in many stores.
- More on products used to sterilize garden tools, and their pros and cons: https://gardeningsolutions.ifas.ufl.edu/care/tools-and-equipment/disinfecting-tools.html
I suspect that I may have a wilt disease in my garden. Will I still be able to grow tomatoes and other vegetables?
Choosing disease resistant tomato varieties is a way for gardeners to prevent the losses due to wilt diseases. Many disease-resistant hybrid tomato plant varieties have been developed and are available to the home gardener. They can be found at our yearly Great Tomato Plant Sale, in seed catalogs, and at local garden centers. The letters V and F following the variety name in seed catalogs, on seed packets, or plant labels denote varieties that are resistant to Verticillium and Fusarium wilts.
It is unfortunate that nearly all heirloom tomato varieties are susceptible to wilt disease. Heirloom tomato varieties would be better grown in containers with fresh potting mix or in a garden area that has not developed the pathogens (for example, an area in which you have never previously grown tomatoes or other crops that are vulnerable to the wilt diseases).
In addition to tomatoes, several vegetable plants including peppers, eggplants, potatoes, squash, and melons can suffer from Verticillium wilt. The Fusarium fungus specific to tomatoes will only affect tomatoes and will not cause disease in other vegetables. If you plan to grow other vegetables in the same garden bed where a tomato plant suspected of having Verticillium wilt has grown. Check the links below or do an internet search to determine whether the variety you want to grow is susceptible to the wilt diseases. For example, you can search “is broccoli susceptible to Verticillium wilt?”
Soil solarization is another method that can be used to reduce the amount of these pathogens in the soil. It involves heating the soil by covering it with clear plastic for four to six weeks during the summer. It is most effective when day length at its longest, and temperatures are high.
Links to additional information:
• Soil solarization: https://ipm.ucanr.edu/PMG/PESTNOTES/pn74145.html
• Verticillium wilt: http://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/tomvertwilt.html
• Fusarium wilt: https://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/fusariumwlt.html
• Plants resistant or susceptible to Verticillium wilt: https://depts.washington.edu/hortlib/resources/ucdavis_verticillium.pdf
• Plants susceptible to Fusarium wilt: https://extension.usu.edu/pests/research/fusarium-verticillium-wilts
To find great gardening info, a list of previous blog postings, and information on our Great Tomato Plant Sale go to our website: https://ccmg.ucanr.edu/
Help Desk of the UC Master Gardeners of Contra Costa County (SMH)
When tiny tree-killing beetles first arrived in Southern California several years ago and began destroying urban and riparian forests, they raised widespread concerns among both tree experts and affected communities. More recently, invasive shothole borers have captured far less attention, and many people may think the pest threat is over. Unfortunately, it's not!
While significant progress has been achieved in invasive shothole borer research, surveying, trapping, and management programs, these beetles are still an ongoing threat to the state's urban and wildland trees. Continue reading to find out what you can do to be part of the solution to this invasive pest issue.
What are invasive shothole borers?
Invasive shothole borers (ISHB) (Figure 1) are sesame seed-sized beetles. They tunnel into trees and introduce a fungus that they use as their food source. As the fungus grows, it causes a plant disease called Fusarium dieback that leads to branch dieback, tree decline, and, in many cases, tree death.
The beetles and fungi can live and reproduce in a wide range of tree species including more than 65 types of trees found in California. The most highly susceptible trees include many species that are commonly used for landscaping like sycamores, some oaks, cottonwoods, and box elder. Invasive shothole borers can attack healthy, stressed, or diseased trees.
What's the problem?
Urban trees provide us with many benefits to our health and our economy. The trees around us reduce our stress levels, provide shade, allow for energy conservation, improve air quality, reduce stormwater runoff, and provide habitat for wildlife. It is important to protect them from invasive pests, like invasive shothole borers, which could potentially kill one out of three urban trees in California.
ISHB-infested trees can quickly become a public safety hazard. Trees with heavily infested branches can be especially hazardous. The combined damage of the fungal disease and the beetle's tunneling activity weakens the wood, causing limbs to break and fall (Figure 2). In addition, severely infested trees will become a constant source of beetles that can disperse and infest neighboring trees.
Where are they found?
These non-native beetles are now established in many areas of Southern California and the Central Coast. Female beetles are capable of flight over short distances, allowing the pest and its associated fungi to spread into new areas. Beetles can also be transported in infested firewood and green waste, leading to dispersal over much greater distances.
What to look for
Because they are very small and spend most of their lives inside their tree hosts, you probably won't see the beetles themselves, but there are several common signs and symptoms associated with their infestations: ?Beetle entry holes: When the beetles tunnel into the trees, they make small, perfectly round holes, each about the size of the tip of a medium ballpoint pen (Figure 3).
- Tree response symptoms: One or more of the following symptoms usually accompany the presence of entry holes (symptoms vary by the tree species): dark, wet staining; thick gumming; sugar-like buildup; or boring dust (resembles fine sawdust).
- Dieback: Dead or wilting branches can be a sign of a severe infestation. If you see dieback on trees, check for entry holes on the trunk or the branch collars.
What you can do
Several steps can be taken to prevent pest problems and manage infestations.
- Keep your trees healthy. Proper irrigation and maintenance will keep trees strong and help protect them from ISHB and other pests.
- Check your trees. Look for the common signs and symptoms listed previously. Regular monitoring ensures that infestations are managed early, before they cause dieback or tree death.
- Confirm suspected infestations using the detection tool on www.ishb.org. ?Know your management options. When possible, pruning infested branches is recommended. Low and moderately infested trees can be treated. You will need to contact a licensed professional to apply the treatments. Severely infested trees may require removal.
- Take care of green waste. The beetles can survive in cut wood for weeks or even months. Proper disposal of green waste includes chipping infested wood, followed by solarizing or composting the chips.
- Consult a professional. A certified arborist or pest control professional would be able to provide recommendations based on the conditions of your tree. Your County Agricultural Commissioner's office and UC Cooperative Extension office may have more knowledge about current ISHB monitoring and management programs in your area.
- Use locally sourced or heat-treated firewood. These beetles and other tree-killing insects often reach new locations by hitchhiking in firewood. Buy firewood where you will use it, and only buy the amount of firewood you need.
Visit www.ishb.org for more information about invasive shothole borers.
Small beetles are causing big problems in Southern California. Two closely related species, the polyphagous shot hole borer and the Kuroshio shot hole borer (collectively referred to as invasive shot hole borers), have been attacking more than 60 species of trees. These invasive beetles create a series of tunnels, or galleries, where they lay eggs and cultivate a Fusarium fungus to use as a food source. The fungus causes branch dieback, general tree decline, and can result in tree death. The beetles have been found in Los Angeles, Orange, Riverside, San Bernardino, Ventura, Santa Barbara, and San Diego counties.
What should you look for?
- Perfectly round entry holes about the size of the tip of a ballpoint pen
- Wet staining, gumming, white powdery exudate, or frass associated with holes
- Dead or wilting branches on trees
- Author: Ben Faber
The calls have come in. We've gone from cool to hot and Dry Root Rot of Lemon has struck, It's shocking how fast the trees go down.
Dry Root Rot has menaced growers in Ventura County for many years. In the ‘50's and ‘60's it seemed most prevalent on older orange trees. A few years after the wet winter of 1968-69, dry root rot became an increasing problem among citrus trees of all ages. At that time, most of the damaged trees were on sweet rootstock (susceptible to Phytophthora), and growing in fine-textured soils or soils with poor drainage. A few years after another wet winter/spring (of 1983), dry root rot again reared its ugly head, but this time predominately on young lemons.
The disease is caused by the fungus, Fusarium solani. This fungus is most likely present in all citrus soils in California. It is a weak pathogen in that by itself it will not attack a healthy tree. However, experiments conducted in the early 1980's by Dr. Gary Bender, showed that when seedlings were girdled, root invasion occurred. In the field, the fungus can infect trees once gophers have girdled the roots or crown. A Phytophthora infection will also predispose trees to Fusarium, as will asphyxiation. Therefore, the mere presence of the fungus in the orchard soil will not lead to the disease.
Fusarium is a soil borne fungus that invades the root system. Once infected, the entire root will turn reddish-purple to grayish-black. This is in contrast to a Phytophthora infection which, in many cases, will attack only the feeder roots, but when larger roots are infected, only the inner bark is decayed and it does not discolor the wood. In addition, when observing the cross section of a dry root rot infected trunk, a grayishbrown discoloration in the wood tissue can be observed.
Dry root rot is a root disease, but symptoms of the root decline are seen above ground. They are similar to any of the root and crown disorders such as Phytophthora root rot, oak root rot fungus (Armillaria) and gophers. The trees lack vigor, leaves begin to turn yellow and eventually drop (especially in hot weather) causing twig dieback. Finally, the foliage will become so sparse that one will be able to see through the canopy of the tree. A period of two to three years may pass from the time of invasion until noticeable wilt. Many times, the tree will collapse in the summer, after a period of prolonged heat. In the case of dry root rot, the collapse is so rapid that the tree dies with all the leaves still on the tree. When looking for symptoms of dry root rot, keep an eye out for symptoms of other maladies as well — Phytophthora, oak root rot fungus and gophers being the most prevalent.
As mentioned previously, in order for Fusarium to infect a tree, there must be a predisposing factor such as girdling from gopher feeding. However, since many trees collapse from dry root rot without any apparent predisposing factor, there are obviously other factors which we have yet to identify. Therefore, in 1998, a grower survey was developed, along with intensive soil and leaf sampling, to attempt to identify as many new predisposing factors as possible. They might be elements in the soil, either deficiencies or excesses, or specific cultural practices such as irrigation patterns or fertilizer practices. Twenty orchards were identified from which 20 soil and 20 leaf samples were taken in diseased areas and another 20 soil and 20 leaf samples were taken from adjacent healthy areas. The owners or managers of the properties were given a questionnaire to complete regarding a variety of cultural operations. The objective was to identify those factors that would correlate well to trees becoming infected with dry root rot.
Soil analysis - The following laboratory procedures were conducted to see if there was any correlation between the disease and either deficiencies or toxicities of these elements or
conditions: sodium, boron, salt level, pH and soil type (sand, loam, clay). For these elements or conditions, no correlation was found. It would appear that for our sampling sites, these conditions, whether favorable or not (toxic or deficient), did not play a major role in predisposing the tree to dry root rot.
Leaf analysis - The following elements were analyzed for their concentration within the leaf: nitrogen, potassium, phosphate, manganese, magnesium and zinc. Of these, three correlations were found. Zinc and manganese levels were substantially higher in diseased trees. The third correlation showed a potassium deficiency in diseased trees. However, we do not believe that dry root rot is caused by elevated levels of zinc or manganese, or by potassium deficiency, but rather are a result of the disease. Unfortunately, it seems that we have still not identified any elements in leaf analysis that truly correlates and points to a predisposing factor for disease development.
Control Measures – What Works and What Does Not
Early experiments conducted by Menge, Ohr and Sakovich showed that the following circumstances or operations do not influence the incidence of this disease: fungicidal treatments, wounding the tap root at time of planting, sandy versus clay textured soils, spring versus fall planting and soil mounding.
- In choosing your nursery tree, the choice of rootstock is not important in that, as far as we know, all rootstocks are susceptible to this disease. However, since Phytophthora is a major component in dry root rot development, choosing a rootstock like sweet orange would certainly put those trees in a high risk category. We recommend that growers use Phytophthora resistant rootstocks like C35 or Citrumelo.
Phytophthora. Publications written in the 1970's, and again noted by our survey, showed that Phytophthora is a major culprit in the dry root rot complex. To control dry root rot, it is essential that the Phytophthora, when present, be controlled. This can be accomplished by fungicidal treatments, and by the proper application and timing of irrigation water. Overwatering creates a favorable environment for the multiplication of the Phytophthora fungus.
Gophers. It is well known that gopher damage provides entry points for Fusarium. Controlling gophers is an important factor in reducing the potential of infection by Fusarium.
We presently have no direct control for dry root rot. To control the disease, we must control the predisposing factors such as gophers, Phytophthora, poor drainage and over-watering. If the predisposing factor(s) cannot be identified for a given diseased orchard, it will indeed be difficult to control the disease. Two things are certain though: 1.) There are no chemicals to date which will control this disease; and 2.) Presently, there are no rootstocks resistant to the disease.
Listen to Akif Eskalen tell the Dry Root Rot story
- Author: Mark Bolda
While it's pretty common for Californians to set aside their complaints about rainy weather because we need the water, the flip side for the Central Coast strawberry industry is ruined fruit and plant problems.
I've been seeing a number of fields with the problem of Photo 1 below. Plants are barely growing, the foliage is discolored and the overall aspect is not great.
It's best to take a careful, step by step approach to these problems. Splitting open a crown of one of the plants from the field shown in the first photo shows no discoloration common to many soil diseases (and in this case diagnostic testing confirmed that). The discoloration of the foliage is consistent with a lack of nutrition, but that plants very close to the ones doing poorly are doing great belies the idea that the field as a whole is lacking.
Let's look at the soil of surrounding these plants for a moment. There is a lot of water associated with these areas (close observers of Photo 2 below, and I know there are many since they want to figure out whose field this is, will see that there has been standing water indicated by the cracked soil) engendered by being a bit lower than the other part of the field, or being on the heavier side of soil type. Other areas, which are not as low or not as heavy, not nearly as many sick plants, if any at all.
How then does one explain the lack of growth and more so the mineral deficiencies so evident in the leaves? Easy. An excess of water around the plant roots create a near, if not completely, anaerobic condition and interfere with the processes needed to take up minerals from the surrounding soil which in turn impede growth.
With the above steps completed, I'd feel pretty confident on making the call that this is water related. So much in fact that I'm writing a blog about it.
To be sure, disease is out there as evidenced by the third and last photo. These plants are very similar to the others, although the spotty pattern in the field gives one the sense that it's not excess moisture. Splitting open the crown revealed discoloration, and further testing at the diagnostic laboratory confirmed Fusarium.