Potato Curly Top Virus – Learn About Curly Top Management In Potatoes
By: Amy Grant
Potatoes are susceptible to a number of diseases as is historically illustrated by the Great Potato Famine of 1845-1849. While this famine was caused by late blight, a disease that destroys not only the foliage but the edible tuber, a bit more benign disease, curly top virus in potatoes, can still wreak some havoc in the potato garden. What causes potato curly top virus? Read on to find out as well as the symptoms of potatoes with curly top and about curly top management.
What Causes Potato Curly Top Virus?
The pathogen is transmitted by the beet leafhopper, Curculifer tenellus. As its name indicates, the leafhopper pest transmits the disease to a number of crops and weeds, including:
Both the leafhopper and virus survive on a wide range of weeds and wild plants. The leafhopper ingests cell sap, which contains the virus, which then incubates in the leafhopper for 4-21 hours before being transmitted. The disease is then transported through the plant’s tissues.
Symptoms of Curly Top Virus in Potatoes
Potatoes with curly top often have dwarfed yellow, rolled or cupped up leaves. Foliage becomes mottled yellow and leaflets tend to roll up. Veins of outer leaflets remain green but the rest of the leaflet turns yellow. Infected tubers are often small and sometimes elongated, and aerial tubers may form.
Symptoms of curly top in potatoes appear after 24 hours with hot temperatures and more slowly in cooler temps.
Curly Top Management
Curly top is transmitted in potato seed pieces, so one method to control the disease is to use certified seed potatoes.
An obvious control method would be to control the leafhopper population but, unfortunately, this has proven to be difficult as insecticides are not effective. Commercial growers instead resort to mesh mechanical barriers over susceptible plants. A more realistic approach to curbing the insects is to control the weed population, particularly those weeds that leafhoppers find most appealing, such as Russian thistle.
Once symptoms appear, it is best to pull the potato plant(s) out and destroy it/them.
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How To Treat Potatoes With Curly Top: Managing Curly Top Virus In Potatoes - garden
It appears that curly top virus (CTV) has again impacted vegetable crops across Yavapai County this summer. I have visited gardens or received reports of CTV from Prescott, Prescott Valley, Camp Verde, and Cottonwood. The virus has been reported primarily on tomatoes, but I have observed symptoms on green been, peppers, and squash. For years, CTV has been an issue in the Verde Valley. The first records of CTV in our area come from Camp Verde growers in the 1860s and it probably impacted Native American farmers prior to that time. This year, I have heard that it has impacted about 50% of the Verde Valley tomato crop.
Viral plant diseases are difficult to manage as there are complex interactions between the pathogen (virus), hosts (crop plants), vector (organism that transmitted the virus), and environment. Because of these uncertainties, it is difficult for vegetable growers to adopt CTV management strategies and know how and when to apply them.
CTV is found across the western U.S. and is transmitted to crop plants by the beet leafhopper (Circulifer tenellus). The virus survives from season to season on weeds: usually those in the mustard and goosefoot (including lambs quarter and Russian thistle) families. Beet leafhoppers feed on weeds in the early spring and transfer the virus to crops including tomatoes, beets, peppers, squash, beans, cucurbits (squash, melons, and cucumbers), spinach, potatoes, and other crops.
After the beet leafhopper initially ingests plant cell sap containing the virus, the virus incubates in the leafhopper for 4 to 21 hours before it can be transmitted. Once incubated, the virus is transmitted to other host plants by the leafhopper. The disease is transported within the plant through the phloem tissue and symptoms usually begin to appear after 24 hours in hot temperatures and more slowly in cooler temperatures.
When a susceptible plant becomes infected, leaves become puckered and stunted. Tomato leaves curl and roll upward and the main leaf petiole curves downward. In time, the leaves also become leathery, veins turn a purplish color and the interveinal leaf area turns yellowish. Infected plants will not recover and eventually the plant stops growing and dies. Infected tomatoes may ripen even when immature however, edible size fruit are likely to be bitter. Once you observe definite symptoms, it is best to pull out the plant and destroy it.
CTV cannot overwinter in the soil it must remain in a living plant. Plants cannot be infected by planting them in soil where infected plants grew last year or by use of compost from infected plants. CTV is not transmitted in plant seeds, but can be spread in potato “seed” pieces. Similarly, the virus is not spread from generation to generation in leafhopper eggs.
Spraying insecticides on tomato plants is not an effective leafhopper control strategy. In fact, leafhoppers do not prefer tomatoes as a food source. They inadvertently land on the plant, feed, and then move on. Plant pathologists say there is little secondary spread of CTV from one crop plant to the next within a field. While I’d like to believe them, I and many growers feel we have observed evidence the disease can be spread from crop plant to crop plant in the field.
One preventative strategy is to control weeds adjacent to cropped areas before transplants are planted. This may be of little value since beet leafhoppers are known to fly long distances. Fine mesh barriers (floating row cover or other horticultural fabric) could prove to be a viable management strategy to prevent leafhoppers from feeding. The most critical time to have the plants covered would be early to mid-season. Most growers in the Verde Valley keep several replacement plants in containers to fill in where CTV infected plants have been removed.
A few years ago, we experimented with planting the four CTV resistant tomato varieties: Roza, Rowpac, Columbia, and Saladmaster. Most of the gardeners and growers concluded that these were not the best tasting tomatoes and went back to their favorite non-CTV resistant varieties. In addition, I have observed another virus on tomato which I believe is cucumber mosaic virus (CMV). CMV is vectored by aphids and the symptoms include “shoestringing” of leaves. Recommendations are the same – remove infected plants and destroy them. I have included photos of CTV and CMV as well as links to publications on the web version of this column (see web address below).
Follow the Backyard Gardener on Twitter – use the link on the BYG website. If you have other gardening questions, call the Master Gardener help line in the Camp Verde office at 928-554-8999 Ext. 3 or e-mail us at [email protected] and be sure to include your name, address and phone number. Find past Backyard Gardener columns or provide feedback at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.
Publication: Curly Top Virus, New Mexico State University Cooperative Extension Service, http://aces.nmsu.edu/pubs/_h/h-106.pdf
Publication: Recognizing Tomato Problems, Colorado State University Extension
Close up photo of curly top virus symptoms on tomato, Colorado State University Extension, from: http://www.coopext.colostate.edu/TRA/PLANTS/curlytopvirus.shtml.
Whole plant photo of curly top virus symptoms on tomato, Colorado State University Extension, from: http://www.coopext.colostate.edu/TRA/PLANTS/curlytopvirus.shtml.
Leaf with "shoestring" symptoms of cucumber mosaic virus on tomato, University of Arkansas University, from: http://plantpathology.uark.edu/3636.htm.
Beets, tomatoes, peppers, beans, potatoes, spinach, cucurbits, many ornamentals, and weeds such as Russian thistle (tumbleweed) and mustard
- Leaf and fruit deformation
- Leaves turn yellow with purple veins.
- Leaves twist and curl upward.
- Leaves become thickened, stiff, and crisp.
- Petioles curl downward.
- Premature fruit ripening
- Reduced fruit quality and yield
- Infected young seedlings may die.
Beet leafhopper (Circulifer tenellus)
Warm temperatures and dense leafhopper populations
- Plant virus-free transplants
- Control weeds and insects
- Remove infected plants
- Cage young plants in home gardens
Curly top virus (CTV), or beet curly top virus (BCTV) as it is more formally known, is widespread throughout arid and semi-arid regions of the world. The virus is common in the western United States from Mexico to Canada and in the eastern Mediterranean Basin. The virus has a wide host range, causing disease in over 300 species in 44 plant families. The virus appears to be restricted to broad-leafed plants, as no monocotyledonous plants have been identified as hosts for this virus. The most commonly infected hosts include sugar beets (for which the disease was first named), tomatoes, peppers, beans, potatoes, spinach, cucurbits, cabbage, alfalfa, and many ornamentals. The virus also survives in many weeds, such as Russian thistle (tumbleweed) and mustard.
Symptoms vary depending on the host however, this disease also produces some general symptoms. Other factors that relate to the type and severity of symptom development include virus strain and host physiology. The virus exists in many different strains, which vary in the severity of symptoms produced particularly in relation to the host. Severity of disease is also dependent on the age of the plant when infected. For example, when young plants are infected they will often die shortly after infection. When plants are infected after the seedling stage, the plants survive but are yellow and stunted. Infected leaves of some hosts, particularly tomatoes and peppers, become thickened and crisp or stiff, and roll upward as the petioles curve downward. The leaves turn yellow with purplish veins. Leaves of other hosts such as beets become very twisted and curly. In most cases, yield is reduced, and the fruit that is produced ripens prematurely. The immature, dull and wrinkled fruit is a good diagnostic symptom for tomatoes infected with CTV. If plants are infected after they have begun to set fruit, it is not uncommon to see infected and healthy fruit on the same stem.
This disease is transmitted (vectored) from infected to healthy plants by a small insect called the beet leafhopper (Circulifer tenellus). The leafhopper is an effective vector because it is able to transmit the virus after feeding on an infected plant for as little as 1 minute and can subsequently transmit the virus for the remainder of its lifetime. The virus is not passed on to leafhopper progeny. Although leafhoppers that feed on infected plants are able to transmit the virus for their entire life, the effectiveness of transmission is reduced when the insect does not continually feed on infected plants.
While the disease can occur in commercial fields, it is particularly troublesome in home garden situations. The occurrence of this disease in home gardens may be due, in part, to the presence of alternate hosts that leafhoppers prefer to feed on, as well as an increased likelihood of infected source plants in the area.
There are no chemicals available for controlling the virus, but several cultural practices can help reduce or eliminate infections. Although resistance to curly top is not known, growers may benefit from trying to identify cultivars that are somewhat tolerant of the virus. Good sanitation practices, such as weed and insect control, are also essential in limiting the occurrence of the disease. Home gardeners may also consider planting susceptible hosts, such as tomatoes and peppers, in a slightly shaded part of the garden, as leafhoppers prefer to feed in sunny locations. If the garden is in full sun, it may be helpful to place a netted cage over the plants when they are young. This netted material will provide a small amount of shade and, if the holes are small enough, may actually prevent leafhoppers from getting to the plants. If a cage is used, be sure the plant doesn't actually touch the netted material, as this will reduce the effectiveness. Remove cages when the plants are mature, as they are less susceptible to infection and will benefit from increased light for fruit development. All diseased plants should be removed from the field or garden as soon as they are noticed so that they do not continue to provide a source of the virus for transmission to healthy plants.
Original author Dr. Emroy L. Shannon,
Professor Emeritus, New Mexico Cooperative Extension Service.
New Mexico State University is an equal opportunity/affirmative action employer and educator. NMSU and the U.S. Department of Agriculture cooperating.
Reprinted May 2001
Electronic Distribution July 2001
Curly Top Tomato Virus
Last year, the Beet Leafhopper which transmits ‘Curly Top Tomato Virus’ was rampant in our gardens and devastated many tomato plants. I lost 50% of my tomato plants. The Beet Leafhopper flies in on the winds in early June through July, jump on the tomato plants and taste them. They don’t even like to eat tomato plants but sample them, transmitting the disease in the process.
Identifying Beet Leafhoppers
You will know if they are here as they come in waves and when you walk around your garden, you’ll see a lot of jumping little green bugs that fly off when you walk by. Then they leave—flying to the next garden. Because of this, you can’t really spray anything to get them—here today, gone tomorrow. By the time you notice something is wrong with your plant, they are long gone. It takes about 2 weeks for symptoms to show up.
Your tomato plant leaves will start to curl and the underside of the leaves will turn a purplish color The leaves then start to wilt and the plant will look stunted. You might think it needs water but it doesn’t, it is sick and won’t recover. ‘Curly-Top’ is only transmitted from bug to plant is NOT transmitted from plant to plant hence you will see a healthy plant next to a sick plant.
There is NO CURE for this virus and if your tomato (or pepper for that matter) shows signs of the disease, you should pull the plant. You could leave the plant in BUT if another wave of leafhoppers come by and a healthy leafhopper bites your sick plant, it only takes 10 minutes in 90°F weather for it to be able to transmit the disease to one of your healthy plants. The best thing to do is pull any sick plant and dispose of it.
Leafhoppers do not like shade and if your plants are partially shaded, that may help keep them off but since most of us grow tomatoes in full sun that might be difficult.
Row cover over the tomato plants in my garden
Another thing you can do is create a physical barrier between the bugs and your plants. This year, I’m covering my tomato plants with row cover until the bugs pass. Wrap the row cover around your tomato cage and put a piece on top of the cage BEFORE they come.
Lastly you could put out some tomatoes later in the season after the bugs leave. Last year when I was out at the Santa Fe Community Garden I noticed many rows of sick tomato plants but one row of perfectly healthy plants and when I asked about them, it turned out they were put out about a month later than the rest of them and by then the leafhoppers were gone.
Dry, sunny, windy weather are perfect conditions for the leafhoppers so look out this summer-conditions are ripe again!