Tuesday, June 23, 2009

Curly Top and the Beet Leafhopper

Because of the seriousness of the curly top blight in local gardens (actually throughout the Western United States), I have researched the subject and provide the following information.

This top picture is of a healthy tomato plant from my garden.

The second picture is of a Curly Top infected tomato from my garden

General Information
Causal Agent: Beet Curly Top Virus (BCTV) Hosts: Tomatoes, beans, pepper, spinach, beets, and cucumbers.
Symptoms: Leaves of infested plants are dwarfed, crinkled, rolled inward, and cupped upward. Veins on the underside of leaves usually have a purple discoloration, may be roughened, and often produce swellings or spine-like outgrowths. Roots are stunted and may exhibit a proliferation of secondary rootlets.
BCTV is transmitted to/from plant to plant by the beet leafhopper, Circulifer tenellus. Both the virus and the beet leafhopper have very wide host ranges. Once acquired by the leafhopper, BCTV is carried for the rest of the leafhopper's life, and thus long distance spread is common. Infected plants are usually scattered in a field. The beet leafhopper acquires the virus from infected crop plants or weeds such as wild mustard and Russian thistle. Only brief feeding periods (minutes) are required for the leafhopper to acquire the virus and transmit it to new plants. Plants begin to show symptoms about 7 to 14 days after they are first infected by a leafhopper. Tomato is not a preferred host for the beet leafhopper; however the leafhoppers transmit the virus to tomatoes while sampling it.

Curly Top facts
a. Curly Top is a blight transmitted by the Beet Leafhopper. Although tomatoes are not its preferred host, leafhoppers are fairly indiscriminate, and tomatoes get infected along with beets, beans, melons, squash, potatoes, spinach, peppers, cucumbers and other garden plants. Even Pumpkins have been infected in some states.

b. When humidity is above 50%, Curly Top is nonexistent; thus the desert southwest is very susceptible to this disease.

c. There is no cure, once infected, the plant fails to thrive, will not set additional fruit, and will usually die. Remaining fruit will be of low quality, underdeveloped, and of poor quality and flavor.

What Doesn’t Work

a. Spraying for the Beet Leafhopper is ineffective since the Leafhopper migrates, usually coming down from hillsides as the weather warms. And although spraying will kill the leafhopper, the damage is done before the leafhopper dies.

b. Commercially, there are some insecticide spraying programs, and soil treatments that are effective, but for the home gardener, they are either not available or impractical.

c. Some of the cultural practices of commercial farmers, are also impractical or irrelevant to the home gardener. For example, planting large, thick fields of tomatoes seems to repel the Leafhopper, but gardeners can’t do this.

d. The State of California is investigating the introduction of predators and parasites for control of Beet Leafhopper, but to date, no solution has been found.

e. Covering tomatoes with a mesh or screen to keep the leafhoppers out. Most mesh is not tight enough to keep the leafhopper out, and if it is tight enough, the mesh will also keep out sunlight and create too much shading, and stunt plant growth.

What Might Work
a. There are possibly two or three resistant varieties, but all tomato varieties are susceptible. Ropac and Columbia seem to be resistant, but no immune, to curly top. Floramerica is another variety reported to be resistant, though it's not been confirmed in our area. Bruce Church in Hurricane experiences about 80% success with Ropac and Columbia.

b. Planting tomatoes later in the season, for the Hurricane Valley this would be mid-May to mid-June. Leafhoppers seem to be less prevalent by this date, and moved on to their more favored plants like Russian Thistle, Mustard, and other weeds.

c. Creating dense stands of tomatoes seems to repel the leafhopper, but for most home gardeners, this is impractical. Still, if you can plant in a square instead of a row, you will probably create some protection against the leafhopper.

d. Eliminating Russian Thistle, plantain, and other weeds is also somewhat effective, since the Leafhopper prefers weeds, particularly the Russian Thistle.

e. Creating an enclosed, clear plastic “greenhouse” over the tomatoes, for the early growing period, in theory, should protect the tomatoes from the Leafhopper, but the “greenhouse” must be tight as to make it impenetrable by the Leafhopper. If this can be maintained until mid-May, when it would probably be impracticable and inadvisable to keep the tomatoes inside the “greenhouse.”

f. Shading, which lowers light intensity and retards evaporation, probably delays leafhopper visits, decreases the infection rate, and reduces symptom expression. However, tomatoes do not like being shaded (they prefer full sun), so there is an adverse affect to this practice.

g. New Mexico State University has tested the use of applying a white kaolin mineral product (3% kaolin suspension) on tomatoes and peppers, and the treatment has proven effective against curly top. But row irrigation or drip irrigation must be used since sprinklers and rain will wash the kaolin off the plant and eliminate its effectiveness. Kaolin is a soft, earthy, usually white mineral...and don't ask me where you get Kaolin. It is probably available someplace.

h. Bruce Church in Hurricane says a spray of reconstituted dry milk is effective (From Utah State info), and he uses it. Dr. Sylvan Wittwer confirmed to me that milk is effective as both a repellent of the leafhopper and as an infection preventative. I tried this only one year and it was effective.

A Few Mid-Season Observations

With the warmer weather my corn, tomatoes, cantaloupes and other vines, have all really taken off. Following, are a few mid season observations:

1. In Toquerville, there is little or no advantage to planting early. The ground is too cold, the winds too strong, and plants tend to not grow much until April or May.

2. All vines (cantaloupes, crenshaw melons, cucumbers, squash, pumpkins, etc) seem to do really well in this area. Plant them in early May, and you still have plenty of time for them to mature.

3. The tomato curly top disease is very bad, and very frustrating to try to overcome. There is essentially no effective prevention, and no cure, so the leafhoppers just infect the tomatoes, and there isn't a whole lot you can do about it; except to pull out the plant and replace it. The six plants I replaced are all doing well, setting on tomatoes, and none of them have become infected with the curly top blight. Unless I learn differently, I'm assuming planting tomatoes later is better than planting early, because you avoid the curly top blight.

4. The cool May and June this year was ideal weather for broccoli, but I planted broccoli in early March, and have had nearly 8 weeks of broccoli harvest so far. Also, I've not been bothered by aphid or leaf worms--so far.

5. We had a huge pecan harvest last year, but I have very few pecans this year. Pecans do altenate between heavy and light harvests, but I didn't expect it to be this thin. Also, I've observed that last year, my pecan trees did not have sap on them, nothing observable anyway. This year, however, with hardly any pecans on the trees, the sap is very heavy in all trees. Is there a connection between the "off year" and heavy sap?

Tuesday, June 9, 2009

June Report

I have had success and failure in my garden so far this year. Beets, Onions, Peas, Carrots, Broccoli and Summer Squash have been very successful.

Cauliflower was mostly a failure. I'm not sure why, but the plants did not grow for a long time, when they did grow, they looked good, but the heads were strange, an odd color, and the flavor was poor.

Tomatoes continue to suffer from "Curlytop" brought by the Beet Leafhopper. About half my plants were infected and I have taken them out. I have replaced the plants, mostly as an experiment to see how they do being planted this late. I have never planted tomatoes this late in the season, but in Toquerville, I suspect they may still be productive. Time will tell. In researching this devastating disease, it appears the only real solution is to cover the tomatoes in a greenhouse structure until about this time of year when the leafhoppers appear to be gone. Apparently, no pesticide or cultural practices are very effective.

The broccoli is some of the best I've ever grown, beautiful heads, and large flowerettes continue to produce wonderful broccoli.

The carrots are probably the best I've ever grown also, very good quality, long, nicely shaped carrots.

The zucchini and crookneck squash has also been very good. I began harvesting the last day of May, and the quality is excellent.

All my vines are thriving, Ambrosia Cantaloupe and Crenshaw Melons look impressive, and the corn (Miracle Corn) also looks excellent.

I have also planted Big Max Pumpkins, Toquer Squash (excellent if you haven't tried it), Spaghetti Squash, and watermelons. All are doing very well.