More Connecticut greenhouse growers and retailers are using biological controls to manage insect and diseases (Photo of greenhouse). Here you can see a variety of spring plants for sale that were grown using biological controls (beneficial insects and mites, and biologically based fungicides). As an example, this yellow gerbera daisy flower was grown using biological controls. (yellow gerbera daisy). This is to prevent damage from western flower thrips that can damage flowers (pink gerbera daisy). Small predatory mites (photo of bags in plants) are placed in the crop that prey upon the small thrips in the flowers. Here the predatory mites are contained inside a controlled release sachet containing bran and a additional food source for the beneficial mites. The small predatory mites emerge from these small paper sachets over a 4 to 6 week period preying upon western flower thrips. (Note: western flower thrips are primarily a concern in greenhouse production, not in the home garden). Source: Leanne Pundt, UConn Extension Educator in Greenhouse IPM.
By Jude Boucher, UConn Extension Educator, Commercial Vegetable Crops
Introduction (Current Fungicide Program)
Before I can talk about this experiment, I need to remind you of how and why we use specific fungicides on pumpkins. I’ve talked about fungicide sprays on pumpkins before and mentioned how there are four annual diseases that we can protect our pumpkins from with these products: powdery mildew (PM), Plectosporium blight (Plecto), black rot (BR) and Downy Mildew (DM). We tend to design a fungicide spray schedule around PM, which is the most common disease on cucurbit crops and often the first to show up. The basic idea is to slow disease spread with the fungicides by limiting spore formation, new leaf infections, and stem and fruit problems, so that you maximize your yields and net profits.
Conventional tillage and rye-mulch strips for DZT
Systemic fungicides, which move through the plant, usually provide the most effective control of PM because it is impossible for any sprayer to provide good coverage, where the infection first occurs, on the underside of the lower, older leaves in a waist-high pumpkin patch. As part of our resistance management strategy we use each systemic family only one time each season. That’s because, unlike with protectant fungicides, that have several modes-of-action to stop infection, systemics tend to have a single mode-of-action which is easily skirted by the billions of spores that are encountered after each spray. To help slow resistance, and to provide control of Plecto and BR, we also add a protectant to the tank mix during each application. So our spray program in recent years has gone something like this: Quintec + Bravo (i.e. chlorothalonil), Procure + Bravo, Pristine + Bravo, and then we switch to two protectants for the remainder of the sprays (sulfur + Bravo). You could also use the Pristine in your second application and mix it with the protectant sulfur, to rest the Bravo, while still providing good protection against PM, Plecto and BR. An additional product that works on water molds may be added to the spray mix late in the season if or when DM shows up, but we will talk about applications for water molds another time.
Planting pumpkins in conventional and DZT plots.
To determine when to make the first application, scout 50 lower leaves each week after the plants run, and spray when you find the first small, round, colony of white powdery mildew spores (usually on the underside of the leaf). Then, we usually continue to make applications at 10-day intervals until mid-September.
Spray Interval and Tillage Experiment
Now that you remember the fungicide program, here is the “spray interval” experiment that we ran at the UConn Plant Science Research Farm during the last two summers. Our starting hypothesis was that with a resistant pumpkin variety, you should be able to stretch your spray interval and still produce marketable pumpkins.
Pumpkin with damaged (unmarketable) handle.
We used a split-plot design with 2 tillage methods (Fig. 1) and 4 spray intervals, and replicated the 15’ X 40’ plots 4 times each, for a total of 32 plots in each experiment. We planted 3 rows of pumpkins per plot that were spaced 5 feet between rows (Fig. 2) and 2 feet between plants in the row. Half the pumpkins were planted on conventionally-tilled strips prepared with a plow, harrow and cultipacker, while the other half were planted on a narrow (8”), deep zone tilled seedbed through a killed rye cover crop. The spray interval treatments consisted of no spray, 21 days, 14 days and 10 days.
In 2011, we conducted two similar but separate experiments with different PM-resistant pumpkin varieties: ‘Gladiator’ and ‘Magic Lantern’. In 2012, we ran a single experiment with Gladiator. Pumpkins were planted on June 6, 2011 and June 8, 2012 and harvested September 12 and 16 the first year, and September 7 the second year.
Unsprayed pumpkin plot with powdery mildew damage.
The first spray for PM was applied on August 12, 2011 and on July 27, 2012. The same sequence of fungicides mentioned above were used in each treatment, except that we used the chlorothalonil brand Initiate instead of Bravo. We did not complete the sequence of 3 systemics + protectant applications before harvest for the 21d treatment either year (only two applications were made to these plots). In 2011, total rainfall for the year exceeded 63 inches in Storrs, with the remnants of Hurricanes Irene and Lee adding to the extreme wetness in late August and early September, while 2012 had “normal” rainfall for the season and year (42.4 inches for the year).
Powdery mildew damage to leaves (Fig. 3), Plecto damage to vines (Fig. 4), and fruit stem or handle (Fig. 5) damage were rated on a scale of 0-5 or 0-3 for no damage to severe damage (i.e. leaf death or no handle). The fruit were weighed at harvest and the percent marketable fruit were calculated. A marketable fruit was considered to be at least 3 pounds and have a stem rating of 2 or less (medium to no damage).
2012 (“Normal”-Rainfall-Season Results)
There was not much difference between pumpkins grown with the two tillage methods for any of the factors measured in 2012. However, there were big differences between the different spray intervals. The 10d (average leaf rating of 2) interval provided better PM control than the 14d or the 21d (rating of 3), which did better than no spray (rating of 4.3). Both the 10d and the 14d spray interval provided better vine protection from Plecto than the 21d interval or no spray. Again, both the 10d and 14d spray interval provided better stems (handles) than the 21d interval, which was better than the treatment that did not get sprayed, where most handles were not marketable. Average fruit weight ran about 13 pounds for the 10d and 14d interval plots and about 11 pounds for the 21d and no spray treatments. Almost all (95-100%) of the fruit were marketable for the 10d and 14d spray intervals, while 75-90% were marketable for the 21d interval (90% in the DZT plots), and only 40-50% were marketable for the unsprayed plots. We could conclude that in a year with normal rainfall, even with a resistant variety like Gladiator, we shouldn’t stretch the spray interval to more than 14 days. Since both the 10d and 14d treatments received 4 applications in 2012, there was no reduction in fungicide use when increasing the interval by 4 days. However, since pumpkins generally yield about 20 tons per acre, at a retail price of $0.50/pound in CT, you would make $19,000-$20,000 gross profits (roughly $6,500 wholesale at $0.17/lb.) by using fungicides on a 10d or 14d interval, compared with half that amount or less if you didn’t use fungicides.
2011 (Wet-Season Results)
I’ll shorten the 2011 story by just talking about the percent marketable fruit results, because in the end, that is what will determine how much money you will make from your pumpkin patch. With all the rain in August and September of 2011, improving drainage with deep zone tillage (DZT), and possibly having a rye mulch for the fruit to grow on, made a big difference compared with growing pumpkins on bare ground with conventional tillage.
Plectosporium damage to vines.
Between 80-95% of the Gladiator fruit were marketable in the sprayed DZT plots, but only 65-70% were marketable in the sprayed conventionally-tilled plots, while only 50-55% of the fruit were marketable in the unsprayed plots for either tillage method. This is an increase in yields of 15-25% in sprayed DZT versus conventionally-tilled plots. That means that increased yields from as little as 2 acres of retail pumpkins could pay for a new zone builder. A 2008 compaction survey showed that this research farm field was one of the few vegetable fields in the state without a plow pan. Imagine how much better yields might be if you were using DZT on a field with a plow pan (89% of CT vegetable fields) and poor drainage.
Ironically, with more wet weather in 2011, there was not a big difference in marketable fruit between the different spray intervals for Gladiator, as long as they were sprayed (15-40% decrease in yield when left unsprayed).
The wet 2011 season reduced yields for Magic Lantern much more than for Gladiator. For the conventionally-tilled, 14d and 21d spray interval plots, Magic Lantern only yielded 25-35% marketable fruit, compared with 45-70% for DZT plots with the same spray intervals (a yield difference of 20-35%). For Magic Lantern, both tillage methods yielded 60-65% marketable fruit for the 10d interval, but only 5-15% for the unsprayed plots. Spray intervals made very little difference for DZT plots, but a tight schedule (10d) made a big difference for the conventionally-tilled plots. However, the highest gross profit you would have made with this variety, even with DZT, was $14,000 per acre, compared with $19,000 for Gladiator.
Our final conclusions would be that Gladiator performs better than Magic Lantern in a wet year, it pays to DZT in a wet year, it pays to use fungicides any year, and you probably want to stick with a 10 or 14-day spray schedule even with resistant varieties.
By Jude Boucher, UConn Extension Educator, Commercial Vegetable Crops
Recap of 2012 Outbreak in CT
During the week of June 20, 2012, a Prospect, CT homeowner brought late blight (LB) infected tomato plants to the CT Ag Experiment Station diagnostic center. The homeowner had purchased the plants from a local supermarket, but when contacted, the supermarket management did not provide the source of the infected plants. Since LB is not listed as a restricted pest in CT, the state has no authority to force a vendor to stop selling infected plants or to reveal where they purchased infected plants, so that a future epidemic might be avoided by cleaning up the problem at the source. We could only assume that there were plenty of gardens with infected tomato plants around Prospect.
Late blight lesions on tomato leaf. Photo by Joan Allen, UConn diagnostician.
I recommended that all organic farms begin to apply preventative applications of copper, and all conventional farms start their early blight fungicide program to stop low levels of LB spores. Late blight spread is usually favored by cool temperatures and frequent precipitation, and July was the warmest month on record and completely dry through most of the state for the first three weeks. However, LB can spread when relative humidity nears 100%.
On July 13, two organic farms reported outbreaks of LB in both the eastern and western portions of the state. It was recommended that these farmers destroy their infected field tomatoes and potatoes to help prevent further spread of the disease and to save high tunnel tomatoes at these sites from becoming infected. I also recommended that all conventional farms begin preventative applications of the stronger, mobile, late blight-specific fungicides on their tomato and potato crops. By late July many more organic farms that did not use copper reported LB outbreaks, and by late August most organic farms had infected tomatoes and potatoes. In early September with more rain and cooler temperatures, conventional farms that had not switched to the stronger LB fungicides began reporting crop losses. There were even a few farms using the stronger fungicides that reported finding LB, but as far as I know, the fungicides prevented extensive crop loss in all cases. Many growers’ crops survived the 2013 outbreak, but again at great expense. So what can you do to stop the disease in 2013?
What you need to know about late blight
Late blight lesions on tomato stem. Photo by Joan Allen, UConn diagnostician.
Late blight (Phytophthora infestans) is a water mold that can cause complete loss of potato and tomato crops in as little as 7 to 10 days after infection. This disease caused extensive crop losses in Europe during the mid-1800s, including the Irish Potato Famine. It is closely related to Phytophthora blight (P. capsici), which is so destructive to solanaceous, cucurbit and leguminous plants, and infests soils on farms for decades, even in the absence of a host. Unlike Phytophthora blight, LB doesn’t form long-term resting spores (oospores) in our area, so it doesn’t overwinter in the soil. That’s the good news! However, there are places in the world, such as Scandinavia, Mexico and South America, where the two “sexual” mating types have crossed or “mated” to produce a LB strain that does produce oospores, and where late blight is an annual problem on infested farms. Cooperation between growers to help prevent LB outbreaks is crucial to prevent a scenario where both mating types occur in our region and become a permanent, annual problem. In short, the more years we have a state- or region-wide outbreak with our current strain(s) of LB, the higher the odds that the second mating type shows up and results in a sexual cross, oospores, and a permanent LB problem. Such a cross could also produce fungicide-resistant offspring.
The strain of LB that we have been experiencing in the northeast, spreads by producing sporangia (secondary spores), which are capable of moving 30 to 40 miles on the wind. However, Long Island Sound frequently acts as a barrier to protect CT farms from LB outbreaks on the island. So, typical spread of the disease may be more localized than what is indicated by the maximum range of spore flight, but may be influenced by large storm systems, such as Hurricane Irene or even prevailing wind direction.
Zoospores (that swim) are produced in the sporangia, and either the sporangia directly or the zoospores can penetrate the leaf surface and start the infection. Usually, a thin film of water is needed for the spores to penetrate the leaf cells, but as mentioned, even extreme humidity will provide enough water for infection to occur. The optimum temperature for infection is between 54 to 75 degrees, but during 1 to 2 days of extreme humidity, infection may take place at up to 86 degrees F. Cool August and September nights that produce heavy morning dews (i.e. 100% relative humidity) are perfect for LB infection.
Because spore deposition and leaf wetness time are limited in greenhouse and high tunnel conditions, tomato plants grown inside usually remain LB-free, unless there is a source of spores almost adjacent to the houses. However, due to high humidity in some tunnels and greenhouses, when infection does occur, it can cause rapid and extensive crop losses.
LB survives the winter on potato tubers or may arrive on infected tomato transplants in the spring (as it did in 2009). This disease organism requires living tissue, so tubers that have frozen near the soil surface will not allow the disease to survive. Growers should control volunteer potatoes that sprout from deep within the soil of the previous year’s potato patch or from cull plies to prevent the disease from surviving the winter. You should only plant certified disease-free potato seed stock. Never save your own seed stock from a previous year if LB was on the farm or use table stock for seed. LB will not survive in tomato seeds or on the dead residue of the previous tomato crop. If possible, always grow your own tomato transplants from seed to avoid LB problems in the greenhouse and field. Inspect all tomato transplants arriving on your farm for signs of LB, and reject, or bag and dispose of infected transplants.
Late blight lesions on tomato fruit. Photo by Joan Allen, UConn diagnostician.
Growers should inspect tomato and potato plantings weekly for signs of LB. Suspected incidences of LB infection should be confirmed by bringing a sample plant to a diagnostic lab at the CT Ag Experiment Station in New Haven or Windsor, or to the UConn lab in the Radcliff-Hicks Building in Storrs. If LB is confirmed, alert your local vegetable crops Extension Educator (yours truly) so that growers throughout the state and region can be alerted and respond to the LB threat. Tracking the outbreak back to the source of the first infected plants is also a crucial part of combating future outbreaks, so that we can help a grower clean up and eliminate the problem before they start an epidemic the following year too. All tomato and potato growers should call or access the UConn Vegetable IPM Pest Message (860-870-6954, http://ipm.uconn.edu) every Friday afternoon during the summer, to see if late blight has been found in CT and to catch up on current fungicide recommendations.
At the beginning of the outbreak, it is essential that the first few growers with infected plants destroy their crop to help prevent a full blown outbreak from occurring, starting with neighboring farms. Infected potato plantings can be plowed under, harrowed, flamed or burned down with a contact herbicide, such as diquat or paraquat. Trellised tomato plants should be cut at the base and at mid-trellis height to kill the plants and help remove the trellis twine. They should then be treated as described above. Spores are inactivated within hours when exposed to high levels of UV light, so plantings that are sporulating should be handled or tilled down on a sunny day to minimize the possibility of disease spread. Obviously, once several farms are involved in an outbreak, the need to destroy the crop diminishes, as it can be assumed that the spores are on the wind.
There are active LB resistant-tomato breeding programs at Cornell University and at some seed companies, but variety choices are still limited. ‘Mountain Magic’, ‘Plum Regal’, ‘Jasper’ (cherry) are recently listed resistant varieties, while other heirlooms such as ‘Mr. Stripy’ and ‘Striped German’ have held up well in recent outbreaks. For potatoes, some varieties have more tolerance, such as; ‘Elba’, ‘Kennebec’, ‘Allegany’, ‘Sebago’, ‘Rosa’, ‘Defender’, ‘Jacqueline Lee’ and ‘Ozette’.
Managing late blight with fungicides
Protectant fungicides are not mobile within the leaf or the vine and thus, often result in lower rates of coverage, and tend to be less effective than systemic or mobile fungicides registered for LB. Some of the protectant fungicides registered for late blight control on tomatoes and potatoes include; copper (i.e. Champ), chlorothalonil (i.e. Bravo), and mancozeb (i.e. Dithane). Protectant fungicides usually provide some degree of protection under light disease pressure (few spores in the air and weather conditions that do not favor LB infection).
Mobile fungicides (systemic and translaminar) result in better under leaf coverage and tend to be more effective against this disease. Some of the more effective products include; cyazofamid (i.e. Ranman), propamocarb (Previcur Flex), fluopicolide (i.e. Presidio), mandipropamid + difenoconazole (i.e. Revus Top), cymoxanil (i.e. Curzate), and cymoxanil + famoxadone (Tanos).
When designing your own fungicide program, you should be looking for products with short day-to-harvest (dh) restrictions so that you can harvest tomatoes as they ripen; a short re-entry interval (REI) so that you or your crew can work in the field when needed; and a product that can be applied several times during one season, so you don’t have to buy too many different fungicides. Because of long dh intervals, some products, such as Dithane and Previcur Flex will only be useful before tomato fruits color. Remember, that as part of your resistance management program with mobile fungicides you should always alternate between two different pesticide groups or families and mix each mobile fungicide with a protectant. The protectant fungicide will also provide control of other important diseases such as early blight and Septoria leaf spot. They should be applied on a 7 to 10 day interval. Here is a list of some of the LB products and important label considerations to help you design your spray schedule.
chlorothalonil (Bravo), 7dh, REI 12h, Group M5, should be limited to 50% of applications each season to prevent early blight resistance.
copper (Champ), 0dh, REI 24h, Group M1,
mancozeb (Dithane), 5dh, REI 24h, Group M3,
cyazofamid (Ranman), 0dh, REI 12h, Group 21, limit of 6 applications per season.
cymoxanil (Curzate), 3dh, REI 12h, Group 27, limit of 6 applications per season.
cymoxanil + famoxadone (Tanos), 3dh, REI 12h, Groups 27 & 11, limited to 50% of applications each season.
fluopicolide (Presidio), 2dh, REI 12h, Group 43, limit 3 to 4 applications per season, not registered for potatoes.
mandipropamid + difenoconazole (Revus Top), 1dh, REI 12h, Groups 3 & 40, limit of 4 to 5 applications per season.
propamocarb (Previcur Flex), 5dh, REI 12h, Group 28, limit of 6 applications per season
Much of the information in this article was consolidated from several LB fact sheets written by Meg McGrath and Tom Zitter at Cornell and Mary Hausbeck at Michigan State, as well as several other sources.