to the weekly Vegetable Pest Message
from the University of Connecticut Cooperative Extension System
Week of July 20th Vegetable Pest Message
Click here for previous Pest Messages
Welcome to the University of Connecticut Cooperative Extension System’s Vegetable Pest Message.
This week’s message will cover:
• Spraying for Late blight
• corn earworm
• European corn borer
• powdery mildew on pumpkins and winter squash
• downy mildew on lettuce
• Tomato hornworm
Spraying for Late blight
We now have late blight on at least 3 organic farms in CT. This is the disease that caused the Irish potato famine and can destroy a whole field in as little as three days and spreads up to 40 miles on the wind. All CT vegetable farmers should be applying the stronger LB fungicides to their tomatoes and potatoes on 5-10 day intervals. When choosing an effective fungicide program, there are several important considerations you need to think about before purchasing or applying products. Some of these include: how well the product works against late blight and possibly the other fungal diseases such as early blight, Septoria leaf spot and Anthracnose ripe rot; how many applications you are allowed per season; how many days prior to harvest you must stop spraying; the price; and for those who grow both tomatoes and potatoes, is it registered for both crops. I am going to talk about several of the more effective products and provide some of this information. Hopefully you will find it helpful in making your fungicide decisions and not too confusing.
Three of the most effective LB products include Ranman, Presidio and Previcur Flex. These three fungicides would all need to be mixed with another fungicide such as Bravo, Inspire Super or Dithane, that will control at least early blight and ripe rot, and SLS if that is present in your field. Ranman has a 0 dh restriction on tomatoes and 7 dh on potatoes and can be used 6 times per season, while Presidio must be used at least 2 days-before harvest and is only registered for tomatoes. Previcur flex must be used 5 days before harvest for tomatoes and 14 dh for potatoes, which pretty much excludes its use on tomatoes once you start picking. It can be applied only 6 times in the field and twice in the green house on tomatoes.
Two other effective LB materials, which come as pre-mixes, so that they control the other important fungal diseases too, include Revus Top and Tanos. The Revus part controls the late blight and the Top part controls the EB, SLS and ARR. Revus Top can be used 4 or 5 times per season, depending upon the rate of application used, and has a 1 dh restriction on tomatoes and 14 dh on potatoes. Tanos contains the same active ingredient that is in Curzate and a group 11 strobiluron fungicide similar to Cabrio or Quadris. The Curzate controls the late blight and can burn out lesions for a couple of days after infection, so Tanos or Curzate are good choices after a rainy period. Only 50% of the applications can contain Tanos, and it has a 3 dh retriction on tomatoes and 14 dh on potatoes. Tanos can be used alone but Curzate would have to be used with another product to control the other fungal diseases and has 5 dh on tomatoes and 14 dh on potatoes. Revus can also be purchased separately instead of as a pre-mix, but can only be used on tomatoes and must be mixed with a broad-spectrum fungicide, so you might as well buy it as Revus Top.
Well there are more choices in the New England Vegetable Management Guide. However, to keep it simple, you can just add Ranman or Presidio to your normal early blight fungicide applications and be safe. Remember to alternate between at least two LB products for resistance management. Another option would be to alternate between Revus Top and Tanos. If you’re looking for the program with the shortest dh restrictions to simplify your tomato harvest, then you may want to rotate between Revus Top and a mix or Ranman and Bravo, which would be just 1 dh.
Keep in mind that customers on at least a couple of farms back in 2009 when we had the LB epidemic before, complained of tomatoes that tasted like chemicals, so you should not apply any more applications than are necessary to keep the planting protected. For instance, do not apply copper unless you have a bacterial disease such as spec, spot or canker in your field or unless you are an organic farmer. All organic farms should be applying copper in a preventative manner on a weekly basis. Copper is not a strong enough fungicide to protect the crop once you have LB on your farm, but just might be enough protection to stop the initial spore that floats in on the wind, depending upon how favorable or unfavorable the weather is for LB infections.
We captured a nightly average of between O.2 and 0.5 CEW moths in pheromone traps this week at farms in Berlin, W. Suffield and New Hartford. These sites are on a 6 day spray schedule on fresh silking corn. Farms in Wallingford and Shelton captured between 0.5 and 1 moth per night and are on a 5-day spray schedule on fresh silking corn. I didn’t get any readings from the CT River Meadows this week, those folks may still be on a 4-day schedule.
Here are the CEW thresholds:
Moths/night spray interval
0-0.2 No spray
0.2-0.5 6 day schedule
0.5-1 5 day schedule
1-13 4 day schedule
>13 3 day schedule
European corn borer
Traps in East Windsor failed to capture any ECB moths two weeks ago, captured 26 last week and captured 65 this week. That’s the highest number we’ve captured in several years and means that this site should have begun borer sprays on peppers this past week. One Coragen application may take him through the entire second generation flight while sparing natural enemies that control aphids, but then again, he may need a second spray with Intrepid or Radiant after 2 or 3 weeks. Traps in Shelton captured 10 borer moths and were also over the 7 moth per week threshold, so will begin spraying peppers next week. Traps in berlin captured only 4 moths, while those in New Hartford failed to capture any moths. Those sites are not spraying peppers at this time.
I expect to start finding a few bore larvae in pre-tassel stage sweet corn this coming week or the following week. We still have not found any fall armyworm moths or larvae this season in young corn.
Powdery mildew on pumpkins and winter squash
I found the first powdery mildew on pumpkins this week in Ellington. You should scout the bottom side of 50 older leaves in each of your pumpkin fields and begin spraying at 10-day intervals when you find the first small, white PM lesion. Here is one of the best spray programs you can run for fungus diseases and resistance management on these crops:
Spray 1: Quintec and Bravo
Spray 2: Procure and Bravo
Spray 3: Pristine and Dithane or Pristine alone
Spray 4: Microthiol sulfur and Bravo
Spray 5: repeat the sulfur and Bravo
Pristine can cost anywhere from $50-150 per acre, depending upon where you shop, so you’d be smart to shop for price on this one, and if you choose to skip any of these applications that may be the one you want to pass on. Pristine is a premix of Boscolid and the same active ingredient as in Cabrio. The Cabrio is as good as anything we have when it comes to fighting Plectosporium blight, so if you have that disease in your field you may not want to skip the pristine application or you may want to apply Endura and Cabrio, if that is any cheaper. Endura contains a higher concentration of boscolid and is registered for cucurbit crops.
If you are looking for a cheaper program you can try substituting sulfur in for every other application to control powdery mildew, stick to dithane or a generic Bravo for the fruit rots and try ProPhyt or another Phosphoric acid type product when DM gets here. We haven’t yet detected any downy mildew on cucurbits, but when we do, you will simply add one of the LB products I described earlier to your next spray for PM and fruit rots on pumpkins.
Organic growers should use sulfur for powdery mildew control and might want to try copper for fruit rots and downy mildew. Keep in mind that copper may cause phytotoxicity to many new pumpkin varieties.
Downy mildew on lettuce and brassica crops
A couple of growers have reported great success fighting DM on lettuce and Brassica crops with one of the phosphorous acid type-products such as ProPhyt or Fosphite. You may want to give it a try if you run into DM on these crops.
THW are beginning to be found in the field, but not in the same numbers that we were finding them the last couple of years. This pest is easy to control with selective insecticides such as Dipel or Radiant, if you find that you have enough of a population to worry about. Caterpillars with white wasp pupae attached should be moved to an end plant if possible so that they are not sprayed. An easy way to assess whether you have many or just a few hornworms is to look at the black plastic below the tomato plants. The feces or frass of the hornworm is easy to spot on the plastic as large black or brown pellets.
That’s all for this week. This message will next be updated on Friday afternoon July 27th.
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