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Welcome
to the weekly Vegetable Pest Message
from the University
of Connecticut Cooperative Extension System
Week of August 31st 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:
• Corn earworm trap counts
• Downy mildew on broccoli and crucifers
• What works on cucumber downy mildew
• Phytophthora on melons
Corn earworms
CEW moth numbers in pheromone traps around the state seemed to hold steady this week at the few sites that I have numbers for. In Berlin traps captured 0.25 earworm moths per night which kept them on a 6-day spray schedule on fresh silking corn. Traps in New Hartford and Goshen both captured 3 moths per night and the hills area of the state remained on a 4-day spray schedule. The data was a little old in Northford and Wallingford, but when last checked the traps captured between 1 and 2 moths per night which kept them on a 4-day schedule too. In Glastonbury, one grower reported capturing 18-20 moths per night this week, so folks in the CT River Meadow remain on a 3-day spray schedule on fresh silk.
Here are the CEW thresholds:
Moths/night spray interval
0.2-0.5 6 day schedule
0.5-1 5 day schedule
1-13 4 day schedule
>13 3 day schedule
Downy mildew on broccoli and crucifers
In late summer when we start to get these cool nights and heavy dews, downy mildew becomes a real threat to broccoli8, cauliflower and to a lesser extent, cabbage and other crucifers. Leaf and stem spots begin as purple specks, which expand into yellow or brown irregularly-shaped patches. So if the leaves of your broccoli are yellowing right now, they probably have DM which can also get into the head and predispose the florets to infection by bacterial soft rot organisms. Controls include using resistant varieties, reducing the crowding of plants in late plantings, and using fungicides such as Ranman, Revus or a phosphoric acid-type product, such as ProPhite or Fosphite.
What works on cucumber downy mildew
Some growers who did not apply a fungicide in time or did not use the right product have mentioned that downy mildew on cucumbers seems impossible to control this year. That’s not true. We have many growers who have learned to recognize the symptoms of this disease and caught it when it first entered their fields and have achived great control this year with Ranman and Tanos, to name just two products that we know are working on the strain we have in CT this year. One grower is growing two varieties in the same planting and noticed that the DM resistant variety is holding up real well this year, while the other plants have numerous brown lesions on the leaves. But even on his susceptible variety, he is keeping the disease from getting any worse with Ranman and Tanos.
Phytophthora on melons
One of the growers I am working with found maggots in the bottom of his muskmelons and wanted to know what pest it was and what insecticide he should use to stop the infestation. I told him that this was a case of which came first, the chicken or the egg. I told him that, even though some of the melons that were infested were growing on the black plastic, I thought there was a slight soft spot and some disease that was attracting flies drawn to rotting fruit. The UConn diagnostic lab was able to incubate the melon and found that it was infected with Phytophthora blight. So in this case, the plants had not collapsed, but the fruit were just starting to rot, which was attracting flies. The lesson here is to make sure that you are fighting the right pest before reaching for a pesticide.
That’s all for this week. This message will next be updated on Friday afternoon September 7th.
Jude Boucher
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