I’ll be on vacation next week, so there will be no pest message, but be sure to check the message again on August 1, for an update on corn and cucurbit pests. Jude

• Corn pests
• Bacterial leaf spot on peppers
• Septoria leaf spot and Phytophthora on tomatoes
• Plectosporium on summer squash
• Cercospora leaf spot on spinach, beets and Swiss chard
• Colorado potato beetle & potato leaf hopper on eggplant and potatoes
• Imported cabbageworm & dimondback moth larvae on cabbage

Corn pests
Growers in Shelton, Northford, Berlin and East Hartford all captured between 2.5 and 8 corn earworm moths per night this week and are on a 4-day spray schedule on fresh silking corn. Most growers around the state should be on a 4-day schedule unless the traps on your farm tell you differently. One farm in Falls Village only captured 0.7 moths/night and is on a 5-day schedule, and another farm in East Lyme failed to capture any moths. We checked the trap top for holes to be sure that the moths were not escaping in East Lyme, like they were on one farm last week, but the trap was sound. It could be that because East Lyme has not had rain in 4 weeks that there are very few moths arriving in that town. Normally, I would have recommended that he stop spraying silking corn until he captured more moths, but since most other farms in the state are on a 4-day schedule, we put him on a 6-day schedule, just to be conservative, and set up his second trap, to confirm the results he is getting in his first trap. We had one other farm this week that failed to capture any moths. However, they failed to push the inner funnel back up last time they emptied the trap, so that moths could not enter the trap. They stayed on a 4-day schedule on silking corn.

We captured 1-2 fall armyworm moths in Shelton, Northford and East Hartford this week. We are also beginning to find low levels of FAW infestations in young mid-whorl and late-whorl stage plantings. Infestations ranged from 2-7% of the plants and did not require treatment. The action threshold for FAW on PT stage corn is 10% and 15% for whorl stage plantings. Continue to scout your corn this coming week for this pest and remember that, unlike ECB that lays its eggs randomly throughout the whole field, FAW tends to target one end of a block, so you should walk the entire length of each block while scouting.

European corn borer traps were empty again this week all over the state. That means that it will be at least 2 weeks before we start spraying peppers for this pest or seeing them in young corn.
 

Here is a list of infestations found at different sites while scouting sweet corn this past week. *means that the planting is over threshold and should be sprayed. MW=mid-whorl, LW= late-whorl, PT=pre-tassel, S=silk. 

Update on Impact herbicide on sweet corn
Here is some first hand information that is bound to help. I made 4 weekly plantings of Bt sweet corn at the UConn Research Farm for my CEW threshold experiment, and did not apply any pre-emergence herbicide. Then I came back and hit all 4 plantings at once with 3/4 ounce Impact, 1.5 gallons of methylated seed oil, and 2 pounds of ammonium sulfate, and 10 days later there is hardly a weed left alive in any of the plantings. The weeds in the oldest planting were 6 inches tall when I sprayed, with 3 inch weeds in the second planting and 1 inch weeds in the third, but very few emerged weeds in the 4th planting. I had a complete thick carpet of most common broadleaf weeds (pigweed, lambsquarters, ragweed, galinsoga, purslane, etc) and plenty of crabgrass. The purslane is not listed on the Impact label as being a susceptible weed, but there are only a few plants with one or two green leaves left. It remains to be seen how much regrowth I get from the purslane and newly emerging weeds, but I am hopeful that I now have a nice stale seedbed that will remain fairly clean for the season. The initial results look very promising for a complete post-emergence weed control program, with very little active ingredient, for fields that have the right combination of weeds. I'll let you know how I make out. If you are going to try this, make sure you use the oil and nitrogen in the mix for a better kill, and do not wait too long. I have seen poor results when folks let the weeds get too tall. The label calls for a maximum of 6 inches for most weeds.

Bacterial leaf spot on peppers
We found bacterial leaf spot on peppers on one farm last week and two additional farms this week. This disease thrives when the nights stay warm and humid. Growers should scout their pepper plantings weekly for this disease looking for dark, irregular-shaped lesions along the margins of the leaves, on 2 or more adjacent plants. This disease spreads so fast that you will almost always find more than one plant infected. Sometimes you can just rogue out or remove a few plants and stop the site of the initial infection and head off a large scale epidemic. Other times you need to start spraying all susceptible pepper varieties with an effective copper formulation. Newer formulations, such as Kocide 3000, help put more copper ions in suspension and fight bacterial diseases much better than older formulations. Remember to upgrade to a newer formulation when you need to restock. Peppers should be rotated to new ground each year, because this disease survives in the old crop residue for up to two years, and you should plant resistant varieties of bell peppers to help minimize disease loss and spraying.

Also, if you have pepper maggot on your farm, you should be applying the second and final spray of Orthene or dimethoate for that pest this coming week, or 8-10 days after your first spray.

Septoria leaf spot and Phytophthora on tomatoes
We found our first outbreak of Septoria leaf spot this week. This disease starts on the lower leaves like early blight, but the lesions are smaller and have an ash-grey center, and it tends to be more aggressive than early blight. This disease also relies on long periods of leaf wetness for infection to occur, so like EB, anything that you can do to encourage rapid drying helps (trellis, prune, site selection, trickle irrigation instead of overhead, etc.). Last year a grower had great results holding this disease in check with Cabrio, even after getting a late start.

Another grower called in and described the classic symptoms of Phytophthora - plants sick and dying after heavy rain, worse in low wet end of field, spreading up the rows, etc. He is bringing some plants to the CT Agricultural Experiment Station for confirmation. If it is Phytophthora, it all comes down to water management: you can not let any water stand or pool in the field. Anything that helps drain the field needs to be done to manage this disease, that includes, sub-soiling both before planting and between rows after planting, planting in a direction that allows the water to flow out of the field, removing soil between the beds at the end of the field, breaking the beds in low spots to allow the water to flow out, and also power washing muddy machines and tires so you don’t move the spores to new fields. I am convinced that we saved the tomatoes at Nelson Cecarelli's farm this year by sub-soiling between the rows. He had a few plants go down to Phytophthora early, in the low spot where you could see that there had been standing water between the rows from an earlier storm. Subsoiling before the next big storm allowed the water to soak through the plow pan, which eliminated the pooling problem, and kept his plants high and dry and disease free.

Plectosporium on summer squash
We found our first case of Plectosporium blight on summer squash this week. Look on the vines or stems for tiny white slits or lesions that are pointed on both ends. This disease is very aggressive and will kill the plants or rot the fruit if the season turns wet. Applications of Bravo or strobiluron fungicides, such as Pristine, Quadris, Cabrio, or Flint, can help slow disease spread. Downy mildew is not yet in CT and the site that tracks the disease has a low risk forecast out for southern New England at this time.

Cercospora leaf spot on spinach, beets and Swiss chard
This is straight out of the UMass Extension Newsletter, Vegetable Notes. Cercospora leaf spot is the most common disease on these leafy greens. Leaf spots have white centers and red margins. The disease can be a problem at this time of year because it is favored by high temperatures, high humidity and long periods of leaf wetness from due or rain. Management includes crop rotation, not waiting for regrowth on infected plantings after the initial harvest, and spacing successive crops far from early planting. Again, Bravo type products and the stobilurins are effective at controlling this disease.

Colorado potato beetle & potato leaf hopper on eggplant and potatoes
Adults CPB are laying second generation eggs right now. Also, PLH were at very high levels and required treatment on eggplant this week at a couple of farms I visited. Provado will provide control of both these pests and spare most beneficials that control spider mites.

Imported cabbageworm & dimondback moth larvae on cabbage
Remember to alternate between products to help prevent resistance when diamondback larvae are in your field. Effective materials include XenTari, SpinTor, Entrust, Avaunt and Intrepid.


That's all for this week. This message will next be updated in two weeks on Friday afternoon August 1.

Jude Boucher

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