Welcome to the UConn Vegetable Pest Message. This message is being recorded on Friday afternoon, September 6th, by Jude Boucher.
This message will cover:
Corn earworm/tomato fruit worm
Fall armyworm alert
Northern corn leaf blight alert
White mold on beans
Aphids on cucurbits and Brassica crops
Corn earworm/tomato fruit worm
Earworm pressure in corn increased this past week so that many growers are now on a 4-day spray schedule on fresh-silking corn. This schedule can be safely stretched by a day if we have three days in a row where temperatures fail to reach 80 degrees F, or if you are using an insecticide with a long residual period such as Coragen, Warrior or Mustang.
In Berlin, Shelton, and two farms in Suffield growers captured between 1.3 and 3 moths per night dictating a 4-day schedule on fresh silking corn. A third site in Suffield captured just 0.5 moths per night and is still on a 5 or 6-day schedule.
Remember that the corn earworm is also the tomato fruit worm and often attacks tomatoes at this time of year as fresh silk begins to be less abundant in the area. You may want to include a selective insecticide, such as Intrepid or XenTari, Entrust or Radiant, with your next tomato fungicide application.
Fall armyworm alert
The last couple of weeks I have been warning you to expect high numbers of FAW moths and larvae based on the record high trap captures and infestations they were seeing down on Long Island. Well they have arrived! One field of pre-tassel stage corn in Glastonbury had 38% of the plants infested with FAW larvae, while another in Shelton had a 60% infestation. The Shelton farm also reported a 50% infestation on their late whorl stage corn. Remember when the tassel pops open, this worm can’t bore into the stalk like a ECB, so it makes a beeline for the tuft of leaves where the ear will form, and will infest the ear before silk forms, and before you can put on a silk spray. All growers should be scouting young corn stands for FAW damage at this time, especially pre-tassel stage plantings, so that you can kill the worms before they migrate to the ear zone. Sometimes it takes two applications about 3-5 days apart to expose the un-opened tassels in all the plants and get a good kill.
Warrior and other synthetic pyrethroids have a spotty history when battling FAW: usually they work, but sometimes they don’t. Products that seem to work more consistently against this pest include Coragen, Radiant, Entrust, and Avaunt. Scout 50 plants in groups of 10 and look through the fingers of the un-opened tassels in pre-tassel stage blocks for live caterpillars. Larger FAW larvae will have produced a lot of ragged leaf feeding when they were younger, making it easy to spot plants infested with large worms. However, small worms can infest the pre-tassels before they open without producing much, if any, feeding on the leaves, so look closely through the tassel fingers for the larvae. FAW can also infest silking corn when in high numbers, but CEW sprays will also control the FAW hatching during silk.
Northern corn leaf blight alert
Last October I published an article in UConn’s ‘Crop Talk’ Newsletter warning you to plant only NCLB resistant varieties late in the season. Well, the disease is back! I saw one field in the northern part of the valley, with two different susceptible varieties that had lesions all the way up to the top leaves, just after they started silking. It is doubtful that the grower will be able to market this corn, because in three weeks the husks will all be grey and brown, and no amount of fungicide will save them now. The disease is now present in fields throughout the state, but is just getting started at some sites or is being contained by resistant varieties.
This disease is favored by warm rainy weather, long dew periods and fog that helps keep the leaves wet for extended periods. It overwinters on the residue of the crop, so all sweet corn fields should be harrowed immediately after harvest to encourage rapid decomposition of the foliage and to reduce spread of the disease to younger blocks. Out West, they recommend rotating out of corn for one season after a bad infection for conventionally-tilled corn and for two seasons for reduced- or no-till plantings.
There are two types of resistance: partial and race-specific. Race-specific resistance may not protect the corn from all strains of the disease, but usually restricts lesions development to small yellow spots that do not form spores. I saw this type of lesions in fields in Glastonbury and one farm in Suffield. Partial-resistant varieties offer broader protection against more strains of NCLB, but may produce a few small or even fully developed lesions with spores. However, partial resistance will delay the development and spread of the disease until later in the silking process which reduces the potential for economic damage.
Lesions are usually elliptical or eye-shaped, grey to brown and about 5 inches long. They start on lower and waist-high leaves in the center of the block where humidity is the highest. For susceptible varieties, and for resistant varieties planted adjacent to infected susceptible varieties, the lesions will spread up the plant until the whole plant looks dead by harvest. The kernels are still eatable, but the poor husk color tends to render the corn unmarketable.
Fungicides can help control the disease, but will prove to be cost prohibitive for wholesale growers in most years. Fungicide applications should start when the first lesions are found on susceptible varieties at pre-tassel or early silk. Two applications are recommended at 7 day intervals. Only early silk or even pre-tassel applications will help control the disease. Late applications will not help and will hasten pesticide resistance problems. Systemic products work better than protectants, but a protectant should always be mixed in with the systemic to help slow resistance. There are two families of systemics that work: group 3 and group 11. They should be mixed with Bravo (14dh), Dithane or Manzate (7dh). Group 11 systemics include Headline and Quadris (both 7dh). Group 3 products include Tilt, Bumper, Fitness, Propimax, AMTide Propiconazole and Proline. Proline has a supplemental label for sweet corn. The group 11 products will also help control rust on susceptible varieties, as will the protectants, but again it is much cheaper and more effective to choose rust and NCLB resistant varieties than to spray fungicides, which drives the costs of production up without any reimbursement.
An example of a fungicide program for NCLB would be to apply Headline + Bravo the first week and Tilt + Dithane the second week. Be aware that some of the products mentioned have longer dh restrictions for fodder.
White mold on beans
With rainy weather, this disease produces a fluffy white sporulation on the bean pods making them unmarketable. It is caused a Sclerotinia fungus that can stay in the soil for 7 years after an outbreak. A fall application of Contans, a competitive fungus, can reduce the amount of Sclerotinia spores in the soil. Removal of diseased plant material is also recommended. Beans should be planted with wide spacing to encourage drying of the field. Tiny mushrooms will eject spores from the soil on to the dying petals of the flowers during bloom causing infection of the pods. Large bean producers use one or two fungicide applications during bloom if the weather or soil is wet. Two applications are necessary during prolonged wet periods, when the bean plants are large and the canopy is dense, and when narrow row spacing is used. Some fungicide spray options include Bravo + Topsin-M, Bravo + Endura or Bravo + Rovral.
Aphids on cucurbits and Brassica crops
Some growers are starting to have problems with aphids on cucurbit vine crops or on Brassica crops. Insecticides are listed under specific crops in the New England Vegetable Management Guide. You can buy a hard copy of the guide or access the guide on-line at www.nevegetable.org.
That’s all for this week. This message will be updated next Friday afternoon September 13th.