Vegetable IPM Update 8/14/24

Sweet Corn

Fall armyworm (FAW)  infestations remain present, although they have become lighter and more sporadic in most scouted locations in central and northern NJ counties.  Re-infestations following treatment can and have occurred.    Because FAW moths are highly mobile, it is important to monitor fields at least weekly for signs of infestation.   Whorl stage plants are prime targets for egg laying.  Delays in treating whorl stage infestations can lead to stunted plants and poor ear size.

Newly hatched FAW larvae cause holes and scratches on leaves that are similar to ECB feeding, except that they tend to be more concentrated and always lead down into the whorl  (see photo at left).  As the larvae grow, the feeding becomes more destructive, with large ragged holes and obvious droppings deposited in the whorl (see photo at right). 

We will provide updates on new FAW appearances and severity as reports come in.  FAW are resistant to synthetic pyrethroids.  Effective sprays should include IRAC grp. 5 (spinosyns) or IRAC grp. 28 (diamides).  The carbamate (IRAC grp. 1A) Lannate is also still effective.  Sufficient water should be used in the applications to allow the solution to penetrate the layer of droppings that may have formed above the caterpillar.

Corn earworm (CEW) moths captures from northern and central blacklight traps are still rising.   Pheromone trap information is available from all northern and central sites, but is limited  from southern New Jersey.  Overall, pheromone catches are also rising.  South Branch (Somerset) and New Egypt (Ocean)  locations had the highest activity this week, but pheromone catches overall were higher (see pheromone trap may below).  There are a few pheromone traps registering abnormally low catches.  We attribute this to poor trap placement, and will try to correct these as soon as possible.  We should expect further CEW increases, particularly with the passage of  the tropical depression later this week.  We will use a combination of pheromone and blacklight trap types to derive silk spray schedules by region.  Silking corn is at risk of CEW infestation at this time.  Be sure to access information from this publication in the upcoming weeks to determine how frequently you should treat silking sweet corn to protect it from CEW infestation.

The highest nightly blacklight trap catches of CEW for the week ending 8/14/24 are as follows:

The highest nightly pheromone trap catches of CEW for the week ending 8/14/24 are as follows:

Using our current pheromone- based thresholds (30″ Hartstack trap) developed by the Univ. of Delaware, nightly corn earworm moth catches translate to:

0 moths – 6-7 day spray schedule

1 moth – 5 day spray schedule

2-20 moths – 4 day spray schedule

>20 moths – 3 day spray schedule

Silking Spray Schedules*:
South – 3 days

Central – 3 days

North – 3-4 days

*These recommendations are based on regional catches.  Adhere to tighter spray schedules if indicated by local trap catches.  Synthetic pyrethroids alone should NOT be used for corn earworm (CEW) protection on silking corn, or for fall armyworm (FAW) management at any stage.  Control with these materials is very inconsistent.

Field scouts are finding corn leaf aphid (photo at left) in almost every planting of pre-tassel and tassel stage sweet corn.  This pest can build to very high numbers on plants, and with repeated use of pyrethroid insecticides, can become a contaminant as it infests corn ear husks.  If aphids are detected in tassels just prior to silking, consider adding the neonicotinoid acetamiprid (Assail, Anarchy) to the regular silk spray material(s).  Methomyl (Lannate) is also useful at limiting aphid populations.

Tomatoes

With dramatic increases in CEW (aka. tomato fruitworm) moth numbers, it is important to monitor fields for the appearance of injury in tomato plantings.  The CEW moth often lays eggs near flower clusters near the upper canopy of plants, resulting in larval damage to green fruit in very visible areas (see photos at left).  Larvae typically enter the shoulders of fruit, and may move around, causing injury to multiple fruit. Local pheromone trap catches approaching 20+ CEW per night may warrant preventive sprays for this pest.  At minimum, growers should be checking fields for the presence of fruitworm injury.  Just as with CEW in sweet corn, effective materials in tomatoes include IRAC 5 (spinosyns) and IRAC 28 (diamides).  See the Tomato Section from the 2024-25 Guide for a complete list.

Native brown stink bugs are active in tomato fields.  These true bugs (see photo of Euschistus sp. nymph below at left), move into irrigated tomato fields, mate, and deposit eggs.  Feeding results in “cloudy spot” (see photo at right below).  Increases in stink bug injury are often found by crews picking the fruit.  Growers should consider 1-2 insecticide applications to limit fruit injury if this damage is increasing in harvested fruit.  If actively scouting fields, insecticides should be considered if stink bug adults, nymphs or new fruit injury is found in 2 or more sample sites in a 10 site sample.  Insecticides that are effective on stink bugs include pyrethroids and neonicotinoids (see Tomato Section from the 2024-25 Guide), so care should be taken to avoid contact with foraging bees.

Beet Armyworm

Beet armyworm (BAW) numbers in pheromone traps in the Woodstown area of Salem County remained very high over the past week.  Thanks to a grower cooperator in that area, we know that catches are 70/night over the past week in local traps.  This pest can cause significant injury on peppers as well as leafy greens like swiss chard, and kale.  Monitor pepper fields weekly for signs of feeding.  BAW larvae (photo at left) feed in the developing foliage in terminal growth of plants.  Initially, leaves are skeletonized, but as larvae grow, they will move onto fruit and damage these as well.   In northern NJ, BAW is an occasional, and typically low level pest of cole crops.  Infestations tend to be very local for unknown reasons.  As with other armyworms, BAW is difficult to control with pyrethroid insecticides.  Effective materials include spinosyns (IRAC 5) and diamides (IRAC 28).

Cucurbit Crops

Cucurbit downy mildew (CDM) is active on cucumbers throughout NJ.    Look for chlorotic areas bordered by veins on the upper leaf surface (photo at lower right).  If conditions are moist, dark sporulation may be found on the lower leaf surface (photo at lower left).

 All cucumber and cantaloupe plantings should be protected, and growers of all cucurbit crops should be alert to the possibility of additional crop infections with the passage of the tropical weather system later this week.  Useful materials for CDM may be found in the Cucumber Section of the 2024/25 Commercial Vegetable Production Recommendations.  A sentinel plot has been established at Snyder Farm in Hunterdon County.  This plot consists of pumpkin, watermelon, cantaloupe, butternut, acorn, cucumber and kabocha squash will be used to indicate the presence of cucurbit downy mildew in the region, and what crops are affected.  As of 8/14/24, CDM had not been detected on any of these crops except cucumber in the sentinel plot, nor has CDM been found on any scouted field in northern and central NJ except cucumber. 

Powdery mildew (PM) thresholds (2 infected leaves/50 leaf sample) is now present in all fields.   Once PM lesions (photo at right) begin to appear, the protectant fungicide program for this disease should be initiated.  The program generally includes a combination of broad spectrum protectants and more targeted, locally systemic fungicides.  For a complete list of suggested materials, see the Pumpkin and Winter Squash Section of the 2024/25 Commercial Vegetable Production Recommendations.  Ideally, a fungicide program should include a rotation of 3 different FRAC code materials combined with broad spectrum protectants in each application.

Cole Crops

With fall plantings now establishing, it is typical for diamondback moth larvae ((DBM) see photo at right) to become the dominant caterpillar pest in many cole crop fields.  This pest can multiply quickly, with a generation completed in under 2 weeks with high temperatures.  Furthermore, this pest is not responding to chlorantraniliprole (Coragen) in many parts of the state.  Effective materials continue to be IRAC 5 materials (spinosyns), and the IRAC 6 material, ememectin benzoate (Proclaim).  Be sure to check the Cole Crops Section of the 2024-25 Commercial Guide for specifics, as PHI’s and crop labels vary.  It is important to return to treated fields within 2-3 days to assess the efficacy of the insecticide applications.  Effective materials should eliminate DBM larvae within 48 hours.

Harlequin bugs (photo at left) seem to be more prevalent in cole crop fields this year.  This colorful stink bug will cause a cloudy spot-like injury on leaves of all brassica plants.  This injury is particularly problematic on leafy greens like collards and kale. While scouting, note the presence of adults, eggmasses (photo at right, by Mike Raupp of U of Md) and injury to plants.  If bugs are active in more than one site in a ten site sample, consider applying an insecticide.  For conventional insecticide recommendations, see the Cole Crops section of the 2024-25 Commercial Vegetable Guide.  Organic options are limited to pyrethrum products.  Mechanical barriers, like row covers, may help limit injury.

Thank you!

The Vegetable IPM Program wishes to thank the following Field Technicians, without whom much of the information presented weekly here would not be available:

Chris Cloutier

Hamna Khalid

Alexandra Suszko