Vegetable IPM Update 8/26/20

Sweet Corn

European corn borer (ECB) adults continue to be very low, and no map will appear in this edition.

The highest nightly trap catches of ECB for the week ending 8/26/20 are as follows:

Fall armyworm (FAW) larval infestations have stabilized at low to moderate levels.  Infestations generally are in the teens to low 20% range, but  FAW could increase dramatically with the arrival of  storms, resulting in significant injury to whorl and even seedling stage corn.  Injury from newly hatched larvae shows up as “window panes” or areas where leaf tissue has been eaten down the the lower epidermis (see photo at far left).  This injury leads down into the whorl.  As larvae gain size, they begin to consume leaf tissue in its’ entirety, creating ragged holes and lots of droppings (see photo at near left).  FAW can be tough to manage because it is resistant to synthetic pyrethroid insecticides (IRAC 3A) and because larvae are often covered by their own droppings, making contact with the insecticide more difficult.  Treat when 12% or more plants exhibit FAW injury alone, or in combination with ECB injury.

Corn earworm (CEW) moth captures have increased in central and southern New Jersey blacklight traps over the past week.  Trap catches, both blacklight and pheromone, are showing signs of a possible large increase within a week.  The current population poses a significant risk to silking corn.  Catches remain somewhat variable (see map at left), with green areas on this map representing a 3-day spray schedule.  Note that there continues to be disagreement between blacklight and pheromone trap maps with regard to the southwestern counties.  See pheromone trap information below.

The highest nightly trap catches of CEW in black light traps for the week ending 8/26/20 are as follows:

CEW pheromone trap catches have increased dramatically in some of the southernmost traps (see CEW pheromone map at left).  The blacklight network continues to indicate a more conservative schedule in Morris, Warren and Sussex counties, while the pheromone network indicates a more conservative schedule in Salem and Cumberland counties.  Areas in green on the pheromone map represent  a 4-5 day schedule and red areas indicate a 3 day schedule.  The number of pheromone traps deployed is much lower, resulting in much broader color bands on the map.  With traps in Cape May County and along the bayshore registering very high catches, growers should be alert for the possibility of a large influx of moths at any time.  The current population is a serious economic threat, and it is essential that the more conservative schedule be adhered to in any given area.  Further, it is important to use effective materials to manage this pest on silking corn.  Insecticides in the IRAC 28 class (Coragen, Besiege, Exirel) and IRAC 5 (Radiant, Blackhawk, Entrust (OMRI approved)) remain among the most useful insecticides against CEW.

The highest nightly trap catches of CEW in pheromone traps for the week ending 8/19/20 are as follows:

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.

As night temperatures moderate, and dew periods lengthen, northern corn leaf blight (NCLB) will increase in frequency and severity.  This fungal disease causes elongated gray streaks on leaves.  The lower leaf surface will develop greenish-gray sporulation.  If cooler, moist conditions persist, this disease can invade enough tissue to limit ear size.  Lesions can also develop on husks, resulting in an unsightly ear.  If these lesions are discovered in the pre-tassel stage or earlier, fungicide applications may be warranted.  Realistic control of this disease requires a combination of protectant (mancozeb, chlorothalonil) and locally systemic fungicides in FRAC groups 3,7 and 11.  For a complete list of materials, see the Sweet Corn Section of the Commercial Vegetable Production Recommendations.

Pepper weevil (PW)

Another farm was found being infested with weevils bringing the known total to 6.  After the initial discovery of weevils at one farm back in July, no further weevils have been captured there, so that there the possibility that timely spraying may eliminate the weevils before they become established.

To get a snapshot of the weevil status at another farm, 7 plants in a 20-foot section of row were stripped and examined for weevil signs and then cut open to determine whether the fruit were infested.  Of the 43 total fruit there was 1 less than an inch in diameter and infested; 7 were in the 1 to 2 inch diameter range, all infested; 16  were in the 2-3 inch range, 4 infested; and 19 were in the 3 inch + range with 2 infested.  Smaller fruit were either non-existent or infested 100%, the 2-3-inch fruit were 25% infested, and the 3 + inch fruit were 11% infested.

Most of these plants had very small buds that were forming to produce new flowers, but unless the weevils are sprayed before they bloom the weevils will infest and cause abortion of the new fruit.  We are still looking for better ways to manage weevils.

As for control materials, Florida insecticide trials indicate that Actara, Vydate, Harvanta, and Torac provide the best results, however, there is a broad range of materials including pyrethroids and neonics that can kill the adults.  The hope is to eliminate the weevil population before it becomes established in the field.  A combination of spraying, trapping, and removal of aborted fruit would help to manage this pest.

Pheromone trap catches of beet armyworm (BAW) have decreased in southern NJ traps.  However, scattered individual larvae have appeared in some northern NJ cole crop fields, indicating that there is some larval population active in the state.  Growers should be alert to the potential for infestation from this pest.  Look for clusters of pepper plants with lace-like damage to foliage near growing points (see photo at upper left).  The green caterpillars will be found among these damaged leaves (see photo at lower left).  After consuming foliage, BAW can begin to damage fruit directly.  It is also important to note that BAW, like FAW, is resistant to synthetic pyrethroid insecticides.  For this reason, materials in the IRAC 5 and 28 classes should be used in response to an infestation.

The highest nightly trap catches of BAW in pheromone traps for the week ending 8/26/20 are as follows:

Pumpkins and Winter Squash

The cucurbit downy mildew (CDM) sentinel plot  at Snyder Farm in Hunterdon County has CDM on cucumbers as of 8/18/2020.  This plot, consisting of pumpkin, watermelon, cantaloupe, butternut, acorn, cucumber and kabocha squash is used to indicate the presence of cucurbit downy mildew in the region, and what crops are affected.  As of 8/25/20, there was no CDM detected on any of the other cucurbit types, and all reported infections in our region have been on cucumber, with one from Long Island reported on muskmelon.  For regional information on this important disease, see the Cucurbit Downy Mildew Forecast webpage:  http://cdm.ipmpipe.org/.  As of this Wednesday (8/26/20), New Jersey was rated at low risk for new infections by CDM from current regional sources.

All pumpkin/gourd/winter squash fields in the scouting program have now reached the powdery mildew (PM) threshold.  When scouting 50 plants (5 consecutive plants each, in 10 random locations), look within the canopy and observe the upper and lower surface of two older leaves per plant.  PM generally doesn’t appear until fruit enlargement is occurring.  Initial lesions will be fairly small and isolated (see photo at far left).  As the disease progresses, lesions will spread out, giving the leaves a dusty appearance (see photo at near left).  A PM fungicide program incorporating both protectant and locally systemic materials should be initiated when PM is found on two or more leaves in a 50 plant (100 leaf) sample.  Fungicides and suggested rotations are found in the Pumpkin and Winter Squash section of the Commercial Vegetable Production Recommendations.  Consider the addition of copper hydroxide to the fungicide program if bacterial leaf spot has been detected in the field.

Melon aphid populations have begun to appear in some pumpkin and winter squash fields.  This aphid builds to heavy populations that result in the deposition of sticky droppings on the surface of fruit.  If melon aphids (see photo at left) appear in more than one sample site in a 10 site sample, consider treating to minimize the appearance of droppings.  Insecticides effective at managing this pest are found in the Pumpkin and Winter Squash section of the Commercial Vegetable Production Recommendations.

Tomatoes

Corn earworm (tomato fruitworm) infestations have expanded into northern NJ, and should be expected on late tomato plantings all over the state.  As this pest arrives in grater numbers through late summer, it is important to monitor plantings for injury.  Female moths lay eggs near flower clusters high on the plant.  Larvae hatch and bore into fruit in the upper or outer canopy (see photo at right).  If fruitworms or fresh injury are discovered in more than one scouted site, consider an insecticide application in the IRAC 5 or 28 class (see sweet corn section).  Repeat applications may be necessary as long as moth counts remain high in any given area.

Brown Marmorated Stink Bug

Brown marmorated stink bug (BMSB) activity has decreased further in blacklight traps throughout New Jersey.  This is often the case late in the summer.  Bugs become less attracted to light traps and are caught in greater numbers in pheromone traps.   While this pest has generally declined as a threat to peppers, it remains a significant threat to tree fruit.

The highest nightly catches of BMSB in black light traps for the week ending 8/26/20 are as follows:

Cole Crops

Fall plantings of cole crops are well underway at this time, and are frequently infested by imported cabbageworm (ICW) and diamondback moth (DBM) larvae.  At this time, cabbage looper (CL-photo at left) and cross striped cabbage worm (CSCW-photo at right) are also causing injury to these crops.

Check 5 consecutive plants each in 10 random locations throughout the planting.  Consider treating if caterpillars are found on 10% or more plants that are in the 0-9 true leaf stage.  From 9-leaf to the early head stage (in broccoli, cauliflower, and cabbage) infestations up to 20% may be tolerated.  Once heads begin to form, a 5% threshold should be observed to protect the marketable portion of the plant.  For leafy greens such as collards and kale, 10% plants infested is the threshold throughout.

Some populations of DBM are resistant to carbamate and synthetic pyrethroid insecticides.  The lack of DBM control with these insecticides has been noted in NJ previously.  It is important to distinguish between common cole crop pests for this reason.  DBM larvae grow to a length of approximately 0.5”, and taper toward both ends (see photo at right).  These caterpillars thrash violently when disturbed.  Newer chemistries that specifically target caterpillar pests are effective against DBM as well as all other caterpillar pests of cole crops.  These materials include (active ingredient – trade name (IRAC* code)):

Spinosad/Spinetoram – Entrust(OMRI)/ Radiant (5)

Chlorantraniliprole – Coragen (28)

Cyantraniliprole – Exirel (28)