Vegetable IPM Update 8/28/19

Sweet Corn

Note:  Traps in some portions of southern New Jersey were not serviced over the past week.  The impact of this will be addressed in individual sweet corn pest sections.

European corn borer (ECB) moth captures have decreased generally over the past week and no map will appear in this addition.  Feeding in late season whorl and pretassel corn in northern NJ has increased, with some plantings exceeding the 12% threshold.  This week, unsprayed sweet corn in the sentinel plots (Providence) at Snyder Farm in Hunterdon County had 47% ECB infested ears, despite little indication of adult activity in the area.  Most of these larvae were in the tips of ears, which underscores the importance of the silk spray schedule in not only controlling CEW, but ECB that move from tassel to ear during the silk period.   In combination with fall armyworm (FAW) feeding, action thresholds have been exceeded in all areas of the state.

Growers should continue to scout whorl and pre-tassel stage plantings weekly and consider treating when infested plants exceed 12% in a 50 plant sample.  As plantings proceed to the pre-tassel stage, ECB larvae may be found in emerging tassels.  It is a good idea to treat individual plantings as they move into the full tassel/first silk stage one time.  This eliminates any ECB larvae that have emerged with the tassels as they begin to move down the stalk to re-enter near developing ears.

Useful insecticides for this particular application include synthetic pyrethroids (IRAC Grp 3), spinosyns (including OMRI approved Entrust) IRAC Grp 5), and diamides such as Coragen (IRAC Grp 28) or materials such as Besiege which include the active ingredient in Coragen.  Synthetic pyrethroids alone should NOT be used for corn earworm (CEW) protection on silking corn.  Control with these materials is very inconsistent.

The highest nightly black light trap catches of ECB for the week ending 8/28/19 are as follows:

Corn earworm (CEW) moth catches increased dramatically beginning late last week in all traps.  Overall, CEW numbers now represent a sizeable late summer migratory influx.  While moth counts declined somewhat with cool night temperatures since the weekend, we are still experiencing high activity.  The white area in southwestern NJ on the blacklight map (left) should be considered to be solidly in the 3-day silk spray schedule zone.  We are missing trap data in that area, but activity should be similar to surrounding areas.  There continue to be some exceptionally high catches in southern NJ pheromone traps this past week (see pheromone trap map below at right).    There are now economically damaging populations of this pest throughout the state, and all areas are at extreme risk of crop injury if strict silk spray schedules are not observed.   Red areas on the on the pheromone trap map indicate a 3-day silk spray schedule, while green indicates a 4-5 day silk spray schedule. Blue areas represent a 5-6 day schedule, and white areas are 6-7 day.  Taken together, blacklight and pheromone traps are indicating 3-day silk spray schedules throughout the state.  There are far fewer CEW pheromone traps than blacklights, and the resulting map has much broader color bands as a result.  It should also be noted that the pheromone traps are much more sensitive than blacklights.  Therefore, the number of moths caught in pheromone traps required to generate a specific spray interval is much higher than the number caught in blacklight traps.   It must be stressed that there is high variability in these catches, and growers should consult with their IPM practitioner on recommended spray schedules.

The highest nightly CEW pheromone trap catches for the week ending 8/28/19 are as follows:

Fall armyworm (FAW) feeding has remained unchanged, with infestations now found all over the state. We still  are not seeing extensive feeding, but thresholds have been exceeded in all areas.  Growers should scout all fields from pre-tassel stage down to early whorl stage.  This pest causes extensive foliar damage on whorl stage corn (see photo  at left), can also infest ears, and is capable of killing small plants.  FAW larvae are brown in color (see photo at right), with an inverted “Y” pattern on their head capsule.  They are much larger than ECB when fully developed.  FAW is even more consistently resistant to pyrethroid insecticides.  For this reason, the same insecticides classes now recommended for CEW control should be utilized for FAW management.

Northern corn leaf blight (NCLB) is increasing in northern NJ sweet corn plantings, and may be present elsewhere.  This disease causes elongated gray lesions, starting on older foliage (see photo at left).  If uncontrolled, NCLB can result in enough foliage loss to limit ear size, as well as forming lesions on the husk leaves.  Growers should be scouting for this disease when checking for insect injury.  Control is necessary if lesions appear while plants are in the whorl stage.  Heavier dew periods, common throughout August, favor disease development. Fungicides in FRAC groups 3, 7 and 11 are labled for control of this disease in rotation with chlorothalonil.  See the 2019 Commercial Vegetable Production Guide for suggested materials.

Corn leaf aphid populations have begun appearing in pre-tassel stage sweet corn.  These aphids (photo at right) may be found in the emerged tassel while scouting for other insects.  These insects are not controlled with IRAC group 5 or 28 insecticides, and pyrethroids are ineffective at killing aphids but very good at killing beneficial insects.  Therefore, if corn leaf aphids are found in tassels, it is advisable to add the IRAC group 4a material Assail in with the first silk application for worm control.

Silking Spray Schedules*:

South – 3 days

Central – 3 days

North – 3 days

*These recommendations are based on regional catches.  Adhere to tighter spray schedules if indicated by local trap catches.  To repeat: 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.

Peppers

Pepper weevil

Weevil counts have fluctuated, with some of the initially infested farms recording no weevil catches this past week.  Either the infestations are light, or they did not establish populations in some of the fields.  One farm near Folsom had a significant increase in trapped weevils recently, but no damaged fruit have been found.  Fortunately, we are approaching the end of the season so that losses will be minimal for newly infested fields.  The one farm that had been severely infested probably became so in May.

As a reminder:  Areas near food processing plants and land fills, especially those that accept vegetative waste are high risk areas for pepper plantings.  Ideally, fields should be at least 1 mile from these facilities, or more.  In these higher risk areas yellow sticky cards with pheromone lures should be deployed on the pepper field borders in the early growing season to help detect the presence of weevils.

Pheromone traps established for beet armyworm (BAW) in the southern counties continue catching adults, although numbers have declined somewhat.

BAW can reach levels that result in damage to pepper plants, and injury has been reported in southwestern NJ.  Growers in the southern counties should be alert for the appearance of severely defoliated terminals (see photo above at left) on pepper plants.  Small BAW larvae (photo at right) feed on these leaves before turning to fruit as they increase in size.  As with FAW, beet armyworm is resistant to pyrethroid insecticides.  Insecticides now recommended for CEW and FAW control are useful for BAW management.

Tomatoes

With CEW numbers at high levels, tomato growers should be alert to the possibility of fruitworm injury (see photo at right).  CEW moths are attracted to blossom clusters in the upper canopy of plants.  They lay eggs there, and larvae penetrate the nearest fruit without feeding on foliage.  Thus, injury typically occurs on fruit in the upper and outer edges of the plant.  With current CEW pheromone trap catch levels in south Jersey, it may be wise to treat preventively for this pest until numbers subside.  If scouting, growers should consider an application to limit damage when the first sign of injury occurs.  Insecticides in the IRAC group 28 (Coragen, etc.) and group 5 (Radiant, Entrust) are good choices, as they are effective against CEW and are less toxic to beneficial insects.  The use of synthetic pyrethroids (IRAC 3) can increase aphid and mite populations.

Pumpkins and Winter Squash

Cucurbit downy mildew (CDM) is active on cucumbers, pumpkins, acorn squash and butternut squash in NJ.    All growers should be applying appropriate fungicides for downy mildew on all cucurbit crops at this time.    For regional information on this important disease, see the Cucurbit Downy Mildew Forecast webpage:  http://cdm.ipmpipe.org/.  Pumpkin and winter squash fields should also be managed for powdery mildew (see photo at right).  Thresholds (2 lesions/50 older leaves) have been exceeded in most fields.    See the Pumpkin and Winter Squash section of the 2019 Commercial Vegetable Production Guide for suggested powdery and downy mildew control materials.

In addition, numerous instances of plectosporium blight have been discovered on pumpkin and winter squash fields recently.  This disease is favored by wet soil conditions and may be confined to low spots in fields, or may infect many plants along the path water takes as it runs off after rains.  The fungus Plectosporium causes numerous white, dry lesions on stems, petioles and fruit rinds (see photo at right).  In severe cases, infected stems and petioles become brittle and the plant ceases growing (see photo at left).  Growers are advised to include chlorothalonil in every spray, as this material is considered to be the most useful at limiting further infection.  However, under the wet conditions we have experienced in recent years, this disease has proven difficult to control even with rigorous fungicide programs.

Brown Marmorated Stink Bug (BMSB)

BMSB numbers in blacklight traps declined over the past week and no map will appear in this edition.   Blacklight catches are likely a better indicator of stink bug activity (movement) than of actual numbers in a given area.  Growers with crops that are potential targets of this pest should be scouting for BMSB or increases in stink bug injury.

The highest nightly catches of BMSB in black light traps for the week ending 8/28/19 are as follows: