WNC Orchard Insect Populations

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Research Station in Mills RiverMay 1, 2018

On Monday we finally captured our first codling moth at the Research Station in Mills River. The lateness of this capture was surprising in that there are high populations in the orchard at the research station. However, the month of April was cool, particularly after dusk when codling moth flight begins. Codling moth flight is severely curtailed at temperatures below 60°F. Temperatures exceeded 60° between dusk and midnight on only 12 of 31 days in April, and of those 12, only 6 days had temperatures >60° for more than a 2 hour period. This may help explain the late biofix in the Hendersonville area. However, Bill Hanlin reported codling moth biofix on 15 April in Wilkes County, so this date does vary within the region. Even with this early biofix date, Wilkes County is still at only about 140 DD, and initial sprays for coding moth are not predicted for at least another week.

In most production areas in NC we remain at the petal fall stage. Key pests to be controlled at this time include plum curculio, oriental fruit moth (if not using mating disruption), rosy apple aphid (if not controlled prebloom). In some orchard green fruitworm may also be an issue, although widespread occurrence of this pest does not seem evident this year.

Extended Bloom and Risk to Bees

The 2018 bloom season is one of the longest in recent memory, with something in the orchard blooming since early April. This presents challenges to making petal fall insecticide applications in a timely manner that will minimize exposure to pollinators remaining in the orchard. Even in situations where hives have been removed from an orchard, bees from hives in nearby orchards or wild bees are likely foraging in trees with blooming flowers. Below are some guidelines to follow when making petal fall applications.

The Label:  For neonicotinoid insecticides and other recently registered products that are highly toxic to bees, the label’s Bee Advisory Box highlights those areas on the label where special precautions are required to protect pollinators. For most products that fall under this category, one of the following conditions must be met if applications must be made before flowering is complete and all petals have fallen:

  • Application is made after sunset
  • Application is made when temperatures are below 55°C
  • Beekeepers are notified no less than 48 hours prior to the time of the planned application so that the bees can be removed or otherwise protected
  • Application is made due to an imminent threat of significant crop loss, and documented determination consistent with an IPM plan or economic threshold is met. Every effort should be made to notify beekeepers no less than 48 hours before the application.

Some products that are highly toxic to bees still lack the Bee Advisory Box, but caution statements are usually highlighted in bold print. In most instances warnings state that the product should not be applied when target crops are in bloom, and that limiting applications to within 2 hours of sunrise or sunset will minimize risk to bees.

Insecticide Effects:  There is considerable variation among insecticides in their toxicity to bees, but very few are essentially non-toxic. Intrepid is one example of a product commonly used in apples that is non-toxic. However, several have very low levels of toxicity, and their labels do not contain warning statements. For those that are highly toxic, several of the neonicotinoids, including Admire, Actara, Belay and Venom, present a greater threat than others because they are systemic products that can accumulative in the nectar and pollen and can have effects on the entire hive.

Hence, if a petal fall insecticide application must be made with some blooms still in the orchard, read the label of the product to be applied to be sure you are within the letter of law. Below is a table of insecticides commonly used at petal fall to target key pests and their toxicity to bees.

Petal Fall Insecticide Recommendations Based on Selectivity Against Pests and Safety to Honey Bees
Chemical Toxicity to Bees* Plum Curculio Rosy Apple Aphid Oriental Fruit Moth San Jose Scale Green Fruit Worm
Actara HT E E F
Admire HT E
Assail MT F E G F G
Belay HT G E
Sivanto LT E
Avaunt MT E E E
Imidan HT E G G
Sevin HT F F G
Diazinon HT F E E
Centaur LT E
Esteem LT F G E G
Movento LT E E
Voliam Flexi HT E E E E
Intrepid NT G E
*HT=Highly toxic, MT=Moderately toxic, LT=Low toxicity, NT=Nontoxic

Learn more about southeastern apple insect pests at the Apple Insect Management page.


2018 Average Weekly Trap Captures*

HENDERSON COUNTY
Insects per trap
Apr 16
Apr 23
Apr 30
Codling Moth
0.0
0.0
0.5
Oriental Fruit Moth
100.0
90.0
38.0
Tufted Apple Bud Moth
0.0
0.0
0.0
Redbanded Leafroller
1.0
2.0
1.0
Obliquebanded Leafroller
0.0
0.0
0.0
Lesser Appleworm
0.0
0.0
Apple Maggot
Brown Marmorated Stink Bug (commercial – mountains)
0.0
0.0
0.0
Brown Marmorated Stink Bug (commercial – upper piedmont)
0.3
0.3
1.3
Brown Marmorated Stink Bug (research – unsprayed)
0.0
0.3
0.3
Spotted Tentiform Leafminer
5.0
0.0
0.0
Dogwood Borer
0.0
Peachtree Borer
0.0
0.0
0.0
Lesser Peachtree Borer
0.0
0.0
13.0
San Jose Scale
0.0
0.0
0.0
*Note that averages presented here are intended only to illustrate the timing of insect emergence and fluctuations in population activity, and not as general indicators of population levels. Some orchards included in these averages have significantly higher or lower populations than most commercial orchards in the area, resulting in averages that are sometimes skewed from what is typical. The only way to have an accurate assessment of an individual orchard’s populations is to set up traps in that orchard.

2018 Accumulated Degree Days


Henderson County
 Biofix
Apr 16
Apr 23
Apr 30
Codling Moth
Oriental Fruit Moth
Apr 2
103
171
247
Tufted Apple Bud Moth

About degree-day models: The degree day (DD) models predict adult emergence and egg hatch of each generation. They do not predict the intensity of populations, which can be assessed by using pheromone traps. Hence, the models should be used to help gauge the time period when control is most likely needed, and pheromone traps provide information on the need for and frequency of insecticide applications. For full details, read “IPM Practices for Selected Pests” in the Orchard Management Guide.

CODLING MOTH:

  • 1st generation: Egg hatch begins at about 350 DD after biofix and is completed by 1050 DD. The most critical period for insecticidal control is from 350 to about 750 DD.

  • 2nd generation: Egg hatch of the second generation can extend from about 1300 to 2600 DD after biofix, but the most critical period for insecticidal control is 1400 to about 2500 DD.

  • 3rd generation: Adults begin to emerge at about 2500 DD after biofix, but the model is less accurate in predicting late-season populations.

ORIENTAL FRUIT MOTH:

  • 1st generation: Only one insecticide application between 400 and 500 degree days is usually necessary, as 1st generation egg-laying is usually low on apple.

  • 2nd generation: Effective 1st-generation control may eliminate the need for 2nd-generation control. If trap captures remain high, insecticides may be needed around 1100 to 1400 DD.

  • 3rd generation: Insecticide may be needed at 2200 DD after biofix.

  • 4th generation: Overlapping generations late in the season make it difficult to predict when 4th-generation egg hatch begins, but continuous egg-laying can occur from August through October. Use traps to determine the need for further insecticide applications.

 TUFTED APPLE BUD MOTH:

  • 1st generation: One well-timed insecticide application between 800 and 1200 DD after biofix will often eliminate the need for further control of TABM.

  • 2nd generation: Only if trap captures exceed 25 moths per trap by 2600 DD is an insecticide application recommended. NOTE: Insecticides targeting 2nd generation TABM are usually not necessary if 1st generation populations were successfully controlled.


2018 Pest Trends (click to enlarge)

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Written By

Photo of Dr. Jim WalgenbachDr. Jim WalgenbachExtension Entomology Specialist (Fruits / Vegetables) (828) 687-0570 (Office) jim_walgenbach@ncsu.eduEntomology and Plant Pathology - NC State University
Updated on May 15, 2018
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