Confusion in the Insect World Due to the Early Season

Posted: April 20, 2012

Looking at the comparisons of accumulated degree-days (base 43) for the last 6 years, as of April 20 we are still about 100-150 DD ahead from any other year or about 200-300 DD ahead of the average DD accumulation for this time of the year. And while this difference is becoming smaller as the spring progresses (especially when compared to the weather pattern during the spring of 2010 season), this unusual weather seems to have caused a lot of confusion in the insect world that surrounds our fruit trees.

While the biofix dates (first sustained moth flight) for redbanded leafroller (RBLR) and spotted tentiform leafminer (STLM) were only few days earlier than usual, the biofix for Oriental fruit moth (OFM) was established on the same day as during the 2010 season (April 03), although a few OFM moths were observed flying on March 22 to 23 in Adams County. Similarly, we started capturing a few codling moth (CM) moths in traps on April 16 to 18, but we still have not yet decided about the exact date for the CM biofix (as of April 20) because of the erratic capture of moths over the past few nights.

The biofix, which is defined as the beginning of sustained adult moths activity, is usually established based on capture of adult male moths in pheromone traps. A correctly established biofix should help to better predict development of pest populations in the field. The established insect developmental models are based on certain low and upper temperature development thresholds, which are used to calculate the accumulation of heat units (degree-days, DD).  Based on various field and laboratory observations, we can accurately correlate the accumulation of degree-days with consecutive phases of insect development for various pest populations. Also, the development of insects is normally very well correlated with the development of the host plants that are utilized by various stages of insect pests. The confusion for the 2012 season is that the plants seem to be developing at a different pace than the insects. Although, a small portion of insect populations are likely still well correlated with plant development, a larger portion of particular pest populations are most likely developing at a slightly different pace.  For example, when apple bloom is over and we are trying to manage the pest complex with a post–bloom application (i.e., petal-fall) of insecticides, egg hatch for the first generation of OFM is generally around 40-50% complete by this stage. However this year, based on OFM model predictions the post-bloom treatment applied during the week of April 22 should be almost perfectly timed for 5 to 10 percent OFM egg hatch period. This example of confused OFM populations in 2012 should serve as another strong reminder for using on-site monitoring when deciding what pests and when we need to apply appropriate control measures. This season, past experiences most likely will not provide the correct direction on when is the best timing to control various pests. Only direct, on-site monitoring will provide the most accurate view of pest population dynamics.   

The brown marmorated stink bug (BMSB) adults are also leaving their overwintering sites and initiating early feeding on plenty of available green plants. However, this season it seems that at the time of this BMSB initial activity, plenty of food is already available and emerging overwintering adults will find perfect conditions for their development. In the next issue of the Fruit Times Newsletter (May 2012) we will present more detailed brown marmorated stink bug management recommendations based on information generated during last season.

First Generation Codling Moth

At the Penn State Fruit Research and Extension Center (FREC) this year, biofix for codling moth (CM) is still not established (April 20) although individual moths were already captured in pheromone traps placed in orchards around the Center. The first recommended application of larvicidal insecticides to control this pest in most orchards should be made at about 300-350 DD50. The recommended, broad-spectrum larvicidal insecticides to control CM include: Altacor, Assail, Avaunt, Belt, Calypso, Delegate, Guthion, Imidan, Tourismo and Voliam Flexi or Voliam Xpress. (Reminder: during the 2012 season, restrictions are in place for the use of Guthion (azinphos-methyl) allowing only 3.0 lb of formulated product per entire season). A second insecticide application against CM, depending on pest pressure, is usually needed around 14 to 17 days after the first application. During the last few years we observed an extended flight of CM, sometimes lasting until the end of June. If you continue to catch significant numbers of CM adults in orchards during June and you have already made two applications for CM, a 3rd insecticide application may be needed during this period as well.

If mating disruption (MD) is planned for the control of CM, in order to maintain the efficacy of the MD products during the later part of the season, the dispensers should be placed in orchards in the beginning of May. Although this timing may be slightly late compared to our previous recommendations (before the beginning of CM flight), with a time-limited release of MD pheromones from dispensers (usually around 120 days), it may be important to maintain effective CM disruption later in the season, especially during the harvest.    

We can not stop emphasizing the importance of insect monitoring in each orchard, especially now with the possible pressure from brown marmorated stink bug (BMSB).

Tufted Apple Bud Moth and Obliquebanded

Similarly as with other pests, during the 2012 season, monitoring will remain the most important tool to make decisions on the correct timing for management of TABM. In the majority of PA orchards where leafrollers are present, TABM is the dominant leafroller species responsible for most of the fruit injury.  If Altacor, Belt, Delegate, Tourismo, Voliam Flexi or Xpress, Intrepid or Rimon are to be used for TABM control, 1 to 2 complete, precisely timed applications of those products per brood are recommended. Use of Altacor, Belt, Delegate, Tourismo and Voliam Flexi by June (i.e., second CM control timing) should provide excellent control of both leafroller species. If applying two complete sprays dedicated against TABM, the first application should be made at about 10 to 30 percent egg hatch (500-600 DD base 45) followed by a second application (if necessary) at about 60 to 70 percent egg hatch (800-850 DD). The low rate of Intrepid (8-10 oz/acre) should provide excellent control of TABM larvae but will not control CM or OFM. If applying only one complete application of the above mentioned compounds against TABM, this spray can be made at 30 to 40 percent egg hatch (640-695 DD).

Insecticides that are effective against TABM should also provide good control of OBLR larvae, but at least one additional application of an effective insecticide may be necessary to control this pest in orchards with a history of OBLR infestation. Phenologically, the most effective timing for controlling OBLR larvae usually occurs about the timing for the second applications of insecticides for TABM, followed by an additional application 10 to 12 days later. Two sprays are usually needed for high populations of OBLR. Since the young OBLR larvae prefer to feed inside the growing terminals, the insecticide coverage of fresh growth plays a critical role in the control of OBLR larvae. Only complete sprays are recommended against this pest. The better the coverage, the better the level of larval control that will be achieved. The insecticides recommended for the control of OBLR during this time of the season include: Altacor, Bacillus thuringiensis products, Belt, Delegate, Intrepid, Tourismo, Voliam Flexi or Rimon.

Pear Psylla

Usually, at the petal fall timing, all stages of pear psylla (PP) (i.e., eggs, nymphs, and adults) are present on infested trees. For proper monitoring during the petal fall period, at least 10 leaves per tree (5 spur and 5 recently expanded shoot leaves) on a minimum of five trees per block should be examined.  The action threshold is 0.5 nymph per leaf. The application of Agri-Mek (20 fl oz/acre) still remains as one of the best PP control options at petal fall to PF + 10 days, although we have seen in some situations that control with Agri-Mek is starting to slip somewhat. A penetrating surfactant (i.e., a summer oil at 1% concentration) is a necessary addition to Agri-Mek in order to provide the best residual control. This spray should be applied in at least 100 gals of water per acre.  After this window, Agri-Mek may not provide as effective control. Actara, Calypso, Centaur, Delegate, Movento, Provado, and Nexter also can be used at this time if additional control options are needed. Another option for PP control is the use of kaolin clay Surround®. If a good coverage is achieved, Surround (applied at 25-50 lb/acre) can represent a very effective additional tool for the PP control and also a possible repellent for BMSB.

Green Peach Aphid

Green peach aphid colonies are now starting to become established in many peach and nectarine orchards. A threshold of one colony per nectarine tree or five colonies per peach tree is recommended in Pennsylvania. Currently available neonicotinoid insecticides such as Provado, Actara, Calypso or Assail are very effective against green peach aphids. Watch for predator populations such as ladybird beetles or syrphid fly larvae if aphid colonies remain below threshold or become reestablished following an aphicide application. The presence of predators on about one out of five aphid colonies may lead to successful biological control. 

Pesticide Notes

  • It is the last year for use of azinphos-methyl (Guthion)on apples, pears and cherries. The seasonal total application rate is 3.0 lb of formulated product. It will be illegal to use this product after September 30, 2012.
  • The new label for all products containing chlorpyrifos (e.g., various Lorsban formulations) allows for only a single application per season of products containing this ingredient, either as a dormant application or as a trunk application.
  • It will be illegal to use endosulfan (e.g., Thionex products) after July 31, 2012 on apricots, cherries, nectarines, plums and peaches. The product remains registered for use on pears until July 2013, and on apples until July 2015.

Seasonal Activity of Fruit Pests

2012 season weekly captures of adult moths in pheromone traps located at Penn State FREC Biglerville, PA (Adams County):

Species 16-Mar 23-Mar 30-Mar 6-Apr 13-Apr 20-Apr
RBLR 26 143 16 7 3 6
STLM - 109 89 45 21 25
OFM - 3 55 91 23 303
CM - - - 0 0 4
TABM - - - - 0 0

Key to acronyms: RBLR - redbanded leafroller; STLM - spotted tentiform leafminer; OFM - Oriental fruit moth; CM – codling moth; TABM – tufted apple bud moth.

Degree-Day Table

Accumulated degree-days base 43 F from Jan 01 for each reported year (courtesy of SkyBit, Inc.). The accumulated degree-days for the last date of the current year (April 28) mentioned in the table are based on the weather forecast.

Site/Date 31-Mar 7-Apr 14-Apr 21-Apr 28-Apr
Biglerville, 2012 415 451 503 636 690
Biglerville, 2011 138 179 245 338 454
Biglerville, 2010 194 334 412 486 562
Biglerville, 2009 157 210 242 305 439
Biglerville, 2008 137 178 255 355 472
Biglerville, 2007 213 249 259 290 394

Rock Spring, 2012 323 364 399 513 539
Rock Spring, 2011 78 96 147 203 293
Rock Spring, 2010 141 277 342 408 463
Rock Spring, 2009 116 156 173 226 349
Rock Spring, 2008 61 88 146 240 352
Rock Spring, 2007 147 189 192 218 300

Where trade names appear, no discrimination is intended, and no endorsement by Penn State Cooperative Extension is implied. Recommendations based on conditions observed at Penn State Fruit Research and Extension Center, Biglerville, PA. 

Contact Information

Grzegorz (Greg) Krawczyk
  • Extension Tree Fruit Entomologist
Phone: 717-677-6116
Larry Hull
  • Professor Emeritus of Entomology