Curculio Draws Nigh: Stone Fruit At Greatest Risk As Apple Bloom Wains. May 15th

Overview: Plum Curculio (PC)(Conotrachelus nenuphar) adults have been late to arrive in the Hudson Valley. Sustained cool temperature have kept PC from its migration into orchards. Warm evening temperatures, daytime highs in the 70’s and ample light intensity will prompt the insect complex to begin flying, feeding, and reproducing. PC will begin laying eggs into the cuts made to stone and pome fruit as they exceed 5mm in diameter. Management of PC to these crops should be made at the first sign of activity and is critical at this time to reduce economic losses from this pest.

As of last night, I have not seen PC injury to pear, cherry or peach. Apricots have been severely compromised at the research orchard in Highland. An unsprayed sentinel tree, such as cherry or plum, is a good tell tale for finding the first signs of PC injury. Upon the first stink, management should begin in earnest.

As we are seeing a large disparity between king and lateral fruit size within and across varieties, fruit may be >5mm with many clusters still at early bloom. Selecting insecticides with no contact activity to our pollinators is critical for bees to continue pollinating an already compromised crop from recent freeze events. A list of Bee Safe materials is available in last Mondays Scaffolds of a previous blog titled Apple Bloom: Supporting Pollinators & Managing Pests. May 11th, 2020.

Petal Fall Options for Plum Curculio

In Depth: Early scarring to fruit was observed on the 23rd of May in 2019. With tempertures expected in the high 70’s over the next few days, PC activity could come sooner this season.

Up to this point, evening temperatures have been hovering at or below 50F. PC activity is highly dependent upon temperatures, particularly at night when adults are most active. PC typically do not feed or oviposit when nighttime temperatures are below 50 deg F. In cooler seasons such as this, PC may continue to delay with extended oviposition for 4-6 weeks. As the adults begin to move in cooler weather, they often crawl instead of fly or fly short distances, damaging fruit along the edge first, moving among trees into the orchard center from the edge in commercial orchards. Applications to border trees using bee safe materials may reduce early injury as fruit set, bloom wains and pollination continues.

We presently have 182 accumulated degree days (base 50°F BE) from Jan. 1st and expect petal fall over the weekend in early to mid-blooming varieties. Control measures for PC are needed at PF and 1st cover. In year in which cooler weather prevails and extended PC activity occurs, a 2nd cover may be required. PC management is only needed until 308 degree days have accumulated since petal fall. Monitoring this event over the next few weeks can be done using the Access link to the NEWA Model for PC.

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PC feeding damageApplications for plum curculio should control the pest for about 10-14 days based on materials and weathering.

As PC damage often occurs in the same locations in orchards year after year, PC injury is fairly predictable from past observations. Frequent short interval rains will remove surface contact insecticide residual. A short interval, from petal fall to 1st cover (<7-10 days), should be employed for PC management if residual efficacy is compromised by rain events. Maintaining control of PC during the migration period is essential. If a delay in emergence of PC occurs as cool temperatures return next week, management of PC, even in low-pressure orchards, may be prolonged. In high-pressure orchards, additional sprays along the perimeter of the orchards should be considered until the oviposition model predicts that control is no longer necessary. Remember to keep codling moth on the radar after PF if border applications are not followed up with whole orchard applications. If alternate row applications (ARM) are used, be aware that ARM are very effective against mobile insects such as PC and apple maggot, but less so with sedentary, less mobile insects such as obliquebanded leafroller (OBLR).

Insecticides effective against the PC include Avaunt 30WDG (indoxacarb), the neonicotinoid Actara 25WDG (thiamethoxam), the OP Imidan 70WP, WSP (Phosmet), carbamate; Sevin (carbaryl), and pyrethroids Danitol 2.4EC (fenpropathrin), Asana XL (esfenvalerate), Baythroid XL 1E, 2EC (beta-cyfluthrin), Lambda-Cy 1CS (lambda-cyhalothrin), Warrior 1CS (lambda-cyhalothrin), Proaxis 0.5CS, and pre-mix formulations Endigo ZC (lambda-cyhalothrin / thiamethoxam), Leverage 360 (imidacloprid / beta-cyfluthrin), Gladiator (zeta-cypermethrin / avermectin), Voliam Express (lambda-cyhalothrin / thiamethoxam), Voliam Flexi (chlorantraniliprol / thiamethoxam).

The pyrethroids and phosmet have broad spectrum activity to include PC, EAS, lepidopteran larva (OFM, CM, Lesser appleworm (LAW) and Obliquebanded leafroller (OBLR). They have no activity against rosy apple aphid (RAA) in curled foliage.

Rosy apple aphid control after leaf curl is best accomplished using a neonicotinoid insecticide such as Admire Pro, Assail or Actara 25WDG.

The pre-mix ingredients:
Avermectin must be used with a penetrant to effectively manage mite.
Chlorantraniliprol, the active in Altacor, is excellent against the range of lepidopteran larva with limited spectrum.
Thiomethoxam has no efficacy against internal lepidopteran larva. Exclusive use of this product at 1C will put you at risk for CM larval injury.

Oriental Fruit Moths flight is waining. Nearly 100%% of OFM eggs from the first generation have hatched. A petal fall spray should include an insecticide with lepidopteran activity. Additional applications will also be applied at about 10-14 days after petal fall for the Lep. Complex, primarily Codling Moth, that will also reduce OFM. This second spray against the first generation of OFM is particularly important in high-pressure orchards (past history of OFM fruit damage or high pheromone traps catches, (>10/ trap/ week) to control the remainder of hatching larvae. If this spray is applied at the normal time of a first cover spray (10-14 days after petal fall) it will also control early hatching CM larvae from the first flight of adults.

Codling Moth (CM) flight has yet to occur, and will likely begin this weekend. If this occurs, then egg-laying will likely begin within the next 2 weeks. The first eggs will hatch after 220 DD from first sustained trap capture. Insecticides that need to be present before egg laying (Rimon) should be applied at about 50-75 DD, made shortly after sustained flight. Apply insecticides that target early egg laying period at 100-200 DD. Remember, Actara 25WDG employed at 4.5-5.5 oz/acre is excellent against PC but has no commercial value to manage the lepidopteran complex, specifically codling moth. Select materials with highest efficacy rating against CM if past crops have had internal feeding or stings from CM.

About Peter J Jentsch

Peter J. Jentsch serves the mid-Hudson Valley pome fruit, grape and vegetable growers as the Senior Extension Associate in the Department of Entomology for Cornell University’s Hudson Valley Laboratory located in Highland, NY. He provides regional farmers with information on insect related research conducted on the laboratory’s 20-acre research farm for use in commercial and organic fruit and vegetable production. Peter is a graduate of the University of Nebraska with a Masters degree in Entomology. He is presently focusing on invasive insect species, monitoring in the urban environment and commercial agricultural production systems throughout the state
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