MSU Extension

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.   

Plum curculio overwinter as adults in the soil, litter and ground cover trash in orchards and in surrounding areas. As soon as daytime and evening temperatures exceed 60°F, plum curculio will begin to move, especially when a light, misty rain or humid night co-occurs with early spring warming trends. The weevils move into orchards and begin to feed as leaves begin to emerge. Their feeding activity expands to blossoms, stems and fruit as they become available.

Monitoring

Pyramid traps are the most efficient means of monitoring plum curculio activity early in the season. These traps outperform in-tree screen traps in adult capture about two to one in many seasons. Baiting traps with lures (plum essence or benzaldehyde) significantly increases trap catch, but the addition of pheromone baits only slightly increase (1.2:1) plum curculio captures in either trap.

Traps are a good indicator of likely plum curculio pressure in the area, and should be placed on the borders of orchards where producers or scouts have observed damage in past years. Often these locations have woods, unsprayed orchards, feral trees or other sources of overwintering plum curculio populations. Table 1. provides a guide for evaluating plum curculio population pressure in three fruit crops.

Table 1. Population pressure rating: general trap catch/week bloom to 370 dd50 plum curculio

Management

In low pressure situations in apples and peaches, growers may want to consider only one insecticide between 200 and 250 DD50. In cherries, it is advisable to cover spray trees from shuck split to 400 DD50, and, if plum curculio are still being trapped, include a third cover beyond 400 DD.

Four key factors should be considered when deciding when, how often and with what to manage plum curculio populations in the spring. Note that some growers may want to consider summer generation control of plum curculio in moderate, high or extreme pressured cherry orchards. In these situations, Guthion and Esteem work well. Normally, mid-season controls suppress plum curculio populations in apple and peach orchards, and no summer generation controls are warranted for plum curculio. An exception may occur, when pome and stone fruit management targeting codling moth and leafrollers in mid-season is primarily pheromone disruption or virus (from 1250 DD50 to harvest).

First, historical damage in previous years should be considered. The greater the plum curculio pressure in the previous one or two seasons, the greater the care and focus on plum curculio in the current season. Second, the best timing (Table 2.) depends to a great extent on accumulated degree-days and insecticide(s) chosen. Third, understanding and identifying the chosen insecticide’s performance characteristics is important in evaluating control measures taken. For instance, it helps to know whether or not the insecticide selected has curative activity (kills larvae in fruit), and the length of its residual action window. It is also important to consider the modes of insecticidal activity that each compound has, some relying solely on lethal activity versus those that have repellent, antifeedant and oviposition deterrent effects. Lastly, a number of weather related factors can dictate re-treatment to control plum curculio; especially in processed cherries. Therefore, degree-day accumulation (for timing sprays), rain events (residue wash off), and other seasonal characteristics (like cool and cloudy versus warm and sunny) can affect breakdown of sprays and the need for additional coverage. All of these factors contribute to plum curculio control timing, insecticide selection and re-treatment.

Table 2. Labeled control materials for plum curculio

1. Avaunt should be used first when in a program combination with a neonicotinoid (Actara, Provado, Assail, Clutch or Calypso). Avaunt lethal activity on plum curculio is enhanced with adult injestion. Neonicotinoids are antifeedants, which may prevent Avaunt’s major mechanism of exposure = injestion.
2. For a complete list of insecticides registered or recommended for plum curculio control, see the 2007 MSU Fruit Management Guide (MSU bulletin E-154).

Spring generation plum curculio control

MSU is pursuing a post FQPA USEPA defined reduced risk and OP-alternative spray program, to control plum curculio in apples, cherries and peach. For apples, we are recommending an application of the oxadiazine Avaunt at petalfall to kill mated females before they oviposit. In cherries and peaches, Actara can be used at shuck-off to effectively control plum curculio. If plum curculio populations are low, growers may choose to delay applications for up to a week or two, knowing that Actara and the other neonicotinoids have strong curative activity on larvae. If new oviposition scars are observed, or a larval infestation, or plum curculio trap catch remains high, we are recommending a “bail out” Guthion application between 300-350 DD50 up until the PHI of 15 days in cherries. Guthion has also been shown to have curative activity on PC in cherries, killing larvae that have already begun to develop in the fruit.

In the case of infested apples, larvae will not survive in developing fruit unless the infested fruit falls off the tree, usually during June drop. As Rimon is already being used for codling moth control in the latter part of the plum curculio control window, we are currently developing a protocol for use of Rimon as a control for plum curculio in apple. We are evaluating the effect and timing of codling moth Rimon sprays on reducing plum curculio’s egg laying success.

In our pursuit of more effective plum curculio controls in both organic and conventional crop management, we have been building a plum curculio degree-day phenology model. These efforts link growing degree-days with key plum curculio control periods and registered USEPA defined reduced-risk and OP- alternative insecticides, to bracket ideal spray timings. The accompanying figure early season degree-days with critical plum curculio control periods on both tart cherry and apples.