INSECT and MITE PESTS

 Plum Curculio  

     Plum curculio egglaying and feeding damage has commenced in unsprayed research plots at Highmoor Farm.  The amount damage was substantially higher on Friday June 13 than on June 11 and 12.  There was much more damage on  Liberty and Cortland than Red Delicious.

    The heavy rain on Saturday June 14 will deplete insecticide protection in many Maine orchards.  The amount of rain expected increases from north to south.  Therefore in the Sanford area, there may still be residual plum curculio protection after the rain, depending on how many days prior to June 14 the insecticide was applied.  In the Monmouth and Morrill areas, it appears that the rain will be heavy enough to remove coverage even if it was applied just before the rain.

     The plum curculio re-spray tables for Sanford, Monmouth and Morrill can help with this decision.

     If you have doubts about the status of protection in your orchard after the June 14 rain, you should recover as soon as possible.  Normal temperatures are forecast to return by Tuesday June 17.  It appears that there will be some cloud cover through all of next week, with the next rains forecast for Thursday and Friday, June 19-20.  Fruit size is now at the size preferred by plum curculio.  Putting all this together, I expect plum curculio to be very busy in the coming week. 

     Imidan, Guthion, Avaunt, Guthion provide effective protection.  The pyrethroids Asana and Danitol are also effective, but do so at the cost of harming beneficial insect predators that keep aphids and mites in check.

     In all Maine orchard locations, insecticide coverage will need to be renewed at some point after June 14 in order to provide protection against later plum curculio activity.  In the Sanford area protection needs to be maintained until June 27.  In Monmouth and Morrill protection needs to be maintained until July 1-2. 

     If continued rainy weather reduces the longevity of insecticide applied June 15-19, then there may be need for an additional plum curculio spray this year.  This has happened before.  Experience has shown that in cool springs, late season plum curculio damage can be significant.  Subsequent newsletters will report on the situation as it develops.

     Growers using Surround for plum curculio protection need to understand that the "control window" when using insecticides that kill plum curculios does not apply to where Surround is used.  Surround does not kill plum curculio, it just repels them.  Therefore, where only Surround is used, protection needs to be maintained until plum curculio run out of eggs.  That won't be until mid-July.

 European apple sawfly  damage appears to be heavy this year.    While it is too late to prevent EAS hatch and damage to the apple the egg was laid in, insecticide coverage over the next couple of weeks should prevent EAS larvae from moving to and destroying a second and third fruit in the cluster.  Insecticides used for plum curculio will be effective for EAS.

     Organic growers have limited options to control EAS.  Entrust is an organically acceptable formulation of spinosad  (sold as SpinTor for conventional orchards).  It does not include EAS on the label.  While it might be worth trying on a limited experimental basis to see if it helps prevent damage to additional fruits in a cluster where EAS is present, its best hope for efficacy was against the just hatched larvae.

 Leafminers       

     A leaf mine count in an orchard that had very high trap catches this spring found only two mines on 40 leaves.  With the cool weather though, they could just be late not gone, so we will be checking again early next week.

     Finding more than a total 6-40 mines on 40 interior fruit cluster leaves is indication that control is needed.  The exact threshold is unclear.  "Interior" means near the trunk.  Only use fruit cluster leaves for this sampling.

  European red mites  were hard to find (meaning we didn't see ANY!)  on Red Delicious and Gala trees at Highmoor Farm on Friday June 13.

     The treatment threshold until July 15 is if more than 54% of middle-aged fruit cluster leaves have living hatched mites present, or if there is more than an average of 2.5 mite per leaf.  If you check 40 leaves and find 8 or fewer with mites, then it is safe to assume you are far below threshold.  If you find 16 or fewer leaves out of 40 with living hatched mites, then you are still below threshold but should recheck next week.  If you find 31 or more infested leaves, you can assume treatment is needed.  The New England Apple Pest Guide has more information on the mite thresholds.