An outbreak of pecan leaf roll mite

    Every year I seem to spot just a few leaves distorted by the pecan leaf roll mite (Aceria caryae). Generally, the amount of damage is minor and we can simply ignore this pest. However, this year I have noted several trees in my orchard that are heavily infested with leaf roll mites (photo at right). In the photo, you'll note that the older leaves have thin leaflets but the newest leaves on the end of the shoot appear normal.

      Looking closer at the mite-damaged leaves you will note that the edges of each leaflet are curled upwards and a roll of gall tissue has formed along the outside edge (photo at left). Leaf roll mites are in the eriophyid mite family: a family known for causing galls on plants. 
   I can not find any information on the life cycle of this pest but I don't expect the problem to become more prevalent in my orchard next year. Currently, there are no chemical control measures recommended for this pest but I may try applying a dormant oil spray on infested trees before bud break next spring. For the most part naturally occurring predatory mites keep the population of the leaf roll mites in check.  Hopefully, nature's balance of predators and prey will be restored in the Spring of 2020.

Curled-up pecan leaves

    Growers are seeing some curled-up leaves in their orchards this year. Over the past week, I have spotted two types of leaf distortions in our pecan grove.
     In the photo at right you can see that the 5 leaflets on the end of this leaf are twisted and cupped. This type of damage was caused by the potato leaf hopper during the period of leaf expansion. The holes in the leaflets were caused by sawfly feeding, also earlier this growing season.

    If you take a close look at the underside of a curled-up leaflet, you will note brown necrotic areas along the main midrib and all major veins  (photo at left). When the leaflet was small and very tender, the potato leaf hopper inserted it mouth parts into the vascular system of the leaflet to feed on nutrient rich plant sap. This feeding behavior causes the vascular system to become clogged, stopping the flow of carbohydrates needed for further leaf expansion. Areas of the leaf that rely on those clogged veins for water and nutrients become yellow (lack of nutrients) or turn brown (lack of water). The leaflets curl because affected areas stop expanding while areas that are adjacent to functioning veins continue to expand.
     Potato leaf hoppers migrate through our area every spring. The damage caused by this insect varies from year to year and you will see several trees species affected (including pecan, walnut, ash, & maple).  We do not recommend treating for this transitory insect and just let the tree grow additional leaves to replace the damaged ones.

     A second type of curled up leaf is caused by the leaf roll mite. In the photo at right, note that the margin of the leaflet is rolled into a tight, hardened gall-like structure. As the mite feeds on the edge of a leaflet during leaf expansion, it causes distorted cell growth, creating the "leaf roll".  Leaf roll mites are fairly rare in a native pecan grove and we don't take steps to control what amounts to minimal damage.