Mouse ear is a growth abnormality from a nickel deficiency in pecan trees. This disorder occurs mostly on newly transplanted trees in established orchards. This is the first time I’ve seen it, but it is close to the text book pictures and easy to ID. Mouse ear first appears on the spring growth flush. The most common symptom of mouse ear is a rounded or blunt leaflet tip. Other symptoms include dwarfing of tree organs and necrosis of leaflet tips. The degree of severity with the tree canopy typically increases with canopy height.
There are 4,000 seedling trees in this nursery and probably half are affected by the Ni deficiency. At this point we need to spray a foliar application of nickel now and again in one month. UGA Pecan Horticulturalist Dr. Lenny Wells says mouse ear may consistently reappear from year to year, or appear on occasion. For mouse ear prone sites, it is recommended to have a foliar spray of nickel in med-late April when leaves are in the parachute stage. (Ni is not absorbed in the plant until leaves are in parachute stage.) We follow up with an additional application in late September or early October to prevent mouse in the following spring.
Long-term Management (From Southeast Pecan Grower’s Handbook)
- Monitor leaf and soil samples for availability of Ni to trees.
- Don’t make excessive applications of zinc. Zn competes with and inhibits uptake of Ni. Foliar Zn should only be applied when Zn leaf levels are less than 50 ppm or when visual Zn deficiency symptoms are present. Do not allow soil to become acidic (making Zn more available.)
- Maintain good soil moisture at budbreak. Ni is relatively low in the soil in most orchards, and it is absorbed by the tree in the lowest of many nutrients.
- Maintain soil pH at 6.5.
- Do not give late applications of N, to ensure that senescing foliage can translocate to shoot and bud storage prior to defoliation.
- Manage phosphorus, iron, and copper levels in soils. These nutrients affect uptake of Ni. They may also alter the availability of Ni within the leaf.