Effects of Imazapic Herbicide on Pecan Production

Summary

A persistent problem was identified in pecan orchards throughout southern Georgia, in which pecan trees growing in rows immediately adjacent to peanut fields developed hollow pecans. Experimental research demonstrated that imazapic herbicide can be absorbed by pecan roots extending out into peanut fields, resulting in inhibition of kernel development and shuck split.

Situation

A persistent problem was identified in pecan orchards throughout southern Georgia, in which pecan trees growing in rows immediately adjacent to peanut fields developed hollow pecans. In-shell nut size and appearance was normal; however, the kernels failed to develop. Frequent observations in multiple orchards suggested that this problem only occurred where peanuts were planted adjacent to pecan orchards. It was never observed in orchards adjacent to other row crops. A similar problem was observed in pecan tree rows growing adjacent to highway right of ways in multiple locations. The roots of mature pecan trees can extend to a length twice the width of the tree canopy, therefore activities that occur immediately outside the orchard can have an effect on nearby trees. Because both peanut fields and highway right of ways are commonly treated with the herbicide, imazapic, this chemical was suspected as a potential cause of the problem.

Response

Replicated studies were conducted at a University of Georgia pecan research orchard to evaluate the effects of imazapic on pecan from 2008-2009. Two rates of imazapic (2 oz/acre and 4 oz/acre) were evaluated alongside an untreated control. At harvest, kernel development and shuck split were evaluated. This information will be presented at county pecan production meetings throughout the state as well as in pecan industry magazines.

Impact

Pecan kernel filling was significantly affected by soil application of imazapic in both years of study. Imazapic inhibited kernel production at both rates, with as much as 97% of the kernels failing to develop. This type of damage would make the pecan crop on affected trees virtually worthless. Imazapic also delayed or prevented shuck split. This research demonstrates that imazapic can be absorbed by pecan roots, resulting in inhibition of kernel development and shuck split. As a result, precautions should be observed with the use of imazapic near pecan trees, particularly on soils with a heavy clay content. This becomes particularly important where peanuts are grown in fields adjacent to pecan orchards and along highway right of ways. This research can help to reduce significant economic damage to pecans and minimize conflict between land managers.

State Issue

Agricultural Profitability and Sustainability

Details

• Year: 2009
• Geographic Scope: Multi-State/Regional
• County: Tift
• Program Areas:
  • Agriculture & Natural Resources